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  • Articles  (469)
  • Polymer and Materials Science  (409)
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  • Electrical Engineering, Measurement and Control Technology  (430)
  • Economics  (39)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Photonic network communications 2 (2000), S. 123-133 
    ISSN: 1572-8188
    Keywords: photonic switching ; packet switching ; Clos architecture ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Design guidelines are given to dimension large switches in the optical packet network environment developed in the framework of the ACTS project KEOPS (KEys to Optical Packet Switching). Different possible choices in the architecture and operation of the switch are proposed according to the photonic technology availability. Simulation and analytical tools are used to evaluate switch performance and they have been applied to find out suitable switch configurations that meet packet loss requirements. Results and application examples are given to show the feasibility of a packet switch for high-speed photonic transport with the available technology.
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  • 2
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    Journal of applied electrochemistry 30 (2000), S. 1-12 
    ISSN: 1572-8838
    Keywords: copper deposition ; current distributions ; microvias ; patterned electrodes ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Copper was deposited on micropatterned electrodes in a parallel plate reactor (PPR) using an industrial acid copper plating bath, and the deposit thickness distributions were measured. The plating bath contained, besides copper sulfate and sulfuric acid as main components, small amounts of sodium chloride and an organic additive LP-1TM. Copper deposition was carried out under various flow conditions (laminar and turbulent) and applied current densities. Three patterns, each of them consisting of a series of parallel copper microtracks, were manufactured on the electrode surface. The pattern position was chosen to be parallel or perpendicular to the flow direction, corresponding to the two extreme positions for the industrial plating process of patterned electrodes, in casu the round pattern tracks of minicoils. A multi-ion model was used to simulate copper deposition from sulphuric acid solutions, taking into account flow phenomena controlling the mass transfer rate, and the deposition kinetics. The differential equations were solved numerically by use of the multidimensional upwinding method (MDUM). Copper deposition on plane electrodes was investigated and compared to cd distributions obtained from MDUM-simulations. For the case of perpendicular pattern position in laminar flow, the deposit growth in the vias was also modelled and simulated numerically.
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  • 3
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    Journal of applied electrochemistry 30 (2000), S. 1023-1031 
    ISSN: 1572-8838
    Keywords: alkaline fuel cell ; mathematical modelling ; simulation ; single cell ; thickness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A computational simulation was conducted by using a one-dimensional isothermal model for an alkaline fuel cell (AFC) single cell to investigate influences of the thicknesses of the separator, catalyst layer, and gas-diffusion layer in an AFC. The cell polarizations were predicted at various thicknesses and their influences were also analysed. Thickening the separator layer decreased the limiting current density and increased the slope of the ohmic polarization region. Investigation on the thickness of the anode catalyst layer showed that the optimum thickness varied between 0.04–0.15 mm according to the cell voltage. The thickness of the cathode catalyst layer significantly influenced the cell performance. Also, a limitation of thickness effect in the cathode catalyst layer was observed. This limitation was considered to be caused by the mass transfer resistance of the electrolyte.
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  • 4
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    Annals of operations research 94 (2000), S. 139-162 
    ISSN: 1572-9338
    Keywords: irrigated system ; modeling ; multi‐agent system ; simulation ; social networks ; coordination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract The viability of irrigated systems in the Senegal River Valley is being brought into question today due to their under‐utilization. We assume that their viability depends largely on the way their different components behave and interact. We therefore sought to examine in greater depth today's knowledge of the structure of these systems and activities performed within them. This led to the development of a multi‐agent system model, a kind of virtual irrigated system, with a special focus on rules in use for access to credit, water allocation and cropping season assessment as well as organization and coordination of farmers. The purpose of this paper is to show how this kind of tool is relevant to the study of irrigated systems' viability. As an example it is used to examine the influence of existing social networks on the viability of irrigated systems.
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  • 5
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    Review of quantitative finance and accounting 14 (2000), S. 45-65 
    ISSN: 1573-7179
    Keywords: bid-ask spread ; event study methods ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract This study examines empirical issues associated with the use of bid-ask spreads in event studies. The simulation results indicate that the distribution of average standardized abnormal spread shows little deviation from normality. Simulation results also indicate that the widely used percent spread metric results in test statistics with low power. In contrast, use of a standardized raw spread metric and a simple mean-adjusted expectation model results in well specified and reasonably powerful Patell and Brown-Warner type test statistics. As the abnormal spread series is characterized by high first order serial correlation, it is important to adjust for this serial correlation when using multi-day event windows.
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  • 6
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    Journal of electronic testing 16 (2000), S. 83-90 
    ISSN: 1573-0727
    Keywords: verification ; simulation ; code-perturbation ; coverage ; fault
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We propose a simulation approach that can take a large design and swiftly cover its valid code-level operating states. The approach perturbs the program-control flow during the simulation to dynamically exhaust all branching possibilities in a verification code/program. The heuristic uses the program branching information from preprocessing the test/verification code. Using the branching information the simulation allows automatic run-time forced branching to make possible a full coverage of the instruction space spanned by the verification code/program. The aim is (1) to improve the verification simulation speed and (2) to get higher coverage rate for large core-base designs such as microprocessors or digital-signal-processing (DSP) products. A case study of a 32-bit RISC processor, used in a network system, is conducted. The application code for the processor (MCP, Myrinet control program) is used as a verification program. Despite the deviation from the valid “software-reachable state” of the system due to forced branching, a significant number of hard-to-reach hardware states (that can be reached only through the right mix of codes, often the code segments of an application software) are covered. Using the MCP program over 30% additional coverage is achieved with the proposed approach over ordinary code-based simulation for a fixed verification time. Further, compared to the conventional simulation approach, the proposed heuristic takes about 43% less compute-cycles to achieve same state coverage level.
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  • 7
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    Optical and quantum electronics 31 (1999), S. 1179-1188 
    ISSN: 1572-817X
    Keywords: CW operation ; nitride lasers ; simulation ; VCSELs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A room-temperature (RT) continuous-wave (CW) operation of possible nitride vertical-cavity surface-emitting lasers (VCSELs) is considered in the present paper using a simple VCSEL simulation to give some essential guidelines for their proper designing. It is revealed that a substrate material has a critical influence on a possibility of reaching RT CW thresholds which practically excludes currently used sapphire substrates of relatively low thermal conductivity from this application. SQW nitride VCSELs are found to be very sensitive to an increase in temperature, which is followed by their inappropriate CW-operation characteristics. A moderate increase in a number of quantum wells in VCSEL active regions significantly improves their CW achievements, i.e. decreases RT CW thresholds as well as considerably widens their CW threshold ranges.
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  • 8
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    Optical and quantum electronics 31 (1999), S. 1009-1030 
    ISSN: 1572-817X
    Keywords: all-solid-source MBE ; high-power ; red ; simulation ; transverse structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The laser diode structures reported up to now in literature for the red wavelength range are still far from optimal – mostly because many of the desired characteristics are contradictory coupled. Some of the contradictory coupled laser diode characteristics are investigated and a novel transverse layer structure is proposed. Both optical simulation and a fully self-consistent model are used in a design optimization methodology and simple evaluation and optimization criteria are derived. A number of the analyzed high-power edge-emitting GazIn1−zP/(AlxGa1−x)yIn1−yP/GaAs quantum well laser structures were prepared using all-solid-source molecular beam epitaxy for layer growth and remarkable performances were obtained (continuous wave output powers of 3 W at 670 nm, 2 W at 650 nm, and 1 W at 630 nm; threshold current densities of 350–450 A/cm2 for 670 nm, 500–540 A/cm2 for 650 nm, and less than 700 A/cm2 for 630 nm). The good agreement between measurements and simulations for the prepared structures indicate that significant performance improvements – predicted by the simulations – are still possible. The presented novel structure and design optimisation procedure can also be applied to laser diode structure optimisation in other emission ranges – like, for example, in the case of 800 nm-range edge emitting AlxGa1−xAsyP1−y/GazIn1−zAswP1−w/GaAs laser diodes.
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  • 9
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    Wireless personal communications 11 (1999), S. 45-62 
    ISSN: 1572-834X
    Keywords: SDMA ; smart antenna systems ; capacity ; traffic models ; mobility models ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract One of the most widely used buzzwords in mobile communications of the recent years is Space Division Multiple Access (SDMA). The introduction of an additional space domain multiple access component is likely to boost system capacity, due to the spatial reuse of physical channels within one cell. While early approaches of SDMA system modelling show capacity to be gained in the order of 300 to 400%, there remains some more in depth system analysis to be done, as inhomogeneities in the user distribution are expected to likely cause dramatic drops in the additional capacity gained by SDMA. The spatial distribution of terminals directly influences the number of channels to be gained by spatial multiplexing. Therefore, it is not until detailed models for user distribution, user mobility and the traffic load generated by users are combined with a model of the SDMA radio subsystem, that realistic approximations for these capacity gains are possible. In this paper, we discuss the issues in modelling and simulation of SDMA systems. We present an approach for integrated SDMA system modelling, discuss analytic teletraffic dimensioning methods for macro- and microcellular environments and their relevance to SDMA systems, and present some early simulation results.
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  • 10
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    Journal of nondestructive evaluation 18 (1999), S. 117-126 
    ISSN: 1573-4862
    Keywords: Nondestructive evaluation ; layered cylindrical structures ; cylindrical waves ; simulation ; inverse problem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract For the characterization of the unknown material properties of a layered cylindrical structure, axially symmetric wave signals transmitted and reflected by the structure have been used. Since only a single wave mode propagates in the structure, the measurement and analysis of the transmitted and reflected signals can be simplified significantly. The evaluation of the material properties of the layers can be achieved with great accuracy. In this paper, we first derive the transmission and reflection coefficients for the layered cylindrical structure sonified axisymmetrically by an incident cylindrical wave. We then relate the spectra of the transmitted and reflected wave signals to the transmission and reflection coefficients as ratio functions. The time-domain signals transmitted and reflected by the structure can then be reconstructed from a routine application of the Fourier integrals. A three-layered aluminum/epoxy/aluminum tube is used to illustrate the application of the expressions for both the forward and inverse problems. The results show that the technique developed in this study can be used very effectively for the characterization of layered cylindrical structures.
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  • 11
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    Computational economics 13 (1999), S. 93-101 
    ISSN: 1572-9974
    Keywords: efficiency ; multivariate probit ; quasi maximum likelihood ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Economics
    Notes: Abstract This paper discusses the most efficient estimator among Quasi Maximum Likelihood Estimators using at most two levels of numerical integration, for the multivariate probit model. Simulations show that this estimator is more efficient but not more costly than the second-best alternative. However, its added efficiency depends on the correlation structure.
