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  • Wiley-Blackwell  (119,713)
  • Blackwell Publishing Ltd  (57,817)
  • American Institute of Physics (AIP)  (46,193)
  • 2020-2024  (22)
  • 1990-1994  (149,431)
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  • 1
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    Chapter PRINCIPLES OF PI3K BIOLOGY AND ITS ROLE IN LYMPHOMA (2023)
    Wiley-Blackwell
    Details
    Publication Date: 2024-04-07
    Description: PI3K biology; lymphoma; cancer
    Keywords: PI3K biology; lymphoma; cancer ; thema EDItEUR::P Mathematics and Science::PS Biology, life sciences
    Language: English
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  • 2
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    Targeting Oncogenic Drivers and Signaling Pathways in Hematologic Malignancies (2023)
    Wiley-Blackwell
    Details
    Publication Date: 2024-04-03
    Description: oncogenic drivers; signaling; pathways; hematologic malignancies; cancer
    Keywords: oncogenic drivers; signaling; pathways; hematologic malignancies; cancer ; thema EDItEUR::M Medicine and Nursing
    Language: English
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  • 3
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    Non‐exchangeable stable hydrogen isotope ratios in clay minerals and soil clay fractions: A method test (2022)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2023-01-20
    Description: Stable hydrogen isotope ratios (δ2H values) in structural hydroxyl groups of pedogenic clay minerals are inherited from the surrounding water at the time of their formation. Only non‐exchangeable H preserves the environmental forensic and paleoclimate information (δ2Hn value). To measure δ2Hn values in structural H of clay minerals and soil clay fractions, we adapted a steam equilibration method by accounting for high hygroscopicity. Our δ2Hn values for USGS57 biotite (−95.3 ± SD 0.9‰) and USGS58 muscovite (30.7 ± 1.4‰) differed slightly but significantly from the reported δ2H values (−91.5 ± 2.4‰ and −28.4 ± 1.6‰), because the minerals contained 1.1%–4.4% of exchangeable H. The low SD of replicate measurements (n = 3) confirmed a high precision. The clay separation method including destruction of Fe oxides, carbonates and soil organic matter, and dispersion did not significantly change the δ2Hn values of five different clay minerals. However, we were unable to remove all organic matter from the soil clay fractions resulting in an estimated bias of 1‰ in two samples and 15‰ in the carbon‐richest sample. Our results demonstrate that δ2Hn values of structural H of clay minerals and soil clay fractions can be reliably measured without interference from atmospheric water and the method used to separate the soil clay fraction. Highlights We tested steam equilibration to determine stable isotope ratios of structural H in clay. Gas‐tight capsule sealing in Ar atmosphere was necessary to avoid remoistening. Our steam equilibration method showed a high accuracy and precision. The clay separation method did not change stable isotope ratios of structural H in clay.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:549 ; controlled isotope exchange technique ; deuterium ; montmorillonite ; soil clay separation ; soil organic matter removal ; steam equilibration ; structural H ; USGS57 biotite ; vermiculite ; δ2H
    Language: English
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  • 4
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    Potential erodibility of semi‐arid steppe soils derived from aggregate stability tests (2022)
    Koza, Moritz ; Pöhlitz, Julia ; Prays, Aleksey ; [et al.]
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2023-01-26
    Description: Erosion is a severe threat to the sustainable use of agricultural soils. However, the structural resistance of soil against the disruptive forces steppe soils experience under field conditions has not been investigated. Therefore, 132 topsoils under grass‐ and cropland covering a large range of physico‐chemical soil properties (sand: 2–76%, silt: 18–80%, clay: 6–30%, organic carbon: 7.3–64.2 g kg−1, inorganic carbon: 0.0–8.5 g kg−1, pH: 4.8–9.5, electrical conductivity: 32–946 μS cm−1) from northern Kazakhstan were assessed for their potential erodibility using several tests. An adjusted drop‐shatter method (low energy input of 60 Joule on a 250‐cm3 soil block) was used to estimate the stability of dry soil against weak mechanical forces, such as saltating particles striking the surface causing wind erosion. Three wetting treatments with various conditions and energies (fast wetting, slow wetting, and wet shaking) were applied to simulate different disruptive effects of water. Results indicate that aggregate stability was higher for grassland than cropland soils and declined with decreasing soil organic carbon content. The results of the drop‐shatter test suggested that 29% of the soils under cropland were at risk of wind erosion, but only 6% were at high risk (i.e. erodible fraction 〉60%). In contrast, the fast wetting treatment revealed that 54% of the samples were prone to become “very unstable” and 44% “unstable” during heavy rain or snowmelt events. Even under conditions comparable to light rain events or raindrop impact, 53–59% of the samples were “unstable.” Overall, cropland soils under semi‐arid conditions seem much more susceptible to water than wind erosion. Considering future projections of increasing precipitation in Kazakhstan, we conclude that the risk of water erosion is potentially underestimated and needs to be taken into account when developing sustainable land use strategies. Highlights Organic matter is the important binding agent enhancing aggregation in steppe topsoils. Tillage always declines aggregate stability even without soil organic carbon changes. All croplands soil are prone to wind or water erosion independent of their soil properties. Despite the semi‐arid conditions, erosion risk by water seems higher than by wind.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Keywords: ddc:631.4 ; climate change ; land use ; soil organic carbon ; soil texture ; water erosion ; wind erosion
    Language: English
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  • 5
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    Vertical SOC distribution and aromatic carbon in centuries old charcoal‐rich Technosols (2022)
    Bonhage, Alexander ; Raab, Thomas ; Schneider, Anna ; [et al.]
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2023-01-21
    Description: Charcoal‐rich Technosols on century‐old relict charcoal hearths (RCHs) are the subject of ongoing research regarding potential legacy effects that result from historic charcoal production and subsequent charcoal amendments on forest soil properties and forest ecosystems today. RCHs consist mostly of Auh horizons that are substantially enriched in soil organic carbon (SOC), of which the largest part seems to be of pyrogenic origin (PyC). However, the reported range of SOC and PyC contents in RCH soil also suggests that they are enriched in nonpyrogenic SOC. RCH soils are discussed as potential benchmarks for the long‐term influence of biochar amendment and the post‐wildfire influences on soil properties. In this study, we utilised a large soil sample dataset (n = 1245) from 52 RCH sites in north‐western Connecticut, USA, to quantify SOC contents by total element analysis. The contents of condensed highly aromatic carbon as a proxy for black carbon (BC) were predicted by using a modified benzene polycarboxylated acid (BPCA) marker method in combination with diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy‐based partial least square regression (r2 = 0.89). A high vertical spatial sampling resolution allowed the identification of soil organic matter (SOM) enrichment and translocation processes. The results show an average 75% and 1862% increase in TOC and BPCA‐derived carbon, respectively, for technogenic Auh horizons compared to reference soils. In addition to an increase in aromatic properties, increased carboxylic properties of the RCH SOC suggest self‐humification effects of degrading charcoal and thereby the continuing formation of leachable aromatic carbon compounds, which could have effects on pedogenic processes in buried soils. Indeed, we show BPCA‐derived carbon concentrations in intermediate technogenic Cu horizons and buried top/subsoils that suggest vertical translocation of highly aromatic carbon originating in RCH Auh horizons. Topmost Auh horizons showed a gradual decrease in total organic carbon (TOC) contents with increasing depth, suggesting accumulation of recent, non‐pyrogenic SOM. Lower aliphatic absorptions in RCH soil spectra suggest different SOM turnover dynamics compared to reference soils. Furthermore, studied RCH soils featured additional TOC enrichment, which cannot be fully explained now. Highlights BC to TOC ratio and high resolution vertical SOC distribution in 52 RCH sites were studied. RCH soils non‐BC pool was potentially different to reference soils. RCH soils feature TOC accumulation in the topmost horizon. There is BC translocation into buried soils on RCH sites.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:631.4 ; benzene polycarboxylated acid marker (BPCA) ; black carbon ; charcoal degradation ; charcoal kiln ; pyrogenic carbon ; relict charcoal hearth ; biochar
    Language: English
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  • 6
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    Defining Hydrogeological Site Similarity with Hierarchical Agglomerative Clustering (2022)
    Blackwell Publishing Ltd | Malden, US
    Details
    Publication Date: 2024-02-28
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Hydrogeological information about an aquifer is difficult and costly to obtain, yet essential for the efficient management of groundwater resources. Transferring information from sampled sites to a specific site of interest can provide information when site‐specific data is lacking. Central to this approach is the notion of site similarity, which is necessary for determining relevant sites to include in the data transfer process. In this paper, we present a data‐driven method for defining site similarity. We apply this method to selecting groups of similar sites from which to derive prior distributions for the Bayesian estimation of hydraulic conductivity measurements at sites of interest. We conclude that there is now a unique opportunity to combine hydrogeological expertise with data‐driven methods to improve the predictive ability of stochastic hydrogeological models.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉〈italic〉Article impact statement〈/italic〉: This article introduces hierarchical clustering as a method for defining a notion of site similarity; the aim of this method is to improve the derivation of prior distributions in Bayesian methods in hydrogeology.〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://github.com/GeoStat-Bayesian/geostatDB
    Description: https://github.com/GeoStat-Bayesian/exPrior
    Description: https://github.com/GeoStat-Bayesian/siteSimilarity
    Keywords: ddc:551.49 ; hydrogeological sites ; hydrogeological modeling
    Language: English
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  • 7
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    Toward an adequate level of detail in flood risk assessments (2023)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2024-01-24
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Flood risk assessments require different disciplines to understand and model the underlying components hazard, exposure, and vulnerability. Many methods and data sets have been refined considerably to cover more details of spatial, temporal, or process information. We compile case studies indicating that refined methods and data have a considerable effect on the overall assessment of flood risk. But are these improvements worth the effort? The adequate level of detail is typically unknown and prioritization of improvements in a specific component is hampered by the lack of an overarching view on flood risk. Consequently, creating the dilemma of potentially being too greedy or too wasteful with the resources available for a risk assessment. A “sweet spot” between those two would use methods and data sets that cover all relevant known processes without using resources inefficiently. We provide three key questions as a qualitative guidance toward this “sweet spot.” For quantitative decision support, more overarching case studies in various contexts are needed to reveal the sensitivity of the overall flood risk to individual components. This could also support the anticipation of unforeseen events like the flood event in Germany and Belgium in 2021 and increase the reliability of flood risk assessments.〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: BMBF http://dx.doi.org/10.13039/501100002347
    Description: Federal Environment Agency http://dx.doi.org/10.13039/501100010809
    Description: http://howas21.gfz-potsdam.de/howas21/
    Description: https://www.umwelt.niedersachsen.de/startseite/themen/wasser/hochwasser_amp_kustenschutz/hochwasserrisikomanagement_richtlinie/hochwassergefahren_und_hochwasserrisikokarten/hochwasserkarten-121920.html
    Description: https://download.geofabrik.de/europe/germany.html
    Description: https://emergency.copernicus.eu/mapping/list-of-components/EMSN024
    Description: https://data.jrc.ec.europa.eu/collection/id-0054
    Description: https://oasishub.co/dataset/surface-water-flooding-footprinthurricane-harvey-august-2017-jba
    Description: https://www.wasser.sachsen.de/hochwassergefahrenkarte-11915.html
    Keywords: ddc:551.48 ; decision support ; extreme events ; integrated flood risk management ; risk assessment
    Language: English
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  • 8
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    Small lateral air pressure gradients generated by a large chamber system have a strong effect on CO2 transport in soil (2023)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2024-02-09
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Gas transport in soils is usually assumed to be purely diffusive, although several studies have shown that non‐diffusive processes can significantly enhance soil gas transport. These processes include barometric air pressure changes, wind‐induced pressure pumping and static air pressure fields generated by wind interacting with obstacles. The associated pressure gradients in the soil can cause advective gas fluxes that are much larger than diffusive fluxes. However, the contributions of the respective transport processes are difficult to separate. We developed a large chamber system to simulate pressure fields and investigate their influence on soil gas transport. The chamber consists of four subspaces in which pressure is regulated by fans that blow air in or out of the chamber. With this setup, we conducted experiments with oscillating and static pressure fields. CO〈sub〉2〈/sub〉 concentrations were measured along two soil profiles beneath the chamber. We found a significant relationship between static lateral pressure gradients and the change in the CO〈sub〉2〈/sub〉 profiles (R〈sup〉2〈/sup〉 = 0.53; 〈italic toggle="no"〉p〈/italic〉‐value 〈2e‐16). Even small pressure gradients between −1 and 1 Pa relative to ambient pressure resulted in an increase or decrease in CO〈sub〉2〈/sub〉 concentrations of 8% on average in the upper soil, indicating advective flow of air in the pore space. Positive pressure gradients resulted in decreasing, negative pressure gradients in increasing CO〈sub〉2〈/sub〉 concentrations. The concentration changes were probably caused by an advective flow field in the soil beneath the chamber generated by the pressure gradients. No effect of oscillating pressure fields was observed in this study. The results indicate that static lateral pressure gradients have a substantial impact on soil gas transport and therefore are an important driver of gas exchange between soil and atmosphere. Lateral pressure gradients in a comparable range can be induced under windy conditions when wind interacts with terrain features. They can also be caused by chambers used for flux measurements at high wind speed or by fans used for head‐space mixing within the chambers, which yields biased flux estimates.〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:631.4 ; advective flux ; chamber flux measurements ; static air pressure fields ; wind‐induced pressure pumping
    Language: English
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  • 9
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    Redoxtrons – An experimental system to study redox processes within the capillary fringe (2023)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2023-11-18
    Description: Spatiotemporal characterisation of the soil redox status within the capillary fringe (CF) is a challenging task. Air‐filled porosities (ε), oxygen concentration (O〈sub〉2〈/sub〉) and soil redox potential (EH) are interrelated soil variables within active biogeochemical domains such as the CF. We investigated the impact of water table (WT) rise and drainage in an undisturbed topsoil and subsoil sample taken from a Calcaric Gleysol for a period of 46 days. We merged 1D (EH and matric potential) and 2D (O〈sub〉2〈/sub〉) systems to monitor at high spatiotemporal resolution redox dynamics within self‐constructed redoxtron housings and complemented the data set by a 3D pore network characterization using X‐ray microtomography (X‐ray μCT). Depletion of O〈sub〉2〈/sub〉 was faster in the organic matter‐ and clay‐rich aggregated topsoil and the CF extended 〉10 cm above the artificial WT. The homogeneous and less‐aggregated subsoil extended only 4 cm above the WT as indicated by ε–O〈sub〉2〈/sub〉–EH data during saturation. After drainage, 2D O〈sub〉2〈/sub〉 imaging revealed a fast aeration towards the lower depths of the topsoil, which agrees with the connected ε derived by X‐ray μCT (ε〈sub〉CT_conn〈/sub〉) of 14.9% of the total porosity. However, small‐scaled anoxic domains with O〈sub〉2〈/sub〉 saturation 〈5% were apparent even after lowering the WT (down to 0.25 cm〈sup〉2〈/sup〉 in size) for 23 days. These domains remained a nucleus for reducing soil conditions (E〈sub〉H〈/sub〉 〈 −100 mV), which made it challenging to characterise the soil redox status in the CF. In contrast, the subsoil aeration reached O〈sub〉2〈/sub〉 saturation after 8 days for the complete soil volume. Values of ε〈sub〉CT_conn〈/sub〉 around zero in the subsoil highlighted that soil aeration was independent of this parameter suggesting that other variables such as microbial activity must be considered when predicting the soil redox status from ε alone. The use of redoxtrons in combination with localised redox‐measurements and image based pore space analysis resulted in a better 2D/3D characterisation of the pore system and related O〈sub〉2〈/sub〉 transport properties. This allowed us to analyse the distribution and activity of microbiological niches highly associated with the spatiotemporal variable redox dynamics in soil environments. Highlights: The time needed to turn from reducing to oxidising (period where all platinum electrodes feature E〈sub〉H〈/sub〉 〉 300 mV) condition differ for two samples with contrasting soil structure. The subsoil with presumably low O〈sub〉2〈/sub〉 consumption rates aerated considerably faster than the topsoil and exclusively by O〈sub〉2〈/sub〉 diffusion through medium‐ and fine‐sized pores. To derive the soil redox status based upon the triplet ε–O〈sub〉2〈/sub〉–E〈sub〉H〈/sub〉 is challenging at present in heterogeneous soil domains and larger soil volumes than 250 cm〈sup〉3〈/sup〉. Undisturbed soil sampling along with 2D/3D redox measurement systems (e.g., redoxtrons) improve our understanding of redox dynamics within the capillary fringe.
