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  • 1
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    Micromagnetic coercivity distributions and interactions in chondrules with implications for paleointensities of the early solar system (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Chondrules in chondritic meteorites record the earliest stages of formation of the solar system, potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions. Using first-order reversal curves (FORCs), we map the coercivity distributions and interactions of 32 chondrules from the Allende, Karoonda, and Bjurbole meteorites. Distinctly different distributions and interactions exist for the three meteorites. The coercivity distributions are lognormal shaped, with Bjurbole distributions being bimodal or trimodal. The highest-coercivity mode in the Bjurbole chondrules is derived from tetrataenite, which interacts strongly with the lower-coercivity grains in a manner unlike that seen in terrestrial rocks. Such strong interactions have the potential to bias paleointensity estimates. Moreover, because a significant portion of the coercivity distributions for most of the chondrules is 〈10 mT, low-coercivity magnetic overprints are common. Therefore paleointensities based on the REM method, which rely on ratios of the natural remanent magnetization (NRM) to the saturation isothermal remanent magnetization (IRM) without magnetic cleaning, will probably be biased. The paleointensity bias is found to be about an order of magnitude for most chondrules with low-coercivity overprints. Paleointensity estimates based on a method we call REMc, which uses NRM/IRM ratios after magnetic cleaning, avoid this overprinting bias. Allende chondrules, which are the most pristine and possibly record the paleofield of the early solar system, have a mean REMc paleointensity of 10.4 μT. Karoonda and Bjurbole chondrules, which have experienced some thermal alteration, have REMc paleointensities of 4.6 and 3.2 μT, respectively.
    Description: NSF and INGV
    Description: Published
    Description: B03S90
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: paleomagnetism coercivity ; paleointensity ; magnetic interactions ; meteorite ; Chondrules ; FORC diagrams ; 01. Atmosphere::01.03. Magnetosphere::01.03.01. Interplanetary physics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Arctic low-level boundary layer clouds: in situ measurements and simulations of mono- and bimodal supercooled droplet size distributions at the top layer of liquid phase clouds (2014)
    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC314th Conference on Cloud Physics, Boston, MA, 2014-07-07-2014-07-11Atmospheric Chemistry and Physics, COPERNICUS GESELLSCHAFT MBH, 15(2), pp. 617-631
    Details
    Publication Date: 2017-10-17
    Description: Aircraft borne optical in situ size distribution measurements were performed within Arctic boundary layer clouds with a special emphasis on the cloud top layer during the VERtical Distribution of Ice in Arctic clouds (VERDI) campaign in April and May 2012. An instrumented Basler BT-67 research aircraft operated out of Inuvik over the Mackenzie River delta and the Beaufort Sea in the Northwest Territories of Canada. Besides the cloud particle and hydrometeor size spectrometers the aircraft was equipped with instrumentation for aerosol, radiation and other parameters. Inside the cloud, droplet size distributions with monomodal shapes were observed for predominantly liquid-phase Arctic stratocumulus. With increasing altitude inside the cloud the droplet mean diameters grew from 10 to 20 μm. In the upper transition zone (i.e., adjacent to the cloud-free air aloft) changes from monomodal to bimodal droplet size distributions (Mode 1 with 20 μm and Mode 2 with 10 μm diameter) were observed. It is shown that droplets of both modes co-exist in the same (small) air volume and the bimodal shape of the measured size distributions cannot be explained as an observational artifact caused by accumulating data point populations from different air volumes. The formation of the second size mode can be explained by (a) entrainment and activation/condensation of fresh aerosol particles, or (b) by differential evaporation processes occurring with cloud droplets engulfed in different eddies. Activation of entrained particles seemed a viable possibility as a layer of dry Arctic enhanced background aerosol (which was detected directly above the stratus cloud) might form a second mode of small cloud droplets. However, theoretical considerations and model calculations (adopting direct numerical simulation, DNS) revealed that, instead, turbulent mixing and evaporation of larger droplets are the most likely reasons for the formation of the second droplet size mode in the uppermost region of the clouds.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 3
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    Holocene environment of Central Kamchatka, Russia: Implications from a multi-proxy record of Two-Yurts Lake (2015)
    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 134, pp. 101-117, ISSN: 0921-8181
    Details
    Publication Date: 2022-08-12
    Description: Within the scope of Russian–German palaeoenvironmental research, Two-Yurts Lake (TYL, Dvuh-Yurtochnoe in Russian) was chosen as the main scientific target area to decipher Holocene climate variability on Kamchatka. The 5 × 2 km large and 26 m deep lake is of proglacial origin and situated on the eastern flank of Sredinny Ridge at the northwestern end of the Central Kamchatka Valley, outside the direct influence of active volcanism. Here, we present results of a multi-proxy study on sediment cores, spanning about the last 7000 years. The general tenor of the TYL record is an increase in continentality and winter snow cover in conjunction with a decrease in temperature, humidity, and biological productivity after 5000–4500 cal yrs BP, inferred from pollen and diatom data and the isotopic composition of organic carbon. The TYL proxy data also show that the late Holocene was punctuated by two colder spells, roughly between 4500 and 3500 cal yrs BP and between 1000 and 200 cal yrs BP, as local expressions of the Neoglacial and Little Ice Age, respectively. These environmental changes can be regarded as direct and indirect responses to climate change, as also demonstrated by other records in the regional terrestrial andmarine realm. Long-termclimate deteriorationwas driven by decreasing insolation,while the short-term climate excursions are best explained by local climatic processes. The latter affect the configuration of atmospheric pressure systems that control the sources as well as the temperature and moisture of air masses reaching Kamchatka.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
    Electronic Resource
    Electronic Resource
