Space silicon nitrides

Soluble polysilane polymers can also be used as precursors to silicon carbide. The first such application, using (PhMeSi)n-(Me2Si)m copolymers ("Polysilastyrene"), was to strengthen silicon nitride ceramics. The Si3N4 ceramic body was soaked in polysilane and refired, leading to the formation of silicon carbide whiskers in the pore spaces and a consequent increase in strength. (U)... 

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... 

In some cases it is possible to form bridges of metal using air as the dielectric (150). However, if more than two levels of wiring are required then dielectric spacing is necessary. The ideal dielectric film has excellent adhesion and a low dielectric constant to minimize parasitic capacitances. The most common films include silicon oxide, silicon nitride, and a number of spin-on dielectrics (216). 

Modern ceramic materials now include zirconium oxide (Zr02), titanium carbide (TiC), and silicon nitride (SiN). There are now many more uses of these new ceramic materials. For example, vehicle components such as ceramic bearings do not need lubrication - even at high speeds. In space technology, ceramic tiles protected the Space Shuttle from intense heat during its re-entry into the Earth s atmosphere. In the power supply industry, they are used as insulators due to the fact that they do not conduct electricity (Figure 3.39). 

On top of the image sensor, there is a scratch-resistant transparent covering and protective materials, often in the form of dielectric layers such as silicon dioxide or silicon nitride. In the bulk of the semiconductor there is first a space-charge region. Below this, the field-free bulk of the semiconductor follows, which can be as thin as a few pm or as thick as many 100 pm [7]. 

There are many examples of rational synthesis. A good example is Sialon, in which A1 and oxygen were partly substituted for Si and nitrogen in silicon nitride, Si3N4. The fast Na+ ion conductor Nasicon was synthesized based on understanding the coordination preferences of cations and the nature of oxide networks formed by them. The zero-expansion ceramic CaQ5Ti2P30j2, possessing the Nasicon framework, was later synthesized based on the idea that the property of zero expansion would be exhibited by two- or three-coordination polyhedra linked in to leave substantial empty space in the network [3]. 

Figure 3.10 A large, 2d superlattice of 5.5-nin gold Danoparticles ligated with dodecanethiol on a silicon nitride surface. Note hexatic, close-pacfced structure (like pennies on a table top) and the spacing between the nanoparticles, which is filled with the alkane chains of the ligands, which keeps the gold particles fiom touching, which would lead to irreversible aggregation.

Space shuttle tiles are made of silica glass. We need to be concerned about the impact of space debris. Radomes are made of fused silica and silicon nitride. They have to be transparent to infrared (IR) and radio waves and resist the impact of atmospheric particles. Ceramic bearings are used in low-load applications (watch bearings of ruby or sapphire jewels ), but for high-load and high-speed use metals are often preferred because ceramics have low fracture toughness. 

The a silicon nitride structure has a space group of P31c [7] with its c dimension approximately twice that of p. Where the layers of atoms in P are linked along the [001] direction in the sequence ABAB, the a structure has the sequence ABCDABCD. The CD layer, shown in Fig. 3(b) [8], is similar to the AB layer except that it is rotated by 180OC on the c-axis. The long continuous channels in the c direction of P (ABAB) are therefore closed off to form two large interstices. 

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