    Keywords: ddc:631.4 ; environmental monitoring ; incubation experiments ; redox processes ; soil reducing conditions ; undisturbed soil ; X‐ray microtomography
    Language: English
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  • 10
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    The dilemma of analytical method changes for soil organic carbon in long‐term experiments (2023)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2023-11-17
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈sec xmlns:mml="http://www.w3.org/1998/Math/MathML" id="ejss13362-sec-1003" xml:lang="en"〉 〈p xml:lang="en"〉Long‐term experiments (LTEs) have provided data to modellers and agronomists to investigate changes and dynamics of soil organic carbon (SOC) under different cropping systems. As treatment changes have occurred due to agricultural advancements, so too have analytical soil methods. This may lead to method bias over time, which could affect the robust interpretation of data and conclusions drawn. This study aims to quantify differences in SOC due to changes in dry combustion methods over time, using soil samples of a LTE established in 1963 that focuses on mineral and organic fertilizer management in the temperate zone of Northeast Germany. For this purpose, 1059 soil samples, collected between 1976 and 2008, have been analysed twice, once with their historical laboratory method right after sampling, and a second time in 2016 when all samples were analysed using the same elementary analyser. In 9 of 11 soil sampling campaigns, a paired 〈italic toggle="no"〉t〈/italic〉‐test provided evidence for significant differences in the historical SOC values when compared with the re‐analysed concentrations of the same LTE sample. In the sampling years 1988 and 2004, the historical analysis obtained about 0.9 g kg〈sup〉−1〈/sup〉 lower SOC compared with the re‐analysed one. For 1990 and 1998, this difference was about 0.4 g kg〈sup〉−1〈/sup〉. Correction factors, an approach often used to correct for different analytical techniques, could only be applied for 5 of 11 sampling campaigns to account for constant and proportional systematic method error. For this particular LTE, the interpretation of SOC changes due to agronomic management (here fertilization) deviates depending on the analytical method used, which may weaken the explanatory power of the historical data. We demonstrate that analytical method changes over time present one of many challenges in the interpretation of time series data of SOC dynamics. Therefore, LTE site managers need to ensure providing all necessary protocols and data in order to retrace method changes and if necessary recalculate SOC.〈/p〉 〈/sec〉〈sec xmlns:mml="http://www.w3.org/1998/Math/MathML" id="ejss13362-sec-0003" xml:lang="en"〉 〈title〉Highlights〈/title〉 〈p xml:lang="en"〉〈list list-type="bullet" id="ejss13362-list-0001"〉 〈list-item id="ejss13362-li-0001"〉〈p〉A total of 1059 LTE soil samples taken between 1976 and 2008 were re‐analysed for SOC in 2016〈/p〉〈/list-item〉 〈list-item id="ejss13362-li-0002"〉〈p〉Several methodological changes for SOC determination led to significant different SOC concentration in the same sample〈/p〉〈/list-item〉 〈list-item id="ejss13362-li-0003"〉〈p〉Interpretation and time series of LTE soil data suffer from consideration of analytical method changes and poor documentation of the same〈/p〉〈/list-item〉 〈list-item id="ejss13362-li-0004"〉〈p〉Soil archive establishment, thorough method protocols and diligent proficiency testing after soil method changes ameliorate the dilemma〈/p〉〈/list-item〉 〈/list〉〈/p〉 〈/sec〉
    Description: Brandenburger Staatsministerium für Wissenschaft, Forschung und Kultur http://dx.doi.org/10.13039/501100004581
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100004937
    Description: https://doi.org/10.4228/zalf-acge-b683
    Keywords: ddc:631.4 ; Bland–Altman ; carbon stocks ; data trueness ; Deming regression ; method bias ; soil archive ; soil survey
    Language: English
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  • 11
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    Optimised use of data fusion and memory‐based learning with an Austrian soil library for predictions with infrared data (2023)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2023-12-12
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Infrared spectroscopy in the visible to near‐infrared (vis–NIR) and mid‐infrared (MIR) regions is a well‐established approach for the prediction of soil properties. Different data fusion and training approaches exist, and the optimal procedures are yet undefined and may depend on the heterogeneity present in the set and on the considered scale. The objectives were to test the usefulness of partial least squares regressions (PLSRs) for soil organic carbon (SOC), total carbon (C〈sub〉t〈/sub〉), total nitrogen (N〈sub〉t〈/sub〉) and pH using vis–NIR and MIR spectroscopy for an independent validation after standard calibration (use of a general PLSR model) or using memory‐based learning (MBL) with and without spiking for a national spectral database. Data fusion approaches were simple concatenation of spectra, outer product analysis (OPA) and model averaging. In total, 481 soils from an Austrian forest soil archive were measured in the vis–NIR and MIR regions, and regressions were calculated. Fivefold calibration‐validation approaches were carried out with a region‐related split of spectra to implement independent validations with n ranging from 47 to 99 soils in different folds. MIR predictions were generally superior over vis–NIR predictions. For all properties, optimal predictions were obtained with data fusion, with OPA and spectra concatenation outperforming model averaging. The greatest robustness of performance was found for OPA and MBL with spiking with 〈italic toggle="no"〉R〈/italic〉〈sup〉2〈/sup〉 ≥ 0.77 (N), 0.85 (SOC), 0.86 (pH) and 0.88 (C〈sub〉t〈/sub〉) in the validations of all folds. Overall, the results indicate that the combination of OPA for vis–NIR and MIR spectra with MBL and spiking has a high potential to accurately estimate properties when using large‐scale soil spectral libraries as reference data. However, the reduction of cost‐effectiveness using two spectrometers needs to be weighed against the potential increase in accuracy compared to a single MIR spectroscopy approach.〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:631.4 ; data fusion ; independent validation ; infrared spectroscopy ; MBL ; nitrogen ; outer product analysis ; pH ; soil organic carbon ; spiking ; total carbon
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  • 12
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    Importance of catchment hydrological processes and calibration of hydrological‐hydrodynamic rainfall‐runoff models in small rural catchments (2023)
    Blackwell Publishing Ltd | Oxford, UK
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    Publication Date: 2024-01-19
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉In recent years, many two‐dimensional (2D) hydrodynamic models have been extended to include the direct rainfall method (DRM). This allows their application as a hydrological‐hydrodynamic model for the determination of floodplains in one model system. In previous studies on DRM, the role of catchment hydrological processes (CaHyPro) and its interaction with the calibration process was not investigated in detail. In the present, case‐oriented study, the influence of the spatiotemporal distribution of the processes precipitation and runoff formation in combination with the 2D model HEC‐RAS is investigated. In a further step, a conceptual approach for event‐based interflow is integrated. The study is performed on the basis of a single storm event in a small rural catchment (low mountain range, 38 km〈sup〉2〈/sup〉) in Hesse (Germany). The model results are evaluated against six quality criteria and compared to a simplified baseline model. Finally, the calibrated improved model is contrasted with a calibrated baseline model. The results show the enhancement of the model results due to the integration of the CaHyPro and highlight its interplay with the calibrated model parameters.〈/p〉
    Keywords: ddc:551.48 ; 2D hydrodynamic modeling ; calibration ; direct rainfall modeling ; hydrological processes ; radar data ; runoff formation
    Language: English
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  • 13
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    Onshore thermokarst primes subsea permafrost degradation (2021)
    Wiley-Blackwell
    In:  EPIC3Geophysical Research Letters, Wiley-Blackwell, ISSN: 0094-8276
    Details
    Publication Date: 2024-01-31
    Description: The response of permafrost to submergence can vary between ice-rich late Pleistocene deposits and the thermokarst basins that thawed out during the Holocene. We hypothesize that inundated Alases offshore thaw faster than submerged Yedoma. To test this hypothesis, we estimated depths to the top of ice-bearing permafrost offshore of the Bykovsky Peninsula in northeast Siberia using electrical resistivity surveys. The surveys traversed submerged lagoon deposits, drained and refrozen Alas deposits, and undisturbed Yedoma from the coastline to 373 m offshore. While the permafrost degradation rates of the submerged Yedoma were in the range of similar sites, the submerged Alas permafrost degradation rates were up to 170% faster. Given the abundance of thermokarst basins and lakes along parts of the Arctic coastline, its effect on subsea permafrost degradation must be similarly prevalent. Remote sensing analyses suggest that 54% of lagoons wider than 500 m originated in thermokarst basins.
    Repository Name: EPIC Alfred Wegener Institut
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  • 14
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    Greenhouse gas production and lipid biomarker distribution in Yedoma and Alas thermokarst lake sediments in Eastern Siberia (2021)
    Wiley-Blackwell
    In:  EPIC3Global Change Biology, Wiley-Blackwell, ISSN: 1354-1013
    Details
    Publication Date: 2024-01-31
    Description: Permafrost thaw leads to thermokarst lake formation and talik growth tens of meters deep, enabling microbial decomposition of formerly frozen organic matter (OM). We analyzed two 17-m-long thermokarst lake sediment cores taken in Central Yakutia, Russia. One core was from an Alas lake in a Holocene thermokarst basin that underwent multiple lake generations, and the second core from a young Yedoma upland lake (formed ca. 70 years ago) whose sediments have thawed for the first time since deposition. This comparison provides a glance into OM fate in thawing Yedoma deposits. We analyzed total organic carbon (TOC) and dissolved organic carbon (DOC) content, n-alkanes concentrations, and bacterial and archaeal membrane markers. Furthermore, we conducted one-year-long incubations (4 °C, dark) and measured anaerobic carbon dioxide (CO2) and methane (CH4) production. The sediments from both cores contained little TOC (0.7±0.4 wt%), but DOC values were relatively high, with highest values in the frozen Yedoma lake sediments (1620 mg L-1). Cumulative GHG production after one year was highest in the Yedoma lake sediments (226±212 μg CO2-C gdw-1, 28±36 μg CH4-C gdw-1) and 3 and 1.5 times lower in the Alas lake sediments, respectively (75±76 μg CO2-C gdw-1, 19±29 μg CH4-C gdw-1). The highest CO2 production in the frozen Yedoma lake sediments likely results from decomposition of readily bioavailable OM, while highest CH4 production in the non-frozen top sediments of this core suggests that methanogenic communities established upon thaw. The lower GHG production in the non-frozen Alas lake sediments resulted from advanced OM decomposition during Holocene talik development. Furthermore, we found that drivers of CO2 and CH4 production differ following thaw. Our results suggest that GHG production from TOC-poor mineral deposits, which are widespread throughout the Arctic, can be substantial. Therefore, our novel data are relevant for vast ice-rich permafrost deposits vulnerable to thermokarst formation.