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  • 12
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    Review of quantitative finance and accounting 13 (1999), S. 189-207 
    ISSN: 1573-7179
    Keywords: simulation ; financial statement ; monthly statement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract Many accounting and finance studies investigate the time-series properties of historical accounting records from corporate financial statements. Some of them have recognized the potential benefits of using disaggregated monthly accounting records. Disaggregated data are beneficial because one can use more data points within a relatively short period of time, thus reducing the chance of structural change. The added data points and reduction of the number of variables needed to accommodate potential structural changes can enhance the statistical power of any subsequent analysis. The use of disaggregated data may also improve the predictive ability of time-series analytic approaches. In order to systematically assess various financial indicators and investigate the effects of different organizational characteristics, a large number of monthly statements with certain predetermined characteristics are desirable. However, such statements are not readily available. At best, monthly statements can be obtained from a few volunteer companies. Under this circumstance, simulation of controlled financial statements seems to be a reasonable solution. This research explores a methodology for simulating complete monthly financial statements based on actual company quarterly financial statements. The methodology incorporates the interrelationships among accounting numbers and the effects of exogenous variables. To test the empirical validity and whether the monthly results derived from the quarterly data can accurately track the real monthly figures, we compare the results simulated by the proposed method and those generated by a naive random walk model. We test both complete financial statements for three companies and sales statistics from the retail industry. The results of both tests demonstrate the superiority of the method proposed by this study over a naive random walk model. The proposed simulation method provides an opportunity for researchers to examine the time-series properties of financial statement elements by using the monthly data of a large number of companies. In addition, the simulation approach allows researchers to perform cross sectional comparisons on companies with different characteristics (e.g., sales behavior patterns and degrees of stability) in their financial and economic activities. Moreover, it enables the researchers to manipulate some of these characteristics to test various hypotheses.
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  • 13
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    Analog integrated circuits and signal processing 20 (1999), S. 213-225 
    ISSN: 1573-1979
    Keywords: design ; simulation ; mixed-signal ; VHDL-AMS ; dimensional analysis ; microwave design & quantitative feedback theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Unfortunately, the best solution for one mixed-signal design, is not the best solution for all mixed-signal designs. This is especially true in light of today’s microwave applications that span the range from low-power, low-performance type of devices, through high-power, high-frequency and high-performance applications. Digital designs are automated through the use of the VHDL hardware description language, while the mixed-signal counterparts are automated using the newly developed VHDL-AMS extension. The essential ingredients for mixed-signal design fall into the methodologies of scalable functionality, robust design and feedback techniques. Scalable functionality refers to the non-conventional methodology of dimensional analysis for establishing magnitude relationships between mixed-signal system variables. Robust design of a mixed-signal system, involves the blending of the z-domain (digital) and the s-domain (continuous), resulting in the wp-domain. Robust feedback involves the inherit feedback nature of mixed-signal systems, by providing a methodology of design that emphasizes the use of feedback for achieving the desired robust system performance tolerances despite device parameter uncertainty and noise disturbances.
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  • 14
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    Journal of electroceramics 2 (1998), S. 57-66 
    ISSN: 1573-8663
    Keywords: percolation ; impedance ; geometrical arrangement ; conductivity ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Using a computational methodology, ac impedance spectra of macroscopic mixtures of conducting and insulating hard spheres which have random or regular arrangements of the components are studied. These simulations can be used to calculate the ac electrical properties of a multi-component composite using a personal computer. It is shown in this study that ac impedance spectra are sensitive functions of the filling fraction and the geometrical arrangement of the components, and especially, the impedance spectra of the composite show the abnormal arc originated from the isolated clusters in the composite. From the simulated impedance patterns of the isolated clusters with various length, the abnormal arcs are shown to appear more distinctly when the elongated clusters are arranged along the preferred current line.
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  • 15
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    Advanced Materials for Optics and Electronics 8 (1998), S. 101-105 
    ISSN: 1057-9257
    Keywords: biosensor ; protein immobilisation ; protein modification ; electrochemistry ; nitrotyrosine ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Use of electrosynthetic methodology allows the production of hen egg-white lysozyme (HEWL) either mononitrated at tyrosine 23 or bisnitrated at tyrosines 20 and 23, but never nitrated at tyrosine 53. This is a different sequence from that obtained by the chemical nitrating agent tetranitromethane, and when reduced by dithionite, the selectively modified enzyme can be anchored at pH 5 via the unique aromatic amino group to magnetic beads or other suitable matrices. HEWL so immobilised loses less than 10% of cell-wall lytic activity compared with the approximately 50% loss of activity when immobilised by conventional methodology at pH 9 via essentially random reaction at lysine residues and other functionalities which are nucleophilic at this pH. This result offers promise as a general method for selective protein immobilisation in biosensors and similar applications. © 1998 John Wiley & Sons, Ltd.
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  • 16
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    Advanced Materials for Optics and Electronics 8 (1998), S. 157-160 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 17
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    Advanced Materials for Optics and Electronics 8 (1998), S. 187-193 
    ISSN: 1057-9257
    Keywords: antifouling ; biofouling ; hydrogel ; benzalkonium chloride ; ultraviolet-visible spectroscopy ; underwater optics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: A hydrogel based on poly(2-hydroxyethyl methacrylate) (PHEMA) containing benzalkonium chloride (BAK) can be used as an environmentally acceptable, fouling-resistant material in the marine environment. The loaded hydrogel system is transparent and has the potential to be used in the protection of optical ports in underwater instruments. Ultraviolet-visible (UV-vis) spectroscopy was used to study the optical properties of the material after a marine exposure period. The optical transmittance of PHEMA/ BAK was higher for 10 weeks than that detected for poly(methyl methacrylate) (PMMA), a material currently used in commercial instruments, which confirmed the superior fouling resistance of the PHEMA/ BAK combination. The UV-vis spectroscopic method was quick, relatively cheap and accurate enough to allow the effects of the development of marine fouling on transparent surfaces for use in marine underwater optical applications to be monitored. © 1998 John Wiley & Sons, Ltd.
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  • 18
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    Advanced Materials for Optics and Electronics 8 (1998), S. 247-262 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The synthesis of a number of side chain liquid crystalline polymers for quadratic non-linear optical (NLO) applications is reported. The active chromophore is a charge transfer (CT) biphenyl derivative which possesses mesogenic properties itself. The liquid crystalline behaviour of these polymers was established by differential scanning calorimetry (DSC), optical microscopy and X-ray diffraction. The active chromophores were oriented by the standard corona poling technique and the degree of axial ordering was determined as a function of poling conditions by linear optical absorption. Growth of the second-harmonic generation (SHG) signal was used to probe the induction of polar order. These experiments clearly indicated that liquid crystallinity results in an enhancement of the polar order over that of isotropic materials. The second-order NLO susceptibility tensor components d31 and d33 were measured by the SHG technique. The ratio d33/ d31 was found to be much larger than 3, in agreement with molecular statistical models. Values of d33 up to 30-35 pm V-1 were obtained at 1064 nm fundamental wavelength. These values are essentially not resonance-enhanced, since the chromophore absorption occurs below 350 nm. © 1998 John Wiley & Sons, Ltd.
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  • 19
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    Advanced Materials for Optics and Electronics 8 (1998), S. 317-324 
    ISSN: 1057-9257
    Keywords: gas sensing ; nitrogen dioxide ; stilbene ; biphenyl ; UV-visible spectroscopy ; thin films ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Thin films of a selection of stilbene and biphenyl side-chain substituted liquid crystal polymers based on polysiloxanes were deposited using an automated dip-coating technique and exposed to either 100 ppm NO2 gas and/or concentrated nitric acid vapour, the consequent effect being monitored by changes in the UV-visible spectra of the material. No effective response to NO2 was observed from the biphenylene analogue, but the stilbene derivatives showed spectral changes to suggest that an interaction occurs between the vapour and the bridge position of the stilbene side-chain. The stilbenes also show a marked pre-conditioning phenomenon upon exposure to nitric acid vapour prior to exposure to nitrogen dioxide. This procedure gives a material that has a more reversible response on exposure to NO2 gas than an anagolous film that has not been pre-treated. Copyright © 1998 John Wiley & Sons, Ltd.
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  • 20
    ISSN: 1057-9257
    Keywords: conductive polymers ; polyaniline ; palladium dopants ; platinum dopants ; catalytic hydrogenation ; active centres ; catalyst aging ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The chemical and structural surface-aging effects brought about by the presence of water in emeraldine base (EB) polyaniline (PANI) doped with Pd or Pt protonic acids were studied. IR spectroscopy, XRD, XPS and heterogeneous catalytic hydrogenation (alkyne→alkene→alkane) were applied to characterise the PANI-Pd and PANI-Pt. Interpretation of the results gave the surface characteristics, structure, chemical catalytic activity and stability mainly of PANI-Pd specimens. The unique form of catalytically active centres therein was the surface complex [PdCl4]2- with Pd 3d5/2 BE=337·7 eV. The most promising among the PANI-Pd catalysts studied were those dried in a slow, long procedure (3 months, zeolite 5A). Copyright © 1998 John Wiley & Sons, Ltd.
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  • 21
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    Advanced Materials for Optics and Electronics 8 (1998), S. 121-128 
    ISSN: 1057-9257
    Keywords: self-assembly ; charge transfer ; electron-conducting monolayers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Suitably modified mono- and bimolecular films, including bilayer lipid membranes (BLMs), offer exceptionally good opportunities for probing electric field effects on charge transfer and redox reactions in biosensor and molecular electronics research and development.This work presents the redox reactions of tetracyano-p-quinodimethane (TCNQ) molecules incorporated in a self-assembled octadecanethiol monolayer (SAM) on polycrystalline gold electrodes, depending upon the type of supporting electrolyte cations and their concentration. Our results show that TCNQ-modified Au-SAM electrodes exhibit selectivity versus alkali metal cations in aqueous supporting electrolyte (∽10 kJ mol-1 difference between K+ and Li+ and between Cs+ and K+). The slope of the ‘calibration curves’ for Li+ and K+ is about 59 mV per decade of concentration of the analyte. The explanation of this behaviour is based on the Donnan potential model; however, an ion-pairing effect can also be involved. Our preliminary results show also that the TCNQ molecules within the octadecanethiol monolayer may act as a molecular redox device. © 1998 John Wiley & Sons, Ltd.
