Silica oxynitride

Silicon-containing ceramics include the oxide materials, silica and the silicates the binary compounds of silicon with non-metals, principally silicon carbide and silicon nitride silicon oxynitride and the sialons main group and transition metal silicides, and, finally, elemental silicon itself. There is a vigorous research activity throughout the world on the preparation of all of these classes of solid silicon compounds by the newer preparative techniques. In this report, we will focus on silicon carbide and silicon nitride. 

Progress in the design and fabrication of high-quality optical microresonators is closely related to the development of novel optical materials and technologies. The key material systems used for microresonator fabrication include silica, silica on silicon, silicon, silicon on insulator, silicon nitride and oxynitride, polymers, semiconductors such as GaAs, InP, GalnAsP, GaN, etc, and crystalline materials such as lithium niobate and calcium fluoride. Table 2 smnmarises the optical characteristics of these materials (see Eldada, 2000, 2001 Hillmer, 2003 Poulsen, 2003 for more detail). 

Nitridated silica surfaces are very important in the semi-conductor and microelectronic industries. However, direct ammoniation of silica is -so far- a very uncontrollable procedure the required reaction temperatures are very high (> 1500 K), a lot of side products are formed (typically Si2N20, silicon-oxynitride) and the nitride diffuses into the silica matrix. Direct nitridation of silica should therefore be considered as a bulk synthesis, and not as a surface modification technique. 

Several recent studies7,9,10,23,26 have reported attempts to create silicon nitride by direct ammoniation of silica, usually as a spin-off of the integrated circuit technology research. Most of these studies agree that at temperatures about 1473 K up to 20 -25 % (w/w) nitrogen can be incorporated, but silicon nitride is seldom formed. The final product of this direct nitridation method is silicon-oxynitride (Si2N20) with residual silica. The nitridation is not restricted to the surface, but the N diffuses also into the bulk structure of the silica. No adequate mechanisms were presented to explain the observed reactions. 

Loehman reported on the formation of oxynitride glasses in the system Y-Si-Al-O-N. The silica-rich glasses contained up to 7% nitrogen. The changes in thermal expansion coefficient and the glass transition temperature are tabulated below. 

The infrared and Raman spectra of phosphorous oxynitride PON, a homologue of silica, have been measured at pressures up to 23 Gpa. The moganite and the a-quartz type crystalline forms of PON have been studied. A correlation has been established between the spectra of PON and those of silica. In the moganite type PON a phase transition has been observed at 4 Gpa. Some preliminary results of an ab initio molecular dynamics simulation are discussed. 

The choice of conducting substrate becomes more difficult when postdeposition high-temperature treatments are necessary. This is often the case for complex oxides, such as perovskites or oxynitrides [9], which may require firing at temperatures above 600°C in order to obtain the desired crystalline phase. This prohibits the use of float glass, which softens above 550°C. Certain types of borosilicate glass can be used up to 650 C, while fused silica or sapphire can withstand continuous exposure to temperatures up to 950°C. Unfortunately, the conductivity of ITO films quickly decreases above 350°C. FTO and ITO/FTO coatings are stable up to 600-700 C [2,10], and may still have acceptable conductivities at higher temperatures provided... 

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