The mostly crystallized Si:H having a wide optical band gap and showing a visible photoluminescence at room temperature, has been fabricated by means of a planar magnetron rf sputtering technique in hydrogen gas onto a low temperature (about 100 K) substrate. The materials consist of very small crystalline silicon particles (average diameters: 2–5 nm) surrounded by =SiH2 groups. The observed macroscopic physical properties are explained by the three-dimensional quantum size effects in the ultrafine silicon particles.
The crystal structures of poly(di-n-butyl silane) and poly(di-n-pentyl silane) have been determined by comparing the experimental x-ray diffraction paltern with the theoretical pattern.The side-chain conformation i s mostly determined by the intramolecular steric hindrace as well 3s the van der Wmls interaction between the side chains. The Si backbone conformation of both crystals is a 3 helix. which 1s mainly determined by the intramolecular van der Waals interaction between the nearest-neighbour side chains. On the other hand. the Si backbone conformation of both crystals after a pressure treatment of 1500 MPa is all tmns. which is caused by the YM der Wads interaction between the side chains attached to the second-nearest-neighbour Si atoms.In all c~ses, one of the two CSi-C-C groups in Si(OHql3 or Si(C%Hu)2 is an essentially Irum conformation. whereas the other C-C-Si< gmup has a ci.r-like conformation, which is different from that generally accepted.
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