Results 1 - 10 of 7745
Results 1 - 10 of 7745. Search took: 0.021 seconds
|Sort by: date | relevance|
[en] Highlights: • Shear horizontal wave dispersion in nanolayers with surface effects is examined. • Wave velocity is dependent on the layer thickness and surface elastic constants. • Surface elastic constants can be analytically derived from the wave velocity. - Abstract: In this work, the shear horizontal (SH) wave dispersion in two dissimilar nanolayers is investigated by using the surface elasticity theory in which the surface effects are featured by surface elastic constants. It is found that the SH wave dispersion shows distinct dependence on the nanolayer thickness as well as the surface elastic constants. The larger the surface elastic modulus and/or the smaller the thickness, the higher the phase velocity. In particular, as the wave frequency approaches zero, the analytical relation between the phase velocity in the first mode dispersion and the surface elastic constants is deduced. Thereby, a facile method is suggested to determine the surface elastic constants from the phase velocity of SH waves scattered in nanolayers.
[en] There is considerable experimental evidence that the microstructure has important consequences for polymer-based electronic and optoelectronic applications, but few theoretical and computational models account for it. We produced several realisations of polymer networks exhibiting specific arrangements of C4n+2 H2n+4 molecules at the mesoscopic scale and we carried out computer experiments in which bipolar charge carriers were injected in the polymer system from the appropriate electrodes. Our results show that polymer microstructures resulting from different arrangements of polymer molecules have significant effects on the competition between charge trapping, current transport and recombination within the polymer layer. It was found that current efficiency increases non-linearly with the external applied electric field, the effect being more pronounced for molecular orientations parallel to the electrode surface. In contrast, recombination efficiency shows an opposite behaviour since no significant charge accumulation within the polymer layer is predicted. However, the space-charge effects due to electrons and holes are responsible for most of the recombination events not occurring in neither long or short chains
[en] This paper provides an overview of modern alloy development, from discovery and optimization towards alloy design, based on combinatorial thin film materials science. The combinatorial approach, combining combinatorial materials synthesis of thin film composition-spreads with high-throughput property characterization has proven to be a powerful tool to delineate composition–structure–property relationships, and hence to efficiently identify composition windows with enhanced properties. Furthermore, and most importantly for alloy design, theoretical models and hypotheses can be critically appraised. Examples for alloy discovery, optimization, and alloy design of functional as well as structural materials are presented. Using Fe-Mn based alloys as an example, we show that the combination of modern electronic-structure calculations with the highly efficient combinatorial thin film composition-spread method constitutes an effective tool for knowledge-based alloy design.
[en] In this study, wave functions are used to analyze the transmission of micro-scale particles throughout a sequence of one-dimensional potential barriers. This model can be used to simulate the motion of particles through a crystalline or non-crystalline thin film. Our focus is on the configuration of barriers which can be characterized by their heights, widths and lengths, and on their effects on the transmission probability. As a common phenomenon in crystalline structure, the resonant transmission can be found at classical forbidden energy levels and they form some energy bands. We further investigate the effects of voids and impurities on the transmission of particles by introducing variations to barrier heights. Results indicate that transmission can be weakened or reinforced by the presence of impurities or voids. In order to study more realistic structures, a statistical approach is introduced for us to imitate more variations on the barrier heights. This scheme allows us to study the transmission of particles through amorphous-like thin film. The quantitative results show that resonant energy bands can be significantly reduced by the irregular structures inside an amorphous-like film due to the destructive interference among waves
[en] Recently, with scaling down of semiconductor devices, need for nanotechnology has increased enormously. For nanoscale devices especially, each of the layers should be as thin and as perfect as possible. Thus, the application of atomic layer deposition (ALD) to nanofabrication strategies and emerging nanodevices has sparked a good deal of interest due to its inherent benefits compared to other thin film deposition techniques. Since the ALD process is intrinsically atomic in nature and results in the controlled deposition of films at the atomic scale, ALD produces layers with nanometer scale thickness control and excellent conformality. In this report, we review current research trends in ALD processes, focusing on the application of ALD to emerging nanodevices utilizing fabrication through nanotechnology
[en] Uniformity of electrical performance is critical for thin film modules. The more uniformly that all areas of the module perform the better the overall efficiency will be. Total module performance tends towards the average of localized performance, skewed slightly lower by the width of localized performance distribution. Measurement of overall module efficiency does not give information about performance uniformity. Use of small area devices (SAD's) defined from the module allow standard electrical measurements including light and dark current-voltage (IV/JV) and quantum efficiency to be performed on a small scale. Data from these measurements allows mapping of electrical performance across the module. The structure of types of SAD's is discussed and some examples of efficiency data from JV measurements as used in the optimization of a thin film module manufacturing line are presented. Also a brief discussion of statistical analysis of the data is included.
[en] A recently developed ion beam layer removal method allows the precise determination of complex depth profiles of residual stresses in crystalline and in amorphous thin films on a nanoscale [S. Massl, J. Keckes, R. Pippan, Acta Mater. 55 (2007) 4835]. Recipes and advice for optimal experimental design are given herein to minimize errors in the stress distributions calculated. The calculation procedure of this method is briefly introduced followed by the definition of any sources of error along with their influence on the resulting stress distribution. Finally, the errors as a function of experimental parameters are discussed by means of an example and four model stress distributions
[en] Thermomechanical analysis is presented to study the basic temperature effects on elastomeric substrate of flexible electronics. Strains of a films-on-substrate structure related with three key temperatures are given based on the interfacial continuum model. An improved strain model is given and compared with other two models. The role of the temperature-dependent effects is highlighted and adopted to design a flexible inorganic/organic heterogeneous structure subject to little thermal action. The sensitivity analysis of three key temperatures is investigated, by which proper selection of technological parameter for poly(dimethylsiloxane) fabrication may be determined to eliminate the variation of stress of the interface in circumstances with temperature varying severely. This work contributes to systemic reliability and compatibility, structural design and thermal management of flexible electronics.
[en] In this paper, an extended Hertzian approach will be used in order to develop a tool for the analysis of nanoindentation unloading curves of sharp indenters. The approach is based upon the concept of the effectively shaped indenter introduced by Pharr and co-workers. However, in contrast to the Sneddon formulae used by Pharr, the extended Hertzian approach allows a complete evaluation of the elastic field produced by the effective indenter in closed and elementary form and thus a much more thorough discussion of the effects observed during the indentation experiment. As an example the new approach is used here to determine the critical yield stress of a variety of materials of ultra thin coatings directly from the unloading curves of Berkovich indentations. The results are compared with those of other methods and the deviations are discussed
[en] The formation of trapped states due to mechanical strain dominates the characteristics of a-Si:H thin-film transistors. The behavior of electrical characteristics affected by mechanical strain can be explained by the redistribution of trap states in the bandgap. The disordered bonds may generate a redistribution of trap states, resulting in unstable electrical characteristics, such as threshold voltage, subthreshold swing, and the mobility of carriers. During a mechanical strain, the deep states are redistributed into a Gaussian distribution and are dissimilar to ordinary acceptor-like deep states, which have exponential distributions. It is concluded that the gap state density of an a-Si:H layer under the effects of mechanical strain is fundamental to the reliability and development of flexible electronics. - Highlights: ► The trap formation by mechanical strain dominates the characteristics. ► Weak or broken bonds may contribute to the redistribution of trap states. ► The deep states are redistributed into a Gaussian distribution