    Repository Name: EPIC Alfred Wegener Institut
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  • 15
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    Thermo‐erosional valleys in Siberian ice‐rich permafrost (2021)
    Wiley-Blackwell
    In:  EPIC3Permafrost and Periglacial Processes, Wiley-Blackwell, 32(1), pp. 59-75, ISSN: 1045-6740
    Details
    Publication Date: 2024-01-31
    Description: Thermal erosion is a major mechanism of permafrost degradation, resulting in characteristic landforms. We inventory thermo-erosional valleys in ice-rich coastal lowlands adjacent to the Siberian Laptev Sea based on remote sensing, Geographic Information System (GIS), and field investigations for a first regional assessment of their spatial distribution and characteristics. Three study areas with similar geological (Yedoma Ice Complex) but diverse geomorphological conditions vary in valley areal extent, incision depth, and branching geometry. The most extensive valley networks are incised deeply (up to 35 m) into the broad inclined lowland around Mamontov Klyk. The flat, low-lying plain forming the Buor Khaya Peninsula is more degraded by thermokarst and characterized by long valleys of lower depth with short tributaries. Small, isolated Yedoma Ice Complex remnants in the Lena River Delta predominantly exhibit shorter but deep valleys. Based on these hydrographical network and topography assessments, we discuss geomorphological and hydrological connections to erosion processes. Relative catchment size along with regional slope interact with other Holocene relief-forming processes such as thermokarst and neotectonics. Our findings suggest that thermo-erosional valleys are prominent, hitherto overlooked permafrost degradation landforms that add to impacts on biogeochemical cycling, sediment transport, and hydrology in the degrading Siberian Yedoma Ice Complex.
    Repository Name: EPIC Alfred Wegener Institut
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  • 16
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    BODIUM—A systemic approach to model the dynamics of soil functions (2023)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2024-01-26
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The increasing demand for biomass for food, animal feed, fibre and bioenergy requires optimization of soil productivity, while at the same time, protecting other soil functions such as nutrient cycling and buffering, carbon storage, habitat for biological activity and water filter and storage. Therefore, one of the main challenges for sustainable agriculture is to produce high yields while maintaining all the other soil functions. Mechanistic simulation models are an essential tool to fully understand and predict the complex interactions between physical, biological and chemical processes of soils that generate those functions. We developed a soil model to simulate the impact of various agricultural management options and climate change on soil functions by integrating the relevant processes mechanistically and in a systemic way. As a special feature, we include the dynamics of soil structure induced by tillage and biological activity, which is especially relevant in arable soils. The model operates on a 1D soil profile consisting of a number of discrete layers with dynamic thickness. We demonstrate the model performance by simulating crop growth, root growth, nutrient and water uptake, nitrogen cycling, soil organic matter turnover, microbial activity, water distribution and soil structure dynamics in a long‐term field experiment including different crops and different types and levels of fertilization. The model is able to capture essential features that are measured regularly including crop yield, soil organic carbon, and soil nitrogen. In this way, the plausibility of the implemented processes and their interactions is confirmed. Furthermore, we present the results of explorative simulations comparing scenarios with and without tillage events to analyse the effect of soil structure on soil functions. Since the model is process‐based, we are confident that the model can also be used to predict quantities that have not been measured or to estimate the effect of management measures and climate states not yet been observed. The model thus has the potential to predict the site‐specific impact of management decisions on soil functions, which is of great importance for the development of a sustainable agriculture that is currently also on the agenda of the ‘Green Deal’ at the European level.〈/p〉
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: https://git.ufz.de/bodium/bodium_v1.0
    Keywords: ddc:631.4 ; agriculture ; computational model ; simulation ; soil microbiology ; soil structure ; sustainable soil
    Language: English
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  • 17
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    Temperature and soil moisture change microbial allocation of pesticide‐derived carbon (2023)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2024-03-18
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Temperature and soil moisture are known to control pesticide mineralization. Half‐life times (DT〈sub〉50〈/sub〉) derived from pesticide mineralization curves generally indicate longer residence times at low soil temperature and moisture but do not consider potential changes in the microbial allocation of pesticide‐derived carbon (C). We aimed to determine carbon use efficiency (CUE, formation of new biomass relative to total C uptake) to better understand microbial utilization of pesticide‐derived C under different environmental conditions and to support the conventional description of degradation dynamics based on mineralization. We performed a microcosm experiment at two MCPA (2‐methyl‐4‐chlorophenoxyacetic acid) concentrations (1 and 20 mg kg〈sup〉−1〈/sup〉) and defined 20°C/pF 1.8 as optimal and 10°C/pF 3.5 as limiting environmental conditions. After 4 weeks, 70% of the initially applied MCPA was mineralized under optimal conditions but MCPA mineralization reached less than 25% under limiting conditions. However, under limiting conditions, an increase in CUE was observed, indicating a shift towards anabolic utilization of MCPA‐derived C. In this case, increased C assimilation implied C storage or the formation of precursor compounds to support resistance mechanisms, rather than actual growth since we did not find an increase in the 〈italic toggle="no"〉tfdA〈/italic〉 gene relevant to MCPA degradation. We were able to confirm the assumption that under limiting conditions, C assimilation increases relative to mineralization and that C redistribution, may serve as an explanation for the difference between mineralization and MCPA dissipation‐derived degradation dynamics. In addition, by introducing CUE to the temperature‐ and moisture‐dependent degradation of pesticides, we can capture the underlying microbial constraints and adaptive mechanisms to changing environmental conditions.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Changing environmental conditions alter the MCPA degradation dynamics and the allocation of pesticide‐derived carbon to anabolic or catabolic metabolism.〈boxed-text position="anchor" content-type="graphic" id="ejss13417-blkfxd-0001" xml:lang="en"〉 〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:13510754:media:ejss13417:ejss13417-toc-0001"〉 〈/graphic〉 〈/boxed-text〉〈/p〉
    Description: Collaborative Research Center 1253 CAMPOS (DFG)
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: DFG Priority Program 2322 “Soil System”
    Description: Ellrichshausen Foundation
    Description: Research Training Group “Integrated Hydrosystem modeling”
    Description: https://doi.org/10.5281/zenodo.5081655
    Keywords: ddc:631.4 ; anabolism ; carbon use efficiency ; catabolism ; effect of soil moisture and temperature ; gene‐centric process model ; MCPA biodegradation
    Language: English
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  • 18
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    Bonamia infection in flat oysters (Ostrea edulis) in relation to European restoration projects (2020)
    Wiley-Blackwell
    In:  EPIC3Aquatic Conservation: Marine and Freshwater Ecosystems, Wiley-Blackwell, ISSN: 1052-7613
    Details
    Publication Date: 2024-03-22
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 19
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    Reducing tillage intensity benefits the soil micro‐ and mesofauna in a global meta‐analysis (2022)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2024-03-22
    Description: Soil fauna drives crucial processes of energy and nutrient cycling in agricultural systems, and influences the quality of crops and pest incidence. Soil tillage is the most influential agricultural manipulation of soil structure, and has a profound influence on soil biology and its provision of ecosystem services. The objective of this study was to quantify through meta‐analyses the effects of reducing tillage intensity on density and diversity of soil micro‐ and mesofaunal communities, and how these effects vary among different pedoclimatic conditions and interact with concurrent management practices. We present the results of a global meta‐analysis of available literature data on the effects of different tillage intensities on taxonomic and functional groups of soil micro‐ and mesofauna. We collected paired observations (conventional vs. reduced forms of tillage/no‐tillage) from 133 studies across 33 countries. Our results show that reduced tillage intensity or no‐tillage increases the total density of springtails (+35%), mites (+23%), and enchytraeids (+37%) compared to more intense tillage methods. The meta‐analyses for different nematode feeding groups, life‐forms of springtails, and taxonomic mite groups showed higher densities under reduced forms of tillage compared to conventional tillage on omnivorous nematodes (+53%), epedaphic (+81%) and hemiedaphic (+84%) springtails, oribatid (+43%) and mesostigmatid (+57%) mites. Furthermore, the effects of reduced forms of tillage on soil micro‐ and mesofauna varied with depth, climate and soil texture, as well as with tillage method, tillage frequency, concurrent fertilisation, and herbicide application. Our findings suggest that reducing tillage intensity can have positive effects on the density of micro‐ and mesofaunal communities in areas subjected to long‐term intensive cultivation practices. Our results will be useful to support decision making on the management of soil faunal communities and will facilitate modelling efforts of soil biology in global agroecosystems. HIGHLIGHTS Global meta‐analysis to estimate the effect of reducing tillage intensity on micro‐ and mesofauna Reduced tillage or no‐tillage has positive effects on springtail, mite and enchytraeid density Effects vary among nematode feeding groups, springtail life forms and mite suborders Effects vary with texture, climate and depth and depend on the tillage method and frequency
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: https://doi.org/10.20387/bonares-eh0f-hj28
    Keywords: ddc:631.4 ; agricultural land use ; conservation agriculture ; conventional agriculture ; soil biodiversity ; soil cultivation
    Language: English
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  • 20
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    An aquaculture risk model to understand the causes and consequences of Atlantic Salmon mass mortality events: A review (2024)
    Wiley-Blackwell
    In:  EPIC3Reviews in Aquaculture, Wiley-Blackwell, ISSN: 1753-5123
    Details
    Publication Date: 2024-05-06
    Description: Mass mortality events (MMEs) are defined as the death of large numbers of fish over a short period of time. These events can result in catastrophic losses to the Atlantic salmon aquaculture industry and the local economy. However, they are challenging to understand because of their relative infrequency and the high number of potential factors involved. As a result, the causes and consequences of MMEs in Atlantic salmon aquaculture are not well understood. In this study, we developed a structural network of causal risk factors for MMEs for aquaculture and the communities that depend on Atlantic salmon aquaculture. Using the Interpretive Structural Modeling (ISM) technique, we analysed the causes of Atlantic salmon mass mortalities due to environmental (abiotic), biological (biotic) and nutritional risk factors. The consequences of MMEs were also assessed for the occupational health and safety of aquaculture workers and their implications for the livelihoods of local communities. This structural network deepens our understanding of MMEs and points to management actions and interventions that can help mitigate mass mortalities. MMEs are typically not the result of a single risk factor but are caused by the systematic interaction of risk factors related to the environment, fish diseases, feeding/nutrition and cage-site management. Results also indicate that considerations of health and safety risk, through pre- and post-event risk assessments, may help to minimize workplace injuries and eliminate potential risks of human fatalities. Company and government assisted socio-economic measures could help mitigate post-mass mortality impacts. Appropriate and timely management actions may help reduce MMEs at Atlantic salmon cage sites and minimize the physical and social vulnerabilities of workers and local communities.
    Repository Name: EPIC Alfred Wegener Institut
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  • 21
    Electronic Resource
    Electronic Resource
    Stark effect and excitonic tunneling escape process in semiconductor quantum wells (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4983-4988 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this work, we have numerically integrated in space and time the effective mass Schrödinger equation for an exciton in a semiconductor quantum-well structure. Considering a Coulomb interaction between the electron-hole pair and an external electric field, we have studied the excitonic tunneling escape process from semiconductor quantum wells. Our method of calculation has been applied to types-I, -II, and -III quantum-well superlattices. In addition, we present the calculated excitonic lifetimes for the GaAs/GaAlAs, InAs/GaSb, and HgTe/HgCdTe systems under an external electric field. In the HgTe/CdTe system, the possibility of having similar electron and hole lifetime values is also found if the applied electric field is large enough.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357208
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  • 22
    Electronic Resource
    Electronic Resource
    Two-dimensional model of the ignition phase of high-pressure glow discharges (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5036-5046 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A self-consistent two-dimensional (2D) model of large volume inhomogeneously preionized transient high-pressure glows as used in XeCl lasers is described. The basic concept is to use a curvilinear orthogonal coordinate system generated by conformal mapping of a cartesian system. The model uses the local field approximation and is based on a cartesian 2D model of J.-P. Boeuf and L. C. Pitchford [IEEE Trans. Plasma Sci. 19, 286 (1991)]. As only direct ionization is taken into account, applications are limited to the ignition phase. Application to a discharge between cylindrical rods predicts a high degree of E-field homogenization due to space charges and demonstrates the limits of parallel resistor models. Inside the cathode sheath an explosive formation of a very thin highly ionized layer is predicted. This sheath ignition is also seen in experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357215
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  • 23
    Electronic Resource
    Electronic Resource
    Reliability test of popular fractal techniques applied to small two-dimensional self-affine data sets (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5070-5078 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fractal dimensions of five fractional Brownian motion (fBm) surfaces of 257×257 pixel size, with Hurst exponent H ranging from 0.1 to 0.9, were computed by profile, contour, and surface area analyses. A technique was deemed reliable if it demonstrated accuracy, consistency and sensitivity. Of all the techniques examined, surface area analysis methods, namely, two-dimensional pyramid and Peleg methods, were found to be most reliable and efficient for the data size studied. Hence, these were employed in a preliminary fractal analysis of poly(methyl methacrylate) and poly(styrene) fracture surfaces. The surfaces were imaged at scan sizes ranging from 1–6.5 μm by atomic force microscopy (AFM). The images indicated the existence of fractal structure and a high degree of roughness at microstructural scales for both the surfaces. These observations were supported by the results of the two surface area analysis techniques. A more conclusive study was prevented by severe scoring of the surfaces by the AFM tip at smaller scan sizes and the availability of only a narrow range of scan sizes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358490
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  • 24
    Electronic Resource
    Electronic Resource
    Influence of metal/n-InAs/interlayer/n-GaAs structure on nonalloyed ohmic contact resistance (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5099-5110 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated in detail the influence of interlayer structures on nonalloyed ohmic contact resistance (ρc), in terms of the crystalline defects and the potential barrier at the interlayer/GaAs interface. The interlayer structures are a graded-band-gap InAs/GaAs strained-layer superlattice (graded SLS), a graded-band-gap InGaAs, and conventional SLSs without graded band gaps. A two-layer transmission line model indicates that the barrier resistance in the interlayer highly depends on the interlayer structure: ≤5×10−8 Ω cm2 for the graded SLS and graded InGaAs interlayers and 10−5–10−6 Ω cm2 for the conventional SLS interlayers. To explain the large dependence of the interlayer structure, first, the density and distribution of the misfit dislocations and stacking faults caused by the large lattice mismatch between InAs and GaAs have been investigated in detail by high-resolution transmission electron microscopy. In the graded SLS and conventional SLS interlayers, the influence of the high-density depletion regions spread near the crystalline defects is found to be negligible because of the high doping concentrations (∼1019 cm−3) in the interlayers. Second, the potential barrier at the interlayer/GaAs interface has been investigated by simulating the barrier resistance. The potential barrier profile is calculated self-consistently with Poisson's equation and the Schrödinger equation. Tunneling current through the barrier is analyzed using the Wentzel–Kramers–Brillouin approximation or the numerical wave solution to the Schrödinger equation. The graded SLS interlayer has the effectively smooth conduction band profile without the barriers, which is similar to that of the graded InGaAs interlayer, because of its short period SLS. In the conventional SLS interlayers, the reasonable barrier heights of 0.14–0.26 eV obtained by this simulation indicates that these barriers are the dominant factor which increases the contact resistances. For the low-resistance nonalloyed ohmic contact, therefore, a smooth conduction band profile without band discontinuity is more predominant than the reduction in the crystalline defect density.