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  • 22
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    Advanced Materials for Optics and Electronics 8 (1998), S. 147-155 
    ISSN: 1057-9257
    Keywords: synthesization ; chalcopyrite ; CuGaSE2 single phase ; X-ray diffraction ; stoichiometric deviations ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The dependence of the structural parameters on compositional deviations of CuGaSe2 has been studied. These deviations have been induced along an ingot by a single fusion of the components at 1150 °C and subsequent slow cooling in a stationary ampoule in a vertical furnace. All along the sample a single chalcopyrite phase is present and a compositional gradient along the ingot was found by energy-dispersive analysis of X-rays (EDAX) measurements, the upper part being rich in Ga (series B) and the lower part in Cu (series A), with Cu/Ga ratios of 0·95 and 1·1 respectively. A hypothesis of the existence of two phases in the melt is proposed to explain these facts. The unit cell parameters, anion displacement and Cu and Ga occupation numbers in their sublattices were analysed by X-ray powder diffraction and Rietveld refinement methods. In series A the occupation numbers are near stoichiometry, while in series B a Cu defect appears. In both series, changes in unit cell parameter are related to changes in Cu content, suggesting the presence of a fraction of Cu ions either as interstitials or at Ga sites when Cu is in excess, or of Cu vacancies in its sublattice when there is a Cu deficiency. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 195-199 
    ISSN: 1057-9257
    Keywords: chiral waveguides ; preparation of modified ATR method ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Chiral properties of planar waveguide structures with a core layer formed by a poly(methyl methacrylate) (PMMA) host matrix doped with chiral santonin were investigated by means of a modified attenuated total reflection (ATR) method. Distinct modification of the observed ATR spectra was revealed for right and left circularly polarised incident beams. From comparison of the experimental spectra with theoretical curves, the following specific rotation was obtained: [α]20633=11,200 deg cm2 g-1 (santonin/ PMMA mass ratio 2:1). The origin of the observed optical activity and its influence on the waveguide dispersion characteristics are briefly discussed. © 1998 John Wiley & Sons, Ltd.
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  • 24
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    Advanced Materials for Optics and Electronics 8 (1998), S. 213-213 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 25
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    Advanced Materials for Optics and Electronics 8 (1998), S. 263-267 
    ISSN: 1057-9257
    Keywords: semiconductors ; low-dimensional systems ; crystal structure ; optical properties ; photoluminescence ; Raman spectra ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The structural, optical and related properties (i.e. photoluminescence and resonance Raman spectra) of some synthetic (i.e. unconventional) low-dimensional semiconductor systems such as K2Cd3S4, [CH3SC(NH2)=NH2]3PbI5 and [H3N(CH2)6NH3]BiI5 are reported. They are compared with the properties of the corresponding higher-dimensionality systems. A blue shift of the excitonic bands and an enhancement of their binding energy and intensity were observed by decreasing the dimensionality or the size of the materials active part. The results are similar to those obtained from conventional semiconductors by decreasing the dimensionality or the size and are attributed to quantum confinement of excitons. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 309-316 
    ISSN: 1057-9257
    Keywords: optical gas sensing ; polysiloxane ; azobenzene ; NO2 ; molecular modelling ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Siloxane copolymers having as side-chains azobenzene derivatives bearing different electron-withdrawing and donating substituents were deposited as thin films by dip coating, and their behaviour upon exposure to 100 pm NO2 was studied by UV/visible spectroscopy. Electron-donating substituents at the ortho positions on the aromatic rings in the azo unit have significant influence on the absorbance changes produced by exposure to NO2, and this is explained by modelling, which suggests that interaction between the electrophilic nitrogen atom in NO2 and the electron clouds of the azobenzene skeleton is responsible for the sensing process, rather than the formation of a Wheland intermediate or other product of chemical reaction. Especially effective substituents are methoxy groups in either aromatic ring ortho or the azo linkage, which also produce a significant increase in intensity of the long-wavelength n-π* transition. This moves the optical interrogation signal to a wavelength range of particular benefit for potential applications. Copyright © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 303-308 
    ISSN: 1057-9257
    Keywords: polyaniline ; emeraldine base ; carbon fluoride ; lithium cells ; aprotic solvent ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Polyaniline (PANI) has been used for modification of the electrochemical behaviour of a carbon fluoride ((CFx)n) cathode in a lithium cell. PANI and (CFx)n powders were carefully mixed and the electrochemical properties and kinetic parameters of the composite (CFx)n-PANI cathode were evaluated by galvanostatic and potentiodynamic techniques. An increase in exchange current has been found for electrodes with addition of polyaniline in the form of emeraldine base (EB). During the reduction process of carbon fluoride using 1 M lithium perchlorate solution in organic solvent, the ternary intercalation compound CLixF is formed and then irreversibly decomposed into carbon and lithium fluoride. The insertion of lithium cations into the (CFx)n layered structure is diffusionally controlled, hence improvement in electronic properties of this fluoride material by the presence of conducting PANI chains and enhancement of discharge performance were found for 25% addition of PANI. Copyright © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 285-294 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Field effect transistors with an organic material as active layer are at present essentially used to determine the mobilities in these materials. Until now, in analysing the measured current characteristics, only the simplest (Shockley) model has been used which accounts neither for this type of thin film transistor (TFT), which operates in depletion and accumulation, nor for the nature of the carriers. Starting from two-dimensional simulations for the analogous silicon TFT, we have developed an analytical model for the TFT that accounts for several peculiarities of the current characteristics of this type of transistor. In addition, a first modification has been developed which describes the situation when the charged states are polarons and bipolarons, as is the case in organic materials. Applications to published experimental current characteristics show that a general reanalysis is needed. Copyright © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 111-119 
    ISSN: 1057-9257
    Keywords: PPV ; conjugated polymers ; quasi-particles ; ab initio calculation ; infrared spectra ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We investigate the quasi-particle conformational defects (excitons, polarons and bipolarons) in phenylene vinylene oligomers (PVOs) consisting of up to 12 repeat units. The conformations are determined by minimisation of the total Hartree-Fock energy calculated at 3-21G level. The Hartree-Fock calculations of the excited states are followed by the CI-Singles calculation. The bond length alternation along the oligomer chain is discussed. On the basis of these results the vibrational transitions are calculated. To correct the basis set truncation error, the vibrational frequencies are multiplied by a uniform scaling factor. The types of vibrations are assigned. The theoretical spectra are in good agreement with the experimental infrared vibrational spectrum of poly(p-phenylene vinylene) (PPV). © 1998 John Wiley & Sons, Ltd.
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    ISSN: 1057-9257
    Keywords: gallium nitride ; nanocrystallites ; detonation ; gallium azide ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: High quality nanoscale, phase-pure hexagonal gallium nitride (GaN) crystallites have been synthesized by the thermal induced detonation of molecular precursors of the type (R3N)Ga(N3)3 (R=CH3, C2H5, etc.). The method allows the control of the particle size regime from 2 to about 1000 nm. X-ray diffraction and Rietveld simulations revealed an anisotropic platelet-like shape of the particles. The obtained GaN material was as well characterized by transmission electron microscopy and electron diffraction, photoluminescence spectroscopy, SEM, IR, RAMAN, thermal gas effusion/mass spectrometry, thermal analysis, elemental analysis. Gas absorption measurements (BET method) showed a specific surface area of about 90 m2 · g-1. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 181-186 
    ISSN: 1057-9257
    Keywords: poly(4,7-benzothiophene vinylene) ; polymer interfaces ; conjugated polymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In this paper we determine the LUMO level position of poly(4,7-benzothiophene vinylene) (PBTV), a heterocyclic poly(phenylene vinylene) (PPV) analogue, using tunnelling current measurements. We compare the energy level positions with those measured for PPV and determine their shifts. The experimental results are compared with theoretical predictions and good agreement is observed. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 215-228 
    ISSN: 1057-9257
    Keywords: fullerene ; fullerides ; charge transfer complexes ; spectroscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Some possible uses of vibrational and electronic spectroscopies in characterising the basic interactions in C60 and C70 complexes are pointed out. We report on the wealth of infrared spectra of (usually) single crystals of C60 and C70 clathrates and complexes with organic donors. The changes in the spectral parameters of the complexes in comparison with those of the neutral fullerene molecules are attributed to redistribution of the charge on the spherical C60 or elongated C70 molecules in their compounds. Some general considerations on the origin of the IR, NIR, VIS and UV spectral variations are also given. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 269-276 
    ISSN: 1057-9257
    Keywords: organic charge transfer salts ; conducting polymers ; electronic properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We are exploring the electronic properties of novel materials such as conducting polymer-coated polyester fibres and charge transfer complexes configured in resistive, gated (FET) and diode configurations. In this paper we will consider several areas where we are attempting to make sensors and/ or primitive devices from molecular materials. Our most successful result so far is the temperature-dependent resistivity of polypyrrole-coated polyester fibres. Here we find that the conductivity is thermally activated and produces a reliable, highly sensitive indicator of temperature in a cryogenic environment. Using parallel configurations of fibres, sensors with different limiting resistances can be fabricated. We have also placed insulated electrical gates on single crystals of various metallic and insulating charge transfer salts and have attempted to alter the charge transfer character by the application of high electric fields. With polymethylmethacrylate (PMMA) insulating layers, gate voltages up to 150 V have been acquired with no leakage or heating. Similar measurements on diode devices fabricated from charge transfer complexes with different electronic structures are also in progress, and our preliminary results will be presented. Prospects and plans for developing these materials into viable sensors and devices are discussed. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 277-284 
    ISSN: 1057-9257
    Keywords: calix[4]resorcinarenes ; charge transfer (CT) complexes ; tetracyanoquinodimethane (TCNQ) ; tetracyanoethylene (TCNE) ; non-linear optical (NLO) materials ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Lipophilic calix[4]resorcinarenes - condensation products of resorcinol and lauryl aldehyde comprising four resorcinol units - form electron donor-acceptor complexes with electron acceptors tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE) in organic solvents. Their formation was confirmed by EPR and UV-vis spectroscopy, except for compounds c1 and c3 which did not form charge transfer (CT) complexes with TCNE. Titration experiments involving calixarenes and electron acceptors indicated the presence of species of different stoichiometries. Complexes with ligands c1-c4 were characterised spectroscopically. CT bands appeared in most cases. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 229-245 
    ISSN: 1057-9257
    Keywords: unimolecular rectifier ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Asymmetries in the macroscopic and the nanoscopic DC electrical conductivity through Langmuir-Blodgett multilayers and monolayers of γ-(n-hexadecyl)quinolinium tricyanoquinodimethanide (HDQ-3CNQ, 1) are due to a transition from the ground-state zwitterion to a probably neutral excited-state conformer, thus confirming without a shadow of a doubt the rectification of electrical current by a single molecule. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 1-8 
    ISSN: 1057-9257
    Keywords: electrodeposition ; copper-indium-selenide ; thin films ; layer-by-layer deposition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The electrochemical bath used for growing device-quality CIS (CuInSe2) thin films by co-deposition as well as layer-by-layer (LBL) deposition was characterised and optimised with respect to the film properties. The bath composition was varied by changing the Cu, In and Se ion concentrations in specific ratios in both co-deposition and LBL deposition. The film properties were analysed using techniques such as SEM (scanning electron microscopy), EPMA (electron probe microanalysis), AES (Auger electron spectroscopy) and XRD (X-ray diffraction). The structural, morphological and compositional properties of the films were characterised and their variation is attributed to the bath composition and growth conditions. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 13-22 
    ISSN: 1057-9257
    Keywords: remote PECVD ; silane ; nitrogen ; silicon nitride ; argon dilution ; emission spectroscopy ; metastable states ; atomic nitrogen ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In a series of two papers we describe the effect of argon dilution of the nitrogen passed through the RF discharge region on the plasma composition, growth rate and some characteristics of silicon nitride films deposited by remove PECVD. In this part we report the results of an emission spectroscopic study of the plasma obtained in an SiH4-N2-Ar mixture. It is shown that argon in metastable electronic excited states plays an important role during the RPECVD of silicon nitride films by providing a high concentration of atomic nitrogen which is necessary for the promotion of film growth. In Part II the influence of argon dilution on the growth rate, composition and some properties of silicon nitride films deposited by capacitively and inductively coupled remote PECVD is discussed. © 1998 John Wiley & Sons, Ltd.
