Si amorphous

Amorphous Silicon (a-Si). Amorphous silicon is considered a promising new material.As mentioned above, only a very thin coating is necessary, since the amorphous structure is much better at absorbing sunlight than is the crystalline material. The most common process to produce a-Si is the decomposition of silane by plasma CVD (see Ch. 8). Thicknesses of a few micrometers can be deposited and,... 

Amorphous selenium glasses, semiconductivity in, 12 587 Amorphous semiconductors, 22 127-141. See also Amorphous silicon (a-Si) amorphous silicon growth for,... 

Fig. 7.9 The PL spectra of various silicon-based materials (a) at RT and (b) at 77 K (note the logarithmic scale of the PL intensity) (a-Si amorphous Si, pc-Si microcrystalline Si). After [St8].

Figure 34. Alkali zeolites projected into a portion of the Na-K-Si coordinates. Anal = analcite Ph = phillipsite solid solution Ze = alkali zeolites undifferentiated Alb = albite KF = potassium feldspar Q = quartz Si = amorphous silica, a) low, b) medium, and c) high temperature facies. Shaded areas are two-phase fields.

Figure 36. Representation of the zeolite-clay mineral assemblages found in a systeirf at 25°C and atmospheric pressure where Na is an intensive variable (perfectly mobile component) whereas A1 and Si are extensive variables or inert components of the system. G = gibbsite kaol = kaolinite Mo = montmorillonite Si = amorphous silica Anal = analcite.

Si (amorphous). The data of von Wartenberg 2 who measured the heats of combustion of both the crystalline and amorphous forms of silicon, yield for the latter Qf=—1.0. 

A series of Pt-Si amorphous alloys has been compared with polycrystalline Pt. The activity has been found to be always less than the crystalline metal. Although no grains are present on the amorphous alloy surface, the presence of Si reduces the M-H adsorption strength which is the reason for the lower activity. Oxidation of the surface produces Si02. On oxidized surfaces spillover of hydrogen from Pt to Si02 has been observed [565]. 

In a study of the application of Pd-Si amorphous alloys as selective hydrogenation catalysts [3] it was found that in situ activation provides a route to active and selective catalysts, whereas ex situ activation caused the crystallization of the system into the thermodynamically stable Pd + SiC>2 system, which is indistinguishable in its activity and poor selectivity from conventional catalysts of the same composition. In this study it was possible to show conclusively that all amorphous alloys are not amorphous on their surfaces as they undergo, in reaction gas atmospheres, chemically-induced phase segregation which starts the crystallization process according to Figure 2 (pathway 2). 

Ozone 5% in ojygen 150 2 9 0 no rnolicuiac dagrad 3M Kal-F SI amorphous form... 

Fig. 65. Raman maps of the surface of a lapped Si wafer [275]. (a) Optical micrograph, (b) The ratio of transformed Si (amorphous material and metastable phases) to pristine Si-I. (c) The same, after the wafer surface was chemically etched. Here, all of the transformed phases are removed. Brighter areas in (b) and (c) correspond to higher content of transformed material.

Finally, if instead of c-Si, amorphous Si is used as the starting material, the lithiation behavior is identical to that of the second cycle of c-Si (Fig. 5b, 2nd cycle in red). 

Aluminum phosphorous oxide is one of the representative acid catalysts and the most extensively studied phosphorous oxide. Aluminum phosphate has seven crystalline forms and is isostructural with Si02, the seven crystalline modifications of each being directly parallel. The ions, Al and P , replace Si. Amorphous aluminum phosphate exists in addition to these seven crystalline forms. 

Cr-Si = Crystalline silicon, a-Si = Amorphous silicon, a-Li Si = Amorphous alloy... 

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