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    URL: http://dx.doi.org/10.1063/1.357222
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  • 25
    Electronic Resource
    Electronic Resource
    Fracture of metal-polymer line structures. I. Semiflexible polyimide (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5136-5142 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fracture characteristics of metal/polymer line structures formed by depositing Au/Cr lines on a semiflexible polyimide, pyromellitic dianhydride-oxydianiline (PMDA-ODA), substrate have been investigated using a stretch deformation technique. The delamination behavior, fracture morphology, fracture energy, and energy dissipation rate have been determined as a function of line width and thickness. The metal dimension was found to influence the crack formation mode and morphology. The experimental studies were supplemented by finite-element analysis to evaluate the stress distribution and deformation energetics of the line structure, which takes into account the plastic deformation of the metal and the polymer. Results from this analysis show that the observed fracture characteristics can be attributed to the edge and thickness effects induced by metal confinement. Essentially, the deformation behavior is determined by the mechanical environment induced by metal confinement at the interface. Plastic deformation of both metal and polymer plays an important role in controlling the stress distributions as well as the deformation energetics. The fracture energy of the metal-polyimide interface determined by an overall energy balance method was consistent with that obtained from energy dissipation rate. The average value is 25 J/m2 for the Au/Cr/PMDA-ODA line structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357227
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  • 26
    Electronic Resource
    Electronic Resource
    Intermetallic formation in copper/magnesium thin films—kinetics, nucleation and growth, and effect of interfacial oxygen (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5161-5170 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ resistance measurements, x-ray diffraction, Rutherford backscattering spectrometry, transmission electron microscopy, isothermal and constant heating rate differential scanning calorimetry and Auger electron spectrometry depth profiles have been used to investigate the interactions in copper and magnesium thin films leading to the growth of Cu2Mg and CuMg2 intermetallics. The effect of exposing the reacting interfaces to controlled exposure of oxygen on the nucleation and growth kinetics of such intermetallics was also investigated. It is found that the first phase to form is CuMg2, at about 200–215 °C. It is determined that the formation of CuMg2 occurs by a two step process consisting of nucleation and growth. The nucleation of CuMg2 takes place in a region composed of a Cu/Mg solid solution. The nuclei form at certain preferred sites and grow in directions both parallel and perpendicular to the surface, eventually leading to a continuous CuMg2 layer. The growth of CuMg2 nuclei in the plane of the original interface occurs at a constant rate, whereas the growth in a direction perpendicular to the original interface is found to be diffusion limited. In the presence of excess copper Cu2Mg forms at higher temperatures, with complete conversion to Cu2Mg occurring at about 380 °C. When the Cu surface is dosed with oxygen prior to Mg deposition, ramp rate differential scanning calorimetry (DSC) shows that the nucleation and growth of CuMg2 as well as the growth of Cu2Mg are not disturbed. Dosing the Mg surface with oxygen results in significant changes in the growth of the two phases. In this case a thin MgO layer is formed at the oxygen dosed surface, lateral growth of CuMg2 is unaffected, but vertical growth of CuMg2 across the oxygen dosed interfaces is delayed by 25–30 °C. The growth of Cu2Mg is also shown to be delayed, by 22–54 °C due to the interfacial oxygen dose.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357231
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  • 27
    Electronic Resource
    Electronic Resource
    Calorimetric analysis of thin-film reactions: Experiments and modeling in the nickel/silicon system (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5195-5201 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin-film reactions between nickel and silicon are investigated by differential scanning calorimetry and transmission electron microscopy on evaporated bilayers with different compositions and thicknesses. The thermograms are interpreted by a computer modeling, based on diffusion-controlled growth. Experiments and simulation reveal the simultaneous formation of crystalline Ni2Si and of an amorphous phase of composition probably near NiSi. The derived kinetic data confirm literature values from isothermal experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357238
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  • 28
    Electronic Resource
    Electronic Resource
    X-ray photoelectron diffraction study of YbAs/GaAs(001) and ScAs/GaAs(001) heterostructures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5218-5224 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polar angle distributions of core level photoemission intensities recorded on YbAs/GaAs(001) and ScAs/GaAs(001) heterostructures are presented. They allow first the surface roughness of thin YbAs overlayers to be seen, second to estimate the tetragonal distortion of a strained ScAs film and, third, the most interesting point, to demonstrate in a direct fashion that the mixed (Yb-As) (010) planes of YbAs grow in the prolongation of the As planes of GaAs. The results are compared to those obtained by other authors with various techniques. The main advantage of the photoelectron diffraction method over the other techniques is that it can be performed on very thin epitaxial films (some monolayers) directly in situ under ultrahigh vacuum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357171
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  • 29
    Electronic Resource
    Electronic Resource
    Magnetic field and current distribution in metallized capacitors (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5288-5293 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We attempt to establish the mathematical expression of the current and the magnetic field in a metallized capacitor. The expression of the impedance of this capacitor is also presented. The distribution of the current is discussed through the variation of the capacitor impedance and compared to experimental ones. There is good agreement between experimental and theoretical results. The analytical expressions of the magnetic field and the current also show a dependence on parameter δ2 akin to the skin depth in conductors. δ2 also depends on frequency. When δ2 is smaller than the outer radius of the capacitor, the current distribution becomes inhomogeneous.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357179
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  • 30
    Electronic Resource
    Electronic Resource
    Electrical, optical properties, and surface morphology of high purity InP grown by chemical beam epitaxy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5300-5308 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High purity InP layers have been grown by chemical beam epitaxy using H2 as the carrier gas for transporting the metal alkyl trimethylindium into the growth chamber. InP layers exhibiting Hall mobility as high as 238 000 cm2/V s at 77 K and with a peak value of 311 000 cm2/V s at 50 K and residual Hall concentration of 6×1013 cm−3 at 77 K were grown at 500 °C using a low V/III ratio (2.2) and a phosphine (PH3) cracking cell temperature of 950 °C. The 4.2 K photoluminescence spectra were dominated by donor bound exciton (D0,X)n up to n=6 and free exciton (X) transitions for InP layers grown above 500 °C. All the InP samples exhibited very weak acceptor related photoluminescence transitions indicating very low concentration of acceptors. The energy of these transitions suggests that Mg is the major residual acceptor. Donor impurity identification by high resolution magnetophotoluminescence indicated that S and Si are the major impurities. PH3 has been found to be the major source of S impurities in the present study.
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    URL: http://dx.doi.org/10.1063/1.357181
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    Superconductivity in PtSi ultrathin films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5339-5342 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Normal and superconducting properties of PtSi films with thicknesses of d=2–20 nm have been investigated. The superconducting transition has been observed on the thin films down to d=4 nm. The systematic reduction of the transition temperature with decreasing d (increasing the sheet resistance) has been explained by the localization and Coulomb interaction effects on superconductivity. The temperature dependence of the upper critical field indicates that the PtSi films behave as homogeneous superconductors.
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    URL: http://dx.doi.org/10.1063/1.357186
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    Magnetic and structural properties of CoNiPt(SiO2) alloy films for high-density longitudinal recording (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5361-5370 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic and structural properties of sputtered CoNiPt(SiO2) alloy films have been studied for high-density longitudinal recording media. In-plane coercivity remarkably increases from 1400 to 2500 Oe with an increase of SiO2 content up to 4 at. % and coercive squareness S* slightly decreases from 0.90 to 0.87, while the perpendicular magnetic anisotropy is not changed significantly. Media noise is markedly reduced by the addition of SiO2. Si in the film is shown to be in the form of SiO2 by x-ray photoelectron spectroscopy. In x-ray diffraction, hcp-CoNiPt lattice is observed and the lattice constants of this hcp structure are expanded by the SiO2 addition. Relative integrated intensities of the diffraction peaks from (100) and (002) planes to (101) plane are not dependent on the SiO2 content, which indicates that the average orientation of the c axis of the hcp lattice is not influenced by the SiO2 addition. This agrees with the result that the perpendicular anisotropy is not significantly changed. From the transmission electron microscopy and high-resolution scanning electron microscopy analyses, grain size decreases with the SiO2 addition. Moreover, the outline and shape of crystal grains become sharper with the SiO2 addition of 2 at. % than those in pure CoNiPt. With the 4 at. % SiO2, clear separation among each crystal grain is observed. These changes of the grain structure by the SiO2 addition are attributed to the chemical segregation of the SiO2 at the grain boundary. It is concluded that the development of this grain separation is a major reason for remarkable increase in the coercivity and reduction of the media noise by the SiO2 addition.
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    URL: http://dx.doi.org/10.1063/1.357189
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    A model for the reversible magnetization in amorphous alloys (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5371-5379 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new model is presented which quantitatively describes the reversible magnetization process and its contribution to the magnetization curve in soft amorphous ribbons. It takes into account the role of the coherent moment rotations, through analysis of the orientation distribution of the magnetization vector Is in the sample cross section and its evolution with the applied field. Such analysis relies on the assumption, dictated by magnetic domains observations, of a spatial distribution of local anisotropies, whose intensity and direction are mainly determined by the long-range random stresses quenched in during the process of rapid solidification. The reversible I(H) curve is obtained by integrating the local magnetization contributions with respect to their angular distribution, according to a minimum energy condition involving the Zeeman, the local anisotropy, and the macroscopic anisotropy terms. It is shown that a relatively simple analytical expression for I(H) can be worked out. The model is applied to experimental I(H) recoil curves, which have been determined as a function of the stress-induced anisotropy in positive magnetostriction (Fe81B14Si3C2) and negative magnetostriction (Co80B10Si10) amorphous ribbons. It is shown that the shape of I(H) and its evolution with the applied tensile/compressive stress are correctly predicted by the theory.
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    URL: http://dx.doi.org/10.1063/1.357191
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    Photoluminescence and p-type conductivity in CdTe:N grown by molecular beam epitaxy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5423-5428 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An rf nitrogen (N) plasma source has been used to achieve p-type conductivity in molecular beam epitaxy CdTe layers grown with a Cd overpressure. Photoluminescence and secondary ion mass spectrometry measurements have confirmed the incorporation of the N species, and evidence for the resulting p-type conductivity has been obtained using capacitance-voltage and current-voltage techniques. Net hole concentrations as high as 2×1017 cm−3 have so far been achieved, which contrasts with the normally n-type nature of our undoped CdTe layers.
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    Fluorescence associated with Fe3+ ions in nanostructured Al2O3 (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5453-5456 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fluorescence phenomena of nanostructured Al2O3 without doping and after doping of nano-Fe2O3 (4.61 and 48.01 wt %) were systematically investigated. The results show that a new fluorescence band with a peak position of about 17 500 cm−1 occurs for boehmite, η-Al2O3 and γ-Al2O3 and it disappears for α-Al2O3. This band can be attributed to fluorescence of Fe3+ in the systems with low-order degree (boehmite, η- and γ-Al2O3 and interfaces), which arises from 6A1→4T1 d5 electron transitions of Fe3+.
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    URL: http://dx.doi.org/10.1063/1.357203
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    Measurement of local porosities and dielectric dispersion for a water-saturated porous medium (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5473-5480 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The frequency-dependent conductivity and dielectric constant of a salt-water-saturated porous glass specimen have been measured. The measurements cover the full frequency range of the Maxwell–Wagner dispersion. The experimental results have been compared with the recently introduced local porosity theory and with previous theories. For the purpose of comparing with the local porosity theory experimental measurements of local porosity distributions from digitized pore space images are presented. These experimental porosity distributions are then used for a first experimental test of local porosity theory. The comparison with previous theoretical expressions for the frequency-dependent effective dielectric function shows that local porosity theory constitutes a significant improvement in the quantitative agreement.
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    Wet thermal oxidation of AlxGa1−xAs compounds (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5503-5507 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results are presented on the wet thermal oxidation of AlxGa1−xAs. The growth of wet thermal oxides of AlxGa1−xAs is shown to be linear with time. An O2 carrier gas was found to form a self-terminating oxide for compositions investigated (x(approximately-greater-than)0.4), but required elevated temperatures for substantial growth. The use of a medium oxygen concentration (∼20%) in a N2 carrier formed nonuniform oxides for all compositions investigated. A low O2 concentration (0.1%) in the N2 carrier was found to reduce the activation energy of the oxidation process for Al0.6Ga0.4As from 1.9 to 1.0 eV while increasing the activation energy of Al0.8Ga0.2As from 1.6 to 1.75 eV. For these wet thermal oxides it is observed that lateral oxidation at heterojunction interfaces is enhanced. This enhanced lateral oxidation can be attributed to local stress due to the smaller volume of the growing oxide compared to the volume of the consumed semiconductor.