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    ISSN: 1057-9257
    Keywords: remote PECVD ; silane ; nitrogen ; silicon nitride ; argon dilution ; hydrogen content ; stoichiometry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In Part I we reported the results of an emission spectroscopic study of the plasma obtained in an SiH4-N2-Ar mixture. It was shown that argon in metastable electronic excited states provides a high concentration of atomic nitrogen. In this part we report the results of a study of the influence of argon dilution on the growth rate, composition and properties of silicon nitride films. The exact influence of nitrogen dilution with argon depends on the process parameters and on the method of coupling of the RF power, but it is found in general that a high concentration of atomic nitrogen leads to changes in the relative amounts of Si-Hj and N-Hi bonds and in the Si/N ratio of deposited films. In particular, it is shown that hydrogen incorporation can be reduced and improved stoichiometry can be obtained. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 61-76 
    ISSN: 1057-9257
    Keywords: magnetic molecular materials ; conducting molecular materials ; polyoxometalates ; TTF ; ET ; conducting polymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The different approaches used by the authors for the synthesis of new molecular materials exhibiting simultaneously magnetic and conducting properties are presented here. The aim is to prepare materials where a magnetic and a conducting sublattice coexist and/or interact in order to obtain either coexistence of properties or coupling between them. The strategy described is a hybrid one that combines various types of inorganic metal complexes with planar organic π-electron donors of the TTF family or with organic matrices made of conducting polymers. There are four main combinations: (i) magnetic polyoxometalates with organic donors - this strategy has already produced more than 10 radical salts where a magnetic character coexists with a conducting or semiconducting one; (ii) small magnetic anions with organic donors - in this case one of the most promising results has been the synthesis of one of the very few known examples of magnetic molecular metals; (iii) ferro- and ferrimagnetic oxalate-bridged bimetallic layers with organic donors; (iv) magnetic polyoxometalates incorporated into electrodeposited films of conducting polymers. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 87-91 
    ISSN: 1057-9257
    Keywords: friction coefficient ; wear coefficient ; tribology ; conducting polymers ; 2,6-naphthalenedisulphonate (2,6-NDS) ; 1,5-naphthalenedisulphonate (1,5-NDS) and 2-naphthalenesulphonate (NS) polypyrroles ; sliding test ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: It is known that, with careful control of conditions, polypyrrole films with counter-ions of toluene sulphonic acid sodium salt and methane phosphonic acid sodium salt can be produced with friction coefficients comparable with or even better than PTFE. Here we now report a systematic study of polypyrrole with various planar anions for tribological bearing applications. Thus naphthalene disulphonate-doped polypyrrole has a kind of laminar structure with very good adhesion to the surface. Polymer films were electrodeposited on glass lenses and tested in a friction apparatus for friction and wear measurements. The film orientation was measured by low-angle X-ray diffraction and the surface structure was evaluated by both AFM and SEM for different film thicknesses. The friction coefficient and wear rate of such bearings were measured under loads up to 5 N and at speeds up to 30 mm s-1 and were found to be 0·06 and 0·04 nm mm-1 respectively. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 47-52 
    ISSN: 1057-9257
    Keywords: ligand gated ; channel protein ; biomembrane ; biosensor ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We demonstrate a novel protective configuration for a gated channel biosensor. The bilayer membrane containing the channel proteins is formed by a simple self-assembly technique ensuring continuous coverage of the interface between two slabs of agarose gel by a biomimetic lamella in a fluid state. The gel protects both membrane surfaces from mechanical shock and contact with low-energy media while allowing diffusion of biomolecules up to 10 MDa in weight. The technique has been demonstrated using both dioleoyl-phosphatidylcholine (DOPC) and a phosphatidylcholine lipid cross-linked with a short polysiloxane chain (PSPC). The conductance per unit area of the channel-free membrane produced by this method was less than 25 S m-2 for DOPC and 2 S m-2 for PSPC, and the bilayer nature of the barrier in both cases has been demonstrated by measurement of the capacitance. The applicability to sensors has been confirmed using gramicidin-D, a 1·1 kDa unilamellar lipid bilayer pore former, and partially confirmed using valinomycin, a selective ion transporter. On incorporation of gramicidin the membrane conductance increased by over an order of magnitude. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 93-96 
    ISSN: 1057-9257
    Keywords: ithiolene ; tetrathiafulvalene ; molecular conductor ; molecular magnetism ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The salt [TTF]2[Fe(tdas)2] has been prepared by electocrystallisation and its conductivity and magnetic properties are reported. The X-ray structure has been determined. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 45-45 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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    Advanced Materials for Optics and Electronics 8 (1998), S. 173-180 
    ISSN: 1057-9257
    Keywords: coated hybrid particles ; nanoparticle composites ; surface plasmon resonance ; optical properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Semiconductor/metal hybrid nanoparticle composites have been prepared in a glass host by a modified melt/quench process and examined with respect to their optical properties. The coated hybrid nanoparticles exhibit surface plasmon resonance absorption spectra which are red-shifted compared with that of a dispersion of homogeneous Ag nanoparticles in the same host. The position of the plasmon resonance was a sensitive function of the heat treatment schedule. A theoretical model based on effective medium theory for the coated hybrid particles was used to describe the shift of the plasmon position in the optical spectra as a function of the coating thickness. The calculated absorption spectra of the coated hybrid particles agree well with the experimental results. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 31-37 
    ISSN: 1057-9257
    Keywords: self-assembled monomolecular layers ; chemical modification ; ATR/FTIR' electrical conductivity ; fluorescence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Self-assembled monomolecular layers have been formed on a glass substrate with 3-aminopropyltriethoxysilane. The amino groups were chemically modified with either salicylaldehyde or 4-formylpyridine, then a TCNQ-pyridine CT complex was formed on a limited area of the surface, making a molecular conductive channel. This area is electrically conducting and we have observed it with the aid of SEM and direct measurements. ATR/FTIR and fluorescence spectroscopy were also used to monitor the monomolecular layer formation and modification processes. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 53-60 
    ISSN: 1057-9257
    Keywords: organic conductors ; electron correlations ; dielectric-metal transition ; superconductivity ; Fermi surface ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The electronic structure and superconductivity of layered organic materials based on the bis(ethylenedithio)tetrathiafulvalene molecule (BEDT-TTF, hereafter ET) with essential intra-ET correlations of electrons are analysed. Taking into account the Fermi surface topology, the superconducting electronic density of states (DOS) is calculated for a realistic model of κ-ET2X salts. A d-symmetry of the superconducting order parameter is obtained and a relation is found between its nodes on the Fermi surface and the superconducting phase characteristics. The results are in agreement with the measured non-activated temperature dependences of the superconducting specific heat and NMR relaxation rate of central 13C atoms in ET. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 81-85 
    ISSN: 1057-9257
    Keywords: conducting polymers ; polypyrrole ; optical absorption ; pressure ; piezochromism ; conformation ; infrared spectra ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: A pressure dependence of the optical absorption spectra of BF-4-doped polypyrrole has been observed at pressures below atmospheric pressure. The two absorption bands at photon energies of 1·2 and 3·0 eV depend on the pressure: a decrease in the high-energy absorption is accompanied by an increase in the low-energy absorption and its shift towards lower energies. The Fourier transformation infrared reflection spectra also depend on the pressure in this region of pressures. The results are interpreted as a pressure-induced conformational transition of the polypyrrole chain. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 201-209 
    ISSN: 1057-9257
    Keywords: amorphous molecular semiconductors ; electron-hole pairs ; excitons ; photoconductivity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Processes of charge carrier photogeneration and recombination are investigated in films of poly-N-epoxypropylcarbazole doped with polymethine dye. Films with blocking contacts were illuminated with light from either the region of dye absorption or beyond this region. The kinetics of accumulation and relaxation of electron-hole pairs with lifetimes greater than tens or hundreds of seconds was studied. It is presumed that the reason for the growth of recombination luminescence intensity in an external electric field is connected with the increase in efficiency of radiative recombination stimulated by electrons captured from photogenerated excitons. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 9-12 
    ISSN: 1057-9257
    Keywords: LPE growth ; Ga-Bi solution ; ‘purification effect’ ; photoluminescence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Thick, intentionally undoped GaAs epitaxial layers grown by LPE from Ga-Bi solution with different contents of Bi in liquid solvent (from 0 to 82 at.%Bi) were studied by photoluminescence (PL) at temperature &helvbi;T&helvbd;=2 K. The dependence of the photoluminescence spectrum on the content of Bi in solution was analysed. © 1998 John Wiley & Sons, Ltd.
