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Voyles, Paul Marriner 2012-11-11T17:25:08Z 2012-11-11T17:25:08Z 10000-01-01 2001 Fluctuation electron microscopy is a transmission electron microscopy technique for studying medium-range order in disordered materials. We compute the variance for the image intensity of low-resolution hollow-cone dark field electron micrographs as a function of the diffracting condition and microscope resolution. The variance is sensitive to fluctuations in diffraction from mesoscopic volumes of the sample. It carries information about medium-range order via the three- and four-body atomic distribution functions. Fluctuation microscopy has been applied to the study of amorphous silicon, with and without alloying with hydrogen. We find that amorphous silicon has significant medium-range order, more than can be described by the conventional continuous random network model. The structure is better described by a paracrystalline model, which consists of strained topologically crystalline grains which may or may not be embedded in a more disordered matrix. Experiments show a continuous evolution of medium-range order in films deposited with increasing substrate temperature from the amorphous to polycrystalline regimes, which is counter to the belief that this structural transition is a discontinuous order-disorder phase transition. In the paracrystalline model, this increase is caused by the topologically crystalline grains growing, or occupying a greater volume fraction, or both. Experiments also show that hydrogenated amorphous silicon deposited by a variety of methods shares the paracrystalline structure. The medium-range order of hydrogenated amorphous silicon is affected by exposure to visible-spectrum white light. Films deposited by different methods have different responses, which may be connected to differences in the creation of metastable electrical defects known as the Staebler-Wronski effect. Submitted by Elias Lopez (erlopez2@illinois.edu) on 2012-11-11T17:25:08Z No. of bitstreams: 1 Voyles_Paul_Marriner.pdf: 5345923 bytes, checksum: 897c84f9715da8a6e0223866654e495a (MD5) Made available in DSpace on 2012-11-11T17:25:08Z (GMT). No. of bitstreams: 1 Voyles_Paul_Marriner.pdf: 5345923 bytes, checksum: 897c84f9715da8a6e0223866654e495a (MD5) Previous issue date: 2001 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Elias Lopez (erlopez2@illinois.edu) on 2012-11-14T02:27:19Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:35:26-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Publisher has not yet granted open access permission Publisher has not yet granted open access permission U of I Only http://hdl.handle.net/2142/35205 en Voyles 2001 © amorphous silicon microscopy diffraction paracrystalline dark-field medium-range order (mro) coherence semiconductors hydrogenated applescripts Fluctuation Electron Microscopy of Medium-Range Order in Amorphous Silicon text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.