Crystals, silicon nitride

In a further improvement, the NTD Ge spider-web bolometer developed by the Caltech/JPL group [69], and shown in Fig. 15.10, the absorber is a metallized silicon nitride spider-web structure, and the thermometer is a very small NTD germanium crystal [14], The spacing of the web pattern is much smaller than the wavelength, so it acts... 

The rapid developments in the microelectronics industry over the last three decades have motivated extensive studies in thin-film semiconductor materials and their implementation in electronic and optoelectronic devices. Semiconductor devices are made by depositing thin single-crystal layers of semiconductor material on the surface of single-crystal substrates. For instance, a common method of manufacturing an MOS (metal-oxide semiconductor) transistor involves the steps of forming a silicon nitride film on a central portion of a P-type silicon substrate. When the film and substrate lattice parameters differ by more than a trivial amount (1 to 2%), the mismatch can be accommodated by elastic strain in the layer as it grows. This is the basis of strained layer heteroepitaxy. 

Brink R, Lange H (1994) Investigations on the Synthesis of fine-grained, high-purity j8-Si3N4 Powder by Crystallization of amorphous Precursors. In Hoffmann MJ, Becher PF, Petzow G (eds) Silicon Nitride 93. Key Eng Mat 89-91. Trans Tech Publications Ltd, Switzerland, p 73... 

Garofalini, S.H., and Luo, W.W., (2003), Molecular dynamics simulations of calcium silicate intergranular films between silicon nitride crystals ,/. Am. Ceram. Soc., 86 (10), 1741-1752. 

This type of material is commonly used in the production of semiconductor devices.57 The silica layer is used as a starting layer for integrated circuit (IC) build-up. IC layer materials range from single crystals and doped polycrystalline silicon, silicon nitride, thermally-grown oxide to vapour deposited or sputtered metal or metal silicide layers. Structural adhesion of the various layers is obtained by the application of organosilanes, such as AEAPTS, APTS and GPTS. 

It is not always possible to obtain a low-porosity body by pressureless sintering , i.e. by sintering at atmospheric pressure. For example, difficulties are experienced with silicon nitride and silicon carbide. More commonly it may prove difficult to combine the complete elimination of porosity with the maintenance of small crystal size. These problems can usually by overcome by hot-pressing, i.e. sintering under pressure between punches in a die, as shown in Fig. 8.9. The pressure now provides the major part of the driving force eliminating porosity and the temperature can be kept at a level at which crystal growth is minimized. 

Hardie, D., and K. H. Jack Crystal structures of silicon nitride. Nature [London] 180, 332-333 (1957). 

There are many other binary and ternary silicon compounds of commercial importance. For example, silicon nitride (Si3N4) occurs in two hexagonal forms the a-form and a denser 3-form. The crystal stmctures are very complex, but may be thought of as close-packed nitrogen atoms, with three-eighths of the tetrahedral vacancies occupied by silicon atoms. In this respect it is like Si02, being a three-dimensional network of... 

Si(NH)2] , also referred to as silicon diimide, is a colorless solid. It is insoluble and intractable and decomposes with increasing temperatnre by elimination of ammonia. This degradation proceeds continnonsly, releasing amorphons silicon nitride at approximately 1000°C. Additional heating to 1400 to 1500°C resnlts in the crystallization of a-Si3N4. 

The synthesis of processable precursors for Si-B-N-C ceramics became a goal of intensive investigations as soon as the outstanding thermal and mechanical properties of this system were reported [1,2]. The amorphous phase of Si-B-N-C ceramics can show excellent thermal stability up to 2000 °C without mass loss or crystallization. The role of boron is believed to be to increase the high-temperature stability and to prevent the crystallization and decomposition of silicon nitride above 1500 °C. Primarily, the atomic ratio and chemical environment of boron in Si-B-N-C precursors seem to affect the thermal behavior of resulting ceramic materials. 

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