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    ISSN: 1057-9257
    Keywords: As-S wafers ; X-ray exposure ; microstructuring ; bulk optic element ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The possibilities of ‘resistless’ microstructuring of As36·1S63·9 wafers by soft X-ray irradiation and wet alkaline etching have been investigated. Scanning electron microscopy is used to study the influence of the exposure and processing parameters on the depth and acuity of the patterned structures. Structures 1 μm wide are obtained by irradiation with an energy flux of 2000 mJ cm-2, followed by etching in a solution of pH 10·8 at a temperature of 23°C for a processing time of 18 min. It is established that by X-ray irradiation and suitable processing of As36·1S63·9 wafers, microstructures of a depth up to 0·65 μm could be patterned. The structured wafers could be used as diffraction elements for IR optics. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 163-171 
    ISSN: 1057-9257
    Keywords: chemical-based computing ; reaction-diffusion systems ; polymer materials for chemical computing ; Belousov-Zhabotinsky media ; Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Promising potentialities are opened up by the use of polymer materials for the elaboration of information-processing devices based on reaction-diffusion media. In this work, features of image processing by Belousov-Zhabotinsky media formed on the basis of hydrogel matrices and using catalyst immobilisation on the surface of solid supports have been investigated. Such active media structures have been found to improve significantly the quality of images in the course of their processing by the media. The spatial resolution of the media increases considerably in going from liquid Belousov-Zhabotinsky media and media functioning in polymer matrices to media based on catalyst immobilisation on the surface of solid supports. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 77-80 
    ISSN: 1057-9257
    Keywords: conducting polymers ; polypyrrole ; electrical conductivity ; pressure ; conformation ; glass transition ; Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We describe the observation of a pressure-induced variation in the electrical conductivity of BF-4-doped polypyrrole at pressures below atmospheric pressure. We also show that there are anomalies in the temperature dependence of the electrical conductivity in cyclic measurements at temperatures of 240 and 310 K. The pressure effect is interpreted as a pressure-induced order-disorder conformational transition. The anomalies in the temperature dependence are attributed to the glass transition and melting of the polymer. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 97-99 
    ISSN: 1057-9257
    Keywords: TCNQ salts ; IR spectra ; melting ; charge transfer, electron-phonon coupling ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The infrared spectra (400-7000 cm-1) of three composites based on salts of tetracyano-p-quinodimethane (TCNQ) and methyl-TCNQ with N-alkyl-isoquinolinium cations are measured as a function of temperature (up to about 450 K). The influence of composite melting on the charge transfer and vibrational bands is studied. It is found that melting causes an irreversible transition into a new phase. © 1998 John Wiley & Sons, Ltd.
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    OR spectrum 19 (1997), S. 23-29 
    ISSN: 1436-6304
    Keywords: Job shop scheduling ; dispatching rules ; coordination ; look ahead information ; simulation ; Werkstattsteuerung ; Steuerungsregeln ; Koordination ; Vorausschauende Informationen ; Simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Description / Table of Contents: Zusammenfassung In diesem Beitrag wird ein neuartiger Ansatz zur Koordination dezentraler Werkstattsteuerungsregeln vorgestellt und mit Hilfe einer Simulationsstudie analysiert. Die Koordination basiert auf vorausschauenden Informationen und enthält einen Auftragsnachfrage-/-angebotsmechanismus. Die Simulations-experimente zeigen, daß durch den Einsatz des Koordinationsmechanismus die Leistung herkömmlicher Steuerungsregeln signifikant verbessert wird.
    Notes: Abstract In this paper a new coordination approach for decentralized job shop scheduling rules is presented and analyzed in a simulation study. The coordination is based on look ahead information and contains a mechanism for demanding and supplying jobs. The simulation experiments show that the performance of conventional scheduling rules is significantly improved using the coordination mechanism.
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    OR spectrum 19 (1997), S. 23-29 
    ISSN: 1436-6304
    Keywords: Key words: Job shop scheduling ; dispatching rules ; coordination ; look ahead information ; simulation ; Schlüsselwörter: Werkstattsteuerung ; Steuerungsregeln ; Koordination ; Vorausschauende Informationen ; Simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Description / Table of Contents: Zusammenfassung. In diesem Beitrag wird ein neu-artiger Ansatz zur Koordination dezentraler Werkstattsteuerungsregeln vorgestellt und mit Hilfe einer Simulationsstudie analysiert. Die Koordination basiert auf vorausschauenden Informationen und enthält einen Auftragsnachfrage-/-angebotsmechanismus. Die Simulations- experimente zeigen, daß durch den Einsatz des Koordinationsmechanismus die Leistung herkömmlicher Steuerungsregeln signifikant verbessert wird.
    Notes: Abstract. In this paper a new coordination approach for decentralized job shop scheduling rules is presented and analyzed in a simulation study. The coordination is based on look ahead information and contains a mechanism for demanding and supplying jobs. The simulation experiments show that the performance of conventional scheduling rules is significantly improved using the coordination mechanism.
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    Journal of applied electrochemistry 27 (1997), S. 1254-1264 
    ISSN: 1572-8838
    Keywords: PEFC ; simulation ; gas diffusion electrode
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    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A detailed one dimensional dynamic model of a gas diffusion electrode as part of a complete fuel cell model is presented. Various effects of parameter changes are considered. Comparison of experimental results and simulation is performed and a new approach to simulation of a complete current voltage curve is discussed.
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    ISSN: 1572-9338
    Keywords: integer programming ; discriminant analysis ; simulation
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    Topics: Mathematics , Economics
    Notes: Abstract Although there have been several journal articles on the classificatory performance of mathematical programming approaches to the two-group discriminant problem, there has been no simulation study on the classificatory performance of mathematical programming approaches to the multiple-group problem reported in the literature. This study reports the results of a simulation experiment on the classificatory performance of a single-function and a multiple-function mathematical programming model relative to that of the standard parametric procedures for the three-group problem with small training samples. The effect of second-order terms on the classificatory performance of the mathematical programming models for the three-group problem is also investigated. Furthermore, this study theoretically examines the range of parameter values of a multiple-function mathematical programming model for which its number of misclassifications in the training sample cannot exceed that of a single-function model.
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    Annals of operations research 74 (1997), S. 321-332 
    ISSN: 1572-9338
    Keywords: simulation ; modeling ; aerospace ; air route structure ; free flight ; clustering
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    Topics: Mathematics , Economics
    Notes: Abstract Recent work performed for the Federal Aviation Administration to support the development of future concepts of air traffic management has involved simulation modeling of patterns of airspace usage by commercial and business air traffic. The objective of these efforts has been to investigate the impacts of a pattern of airspace usage known as "free flight", whereby pilots and flight dispatchers have much more freedom to choose, say, direct or wind-optimal routing through airspace. One of the figures of merit investigated is a count of "convergence pairs" as a measure of the complexity of various traffic patterns. These are cases when aircraft in the simulation model fly close to each other. Interestingly, geographic plots of convergence pairs accumulated over time bring out certain features or patterns of congested air traffic flows or flight alignments. However, these plots are also thick with "noise" or extraneous convergence pairs, whose presence detracts from the ability to perceive congested air traffic flows. Cluster analysis has been found to be an effective method of filtering these displays so that the congested flow features are discernible. The process developed for this purpose is based on a two-pass clustering approach. The process has worked well for the simulation modeling performed to date. Classification of the locations of convergence pairs into congested flow corridors is visually appealing, and has helped distinguish differences in contrasting scenarios of airspace usage. The paper presents graphical results and describes the clustering algorithms employed.
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    Annals of operations research 74 (1997), S. 239-257 
    ISSN: 1572-9338
    Keywords: autocorrelation ; L 1 regression ; least absolute deviations ; robust regression ; simulation
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    Topics: Mathematics , Economics
    Notes: Abstract Least absolute value (LAV) regression provides a robust alternative to least squares, particularly when the disturbances follow distributions that are nonnormal and subject to outliers. While inference in least squares estimation is well-understood, inferential procedures in the context of LAV estimation have not been studied as extensively, particularly in the presence of non-independent disturbances. In this work, we study three alternative significance test procedures in LAV regression, along with two approaches used to correct for serial correlation. The study is based on large-scale Monte Carlo simulations, and comparisons are made based on both observed significance levels and power.
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    Annals of operations research 73 (1997), S. 233-252 
    ISSN: 1572-9338
    Keywords: Data Envelopment Analysis ; model specification ; simulation
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    Topics: Mathematics , Economics
    Notes: Abstract The use of Data Envelopment Analysis for estimating comparative efficiency has become widespread, and there has been considerable academic attention paid to the development of variants of the basic DEA model. However, one of the principal weaknesses of DEA is that - unlike statistically based methods - it yields no diagnostics to help the user determine whether or not the chosen model is appropriate. In particular, the choice of inputs and out-puts depends solely on the judgement of the user. The purpose of this paper is to examine the implications for efficiency scores of using a misspecified model. A simple production process is set up. Simulation models are then used to explore the effects of applying misspecified DEA models to this process. The phenomena investigated are: the omission of significant variables; the inclusion of irrelevant variables; and the adoption of an inappropriate variable returns to scale assumption. The robustness of the results is investigated in relation to sample size; variations in the number of inputs; correlation between inputs; and variations in the importance of inputs. The paper concludes that the dangers of misspecification are most serious when simple models are used and sample sizes are small. In such circumstances, it is concluded that it will usually be to the modeller's advantage to err on the side of including possibly irrelevant variables rather than run the risk of excluding a potentially important variable from the model.
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    Journal of productivity analysis 8 (1997), S. 167-182 
    ISSN: 1573-0441
    Keywords: Identifiability ; least squares ; likelihood ; profile ; simulation
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    Topics: Economics
    Notes: Abstract Although conceptually pleasing, normal-gamma frontier models lead to difficult estimation problems. It is shown here that unless the sample size reaches several thousands of observations the shape parameter of the gamma density is hard to estimate, and that this carries over to estimates of the stochastic frontier, the individual inefficiencies, and the allocation of the overall variance to the stochastic frontier and to the inefficiencies.