    Structural and optical characterization of InP/GaxIn1−xAsyP1−y quantum wells and interfacial layers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4033-4039 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Several multiquantum wells of InP/GaxIn1−xAsyP1−y grown by chemical-beam epitaxy have been studied by high-resolution x-ray diffraction, low-temperature photoluminescence, and Raman scattering to characterize interfacial layers between the barriers and the wells. These interfacial layers are created during the initial stage of growth of the quaternary material as a result of the longer transient for the saturation of the group-III elements flux. The combination of x-ray diffraction and photoluminescence allows a precise determination of the interfacial layer thickness and composition grading and shows that interface roughness is of the order of 1 monolayer. Raman scattering confirms these results and is used to determine values of the sound velocity and of the index of refraction in the quaternary alloy material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363363
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  • 5
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357181
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  • 6
    Electronic Resource
    Electronic Resource
    Alloy broadening in photoluminescence spectra of GaxIn1−xAsyP1−y lattice matched to InP (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2633-2639 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low temperature photoluminescence measurements of GaxIn1−xAsyP1−y alloys nearly lattice matched to InP to study the line broadening of the observed band to band and near band gap transitions in these materials were performed. We find that the dominant broadening mechanism is alloy broadening that originates from the spatial fluctuations of the band gap energy due to random anion and cation distribution. A model that assumes that occupation of the group-III sites by Ga and In atoms and of the group-V sites by As and P atoms occurs randomly, is fitted to the photoluminescence spectra of our samples. This provides an excellent description of the experimental results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356239
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  • 7
    Electronic Resource
    Electronic Resource
    Structural and optical characterization of monolayer interfaces in Ga0.47In0.53As/InP multiple quantum wells grown by chemical beam epitaxy (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2640-2648 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have carried out a detailed structural and optical characterization of Ga0.47In0.53As/InP multiple quantum wells grown by chemical beam epitaxy using a well-defined sequence of growth interruption times between successive layers. These growth interruption times result in the formation of interfacial layers which drastically alter the structural properties of Ga0.47In0.53As/InP multiple quantum wells. An analysis of double-crystal x-ray diffraction data reveals that exposure of InP to arsine for 2 s is sufficient to create approximately 3 monolayers of InAs0.55P0.45 ternary under biaxial compressive strain at the InP/Ga047In0.53As interface. Moreover, exposure of Ga0.47In0.53As to phosphine for 2 s results in the formation of approximately 2 monolayers of Ga0.48In0.52As0.21P0.79 quaternary under biaxial tensile strain at the Ga0.47In0.53As/InP interface. We find that long exposures to hydrides (over 5 s) rather than short ones give rise to interfacial layers with less compositional disorder and/or thickness fluctuation. Moreover, photoluminescence and absorption spectroscopy data reveal the negligible effect of InAsxP1−x and GaxIn1−xAsyP1−y interfacial layers on the emission and optical absorption properties of Ga0.47In0.53As/InP multiple quantum wells with sufficiently thick Ga0.47In0.53As layers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361134
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  • 8
    Electronic Resource
    Electronic Resource
    Structure damage in reactive-ion and laser etched InP/GalnAs microstructures (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1488-1491 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Etching of a chemical-beam-epitaxy-grown InP/InGaAs multilayer structure with reactive ion etching (RIE) and laser-assisted dry etching ablation (LADEA) is carried out in order to evaluate the extent of the damage induced by these two etching methods. Micro-Raman spectroscopy indicates a systematic broadening of the phonon lines as a function of depth of a RIE fabricated crater. In contrast, LADEA which is based on the application of an excimer laser for the removal of the products of chemical reaction, shows no measurable changes in the phonon line widths when compared to as-grown material. The results suggest that LADEA has potential for the photoresistless fabrication of damage free microstructures. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360763
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  • 9
    Electronic Resource
    Electronic Resource
    Photoluminescence study of strain relaxation in Ga1−xInxAs/GaAs single heterostructures (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4135-4140 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature photoluminescence (PL) spectra of Ga1−xInxAs/GaAs single heterostructures with 0.07≤x≤0.19 and thicknesses ranging from 10 nm to 5 μm have been analyzed to study strain relaxation. Two series of samples were grown simultaneously on GaAs substrates oriented exactly on (100) and misoriented by 2° towards 〈110〉. In both kinds of samples, the strain induced exciton shift decreases first slowly with increasing thickness and then drops abruptly. This variation is analyzed in terms of the equilibrium critical thickness where misfit dislocations are generated and the kinetics of these dislocations in the relaxation process. The decrease of the exciton energy shift is accompanied by a large reduction of the PL intensity and broadening of the emission. In thicker layers, however, the behavior of the two series of samples is strikingly different. While the layers grown on misoriented substrates have all the characteristics of high-quality unstrained crystals, those grown on (100) substrates have PL spectra dominated by a low-energy emission. These results show that the critical thickness for the generation of misfit dislocations is the same for layers grown on both kinds of substrates but that the relaxation process is different and results in inhomogeneous layers on (100) substrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341324
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  • 10
    Electronic Resource
    Electronic Resource
    Luminescence, level saturation, and optical gain in a single InGaAs/GaAs quantum well (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4854-4857 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature photo- and electroluminescence spectra were performed on InxGa1−xAs/GaAs single quantum wells (x=0.13) under varying excitation conditions. Both types of spectra display strong 11H-associated emission, as well as impurity-related features. Saturation effects are observed for both the intrinsic and impurity emission under high excitation conditions. When optically pumped at energies higher than the GaAs band gap, the InGaAs single quantum well gave optical gains in the 10-cm−1 range, saturating at a pumping intensity of 104 W/cm2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343802
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