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    Optimum particle size distribution of an electrorheological fluid (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5528-5532 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optimum particle size distribution of an electrorheological fluid (ERF) is studied theoretically by the cubic particle chain model developed by the authors. For simplification purposes, the study is limited to a mixture that consists of two different particle sizes, i.e., small particles and large particles, but of the same permittivity. We adopt periodic boundary conditions with two chains in the unit cell. Static yield stress is calculated for three particle configurations. In the first configuration, each chain contains only one particle size, either small or large. The other configurations use chains which are constructed from small and large particles, arranged alternately. However, whereas the second requires particles of neighboring chains to be complementary, the third requires an alternating arrangement. The relative magnitude of the calculated yield stress in these the situations is τ2〈τ3〈τ1. In the first configuration calculated yield stress is independent of the particle size ratio. However in the second configuration, the yield stress increases as the size ratio approaches unity. From the results of these typical cases, we conclude that the ERF consisting of only the same particles gives the largest static yield stress. Also interactions among the chains as a description of the many-body effect is discussed.
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    Nonstationary theory of mode competition in gyrotrons with allowance for small inhomogeneity of the guiding magnetic field (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5580-5585 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-power millimeter wave generators can induce electron cyclotron waves in a plasma which can fulfill many functions (plasma breakdown, heating, current drive) in fusion plasma reactors including both tokamak and stellarator concepts. All these applications require tens of megawatts of power in the frequency range 100–300 GHz and power 0.5–1.5 MW per unit. Among various microwave sources gyrotrons are the most developed source. Because of the heat losses in resonator walls at such high frequencies and powers oversized cavities must be used. In such cavities the mode competition becomes a severe problem. The most advanced theory of mode competition in gyrotrons is the nonstationary nonlinear theory. In the present article we extend this theory by allowing for inhomogeneity of the guiding magnetic field. The importance of this generalized theory is illustrated in the case of a 3 MW 140 GHz gyrotron with a coaxial cavity working in the TE21,13 mode.
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    Scanning tunneling microscopy/spectroscopy studies of conducting polymer polypyrrole (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5595-5597 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrahigh-vacuum scanning tunneling spectroscopy and tunneling spectroscopy measurements of polypyrrole-vacuum-metal and polypyrrole-vacuum-polypyrrole tunneling junctions indicates the existence of three characteristic energy levels, 0.60, −0.40, and −0.65 eV near the Fermi level of an as-grown polypyrrole films. The measured energy levels of −0.40 and −0.65 eV could be attributed to localized filled states and mobility edge, respectively.
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    Clustering in erbium-doped silica glass fibers analyzed using 980 nm excited-state absorption (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4472-4478 
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    Source: AIP Digital Archive
    Topics: Physics
    Notes: A nonsaturable component to the 980 nm excited state absorption (ESA) is found in Er3+-doped silica glass fibers. This anomalous behavior of the ESA provides a way of quantitatively characterizing the degree of clustering in these glasses. It is found that the degree of clustering is greater for higher Er3+ concentrations, and is significantly reduced with the addition of aluminum to the glass. With this method it is also found to be possible to distinguish between true clustering and the occurrence of closely spaced Er3+ pairs in a random distribution.
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    Spectroscopic measurement of atomic hydrogen level populations and hydrogen dissociation degree in expanding cascaded arc plasmas (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4499-4510 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical absorption spectroscopy has been applied to measure the absolute population densities of the first excited levels of atomic hydrogen H*(n=2) and argon Ar*(4s) in an expanding cascaded arc plasma in hydrogen-argon mixture. It is demonstrated that the method allows us to determine both H*(n=2) and Ar*(4s) absolute density radial profiles for H2 admixtures in Ar ranging from 0.7% to 10% with good accuracy. The measured H*(n=2) densities are in the 1014–1016 m−3 range, and Ar*(4s) densities are in the range of 1015–1018 m−3. It has been shown, that the density of hydrogen excited atoms H*(n=2) serves as an indicator of the presence of argon ions and hydrogen molecules in the expanding plasma. A kinetic model is used to understand evolution of H*(n=2) density in the expansion, and to estimate the total atomic hydrogen population density and hydrogen dissociation degree in sub- and supersonic regions of the plasma.
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    Gettering of copper by bulk stacking faults and punched-out dislocations in Czochralski-grown silicon (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4540-4546 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The characteristics of Cu precipitation on various types of defects associated with oxygen precipitation in Czochralski-grown silicon are investigated by transmission electron microscopy and the electron-beam-induced-current technique. Specimens containing dominantly either punched-out dislocations or bulk stacking faults were intentionally contaminated with Cu at various temperatures and cooled at three different rates. Colonies of Cu precipitates developed irrespective of cooling rate, apparently originating from punched-out dislocations developed around oxygen precipitates. In heavily contaminated specimens cooled fast from the contamination temperature, Cu also precipitates on Frank partial dislocations bounding stacking faults. During slow cooling, precipitation of Cu takes place on Frank partials only in lightly contaminated specimens but never in heavily contaminated specimens. Cu precipitates in colonies are thermally more stable than those formed on Frank partials. It is concluded that punched-out dislocations are more favorable precipitation sites for Cu than Frank partials.
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    Thermal expansion of Ni/Cu multilayers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4567-4570 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The coefficient of thermal expansion of electrodeposited Ni/Cu multilayers was obtained by measuring the evolution of membrane resonances and hence the tension as a function of temperature. The apparent thermal expansion coefficient of the multilayer membranes increases as the interface density of the multilayers increases. This increase is analyzed in terms of stress relaxation resulting from sliding of nonperfectly bonded interfaces. The analysis permits the normalization of all thermal expansion data of the Cu/Ni multilayers with layer thicknesses ranging from 20 to 800 nm but not of the thinnest layers, 2 nm thick. The results are consistent with the idea that interfacial adhesion improves as the layer thickness becomes very small, favoring epitaxial growth.
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    Forward elastic recoil measurements using heavy ions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4524-4532 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The application of the elastic recoil detection technique utilizing heavy ions for the analysis of semiconductor samples is demonstrated. With this technique the depth profiles of the primary constituents as well as profiles of all impurities can be measured in one spectrum. Depending on the target material, a depth resolution down to 20 nm can be achieved. All elements except hydrogen can be detected with almost the same sensitivity, namely ∼1×1015 at/cm2 with 136 MeV I in a 30° recoil geometry. For hydrogen, the sensitivity is about four times better.
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    Growth and shrinkage of surface stacking faults in float-zone and Czochralski silicon (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4547-4552 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model for the growth and shrinkage of stacking faults in silicon is presented. It accounts for interstitial traps and a nonuniform concentration of intrinsic point defects. The complete system of balance equations of intrinsic point defects is solved numerically to simulate the kinetics of stacking faults during oxidation under the assumption that float-zone silicon contains less interstitial traps than Czochralski silicon. Investigation of the influence of different interstitial trap concentrations on the growth and shrinkage of surface stacking faults shows that the kinetics of surface stacking faults is not strongly affected by the presence of interstitial traps. Surface stacking faults are expected to grow in float-zone and Czochralski silicon in a similar way.
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    Effect of implant temperature on dopant diffusion and defect morphology for Si implanted GaAs (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4571-4575 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental observations of dopant diffusion and defect formation are reported as a function of implant temperature in Si implanted GaAs. The diffusion of Si during post-implant annealing decreases by a factor of 2.5 as the implant temperature increases from −2 to 40 °C. In this same temperature range, the maximum depth and density of extrinsic dislocation loops increase by factors of 3 and 4, respectively. Rutherford backscattering channeling measurements indicate that Si implanted GaAs undergoes an amorphous to crystalline transition at Si implant temperatures between −51 and 40 °C. A unified explanation of the effects of implant temperature on both diffusion and dislocation formation is proposed based on the known differences in sputter yields between crystalline and amorphous semiconductors. The model assumes that the sputter yield is enhanced by amorphization in the lower temperatures, thus increasing the excess vacancy concentration. Estimates of excess vacancy concentration are obtained by simulations of the diffusion profiles and are quantitatively consistent with a realistic sputter yield enhancement.
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    Models for ultrasonic characterization of environmental degradation of interfaces in adhesive joints (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4643-4650 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we discuss two models of environmental degradation of adhesive joints developed from experimental observation of the joint failure mode. It is found that after severe degradation, failure is dominated by the interfacial mode, i.e., by failure at the interface between adhesive and adherend. The fraction of failure in the interfacial mode was found to be related to the joint strength and to be proportional to the frequency shift of a minimum in the spectrum of the reflected ultrasonic signal. One model considers an interface as an interphase in the form of a nonhomogeneous layer composed of two phases: "soft'' which is viscoelastic (degraded part of the interphase) and "stiff'' corresponding to the nondamaged interphase. Increase of the "soft'' phase fraction corresponds to the process of degradation in the interphase. The second model describes degradation in a form of disbonds filled by absorbed water at the interface. The disbonded interface is modeled by transverse spring boundary conditions, with the complex spring stiffness representing the quality of the bond. The influence of different disbond growth scenarios is considered. Advantages and drawbacks of these models are discussed.
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    Conductance oscillations due to a controllable impurity in a quantum box (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4676-4681 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present calculations of conductance in a multiply connected nanostructure with a quantum box geometry. Well-defined conductance oscillations appear which are attributed to the quantum interference effect in the presence of a controllable impurity in the quantum box. As the strength of the impurity potential is modulated, conductance oscillations arise from the constructive and destructive interference for the two electronic paths around the centrally located impurity and a third tunneling path through the impurity. We discuss the dependence of these oscillations on the size of the impurity, in terms of circulating or bound states in the quantum box formed by multiple reflections of the phase-coherent electron. The conductance oscillations are predicted to be strong for realistic structural parameters and robust against increasing temperature.
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    Scattering mechanisms and defects in InP epitaxially grown on (001) Si substrates (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4705-4712 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carrier concentration and mobility of unintentionally doped InP layers, grown directly on Si using metal-organic vapor-phase epitaxy, have been studied. The formation of antiphase domains (APDs) was found to depend on annealing of the Si substrate in an AsH3 flow prior to epitaxial growth. Dislocation densities determined by the wet chemical delineation technique were (8±1)×107 cm−3, seemingly uncorrelated to APDs in the layers. In addition to a shallow donor and a compensating acceptor, a deep donor was observed affecting the temperature dependence of the free-electron concentration between 77 and 300 K. The electron mobility in this temperature range could be described in terms of the scattering mechanisms which are dominant in homoepitaxial InP, namely, scattering due to polar optical phonons, to ionized impurities, and to space charges. Electron scattering due to either of these mechanisms was strongly influenced by the occurrence of antiphase boundaries (APBs). The space-charge density as well as the degree of compensation of the epitaxial layers increases with the density of APBs. Degraded 300 K mobilities were obtained indicating the effect of local stress at the APB.
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    Carrier transport in polycrystalline silicon films deposited by a layer-by-layer technique (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4728-4733 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transport processes in phosphorus-doped polycrystalline silicon thin films are examined by standard six-electrode Hall effect and conductivity measurements over a wide temperature range, 100–400 K. These films were deposited by a novel layer-by-layer technique at very low substrate temperatures (300–360 °C) using fluorinated precursors, SiFmHn (m+n≤3). The analysis indicated that the grain boundaries are the major barriers to carrier transport. The grain boundary carrier transport is controlled by thermionic emission at high temperatures, whereas at low temperatures, it is dominated by a tunneling process through the barriers. The electrical properties of these films were found to vary as a function of the film thickness. It appears that the grain boundary defects are passivated to a large degree by this novel deposition technique and that the grain boundary barriers are consequently smaller than those in films prepared by other growth schemes.
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    Calculation of hole mobility in doped SiGe alloys using a Monte Carlo method with a bond orbital band structure (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4749-4752 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hole mobility in strained Si1−xGex/Si(001) layers is calculated as functions of temperature and doping concentration for various Ge contents using a Monte Carlo technique. In the Monte Carlo simulation, the band structure is computed by using a bond orbital model, which combines the k⋅p and the tight-binding methods with a strain Hamiltonian. The Fermi–Dirac distribution is employed for heavily doped impurity scattering. The alloy interaction potential of 1.0 eV for the Monte Carlo model is obtained by fitting the measured velocity-field characteristics in strained Si1−xGex alloys. The calculated hole mobilities compare well with experimental results. The strain effect on hole transport is also evaluated.