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    Computational economics 10 (1997), S. 107-118 
    ISSN: 1572-9974
    Keywords: visualisation ; simulation ; linear quadratic control ; observer ; Kalmanfilter
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    Topics: Computer Science , Economics
    Notes: Abstract Simulation of economic models is frequently used in the investigation of economic policy. Yet one of the problems with simulation is that it can be difficult to appreciate the model properties due to the nature of the simulation process. Stochastic simulation, for example, can produce large quantities of output which can be difficult to comprehend. Further, when mathematically sophisticated techniques such as the use of optimal control and Kalman Filtering are applied to models, the simulation process can become even more complex. Visualisation techniques in model building, simulation, and analysis of simulation output can help reduce the complexity. This is especially the case with interactive simulation. In this paper we investigate the use of visualisation in simulation by examining the application of optimal control techniques to a stochastic forward looking analytic economic model. We also use interactive object oriented simulation software where objects, such as components of models or graphs of outputs, can be visually manipulated to form simulation systems. We find that the use of visualisation can make the investigation of policy analysis issues with such models more comprehensible.
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    Teaching business ethics 1 (1997), S. 163-181 
    ISSN: 1573-1944
    Keywords: business ; computer ; ethics ; experiential ; simulation ; teaching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Philosophy , Economics
    Notes: Abstract This paper discusses how to introduce ethical dilemmas into computer-based business simulation exercise to teach business ethics. Simulations have an inherent advantage over other pedagogies for teaching ethics because simulations provide students with both an intellectual and a behavioral exposure to the topic. Issues addressed include considerations before writing ethical dilemmas, the writing of ethical dilemmas, and process issues for introducing ethical dilemmas. An example is developed and discussed. Through the process described, instructors can better prepare students for a lifetime of tough business decisions.
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    Journal of electronic testing 10 (1997), S. 137-149 
    ISSN: 1573-0727
    Keywords: simulation ; yield ; SMT ; MCM ; board ; test ; DFT ; DFM
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Simulation techniques used in the Manufacturing Test SIMulator(MTSIM) are described. MTSIM is a Concurrent Engineering tool used tosimulate the manufacturing test andrepair aspects of boards and MCMs from design concept through manufacturing release. MTSIM helps designers select assemblyprocess, specify Design For Test (DFT) features, select board testcoverage, specify ASIC defect level goals, establish productfeasibility, and predict manufacturing quality and cost goals. A newyield model for boards and MCMs which accounts for theclustering of solder defects is introduced and used topredict the yield at each test step. In addition, MTSIMestimates the average number of defects per board detected at eachtest step, and estimates costs incurred in test execution, faultisolation and repair. MTSIM models were validated withhigh performance assemblies at Hewlett-Packard (HP).
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    Advanced Materials for Optics and Electronics 7 (1997), S. 1-8 
    ISSN: 1057-9257
    Keywords: CdTe ; iodine doping ; electrical activity ; Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The electrical activity of iodine in CdTe is discussed when iodine is introduced into the CdTe by diffusion from the vapour phase. It is compared both with the total concentration of iodine in the diffused CdTe slices and with the electrical activity in CdTe slices which have been annealed under Cd- and Te-saturated vapour pressures.Iodine-diffused slices of CdTe were profiled by secondary ion mass spectrometry (SIMS) to obtain the total iodine concentration and by capacitance-voltage (C-V) techniques to obtain the net concentration of electrically active iodine. After annealing with iodine in the form of Cdl2, the slices were p-type, similar to those obtained when CdTe was annealed in either excess Te or Cd vapour, and they showed no significant increase in electrical activity. If Cd was added to the Cdl2 diffusion source or the CdTe was given a subsequent anneal in cadmium vapour, the slices became n-type. The results indicated that in all cases a neutral layer composed of Cd nIm (m and n are integers) formed on the surface layers, whereas if Cd was involved in the diffusion, some of the iodine existed in an electrically active form deeper into the slice with a maximum concentration of active carriers given by ND - NA ≈ 1017 cm-3. © 1997 John Wiley & Sons Ltd.
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    ISSN: 1057-9257
    Keywords: organic conductors ; optical spectra ; Chemistry ; Polymer and Materials Science
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    Notes: Polarised infrared reflectivity spectra of some ET-based conducting salts of alpha-type structure are measured and compared: (ET)2I3 (I), (ET)2TIHg(XCN)4 (X=S, Se) (II) and (ET)8[Hg4Br12(CH3C6H4CI)2] (III). For both I and II the electronic reflectivity is greater for the polarisation perpendicular to ET stacks. However, a resolved electron vibrational band in the region of 1 100-1 400 cm-1 is observed for II in the polarisation characterized by lower electronic reflectivity in contrast with the spectra of I. Another difference between I and II is the absence of the pronounced plasma edge in the region of 4 000 cm-1 in the spectra of II, which may be due to high electron damping. For III the electronic reflectivity is low and no resolved electron vibrational band in the region of 1 100-1 400 cm-1 is observed. The peculiarities of the electron-vibrational spectra of I, II and III may be due to the details of the crystal structure. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 57-60 
    ISSN: 1057-9257
    Keywords: BETS ; salt ; synthesis ; structure ; conductivity ; magnetoresistance oscillations ; Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: New BETS salts (where BETS is bis(ethylenedithio)tetraselenafulvalene) with (CuCl3)x, Cu2C6, Cu4Cl8 and Fe0.75Ga0.25Cl4 anions have been obtained. The crystal structures and electrical and magnetoresistance properties of Κ-BETS4Cu4Cl8, θ-BETS4Cu2Cl6 and Κ-BETS2Fe0.75Ga0.25Cl4 have been studied. The last two compounds have been found to exhibit Shubnikov-de Haas and angle-dependent magnetoresistance oscillations. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 67-69 
    ISSN: 1057-9257
    Keywords: magnetic BEDT-TTF salts ; IR spectra ; Drude-Lorentz model ; charge transfer bands ; C = C stretching vibrations ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Polarised reflectance spectra of three charge transfer salts of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), β(BEDT-TTF)5M(CN)6 · 10H2O (M ≡ Co, Fe, Cr), are measured in the infrared region 650-6500 cm-1 at room temperature. The reflectance is analysed in terms of the Drude-Lorentz model. Vibrational bands related to C = C stretching are discussed. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 307-310 
    ISSN: 1057-9257
    Keywords: photoreflectance ; photoluminescence ; InGaAs/GaAs quantum well ; type I and II excitonic transition ; Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: InGaAs/GaAs MOCVD-grown quantum wells have been investigated. Photoluminescence (PL) measurements have shown heavy-hole-related excitonic transitions within the temperature range from 10 to 100 K for all samples. In room-temperature photoreflectance (PR), sharp heavy- and light-hole excitonic transitions in the quantum wells have been observed. The transition energies obtained have been compared with values derived from theoretical considerations using the envelope function model including lattice-mismatch-related stress. The heavy- and light-hole transitions have been identified as excitonic transitions of types I and II respectively. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 171-182 
    ISSN: 1057-9257
    Keywords: molecular computing ; molecular image-processing devices ; Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The processing of half-tone images by excitable media functioning based on non-linear dynamic mechanisms was studied. The image-processing operations proved to be somewhat more complicated than in the case of black-and-white images. Analogies between the architecture of neural networks and the structural features of excitable media are discussed. The basic information capabilities of excitable media proved to be close to the capabilities of shunting on-centre off-surround feedback networks. © 1997 John Wiley & Sons, Ltd.
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    Keywords: photopolymerisation ; electron microscopy ; molecular modeling ; Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: By combining the results obtained from an electron diffraction tilting series with solid state NMR and powder X-ray diffraction, it was possible to determine the unit cell parameters and space group of BPABC crystals grown from DMAA solution both before and after irradiation. Subsequently semi-empirical quantum mechanical and packing energy calculations led to a model structure which agreed well with all the electron diffraction data and thus provided insight into the cross-linking mechanism. © 1997 John Wiley & Sons Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 161-170 
    ISSN: 1057-9257
    Keywords: molecular computing ; molecular image-processing devices ; Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Excitable media of Belousov-Zhabotinsky type were used for processing images with several levels of brightness. In this case the image-processing operations proved to be somewhat more complicated than in the case of black-and-white pictures. Excitable media seem to be useful tools for handling some practical applications such as aerial picture processing. Belousov-Zhabotinsky-type media are also simple and convenient experimental models for investigation of the information-processing capabilities of biomolecular systems with complicated non-linear dynamics. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 215-224 
    ISSN: 1057-9257
    Keywords: silicon ; epitaxy ; kinetics ; dynamics ; Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The value of in situ monitoring to study growth dynamics and surface reaction kinetics in a gas source molecular beam epitaxy process is illustrated with reference to the growth of Si films on Si(001) substrates using a beam of disilane (Si2H6). By using a combination of reflection high-energy electron diffraction (RHEED) and reflection anisotropy spectroscopy (RAS), we show first how morphological (long-range order) and local electronic structure effects can be separated in the evaluation of growth dynamics. This involves the measurement of step density changes by RHEED concomitantly with the variation in domain coverage on the Si(001) (2×1)+(1×2) reconstructed surface by RAS. This approach is then extended to investigate the kinetics of hydrogen desorption, which is the rate-limiting step in Si growth from Si2H6. It is shown that over a significant temperature range, zeroth-order kinetics are obeyed and this is explained on the basis of a step-mediated desorption process. Finally we show how this influences the growth rate on substrates of differing degrees of vicinality. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 277-279 
    ISSN: 1057-9257
    Keywords: semiconductor nanoparticles ; adduct ; Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: An improved organometallic route to passivated, high-quality crystalline nanodispersed semiconductors has been developed. Thermolysis of the 1:1 triethylamine adduct of dimethylcadmium and a chalcogenide source can be used to grow 3 nm diameter II-VI quantum dots capped with trioctylphosphine oxide. Samples have been characterised by absorption spectroscopy, luminescence spectroscopy and high-resolution transmission electron microscopy. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 281-293 
    ISSN: 1057-9257
    Keywords: polyparaphenylene ; ion implantation ; doping ; thermoelectric power ; conductivity ; Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: A sensitive apparatus for determining the conductivity and thermoelectric power of conducting polymer films at temperatures between 150 and 450 K is described. Brittle polyparaphenylene films doped by ion implantation with either alkali (caesium, sodium) or halogen (iodine) ions are studied by this method. Analysis of the temperature dependence of both conductivity and thermopower shows that the doping process of this conjugated polymer is efficient only when low parameters of implantation are selected and appears around room temperature. At higher temperatures the thermopower exhibits an anomalous evolution that we attribute to oxygen migration. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 311-316 
    ISSN: 1057-9257
    Keywords: monothiocarbamate ; MOCVD ; cadmium sulphide ; precursor ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Thin films of CdS were grown by low-pressure metalorganic chemical vapour deposition (LP-MOCVD, 10-2 Torr) on GaAs(100) and borosilicate glass using the novel single-source precursor bis(diethylmonothiocarbamato)cadmium(II). The deposition of CdS was observed at substrate temperatures of 300 °C and above. Uniform adherent films of CdS were grown on GaAs(100) at temperatures between 350 and 450°C. CdS films deposited on glass were generally transparent with small crystallites (∽50 nm). Films were characterised by X-ray diffraction and scanning electron microscopy and shown to be of hexagonal phase. A band gap of 2.39 eV was measured for the films of CdS. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 23-28 
    ISSN: 1057-9257
    Keywords: dimethylzinc ; purification ; adduct ; non-chelating diamine ; X-ray structure ; Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The structure of the dimethylzinc adduct with the bidentate amine 1,3-bis(4-pyridyl)propane, [Me2Zn(C5H4N)CH2CH2CH2(C5H4N)]n, 1, has been determined by X-ray diffraction analysis. Crystals of 1 are monoclinic, space group P21/m, with two molecules within a unit cell of dimensions a=5.364(3) Å, b=12.839(3) Å, c=10.618(3) Å and β=92.76(3)°. The structure is polymeric, being composed of [Me2Zn(C5H4N)CH2CH2CH2(C5H4N)] units with the nitrogens within a specific 1,3-bis(4-pyridyl)propane ligand bonding to adjacent zinc centres. The zinc atom is four-co-ordinate, bonding to two carbon and two nitrogen atoms, with the C - Zn - C angle of 145.5(2)° intermediate between that of a linear and tetrahedral bond arrangement. As far as we know, this is the first example of a polymeric alkyl zinc/cadmium amine adduct to have been structurally characterised. © 1997 John Wiley & Sons, Ltd.
