Fluctuation Electron Microscopy of Medium-range Order in Amorphous Silicon
Author : Paul Marriner Voyles
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Page : 360 pages
File Size : 30,42 MB
Release : 2001
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Author : Paul Marriner Voyles
Publisher :
Page : 360 pages
File Size : 30,42 MB
Release : 2001
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Page : pages
File Size : 40,29 MB
Release : 2002
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Author : Paul Marriner Voyles
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Page : 0 pages
File Size : 36,89 MB
Release : 2003
Category : Amorphous semiconductors
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Author : Yeonwoong Jung
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Page : 58 pages
File Size : 11,90 MB
Release : 2003
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Author : Paul Marriner Voyles
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Page : 30 pages
File Size : 14,75 MB
Release : 2003
Category : Amorphous semiconductors
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Page : 9 pages
File Size : 25,91 MB
Release : 2000
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The authors have characterized with fluctuation electron microscopy the medium-range order of hydrogenated amorphous silicon thin films deposited by a variety of methods. Films were deposited by reactive magnetron sputtering, hot-wire chemical vapor deposition, and plasma enhanced chemical vapor deposition with and without H2 dilution of the SiH4 precursor gas. All of the films show the signature of the paracrystalline structure typical of amorphous Si. There are small variations in the degree of medium-range order with deposition methods and H2 content. The PECVD film grown with high H2 dilution contains Si crystals (approximately) 5 nm in diameter at a density of (approximately) 109 cm2. The amorphous matrix surrounding these crystals shows no difference in medium-range order from the standard PECVD film.
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Page : 7 pages
File Size : 42,59 MB
Release : 2000
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Using fluctuation electron microscopy, the authors have measured the medium-range order of magnetron sputtered silicon thin films as a function of substrate temperature from the amorphous to polycrystalline regimes. They find a smooth increase in the medium-range order of the samples, which they interpret in the context of the paracrystalline structural model as an increase in the size of and/or volume fraction occupied by the paracrystalline grains. These data are counter to the long-standing belief that there is a sharp transition between amorphous and polycrystalline structures as a function of substrate temperature.
Author : Lakshminarayana Nittala
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Page : pages
File Size : 29,78 MB
Release : 2006
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Author : William Gregory Stratton
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Page : 146 pages
File Size : 47,20 MB
Release : 2007
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Author : Aram Rezikyan
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Page : 122 pages
File Size : 29,24 MB
Release : 2015
Category : Amorphous substances
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Fluctuation Electron Microscopy (FEM) has become an effective materials' structure characterization technique, capable of probing medium-range order (MRO) that may be present in amorphous materials. Although its sensitivity to MRO has been exercised in numerous studies, FEM is not yet a quantitative technique. The holdup has been the discrepancy between the computed kinematical variance and the experimental variance, which previously was attributed to source incoherence. Although high-brightness, high coherence, electron guns are now routinely available in modern electron microscopes, they have not eliminated this discrepancy between theory and experiment. The main objective of this thesis was to explore, and to reveal, the reasons behind this conundrum. The study was started with an analysis of the speckle statistics of tilted dark-field TEM images obtained from an amorphous carbon sample, which confirmed that the structural ordering is sensitively detected by FEM. This analysis also revealed the inconsistency between predictions of the source incoherence model and the experimentally observed variance. FEM of amorphous carbon, amorphous silicon and ultra nanocrystalline diamond samples was carried out in an attempt to explore the conundrum. Electron probe and sample parameters were varied to observe the scattering intensity variance behavior. Results were compared to models of probe incoherence, diffuse scattering, atom displacement damage, energy loss events and multiple scattering. Models of displacement decoherence matched the experimental results best. Decoherence was also explored by an interferometric diffraction method using bilayer amorphous samples, and results are consistent with strong displacement decoherence in addition to temporal decoherence arising from the electron source energy spread and energy loss events in thick samples. It is clear that decoherence plays an important role in the long-standing discrepancy between experimental FEM and its theoretical predictions.