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    Dynamic instabilities in the power spectrum of deeply modulated semiconductor lasers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4003-4006 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Semiconductor lasers under large-signal direct modulation by a square waveform are found to exhibit a transition from a power spectrum characterized by a fundamental frequency and FM sidebands to a continuous spectrum with a catastrophically broadened linewidth of the order of several GHz. The interesting feature of the phenomenon is that the photon output remains periodic apart from noise-induced fluctuations, and the broadening of the power spectrum is attributed to the sensitivity of the phase of the optical field to a large difference in the relaxation oscillation frequencies in the on and off states as well as the coupling between motions at the intrinsic resonance frequency of the system and the externally-imposed modulation frequency. It is shown that under deep modulation by a periodic injection current, the optical phase becomes aperiodic generating a wide range of new frequencies in the power spectrum. It is also demonstrated that by confining the excursions of the injection current to the region of almost-linear optical response, linewidth broadening may be avoided. Quantitative criteria for determining the boundary of the broadened-linewidth region are presented for several modulation frequencies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357346
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    Thermal diffusivity measurement of near-pseudobinary HgCdTe solid and melt, Te-rich HgCdTe and HgZnTe melts, and pure Te solid and melt by the laser flash technique (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4022-4028 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thermal diffusivities of mercury cadmium telluride, (Hg1−xCdx)1−yTey, and mercury zinc telluride, (Hg1−xZnx)1−yTey, with 0.55≤y≤1.0 and 0.0125≤x≤0.054 65, and of pure Te were measured from 350 to 850 °C by the laser flash technique. The diffusivity of near-pseudobinary Hg1−xCdxTe solids decreased more rapidly with temperature approaching the melting point than did pseudobinary solids previously reported: The solid diffusivity for x=0.028 17 and y=0.55 was 0.83 mm2/s at 371 °C, decreasing to 0.22 mm2/s at 614 °C. The diffusivity of Te-rich (Hg1−xCdx)1−yTey melt increased with x and with temperature: The melt diffusivity for x=0.039 36 and y=0.782 was 0.91 mm2/s at 485 °C, increasing to 4.93 mm2/s at 851 °C. For Te-rich (Hg1−xZnx)1−yTey melt with x=0.0125 and y=0.7944 there appeared to be a minimum diffusivity of about 2.6 mm2/s near 690 °C. The thermal diffusivity of pure Te solid was 0.97 mm2/s at 300 °C and decreases to 0.64 mm2/s at 439 °C. The melt diffusivity of pure Te was 1.52 mm2/s at 486 °C, increased to 3.48 mm2/s at 584 °C. Experimental data presented can be used to calculate the thermal conductivity needed for designing systems capable of growing a better quality single crystal of these materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357349
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    Simple model of foam drainage (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4029-4035 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple model of foam drainage is introduced in which the Plateau borders and quadruple junctions are identified with pools that discharge through channels to pools underneath. The flow is driven by gravity and there are friction losses in the exhausting channels. The equation of Bernoulli combined with the Hagen–Poiseuille equation is applied to describe the flow. The area of the cross section of the exhausting channels can be taken as a constant or may vary during drainage. The predictions of the model are compared with standard drainage curves and with the results of a recently reported experiment in which additional liquid is supplied at the top of the froth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357350
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    Spatially resolved measurement of lattice damage in alpha-particle-irradiated type IIa natural diamond by confocal photoluminescence microscopy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4050-4053 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Confocal fluorescence microscopy has been used to measure the three-dimensional distribution of the H3 color center produced in type IIa natural diamonds by 5 MeV He+ irradiation at a total fluence of 8×1015 cm−2. The peak of the H3 emission occurs 16 μm below the surface of the irradiated side of the diamond, which is in fair agreement with the peak of the vacancy distribution predicted by a Monte Carlo calculation (transport of ions in matter or trim). The H3 distribution is broader in the direction normal to the surface (10 μm full width at half maximum) than the trim calculation. This is attributed to diffusion of vacancies caused by self-annealing during irradiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357353
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    A study of Cu50Fe50 produced by mechanical alloying and its thermal treatment (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4061-4067 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A specimen of Cu50Fe50 equiatomic composition was mechanically alloyed (MA) by ball milling starting from the pure elements, which are immiscible according to the equilibrium phase diagram. Structural analysis by x-ray and neutron diffraction has shown that the mechanical process initially reduces the crystallite size of both elements as a function of the milling time. The diffraction data show that the bcc iron phase is subsequently consumed, due to progressive incorporation of the iron atoms into the fcc copper matrix. The Mössbauer spectra of a specimen MA for 16 h has a broad magnetic profile typical of a Fe-Cu extended solid solution, with some evidence of two local environments of the iron atoms and a small admixture of the γ-Fe. The annealing of these MA treated specimens effects a decomposition of the extended solid solution into FCC copper and both α- and γ-iron allotropes. This decomposition process is discussed in relation to spinodal decomposition and to nucleation-and-growth mechanisms.
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    URL: http://dx.doi.org/10.1063/1.357354
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    Failure of three-dimensional random composites (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4086-4094 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using an optimized bond breaking algorithm, we simulated the failure of three-dimensional networks composed of two randomly interspersed components. We studied the strength and the number of bonds broken prior to the failure instability (the damage). When one phase is of low concentration, damage mostly occurs when the dilute phase is very weak and fails prematurely, although a limited "matrix damage'' mechanism does exist. In contrast, when the composite is a 50/50 mixture and the two phases are macroscopically interpenetrating (both phases percolate), the ability to absorb damage is greatly enhanced. In the interpenetrating phase regime the strength of the composite is, in some cases, enhanced beyond that of the analogous particle reinforced composite. These features suggest that interpenetrating phase composites can have improved properties in comparison to conventional "particulate'' composites. Analysis of the composite is neatly summarized in "damage maps'' which give a quick indication of the regions in which the ability to absorb damage is enhanced. Using lattices of up to linear dimension L=40 we also study the finite-size-scaling laws for the average strength and damage of the networks.
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    URL: http://dx.doi.org/10.1063/1.357358
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    Structure of LaFe9Si4 intermetallic compound (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4095-4098 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The crystal structure of LaFe9Si4 intermetallic compound equilibrated at 1173 K has been determined by the x-ray powder diffraction and refined by the Rietveld technique. The crystal structure belongs to the tetragonal symmetry with space group I4/mcm, which can be derived from the cubic NaZn13-type structure. Each unit cell contains four formula units of LaFe9Si4. The lattice parameters are a=7.932(1) A(ring) and c=11.677(2) A(ring). The calculated density is Dx=6.86(4) g/cm3. In the structure there are five kinds of equivalent positions, i.e., 4a, 16l(1), 16k, 16l(2), and 4d, which are occupied by 4La, 16Fe(1), 16Fe(2), 16Si, and 4Fe(3) atoms, respectively.
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    Fiber-matrix interphase characterization in composites using ultrasonic velocity data (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4121-4129 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A nondestructive method is introduced to determine the effective elastic moduli of fiber-matrix interphases from measured composite moduli. The composite moduli are obtained by measuring the angular dependences of ultrasonic longitudinal and transverse phase velocities in planes along and perpendicular to the fibers. Three independent interphase effective moduli are found using micromechanical multiphase models which were applied after averaging composite transverse moduli to account for the composite orthotropy. Sensitivity analysis shows that errors in the calculated interphasial moduli are approximately ten times those in the composite moduli. Experiments are performed on Si3N4 ceramic and Ti-24Al-11Nb intermetallic matrix composites reinforced with carbon coated silicon carbide fibers. The experimental interphasial moduli for the intermetallic composites agree with literature data after accounting for the interphase microstructure. The interphasial moduli for ceramic composites are lower than those for the intermetallic composite due to imperfect mechanical contact between the interphase and the porous matrix. The use of the method to assess the interphase degradation is demonstrated for interphasial oxidation damage. The analysis helps to determine the morphology of the damaged interphase.
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    Space-charge dipole domains dynamics theory of frequency locking, quasiperiodicity, and chaos in extrinsic Ge (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4159-4163 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Space-charge dipole domain dynamics theory has been used to investigate the frequency locking, quasiperiodicity, and chaos in extrinsic Ge. Our numerical results agree with the experimental phenomena.
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    URL: http://dx.doi.org/10.1063/1.357367
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    Determination of surface roughness of InP (001) wafers by x-ray scattering (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4154-4158 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface roughness of polished InP (001) wafers were examined by x-ray reflectivity and crystal truncation rod (CTR) measurements. The root-mean-square roughness and the lateral correlation scale were obtained by both methods. The scattering intensities in the scans transverse to the specular reflection rod were found to contain two components. A simple surface model of surface faceting is proposed to explain the experimental data. The sensitivities of the two methods to the surface structure and the role of the resolution functions in the CTR measurements are discussed.
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    Monte Carlo studies of ohmic hole mobility in silicon and germanium: Examination of the optical phonon deformation potential (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4192-4200 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Monte Carlo methods which have been widely used for studying high field electron and hole transport, so far have not been applied to the complex problem of Ohmic hole transport. We present a versatile generalization of the Monte Carlo approach for Ohmic hole mobility studies and apply it to pure silicon and germanium. In particular, we examine the role of the optical phonon deformation potential d0 in controlling the temperature dependence of the mobility.
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    Thermal emission of charges at Si3N4-GaAs interfaces plasma pretreated with H2, Ar, and Ar+H2 (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4209-4214 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermal emission of charges has been studied in Si3N4-GaAs structures which were prepared using direct plasma-enhanced chemical-vapor deposition. A comparison has been made of the effects of predeposition plasma treatments using hydrogen, argon, and a mixture of the two. Channel current transient spectroscopy was used in the temperature range 77–350 K. All of the samples exhibited electron emission from an interface-state continuum with energies that were consistent with the interface-state-band model proposed by Hasegawa. When argon and hydrogen were used together two extra processes were observed. One of these was due to an electron trap with an activation energy of 0.05 eV; this response was from states at the remote edge of the depletion region several thousand angstroms from the interface. The necessity for argon and hydrogen suggests that argon had created structural damage permitting the entry of hydrogen atoms to form electrically active complexes in the damaged region. The second process which had an activation energy of 0.05 eV resembled hole emission but, because hole injection was an unlikely process, this observation has been attributed to an interfacial polarization process exhibiting thermally activated relaxation. The corresponding dipole moment per unit area was 1.0×1011 C m. Since this mechanism also required the action of argon and hydrogen it was concluded that this was damage related, with electrical activity produced by the hydrogen atoms.
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    Acoustic-phonon limited mobility in periodically modulated quantum wires (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4231-4236 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate acoustic-phonon scattering in quantum wires subject to a periodic potential along the propagating direction. A technique for modeling the electronic structure of the periodic system is introduced using the imaginary time propagation method. The acoustic-phonon scattering rate is evaluated by taking umklapp processes into account. We found umklapp processes can cause a significant increase in intersubband scattering but is negligible for intrasubband scattering. Overall, the exact treatment of the electron dispersion relation improves the acoustic-phonon limited mobility compared to earlier estimates [H. Noguchi, J. P. Leburton, and H. Sakaki, Phys. Rev. B 47, 15593 (1993)].
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    URL: http://dx.doi.org/10.1063/1.357331
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    Magnetic flux mapping, magnetization, and current distributions of YBa2Cu3O7 thin films by scanning Hall probe measurements (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4244-4255 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mapping of the magnetic flux distribution in a square-shaped superconducting YBa2Cu3O7 thin film was carried out using a scanning micro-Hall probe with a spatial resolution of about 25 μm. Calculation procedures for converting the measured flux map to the film current distribution are discussed. The flux penetration with the applied field perpendicular to the film surface was studied in initially zero-field-cooled samples. With full flux penetration, the film sheet currents follow the sample edges, whereas with partial flux penetration, the sheet currents are more complex and include multiply connected patterns. In both cases the sheet currents change their flow direction abruptly along the sample diagonals where the shielding is more effective, and this results in distinctive minima of the flux penetration. The saturation magnetization for a square-shaped sample of side 2a was found to be identical to that for disc and cylindrical samples of radius a. It is shown that the multiply connected current patterns corresponding to various parts of the hysteresis cycle can be reconstructed from the superposition of two appropriate virgin current distributions. The critical current density was dependent on magnetic flux density, and it was found to follow the Kim model.
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    Electron paramagnetic resonance in heat-treated porous silicon (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4290-4293 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron paramagnetic resonance (EPR) of centers produced in porous silicon (PS) by heat treatment in air is investigated. The properties of these centers are compared with the defects present in as-prepared PS or activated by treatment of the specimens with ethanol. The native defects of PS and those produced by thermal annealing show different saturation behavior of the EPR spectra when the microwave power is increased. Also, their spin-dependent recombination processes are different. The dependence of the EPR line intensity on the thermal annealing time at temperatures of 150–500 °C obeys a law characteristic to a diffusion process with an activation energy of 0.9 eV. This value is close to the activation energy of oxidation of crystalline silicon surfaces with atomic oxygen.
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    Electric field-induced antiferroelectric-to-ferroelectric phase transition in lead zirconate titanate stannate ceramics modified with lanthanum (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4301-4304 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of measurements in situ of electrostrictive strain, dielectric polarization, dielectric constant, and crystallographic parameters as functions of applied electric field in the temperature range 20–200 °C of Pb0.97La0.02(Zr0.66Ti0.11Sn0.23)O3 composition are reported. The antiferroelectric to ferroelectric phase transition with large volume change ΔV=0.35 A(ring)3 is shown to be the dominant mechanism of the field-induced strain. The microscopic nature of the switching mechanism and the variation of the strain versus polarization squared at various temperatures are discussed.
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    URL: http://dx.doi.org/10.1063/1.357315
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    Electrical and optical properties of Li-doped LiBO2 and LiNbO3 films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4327-4331 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Li-doped LiBO2 and LiNbO3 thin films have been studied and their optical and electrical properties determined. With doping the ionic conductivity of the films was found to increase substantially. The highest conductivity obtained with the doped films was about 4.5×10−6 S cm−1. All the films exhibited a high degree of transmission in the spectral region from 350 to 2500 nm. The remarkable increase in the ionic conductivity coupled to the preservation of a high optical transmission makes this doping technique highly attractive for devising ion conductors that can be used in transmissive solid-state electrochromic systems or the so-called "smart windows.''
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    URL: http://dx.doi.org/10.1063/1.357318
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    Phase transition revealed by Raman spectroscopy in screen-printed lead zirconate titanate thick films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4294-4300 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transition from rhombohedral phase to tetragonal in screen-printed lead zirconate titanate (PZT) thick films was studied using Raman-scattering spectroscopy, and the results were compared with those of x-ray-diffractometry investigations. The unfired films were subjected to rapid firing in an air atmosphere at temperatures ranging from 960 to 1150 °C. During firing the composition of the films changed gradually as lead evaporated, which moved the composition of films to the ZrO2-PZT region and resulted in precipitation of ZrO2. This caused the original rhombohedral structure to be converted to tetragonal. Correspondingly, the Raman spectra also changed with increasing firing temperature. The variation in Raman spectra was characterized by three frequency regions, denoted as the low-, intermediate-, and high-frequency region, respectively, which are related to three cubic T1u modes. Moreover, it was also observed that the appearance of tetragonal modes was delayed from the formation of tetragonal structure during the process. This discrepancy suggested the existence of a certain "mismatch'' in structure.