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  • 78
    ISSN: 1057-9257
    Keywords: tetrathiafulvalenes ; cation radical inner salts (betaines) ; intermolecular hydrogen bonds ; uracil derivatives ; guanine analogues ; DC electrical conductivity ; organic semiconductors ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Dimethyl[2,4-dioxo(1 H,3 H)pyrimido]tetrathiafulvalene (1) and dimethyl-[2-amino-4-oxo(3 H)pyrimido]tetrathiafulvalene (4) form unusual inner salts by oxidation in the presence of bases. The insoluble black-green betaines 2 and 5 react with acids to form cation radical salts. Betaine 2 in the presence of acid and bis-(ethylenedithio)tetrathiafulvalene forms the unexpected double salt 8. In order to synthesise the cation radical salts of 1 and 4, it is necessary to use the ultrasonic method owing to the insolubility of the starting compounds. Electrical measurements of the betaines and cation radical salts in pressed samples show an unexpectedly low resistivity with semiconducting character: for betaine 2 ρ(RT) = 840 Ο cm, for betaine 5 ρ(RT) = 10 Ο cm, for salt 7 ρ(RT) = 40 Ο cm, but for double salt 8 ρ(RT) = 50 Ο cm. In the case of salt 8, very low values of activation energy of electrical conductivity of the order of kT were observed. The synthesis and purification of tetrathiafulvalene 4 from 5-amino-7-oxo(6 H)-1,3-dithiolo[4,5-d]pyrimidineselone-2 are described. © 1997 John Wiley & Sons, Ltd.
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  • 79
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    Advanced Materials for Optics and Electronics 7 (1997), S. 83-86 
    ISSN: 1057-9257
    Keywords: photoluminescence ; time-resolved fast spectrocopy ; photoinduced absorption spectroscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We have studied the photophysics of linear trans-quinacridone films by applying a variety of transient and continuous wave photomodulation techniques. Our experimental results demonstrate the ultrafast formation of excimer species which are responsible for the emission. The excimer decay kinetics seems to suggest a predominantly charge transfer character of these emitting species. This is consistent with the long-lived states which we detected on the millisecond time scale. © 1997 John Wiley & Sons, Ltd.
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  • 80
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    Advanced Materials for Optics and Electronics 7 (1997), S. 71-77 
    ISSN: 1057-9257
    Keywords: Monte Carlo simulation method ; nematic liquid crystal ; electric-field-induced Fréedericksz transition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In this paper we present results of the Monte Carlo simulation of a 2D nematic liquid crystal model in the presence of an externally applied electric field. The molecular interactions were described by the Lebwohl-Lasher Hamiltonian. The boundary conditions employed in the simulations corresponded to the experimental configuration frequently used for establishing the Frank elastic constants. The results are compared with the predictions of the phenomenological Ericksen theory. Preliminary results of simulations of an experimentally important case corresponding to the nematic interacting with a spatially modulated electric fluid are presented. © 1997 John Wiley & Sons, Ltd.
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  • 81
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    Advanced Materials for Optics and Electronics 7 (1997), S. 117-121 
    ISSN: 1057-9257
    Keywords: precursor ; MOCVD ; vapour pressure ; adduct ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The vapour pressures of mixtures of dimethylzinc with triethylamine (1), 1,3,5-trimethyl- (2) and 1,3,5-triethylhexahydro-1,3,5-triazine (3) have been studied using static measurement at various mole ratios of ligand to alkyl at 0°C. The results obtained are useful in assessing the suitability of these compounds as precursors for the deposition of group-12-containing materials by MOCVD. © 1997 John Wiley & Sons, Ltd.
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  • 82
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    Advanced Materials for Optics and Electronics 7 (1997), S. 149-156 
    ISSN: 1057-9257
    Keywords: polyaniline ; synthesis ; surface tension effect ; morphology ; SEM ; ESR ; electrical conductivity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Polyaniline (PANI) prepared in water or a water-methanol (1:1) mixed solvent by anodic oxidation of aniline hydrochloride at a potential of 0.8 V (and higher) vs. Ag/AgCl appears to form microrods of almost uniform shape and dimensions: a diameter of 0.7 μm and a length of 2-3 μm or more. A surface point contact Pt or Ir electrode has been used as the working electrode to get a better ordering in the product due to the surface tension effect. The structure observed with a scanning electron microscope (SEM) is complex: the sample is highly porous and looks like a coral reef; the average channel diameter is 1.5 and 2.5 μm for narrow and wide channels respectively. The rods appearing in great number in the sample are surprisingly uniform, particularly with respect to the diameter. The electrical conductivity is of the order of 10-1 S cm-1 for most samples examined. The electron spin resonance (ESR) spectra consist of a strong singlet line (g = 2.0030-2.0039, ΔH =;0.12-0.50 mT); similarly, the infrared (IR) spectra show a strong and broad absorption due to electron excitations and electron-lattice interactions, which we have observed previously for many PANI samples examined in our laboratory. © 1997 John Wiley & Sons, Ltd.
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  • 83
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    Advanced Materials for Optics and Electronics 7 (1997), S. 99-103 
    ISSN: 1057-9257
    Keywords: amorphous molecular solids ; poly(N-epoxypropylcarbazole) ; thermoluminescence ; charge trapping ; charge transport ; energetic disorder ; dipole moments ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The low-temperature thermoluminescence (TL) technique has been applied for probing the energetic disorder in doped poly(N-epoxypropylcarbazole)(PEPC) polymer films. Strong polar dopants were used for varying the degree of dipolar disorder. It was found that (1) the TL of the studied systems can be well interpreted in terms of the disorder model and (2) TL spectroscopy can provide the shape of the deepest part of the localised state distribution and the degree of energetic disorder as well. The charge trap distribution on the high-temperature side of the TL peak appears to be a Gaussian function and its halfwidth correlates well with the disorder parameter obtained from charge transport measurements. An unusual electric field effect on the TL of PEPC doped with strong polar dopants was found and is explained in terms of the contribution of the charge-dipole interaction to the energy of localised states. This effect indicates that the TL phenomenon for the studied systems cannot be explained purely by molecular γ-relaxation in the polymer. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 135-139 
    ISSN: 1057-9257
    Keywords: reaction-diffusion media ; chemical processors ; parallel computing ; cellular automata ; image processing ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In this paper we give a regular proof of the viability of the theory of reaction-diffusion computing. The test problem is to approximate the skeleton of a planar contour, i.e. select sites of centres of bitangent circles which lie wholly within the contour. We have designed both a cellular automaton model and a real prototype of a chemical processor that implement skeleton transformations. In the cellular automaton, segments of the discrete skeleton are computed via interactions of excitation waves, while in the chemical processor the underlying mechanism is the formation of Prussian blue in an agar gel film. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 45-50 
    ISSN: 1057-9257
    Keywords: molecular electronics ; photodiode ; rectifier ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: A few-monolayer zwitterionic, non-centrosymmetric Langmuir-Blodgett film has been sandwiched between two electrodes, one of which is transparent. Curves of dark current density as a function of applied bias were observed to exhibit rectifier-like behaviour and to follow closely the dependences measured from junctions using two metallic electrodes. The transparent indium tin oxide (ITO) electrode discussed here permitted illumination of the organic film during electrical characterisation and it was observed that the electrical behaviour was altered from the dark state. Illumination has the effect of generating a photocurrent even when no bias is applied to the electrodes; in addition, the junction conductance was increased. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 79-82 
    ISSN: 1057-9257
    Keywords: organic conductors ; optical spectra ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Polarised infrared reflectivity spectra of some ET-based conducting salts of alpha-type structure are measured and compared: (ET)2I3 (I), (ET)2TIHg(XCN)4 (X≡S, Se) (II) and (ET)8[Hg4Br12(CH3C6H4Cl)2] (III). For both I and II the electronic reflectivity is greater for the polarisation perpendicular to ET stacks. However, a resolved electron vibrational band in the region of 1 100-1 400 cm-1 is observed for II in the polarisation characterised by lower electronic reflectivity in contrast with the spectra of I. Another difference between I and II is the absence of the pronounced plasma edge in the region of 4 000 cm-1 in the spectra of II, which may be due to high electron damping. For III the electronic reflectivity is low and no resolved electron vibrational band in the region of 1 100-1 400 cm-1 is observed. The peculiarities of the electron-vibrational spectra of I, II and III may be due to the details of the crystal structure. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 61-65 
    ISSN: 1057-9257
    Keywords: silicon backbone polymers ; transport properties ; transient photoconductivity ; light generation efficiency ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Transient space-charge-limited currents (T-SCLCs) were used as a method for examining drift mobility, recombination and transport mechanisms for a typical poly(silylene), poly(methylphenylsilylene) (PMPSi). It was found that T-SCLCs present a unique possibility for injecting constant charge into a material with strong dependence of the generation efficiency on the electric field strength. This charge is given by space charge limitations and is thus independent of the transport properties of the material. The post-transit T-SCLC hole emission signals from deep traps have been measured using post-transit T-SCLCs. A density-of-electron-states distribution for deep trapping hole states with a tail-like exponential and a Gaussian distribution centred at 0.55 eV were found. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 55-55 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: This issue contains papers presented at the 7th International Conference on Electrical and Related Properties of Organic Solids (ERPOS-7). It is a companion issue to Vol. 6. No. 5/6 which contained the bulk of the papers. Unfortunately, not all of the papers could be published in one special issue. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 123-133 
    ISSN: 1057-9257
    Keywords: nanocomposites ; sol-gel ; heteropolymetallates ; photochromics ; holographic data storage ; amplitude grating ; two-wave-mixing recording ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: This paper describes the properties of some new organic-inorganic photochromic layers. They are based on a hybrid organic-inorganic matrix in which tungsten heteropolyoxometallates (SiW12O4-40, PW12O3-40) are entrapped in a network obtained from the reaction of 3-glycidoxy-propyltrimethoxysilane. The high homogeneity of these materials on the nanoscale leads to transparent monoliths and layers of controlled thicknesses up to 40 μm. The optical properties of the blend are emphasised and the construction of amplitude gratings in the materials by two-wave-mixing experiments is described. The results of the optical experiments and the comparison with the theoretical background are used as a model for photochromic holographic storage processes. © 1997 John Wiley & Sons, Ltd.
