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Amorphous Material

The Experts below are selected from a list of 261 Experts worldwide ranked by ideXlab platform

David A. Drabold – 1st expert on this subject based on the ideXlab platform

  • Ab initio estimate of temperature dependence of electrical conductivity in a model Amorphous Material: Hydrogenated Amorphous silicon
    Physical Review B, 2007
    Co-Authors: Tesfaye A. Abtew, Mingliang Zhang, David A. Drabold


    We present an ab initio calculation of the dc conductivity of Amorphous silicon and hydrogenated Amorphous silicon. The Kubo-Greenwood formula is used to obtain the dc conductivity, by thermal averaging over extended dynamical simulation. Its application to disordered solids is discussed. The conductivity is computed for a wide range of temperatures and doping is explored in a naive way by shifting the Fermi level. We observed the Meyer-Neldel rule for the electrical conductivity with EMNR=0.06eV and a temperature coefficient of resistance close to experiment for a-Si:H. In general, experimental trends are reproduced by these calculations, and this suggests the possible utility of the approach for modeling carrier transport in other disordered systems.

Jeffrey C Grossman – 2nd expert on this subject based on the ideXlab platform

  • stress effects on the raman spectrum of an Amorphous Material theory and experiment on a si h
    Physical Review B, 2015
    Co-Authors: David A Strubbe, Eric Johlin, T Kirkpatrick, Tonio Buonassisi, Jeffrey C Grossman


    Strain in a Material induces shifts in vibrational frequencies. This phenomenon is a probe of the nature of the vibrations and interatomic potentials and can be used to map local stress/strain distributions via Raman microscopy. This method is standard for crystalline silicon devices, but due to the lack of calibration relations, it has not been applied to Amorphous Materials such as hydrogenated Amorphous silicon $(a$-Si:H), a widely studied Material for thin-film photovoltaic and electronic devices. We calculated the Raman spectrum of $a$-Si:H ab initio under different strains $\ensuremath{\epsilon}$ and found peak shifts $\mathrm{\ensuremath{\Delta}}\ensuremath{\omega}=\left(\ensuremath{-}460\ifmmode\pm\else\textpm\fi{}10\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}\right)\mathrm{Tr}\phantom{\rule{4pt}{0ex}}\ensuremath{\epsilon}$. This proportionality to the trace of the strain is the general form for isotropic Amorphous vibrational modes, as we show by symmetry analysis and explicit computation. We also performed Raman measurements under strain and found a consistent coefficient of $\ensuremath{-}510\ifmmode\pm\else\textpm\fi{}120\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. These results demonstrate that a reliable calibration for the Raman/strain relation can be achieved even for the broad peaks of an Amorphous Material, with similar accuracy and precision as for crystalline Materials.

Oliver Plümper – 3rd expert on this subject based on the ideXlab platform

  • Amorphous Material in experimentally deformed mafic rock and its temperature dependence implications for fault rheology during aseismic creep and seismic rupture
    Journal of Structural Geology, 2020
    Co-Authors: Sina Marti, Holger Stünitz, Renée Heilbronner, Oliver Plümper


    Abstract Amorphous Materials are frequently observed in natural and experimentally produced fault rocks. Their common occurrence suggests that Amorphous Materials are of importance to fault zone dynamics. However, little is known about the physico-chemical impact of Amorphous Materials on fault rheology. Here we present deformation experiments on mafic fault rock, where Amorphous Material forms due to intense mechanical wear during the experiments. The experiments are run at temperatures from 300 to 600 °C, confining pressures of 0.5 or 1.0 GPa, and at constant displacement rates of ( d ˙ ax) 2 ·10−7, 2 ·10−8 or 2 ·10−9 ms−1, resulting in bulk strain rates ( γ ˙ ) of ≈3 ·10−4, 3 ·10−5 and 3 ·10−6 s−1. At these conditions, the mafic rock Material undergoes intense brittle deformation and cataclastic flow, but sample strength significantly decreases with increasing temperatures – a feature commonly attributed to viscous deformation processes. Microstructural analyses show that after an initial stage of homogeneous cataclastic flow, strain localizes into narrow (2–10 μm wide) ultra-cataclastic bands that evolve into Amorphous shear bands. With the data presented in this research paper, we argue that the temperature sensitivity recorded in the mechanical data is caused by viscous deformation of the Amorphous Material. We suggest that with the formation of Amorphous Materials during brittle deformation, fault rheology becomes significantly temperature-sensitive. This has important implications for our understanding of fault strength and weakening due to the presence of Amorphous Materials. In addition, weak Material along faults will lead to stress concentrations that may trigger seismic rupture.