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    Thermionic refrigeration (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4362-4366 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A refrigerator is described that is based upon thermionic emission. Room-temperature refrigeration is efficient when the work function of the anode is about 0.3–0.4 eV but those low values are unattainable. The refrigerator only operates at higher temperatures.
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    Plasma enhanced chemical vapor deposition of titanium nitride thin films using cyclopentadienyl cycloheptatrienyl titanium (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4377-4382 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of a low oxidation state Ti compound, cyclopentadienyl cycloheptatrienyl titanium, (C5H5) Ti(C7H7) (CPCHT), as a potential source for TiN and Ti in plasma enhanced chemical vapor deposition processes has been investigated. This precursor provides us with a new chemical vapor deposition route to TiN films that offer an interesting contrast to films deposited from Ti(IV) precursors. Film depositions were carried out by introducing CPCHT, with H2 carrier gas, into the downstream region of a NH3, N2, H2, or mixed H2/N2 plasma. Low resistivity (100–250 μΩ cm) nitrogen-rich TiN films with little carbon or oxygen incorporation and good conformality were deposited with activated N2 or NH3 at deposition temperatures of 300–600 °C, inclusive. Mixed H2/N2 plasmas resulted in more stoichiometric TiN films with similar properties. The most striking feature of these films is the absence of columnar grain growth, in contrast to TiN films deposited using TiCl4 or Ti(NR2)4. Although the film texture was influenced by the plasma gas, the average grain size of the films deposited using activated N2 and NH3 was similar. The TiN films that we deposited were effective diffusion barriers between aluminum and silicon up to 575 °C. Depositions using activated H2 resulted in films with significantly less carbon than CPCHT, but still having a minimum of 2.7:1 C:Ti. The lower oxidation state of the precursor did not facilitate the deposition of a Ti-rich film. No depositions were observed with any of the reactant gases in the absence of plasma activation.
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    GaAs asymmetrically doped n-i-p-i- superlattices for 10 μm infrared subband detector and modulator applications (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4407-4412 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical framework for the design of asymmetrically doped n-type n-i-p-i- superlattices for subband detector applications in the 10 μm spectral range is described. Excellent agreement is found with the subband absorption spectra measured in a series of GaAs n-type n-i-p-i- samples and oscillator strengths, transition energies, and dipole matrix elements comparable with conventional quantum-well heterostructure detectors are found. Pronounced IR-absorption modulation by optical pumping with band-gap radiation is seen, due to the enhanced interband recombination time resulting from the type-II n-i-p-i- potential. The prospective advantages of n-type n-i-p-i- devices for the detection and modulation of 10 μm radiation are discussed.
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    URL: http://dx.doi.org/10.1063/1.357334
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    Forward tunneling current in HgCdTe photodiodes (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4420-4425 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Current voltage characteristics of narrow-gap Hg1−xCdxTe photodiodes, fabricated on liquid phase epitaxy and metalorganic chemical vapor deposition grown layers, have been investigated. It is shown that the tunneling-recombination process is the dominant mechanism that determines the dark current at forward and at low reverse bias. This mechanism also determines the junction zero-bias resistance.
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    Optimization of two dimensional gratings for very long wavelength quantum well infrared photodetectors (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4989-4994 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed a detailed study of two-dimensional grating coupling for quantum well infrared photodetectors in the very long wavelength spectral region λ∼16–17 μm. Using calculations based on the modal expansion method we quantitatively explain the double peaked responsivity spectrum. By optimizing the grating parameters we achieve a normal incidence responsivity and detectivity which are three times larger than the 45° angle of incidence geometry.
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    Enhanced photorefractive performance in a photorefractive polymeric composite (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4995-4998 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We characterize the photorefractive behavior of a photorefractive multicomponent polymer composite of PVK-TCP:C60:DEANST. Efficient plasticization of the host polymeric matrix and utilization of a nonlinear chromophore with a large dipole moment provide a large poling-induced electro-optic coefficient. Diffraction efficiencies as high as 40% and asymmetric net two-beam coupling gain coefficients in excess of 130 cm−1, surpassing those of known inorganic single-crystalline photorefractive media, are reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357210
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    Atomic-scale and microscale friction studies of graphite and diamond using friction force microscopy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5022-5035 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Friction between graphite and diamond surfaces against a sharp silicon nitride tip was measured using a friction force microscope (FFM). Atomic-scale friction images of a freshly cleaved highly oriented pyrolytic graphite exhibited the same periodicity as that of the graphite surface; however, the peaks in friction profiles and those in corresponding topography profiles were displaced relative to each other. Using the Fourier expansion of the interaction potential, the conservative interatomic forces between the FFM tip and the graphite surface have been calculated. It is shown that the variations in atomic-scale friction and the observed displacement between the peaks in the frictional (or lateral) force and those in the corresponding topography can be explained by the variations in interatomic forces in the normal and lateral directions. Thus, the observed variation in friction force may not necessarily occur as a result of the commonly believed atomic-scale stick-slip process, but can be due to variation in the intrinsic lateral force between the sample and the FFM tip. At large scan sizes (50×50 nm2 or larger), the variation of friction for graphite and a single-crystal (IIa) diamond was found to correlate with the variations in the local slope of the sample surface, suggesting that a ratchet mechanism is responsible for variations in microscale friction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357214
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    Electron-energy-loss spectroscopy of mass-selected ion-beam-deposited diamondlike carbon (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5063-5069 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous diamondlike carbon (DLC) films grown by low-energy mass-selected ion-beam deposition have been examined by electron-energy-loss spectroscopy (EELS). Films grown using deposition energies of 50, 120, and 300 eV have been studied. For these deposition energies, all films exhibit similar EELS characteristics indicating a very high degree of sp3 bonding. The bulk plasmon resonance is intermediate between that of graphite and that of diamond; however, the properties of the low-energy-loss spectra of the DLC films are more similar to those of diamond. The near-K-edge carbon EELS data from the films exhibit a π* feature which is much smaller than that of graphite or evaporated carbon. The use of previously proposed computational methods on the near-K-edge EELS data indicates that over 80% of the carbon atoms are sp3 bonded. The size of the π* feature is larger for smaller plasmon energies, as expected. The present data are in accord with other analyses of similar films that indicate a broad (∼30–300 eV) energy window for diamondlike film formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357218
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    Production of semi-insulating layers in n-doped InP by Fe implantation (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5085-5094 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed study of Fe implantation and damage annealing in indium phosphide is presented. The technological goal was to obtain thermally stable semi-insulating layers in n-type InP. Different characterization techniques were employed, including structural (x-ray diffraction, Rutherford backscattering spectrometry, and transmission electron microscopy), chemical (secondary ions mass spectrometry), and electrical (current-voltage) measurements. Both undoped and n-type (Sn) doped substrates were implanted with Fe doses ranging from 5×1011 to 2.2×1014 cm−2 and annealed at a temperature of 650 °C. The high doses used to compensate n+ doping caused amorphization of the material. The reordering process of the amorphous layers and its influence on the Fe redistribution properties were studied in detail. The activation of the implanted Fe atoms after annealing was derived. Although the recovery process of the amorphized layer appears to be rather complex, our results show that good crystal quality and full compensation can be reached also for n+ doped substrates, leading to resistivity values above 2×107 Ω cm, even starting from an initial doping level as high as 1.4×1018 cm−3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357220
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    Observation of degradation processes of Al electrodes in organic electroluminescence devices by electroluminescence microscopy, atomic force microscopy, scanning electron microscopy, and Auger electron spectroscopy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5118-5121 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Degradation of top electrodes is one of the most important factors to determine the lifetimes of organic electroluminescence (EL) devices. An organic EL device [indium thin oxide (ITO)/N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4, 4'-diamine (TPD)/tris(8-hydroxy- quinoline)aluminum (Alq3)/Al] was prepared and a morphological change of the Al top electrode was observed during and/or after applying voltage by atomic force microscopy and scanning electron microscopy (SEM). The change in the electrode surface, i.e., the increase in surface roughness was observed during the current flow. The degradation process started from faint dark core parts and propagated into disks with different rates depending on the magnitude of applied voltage. Degraded sites of the Al electrode, which were analyzed as aluminum oxide by Auger electron spectroscopy, protruded into the air on the organic layers. In SEM images of a life-end electrode, discontinuities due to crevasse formation in the organic layers sandwiched by the ITO base and the metal top electrodes were observed in many places. These results confirm that one of the most crucial factors of the degradation process was deformation of metal and organic layers due to heat, gas evolution, and oxidation caused by applied voltage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357224
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    Diffusive buoyancy force and concentration-dependent diffusivities (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5154-5160 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of pressure gradients that develop in diffusion systems consisting of particulates dispersed in a continuous fluid is considered. It is shown that the gradient of chemical potential which drives the diffusion flux induces a pressure gradient that opposes this flux. This effect, which exists in addition to the induced bulk flow, is expressed in terms of a diffusive buoyancy force (DBF). For dispersions consisting of monodisperse particulates in a single-component fluid, the net driving force is the negative product of the volume fraction occupied by the fluid and the gradient of the chemical potential of the particulates. For polydisperse particulates, the DBF is the negative product of the total volume fraction occupied by the particulates and the expectation of gradient of their chemical potential. The joint effect of the DBF and the hydrodynamic hindrance is expressed in terms of a concentration-dependent diffusion coefficient. It is shown that the effect of the DBF yields a fundamental diffusion coefficient Dφ, which is the product of the volume fraction occupied by the fluid 1−φ, and the Stokes–Einstein diffusion coefficient D. The intrinsic diffusion coefficient, which is defined as the product of 1−φ and Dφ, thus becomes the product of the square of 1−φ and D. At steady state the concentration profile cannot be analytically linear unless the buoyancy and hydrodynamic effects are offset by changes of size, energy per particulate and the activity coefficient. Finally, implications regarding the diffusion equation and effects of combined fields on the DBF are considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357230
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    Low-temperature homoepitaxial growth on nonplanar Si substrates (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5185-5189 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The kinetics associated with the breakdown of epitaxy at low temperatures are studied for growth onto a number of Si surfaces, including (001), (117), (115), and (113). These surfaces are all initially generated at trench edges on a single patterned substrate. Growth on each of these surfaces at low temperatures is shown to result in a well-defined crystalline-to-amorphous transition. The epitaxial thicknesses hepi have been measured over a range of substrate temperatures below 280 °C, and activation energies characteristic of this transition were determined. In general, the breakdown in epitaxy occurs such that hepi(001)(approximately-greater-than)hepi(117)(approximately-greater-than)hepi(115)(approximately-greater-than)hepi(113). Growth at slightly higher temperatures, Tsubstrate(approximately-greater-than)300 °C, shows a different microstructure than that at lower temperatures. Epitaxial growth continues for longer times on (113) facets, as compared with (001). These results are discussed in terms of a recently proposed model explaining the breakdown of epitaxy at lower temperatures and an epitaxial temperature for Si.
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    URL: http://dx.doi.org/10.1063/1.357236
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    Thermal stability and crystallization products of amorphous Si:P alloy thin films made by coevaporation of Si and P (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5179-5184 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermal stability and crystallization of amorphous Si:P alloy thin films consisting of 20–44 at. % P have been studied in this work. The results show that the alloys have crystallization temperatures ranging from 850 to 1150 °C, which are all higher than that of pure amorphous Si, and that the variation of resistivity of the alloys during the 120 h aging at 300 °C is small (0.6%). These results indicate that the alloys have a high thermal stability, which is in agreement with the thermodynamic prediction we have made. It has also been observed that the crystallization products for these alloys are different. A new silicon phosphide phase has been observed in the 30 at. % alloy sample and suggested to be possibly a hexagonal Si7P3 phase which has lattice parameters a=5.32 A(ring) and c=13.3 A(ring). The alloy films were deposited onto quartz substrates and Si wafers by coevaporation of Si and P. X-ray diffractometry and transmission electron microscopy were utilized to investigate the crystallization temperature and product of the amorphous alloys.
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    URL: http://dx.doi.org/10.1063/1.357235
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    Control of nitrogen incorporation in ZnTe:N grown by molecular-beam epitaxy using Ar dilution in a N plasma source (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5214-5217 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of Ar dilution in a N plasma source has been used to achieve control of both electrical and optical properties of p-type ZnTe:N grown by molecular-beam epitaxy. Photoluminescence data are presented that show the transition from "pure'' ZnTe emission to that indicative of heavily N-doped ZnTe. A new principal bound-exciton line associated with N impurities is observed at 2.3685 eV. An anomalous red shift in the corresponding donor-acceptor pair peak energy with increasing N concentration is observed at high N concentration and is attributed to the effects of N impurity banding. Trends in p-type conductivity confirmed the ability to control hole concentrations using Ar dilution.
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    URL: http://dx.doi.org/10.1063/1.357190
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    Theoretical electronic properties of silicon-containing bismuth (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5249-5252 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electrical conductivities of n-doped silicon and, in particular Si:Bi, have been investigated for doping levels greater than the impurity critical concentration Nc for the metal-nonmetal transitions. A general feature of the conductivity for concentration normalized to Nc is presented in the order σ(Bi)(approximately-greater-than)σ(As)(approximately-greater-than)σ(P)(approximately-greater-than)σ(Sb). For Si:Bi, the value of Nc is calculated for different criteria. The mobility of electrons presents a lower value compared to Si:P. The results for Si:P and Si:As are compared to the experimental data available in the literature.