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  • 90
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    Advanced Materials for Optics and Electronics 7 (1997), S. 207-211 
    ISSN: 1057-9257
    Keywords: amorphous molecular semiconductor ; dye ; triplet exciplex ; photoconductivity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Results of investigation of the processes of charge carrier photogeneration and relaxation within the exciplex absorption region in films of poly-N-epoxypropylcarbazole doped with the dye rhodamine 6G are given. When the films are illuminated with light from the dye absorption region, new centres of charge photogeneration appear that absorb within the exciplex absorption region. It is shown for the first time that these centres have a long lifetime at room temperature and their temporal concentration changes correlate with EPR photosignal changes. The concentration of centres is independent of the external electric field strength during their generation. These centres are identified as triplet exciplexes. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 225-231 
    ISSN: 1057-9257
    Keywords: vanadium pentoxide thin films ; electron beam evaporation ; optical properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Thin films of vanadium pentoxide have been prepared by the electron beam evaporation technique over a wide range of substrate temperatures. Spectrophotometric investigations have been made on these films in the wavelength range 350-1500 nm to determine the nature of the optically induced transition and the optical band gap. A better fit for the direct forbidden transition than for the indirect allowed transition is observed in all the films. The optical band gap is found to decrease with increasing substrate temperature and the subsequent appearance of a broadband absorption at about 1000 nm is attributed to the oxygen vacancies in the films. The effect of heat treatment in vacuum and oxygen ambient on the optical properties of these films is also reported. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 255-261 
    ISSN: 1057-9257
    Keywords: amorphous molecular semiconductors ; electron-hole pairs ; excitons ; photoconductivity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The photoconductivity of films of amorphous molecular semiconductors increases upon simultaneous photogeneration of singlet electron-hole pairs (EHPs) and triplet excitons and decreases upon photogeneration of triplet EHPs and triplet excitons. An increase in external electric field strength leads to a decrease in the effect of triplet excitons on the film photoconductivity caused by EHP dissociation. It is concluded that under increasing external electric field strength the mobility of charge carriers increases and the velocity of EHP dissociation becomes comparable with the velocity of spin conversion of EHPs interacting with triplet excitons. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 29-34 
    ISSN: 1057-9257
    Keywords: CdTe ; thin films ; ethylene-glycol bath ; photocurrent ; flat-band potential ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: CdTe films were deposited on Ni and conducting glass (SnO2) substrates from an ethylene-glycol-based bath by galvanostatic and potentiostatic methods. The film composition and electrical properties depend on parameters such as working electrode potential current density, deposition temperature, substrate type and post-deposition treatments. It is possible to improve the grain size and stoichiometry of the film by post-deposition heat treatment in air. The conductivity type was determined from the photocurrent-working electrode potential behaviour of the film. Dark capacitance measurements in a 0.5 M H2SO4 solution at 10 kHz showed a linear behaviour, from which the flatband potential Vfb= -0.365 V vs. a saturated calomel electrode (SCE) and the doping density ND = 1.35 × 1018 cm-3 were determined. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 35-38 
    ISSN: 1057-9257
    Keywords: photoluminescence ; time-resolved fast spectrocopy ; photoinduced absorption spectroscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We have studied the photophysics of linear trans-quinacridone films by applying a variety of transient and continuous wave photomodulation techniques. Our experimental results demonstrate the ultrafast formation of excimer species which are responsible for the emission. The excimer decay kinetics seems to suggest a predominantly charge transfer character of these emitting species. This is consistent with the long-lived states which we detected on the millisecond time scale. © 1997 John Wiley & Sons, Ltd.
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  • 95
    ISSN: 1057-9257
    Keywords: tetrathiafulvalenes ; cation radical inner salts (betaines) ; intermolecular hydrogen bonds ; uracil derivatives ; guanine analogues ; DC electrical conductivity ; organic semiconductors ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Dimethyl[2,4-dioxo(1 H,3 H)pyrimido]tetrathiafulvalene (1) and dimethyl-[2-amino-4-oxo(3 H)pyrimido]tetrathiafulvalene (4) form unusual inner salts by oxidation in the presence of bases. The insoluble black-green betaines 2 and 5 react with acids to form cation radical salts. Betaine 2 in the presence of acid and bis-(ethylenedithio)tetrathiafulvalene forms the unexpected double salt 8. In order to synthesise the cation radical salts of 1 and 4, it is necessary to use the ultrasonic method owing to the insolubility of the starting compounds. Electrical measurements of the betaines and cation radical salts in pressed samples show an unexpectedly low resistivity with semiconducting character: for betaine 2 ρ(RT) = 840 Ω cm, for betaine 5 ρ(RT) = 10 Ω cm, for salt 7 ρ(RT) = 40 Ω cm, but for double salt 8 ρ(RT) = 50 Ω cm. In the case of salt 8, very low values of activation energy of electrical conductivity of the order of kT were observed. The synthesis and purification of tetrathiafulvalene 4 from 5-amino-7-oxo(6 H)-1,3-dithiolo[4,5-d]pyrimidineselone-2 are described. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 87-91 
    ISSN: 1057-9257
    Keywords: 1,4-cis-polybutadiene ; direct conduction ; hopping ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: This paper contains results on electrical conduction in 1,4-cis-polybutadiene. Measurements were performed for thin films of thickness from 1 to 10 um with gold and aluminium electrodes. Study was made in the temperature range from 15 to 325 K for two types of polybutadienes: (1) containing 100% of cis form, from Aldrich; (2) containing 96% of cis form, from Philips Petroleum Co. It was found that direct conduction is determined by the Poole-Frenkel effect with some hopping and the Schottky effect. Evaluation of activation energies gave results from 0.3 to 0.36 eV. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 109-115 
    ISSN: 1057-9257
    Keywords: Cd1-xZnxTe thin films ; optical constants ; spectroscopic ellipsometry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Spectroscopic ellipsometry has been used to determine the optical constants - complex dielectric constant (ε* = ε1+ε2), refractive index (n), extinction coefficient (k), absorption coefficient (α) and normal incidence reflectivity (R) - of two-source vacuum-evaporated polycrystalline Cd1-xZnxTe thin films formed on Corning 7059 glass substrates. The experimental spectra were measured in the photon energy range 1.1-5.6 eV. The spectra revealed distinct peaks at energies corresponding to interband transitions. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 141-148 
    ISSN: 1057-9257
    Keywords: atomic force microscopy ; thin molecular films ; lithography ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In this paper we present results concerning the development of a lithographic technique suitable for application to Langmuir-Blodgett films. Controlled ablations of well-defined portions of the film have been made by using a scanning force microscope (SFM). We report the values of the microscope operational parameters that have allowed us either to perform non-destructive imaging or to obtain reproducible ablations of controlled depth. In particular, our analysis has pointed out the importance of the scanning speed in giving rise to such surface modifications. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 183-193 
    ISSN: 1057-9257
    Keywords: GaAs ; redistribution of dopants ; ideal static induction transistor (ISIT) ; molecular layer epitaxy (MLE) ; SIMS ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: An ideal static induction transistor (ISIT) structure was fabricated using molecular layer epitaxy (MLE). The doping method of MLE enabled us to achieve a sufficiently high level of doping for ISIT fabrication. In the fabrication process a low growth temperature was very important for the device structure, which requires very sharp dopant profiles. For the ISIT, two MLE processes, namely source-drain growth and gate regrowth, were required. The electrical characteristics of the source-drain were changed after heat treatment at a temperature higher than 480°C. The effect of the redistribution of dopants of the source-drain structure (n++-i-p++-i-n+) during gate regrowth was clearly shown by SIMS (secondary ion mass spectroscopy) measurements for various temperatures of heat treatment. As a result the doped Se diffused from the n++ source region to the other layers and the doped Zn diffused from the p++ layer to the i-layers. The source was a heavily Se-doped layer at the doping level of (2-3)×1019 cm-3 containing a larger amount of interstitial Se atoms in the lattice. The redistribution of Se from the heavily doped region was detectable even after heat treatment at 480°C for 30 min. For the p++ layer the profile of the C-doped layer was stable even after heat treatment at 620°C for 30 min, but the profile of Zn changed markedly after heat treatment at 480°C for 30 min. In addition, the carbon-doped p++ layer acted as a gettering layer for diffused interstitial Se from the source region. The driving force of the redistribution of dopants results in the electric field in the device structures. © 1997 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 7 (1997), S. 233-240 
    ISSN: 1057-9257
    Keywords: thermal stability ; DSC ; group 13 metalorganic compounds ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The thermal stabilities of a range of group 13 metalorganic compounds previously used as precursors in metalorganic vapour phase epitaxy (MOVPE) or chemical beam epitaxy (CBE) have been investigated using differential scanning calorimetry (DSC). For the trialkyl compounds R3M the thermal stability decreases in the order M≡Al〉Ga〉In and R≡Me〉Et〉iPr〉tBu and the formation of adducts R3ML (L≡OR2, NR3, etc.) leads to an increase in thermal stability. Dialkylaluminium hydride compounds (e.g. Me2AlH) gave the largest energy release. © 1997 John Wiley & Sons, Ltd.
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