Fluctuation Electron Microscopy of Medium-Range Order in Amorphous Silicon
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Voyles_Paul_Marriner |
| Title: | Fluctuation Electron Microscopy of Medium-Range Order in Amorphous Silicon |
| Author(s): | Voyles, Paul Marriner |
| Department / Program: | Physics |
| Discipline: | Physics |
| Degree: | Ph.D. |
| Genre: | Dissertation |
| Subject(s): | amorphous; silicon; microscopy; diffraction; paracrystalline; dark-field; mro; coherence; semiconductors; hydrogenated; applescripts |
| Abstract: | 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. |
| Issue Date: | 2001 |
| Type: | Text |
| Language: | English |
| URI: | http://hdl.handle.net/2142/35205 |
| Rights Information: | Voyles 2001 © |
| Date Available in IDEALS: | 2012-11-11 |
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This item appears in the following Collection(s)
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Graduate Theses and Dissertations at Illinois
Graduate Theses and Dissertations at Illinois -
Dissertations and Theses - Physics
Dissertations in Physics
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