Crystal polycrystalline film

Thin films of metals, alloys and compounds of a few micrometres diickness, which play an important part in microelectronics, can be prepared by die condensation of atomic species on an inert substrate from a gaseous phase. The source of die atoms is, in die simplest circumstances, a sample of die collision-free evaporated beam originating from an elemental substance, or a number of elementary substances, which is formed in vacuum. The condensing surface is selected and held at a pre-determined temperature, so as to affect die crystallographic form of die condensate. If diis surface is at room teiiiperamre, a polycrystalline film is usually formed. As die temperature of die surface is increased die deposit crystal size increases, and can be made practically monocrystalline at elevated temperatures. The degree of crystallinity which has been achieved can be determined by electron diffraction, while odier properties such as surface morphology and dislocation sttiicmre can be established by electron microscopy. 

Sample requirements Very flexible liquids, gases, crystals, polycrystalline solids, powders, and thin films... 

Diamond is obtained as a polycrystalline material by CVD with properties similar to these of natural diamond. Efforts to produce single crystal thin films have so far been largely unsuccessful. 

It is difficult to assess with high precision the crystal planes exposed to the gas phase in low temperature (0°C) polycrystalline films. The assumption has sometimes been made [e.g., Brennan, Haywood, and Trapnell (8) ], that for fee metals the surface consists of an equal exposure of (111), (100), and (110) planes, with a similar assumption for bcc metals with... 

EDSA of thin polycrystalline films has several advantages First of all the availability of a wide beam (100-400 pm in diameter) which irradiates a large area with a large amount of micro-crystals of different orientations [1, 2]. This results into a special t5q)e of diffraction patterns (DP) (see Fig.l). Thus it is possible to extract from a single DP a full 3D data set of structure amplitudes. That allows one to perform a detailed structure analysis with good resolution for determining structure parameters, reconstruction of ESP and electron density. 

A complete analysis of the IR spectra of thienothiophenes 1 and 2 in the gaseous, liquid, and crystalline states was carried out by Kimel feld et a/. The following isotopically substituted compounds were also studied 2-deuterothieno[2,3-h]thiophene (l-2d), 2-deuterothieno[3,2-I)]-thiophene (2-2d), 2,5-dideuterothieno[2,3-h]thiophene (l-2,5-d2), and 2,5-dideuterothieno[3,2-h]thiophene (2-2,5-dj). The IR spectra of oriented polycrystalline films of all compounds were measured in polarized light, and Raman spectra of liquid thienothiophenes 1, l-2d, and 1-2,5-dj, of crystals of thienothiophenes 2 and 2-2,5-d2 and melts of thienothiophenes 2 and 2-2d were analyzed. The planar structure of point-group Cj, for thienothiophene 1 in the liquid and gaseous states was assumed. Then the thirty vibrations of compounds 1 and l-2,5-d2 can be divided into four symmetry classes Aj (11), Bj (10), A2 (4), and B2 (5) the vibrations of molecule (l-2d) (C, symmetry) are divided into two classes A (21) and A" (9). 

A vast number of semiconductor materials have been tested for use as electrodes. Some of these are elucidated in Chapter 28, particularly with respect to their unique properties toward photochemically excited molecules, although most have been used as bulk single crystals and not as polycrystalline films. The two most common semiconducting film electrodes are Sn02 and InOx. 

When we consider silicon films, on the other hand, the nature of the solid deposit is crucial to the behavior of the film. Depending on deposition conditions, we can deposit amorphous, polycrystalline, or single crystal films. As was noted in Chapter 1, the morphology of polycrystalline films can be complex. In the present section, we will review some aspects of polysilicon (poly) thin films deposited by CVD. The final section of this chapter will be devoted to epitaxial silicon thin films. 

In the previous section, we discussed the CVD of silicon thin films. For the pressures and temperatures at which those depositions were carried out, the films were polycrystalline. If the depositions had been carried out at higher temperatures, single-crystal (epitaxial) films would have been possible. In this section, we will discuss some of the factors that govern the growth of epi silicon films. 

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