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    URL: http://dx.doi.org/10.1063/1.357175
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    Time-dependent p-n junction characteristics underneath TiN/Ti contact metal (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5272-5277 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time-dependent p-n junction characteristics (junction depth: xj∼0.2 μm) underneath TiN/Ti contact metal have been determined in terms of contact interface crystallinity. Reverse bias (≥6.0 V) soft-breakdown characteristics result in a leakage current increase during reverse bias and temperature aging stress. It has been elucidated that this degradation is dependent on the crystallinity of Ti-Si interdiffused layers at the contact interface and the p-n junction polarity. The degradation is observed only in amorphous Ti-Si contacted n+-p junctions. Nevertheless, in amorphous Ti-Si contacted p+-n junctions and crystalline TiSi2 contacted n+-p and p+-n junctions, the degradation does not appear. In the case of the amorphous Ti-Si contacted n+-p junction, it is concluded that the time-dependent degradation is caused by diffusion of positively ionized Ti enhanced by the applied electric field.
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    URL: http://dx.doi.org/10.1063/1.357177
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    Calculations of electronic and optical properties of Si/Ge alloys and superlattices: Application to planar waveguides (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5294-5299 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A systematic comparative study between the electronic and optical properties of the strain layer superlattices (Si)10−n/(Ge)n coherently grown on a Si1−n/10Gen/10(001) alloy surface and those of the corresponding bulk alloys Si1−n/10Gen/10 is presented. We find that the superlattices have a smaller fundamental gap than the corresponding alloys; also for energies smaller than 1.5 eV and polarization along the growth plane, the real part of the dielectric function, ε1, for the SLS is larger than that of the corresponding alloy, while for perpendicular polarization, the two dielectric functions practically coincide. The utilization of this property for the construction of planar waveguides is investigated. In particular, the transverse electric modes of a waveguide consisting of a finite thickness SLS (Si)6/(Ge)4, sandwiched between two layers of the alloy Si0.6Ge0.4, are studied. No transverse magnetic modes exist in this structure.
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    URL: http://dx.doi.org/10.1063/1.357180
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    Carrier energy relaxation in multisubband quantum well lasers with hot phonon effects (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5334-5338 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carrier energy relaxation rates via carrier-polar optical-phonon interactions with hot phonon effects are theoretically studied in multisubband quantum well structures. The effects of changing the width and depth of quantum wells on the carrier energy relaxation rate are discussed. Compared to the result of the bulk, we find that the difference in the energy relaxation rate between quantum wells and bulk is rather small. Reducing the lifetime of longitudinal-optical phonons will effectively enhance the carrier energy relaxation rate. The implications in designing high-speed quantum well lasers are also suggested.
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    URL: http://dx.doi.org/10.1063/1.357185
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    Coherent Foucault imaging: A method for imaging magnetic domain structures in thin films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5349-5355 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method for imaging magnetic domain structures in the transmission electron microscope is described. Coherent Foucault imaging provides a direct means of producing a magnetic interferogram which reveals the quantitative distribution of magnetic induction across the specimen. The technique requires the high coherence of a field-emission gun system and the ability to position an aperture accurately to cut part of the diffraction pattern. A simple analytical theory, together with computer simulations and experimental results, is presented to demonstrate the power of the technique.
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    URL: http://dx.doi.org/10.1063/1.357188
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    Magnetic anisotropy and giant magnetostriction of amorphous TbDyFe films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5380-5382 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of internal stress on the magnetic anisotropy and the magnetostriction was investigated in sputter-deposited amorphous (Tb0.27Dy0.73)0.42Fe0.58 films. Films with tensile stress show in-plane anisotropy and giant magnetostriction of λ(parallel)=400×10−6 at 1 T measured in a field parallel to the film plane at room temperature. The magnetostriction rises rapidly to λ(parallel)=200×10−6 at 0.05 T and the coercivity is less than 0.01 T. On the other hand films with compressive stress show perpendicular anisotropy and still higher magnetostriction of λ(parallel)=540×10−6 at 1 T; however, this is by far a slower increase of magnetostriction at small fields. This different behavior is explained by considering the nature of magnetization processes, i.e., domain-wall motion and spin rotation.
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    URL: http://dx.doi.org/10.1063/1.357192
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    Analytical and numerical analysis of Debye–Ramm's equation for the polarization density distribution in polar materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5399-5410 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Due to dipole interaction, the molecular polarization brought about by an external field is significantly lower in condensed matter (liquids) than in a gas. In addition to this, the response of interacting dipoles to stepwise changes of the external field does not follow a simple time exponential. Instead, a spectrum of relaxation times is required to describe such a response. Debye and Ramm [Ann. Phys. 28, 28 (1937)] have attempted to describe the effects associated with rotational hindrances due to dipole-dipole interaction by the following differential equation: ∂f/∂t =(kT/ρ)Δf+(1/ρ)div(f grad u), where f denotes the distribution function specifying the number of dipoles pointing in a certain solid angle, t the time, ρ a friction coefficient, and u the potential of the forces acting on the dipoles. The latter quantity depends both on the external field and on the contribution from the dipole-dipole interaction (internal field). Although unable to solve the above equation explicitly, Debye and Ramm (DR) made some predictions about the solution, concluding, among other things, that the inclusion of an internal field E would yield a process with a discrete spectrum of relaxation times. Finding such prospect highly interesting, we subjected the DR equation to a close study using some advanced mathematical tools (Fourier integral operators etc.). Contrary to the conclusions of DR, we found that the above equation cannot be solved in the way originally described, and that the conjectured eigenfunctions and eigenvalues do not exist. Furthermore, we show that, in contrast to DR's statements, the above equation is not solved by certain classical expressions relating to free-rotating dipoles (no internal field). The lack of physical content of this equation appears to be due to a number of not permissible simplifications.
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    URL: http://dx.doi.org/10.1063/1.357195
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    Photoreflectance and photoluminescence of partially intermixed GaAs/AlGaAs double quantum wells (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5434-5438 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoreflectance and photoluminescence were used to study GaAs/AlGaAs quantum wells (QWs) as they were partially intermixed using SiO2 capped rapid thermal annealing. As the annealing temperature was increased, the experimental photoreflectance results showed spectral features moving to higher energies and merging to form broad peaks. This is explained by changes in the shapes of the originally square wells, which result in a convergence of their subbands around certain energies. The interpretation of these changes showed that the partially intermixed QWs were well described by an error-function profile.
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    URL: http://dx.doi.org/10.1063/1.357199
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    n-type polycrystalline silicon films obtained by crystallization of in situ phosphorus-doped amorphous silicon films deposited at low pressure (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5492-5497 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The low-pressure chemical-vapor deposition of phosphorus-doped silicon film on glass at 550 °C was investigated as a function of silane pressure (1–100 Pa) and phosphine/silane mole ratio ranging between 4×10−6 and 4×10−4. At this low temperature the film is homogeneous in thickness and the silicon is amorphous except for low pressure (1 Pa). Phosphorus concentration varies linearly with mole ratio in amorphous deposited films. The resistivity of films annealed at 600 °C decreases while the incorporation of phosphorus (mole ratio) increases, and varies with phosphorus concentration from 101 to 10−3 Ω cm. For the same phosphorus content, the resistivity is lower if the silicon film is amorphous deposited and subsequently crystallized, than if the film is polycrystalline deposited. Carrier concentration and mobility are measured using the Hall method. Doping efficiency and electrical properties are discussed.
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    URL: http://dx.doi.org/10.1063/1.357167
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    Fundamental electrical properties of fluorinated and N2O plasma-annealed ultrathin silicon oxides grown by microwave plasma afterglow oxidation at low temperatures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5508-5514 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A technique for growing ultrathin silicon oxides of superior quality at low temperatures is indispensable for future submicron device applications. Fundamental characteristics such as the oxide breakdown fields, oxide charges, and interface-state densities of various ultrathin silicon oxides (≤8 nm) grown by microwave plasma afterglow oxidation at low temperatures (400 and 600 °C) were investigated. Fluorination (HF soaking) and low-temperature N2O plasma annealing were employed to improve the properties of the oxides. The breakdown fields of the as-grown silicon oxides were enhanced and the interface-state densities were reduced. The effect of N2O annealing time on the interface-state density was also investigated. A longer annealing time ((approximately-greater-than)1 h) was required to reduce the interface-state density. The effective oxide charge density of 600 °C as-grown oxide was as low as 6×1010 cm−2. Additionally, the breakdown field of the thin silicon oxide grown at 600 °C with 15 min N2O plasma annealing was 12 MV/cm.
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    Quasipotential and the stability of phase lock in nonhysteretic Josephson junctions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5538-5544 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The principle of minimum available noise energy is used to calculate the quasipotential over the state space of a nonhysteretic Josephson junction driven by a rf bias. This potential surface provides an intuitive picture of the dynamics of phase lock and defines a stability parameter, the activation energy for thermally induced phase slippage, which determines the optimum operating conditions for a proposed programmable voltage standard.
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    URL: http://dx.doi.org/10.1063/1.357156
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    Mesoscopic transport in Si metal-oxide-semiconductor field-effect transistors with a dual-gate structure (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5561-5566 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article studies the mesoscopic transport of electrically controllable inversion layers of Si metal-oxide-semiconductor field-effect transistors that use a dual-gate structure. We have developed two kinds of devices: a quasi-one-dimensional device (1D-FET) and a Coulomb blockade device (CB-FET). In both devices, the field effect is used to change the channel structure by introducing potential barriers in the narrow inversion channel. The 1D-FET changes a long diffusive quantum wire into a short ballistic one. Strong oscillations in differential conductance, even negative differential conductance, have been observed at 4.2 K, indicating enhanced modulation of electron mobility by intersubband scattering suppression. The CB-FET, on the other hand, transforms a simple quantum wire into a coupled quantum-dot array. A clear change in transport properties is observed with changes in the barrier height at low temperatures. The experimental results are consistent with the theory of one-dimensional subbands and the Coulomb blockade of single-electron tunneling.
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    URL: http://dx.doi.org/10.1063/1.357159
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    Effect of bias annealing on Au/n-Si Schottky barrier with hydrogen incorporation (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5592-5594 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Au/n-Si Schottky barrier (SB) which contains hydrogen has a 0.10 eV lower SB height (SBH) than that without hydrogen. For the hydrogen-containing SB, zero bias annealing (ZBA) decreases the SBH while reverse bias annealing (RBA) increases it. In addition, ZBA and RBA cycling experiments have been made which reveal a reversible change of the SBH within at least four cycles. The annealing temperature of ZBA and especially of RBA influences the SBH. We interpret the above effect in terms of an interaction between hydrogen and metal-semiconductor interface states.
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    URL: http://dx.doi.org/10.1063/1.357163
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    Lateral carrier diffusion and surface recombination in InGaAs/AlGaAs quantum-well ridge-waveguide lasers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4479-4487 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We measured the increase in threshold currents due to lateral carrier diffusion in InGaAs/AlGaAs quantum-well ridge-waveguide laser diodes. The ridge stripes were fabricated by using both in situ monitored pure Cl2 reactive ion etching and selective wet etching to completely eliminate the spreading current in the conductive upper cladding layer while keeping the ridge sidewalls straight. After comparing the threshold data with a theoretical model, the ambipolar diffusion coefficient is found to be 22 cm2/s in the population-inverted InGaAs layer. This model is based on the calculated optical gain curve and the ambipolar carrier transport in the quantum-well and waveguiding layers. The dependence of carrier lifetime on the local carrier concentration is included in the calculation. Moreover, from another set of devices with the portions of the active layer outside the ridge stripes etched away, the surface recombination velocity is found to be around 1–2×105 cm/s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357279
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  • 99
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    A study of the accuracy of various Langmuir probe theories (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4488-4498 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion and electron densities have been measured in long, low pressure, cylindrical nitrogen and helium dc discharges using computer-controlled Langmuir probes. Cylindrical probe data have been analyzed with a variety of theories in order to determine the latter's accuracy. Electron densities were obtained from the electron saturation currents using orbital motion limited (OML) theories, and from the electron retardation region of the probe trace by integration of the second derivative of the probe current. Ion densities were obtained from both OML and radial motion analysis of the ion saturation currents. Line integrated microwave interferometry and discharge current continuity considerations in the positive column have been used to obtain two independent electron density measurements. While both probe electron density methods agree very well with each other and reasonably well with the independent density measurements, the OML theory applied to the ions overestimates the plasma density by up to a factor of 10. The radial motion theory yields ion densities that show considerably better agreement with the electron densities than the OML theory. Ion and electron densities have also been measured with planar probes, but they were found to perturb the surrounding plasma more than the cylindrical ones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357280
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  • 100
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    Effects of barrier layer and annealing on abnormal grain growth in copper thin films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4516-4523 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Abnormal (100) grain growth has been characterized in predominantly (111)-textured Cu thin films as a function of deposition temperature, annealing temperature and the presence of a Ta or W underlayer. For films deposited at room temperature, bimodal grain size distributions are observed at annealing temperatures at or above 150 °C for Cu on Ta and 100 °C for Cu on W. Suppression of (100) abnormal grain growth was achieved by depositing Cu on either barrier layer at 150 °C. A bimodal grain size distribution was still observed for the film deposited on W at 150 °C but the large grains forming this distribution were found to be (111) oriented. These results are explained as the result of competition between strain energy minimization and surface and interface energy minimization. The (100) growth is shown to be driven by a reduction of the orientation-dependent strain energy that builds up due to the elastic anisotropy of Cu. Films deposited at higher temperatures have a lower yield stress which limits the achievable strain energy driving force, thereby suppressing the (100) growth. Surface energy minimization drives the (111) abnormal growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357283
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