Oxynitrides

Historically, the development of nitrides proceeded slowly until the emergence of silicon nitride during the late 1950s. From that time onwards, the intricacies of the relationship between the two forms of silicon nitride, combined with the observation that, when hot-pressed or sintered into dense products, silicon nitride displayed excellent mechanical properties at temperatures in excess of 1000 °C, propelled silicon nitride into a subject area of intense interest. As a result, it now resides in a well-defined niche as a stmctural material for wear parts and related applications. At the same time, this provided a catalyst for the development of other nitrides, both of a binary and ternary character. Increasing complexity was provided by the observation that, just as with mineral silicates, aluminum could replace silicon in 

Ceramics Scimce and Technology Volume 2 Properties. Edited by Ralf Riedel and I-Wei Chen Copyri t 2010 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-S27-311S6-9 

Those readers interested in the general field of oxynitride structures may also wish to consult previous reviews in this area, as provided by Lang [1], Thompson 2], Marchand [3], and Thompson [4]. 

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Gate oxide dielectrics are a cmcial element in the down-scaling of n- and -channel metal-oxide semiconductor field-effect transistors (MOSEETs) in CMOS technology. Ultrathin dielectric films are required, and the 12.0-nm thick layers are expected to shrink to 6.0 nm by the year 2000 (2). Gate dielectrics have been made by growing thermal oxides, whereas development has turned to the use of oxide/nitride/oxide (ONO) sandwich stmctures, or to oxynitrides, SiO N. Oxynitrides are formed by growing thermal oxides in the presence of a nitrogen source such as ammonia or nitrous oxide, N2O. Oxidation and nitridation are also performed in rapid thermal processors (RTP), which reduce the temperature exposure of a substrate. 

Dielectric Deposition Systems. The most common techniques used for dielectric deposition include chemical vapor deposition (CVD), sputtering, and spin-on films. In a CVD system thermal or plasma energy is used to decompose source molecules on the semiconductor surface (189). In plasma-enhanced CVD (PECVD), typical source gases include silane, SiH, and nitrous oxide, N2O, for deposition of siUcon nitride. The most common CVD films used are siUcon dioxide, siUcon nitride, and siUcon oxynitrides. 

Addition of nitric oxide, NO, to the plasma during Si02 deposition gives siUcon oxynitride films. 

Materials made of siHcon nitride, siHcon oxynitride, or sialon-bonded siHcon carbide have high thermal shock and corrosion resistance and may be used for pump parts, acid spray nozzles, and in aluminum reduction ceUs (156—159). A very porous siHcon carbide foam has been considered for surface combustion burner plates and filter media. It can also be used as a substrate carrying materials such as boron nitride as planar diffusion source for semiconductor doping appHcations. 

Vapor—sohd reactions (13—17) are also commonly used ia the synthesis of specialty ceramic powders. Carbothermic reduction of oxides, ia which carbon (qv) black mixed with the appropriate reactant oxide is heated ia nitrogen or an iaert atmosphere, is a popular means of produciag commercial SiC, Si N, aluminum nitride [24304-00-3], AIN, and sialon, ie, siUcon aluminum oxynitride, powders. 

Figure 6 CBED patterns of aluminum oxynitride spinel along the [001] direction. Symmetries in the patterns contributed to the determination of the point group and space group (a) whole pattern showing 1st Laue zone ring and (b) 0th order Laue zone. Both patterns show a fourfold rotation axis and two mirror planes parallel to the axis. (Courtesy of V. P. Dravid)...

Other phosphorus-based polymers have been investigated and have proved to be of some interest. An example is phosphorus oxynitride, which forms a glass above 1000°C. 

An example of novel basic catalysts the aluminophosphate oxynitrides or "AlPONs"... 

New aluminophosphate oxynitrides solid basic catalysts have been synthesised by activation under ammonia of an AIPO4 precursor. When the nitrogen content increases, XPS points out two types of nitrogen phosphorus bonding. The conversions in Knoevenagel condensation are related to the surface nitrogen content. Platinum supported on aluminophosphate oxynitride is an active catalyst for isobutane dehydrogenation. 

Nitridation of the oxide precursor was performed under pure ammonia flow. Different aluminophosphate oxynitrides AlPONs with variable nitrogen contents were obtained by modif3ring the time and/or the temperature of nitridation (Table 1). 

Four mmoles of malononitrile and benzaldehyde were introduced in a batch stirred tank reactor at 323 K with toluene as solvent (30 ml). Then 0.05 g of aluminophosphate oxynitride was added. Samples were analysed by gas chromatography (Intersmat Delsi DI200) using a capillary column (CPSilSCB-25 m). Care was taken to avoid mass or heat transfer limitations. Before the reaction no specific catalyst pretreatment was done. 

The characteristics of the studied oxynitrides are reported in Table 1. Table 1... 

To evaluate properties of basic catalysts, the Knoevenagel condensation over aluminophosphate oxynitrides was investigated [13]. In this reaction usually catalysed by amines, the solid catalysts function by abstraction of a proton from an acid methylene group, which is followed by nucleophilic attack on the carbonyl by the resultant carbanion, re-protonation of oxygen and elimination of water. The condensation between benzaldehyde and malononitrile is presented below. 

The oxynitride "AlPON" used as support was synthesised as the others. It is well represented by the AlPO3.i6N0.56 formula, its nitrogen content being 6.7 wt.%. This sample has a surface area of 310 m. g-l. 

Three catalysts with different compositions were used in this study. Catalyst A corresponds to the oxynitride precursor. Catalysts B and C contain... 

A novel basic support and catalyst have been prepared by activation of aluminium phosphate with ammonia. Fine control of time and temperature allows to adjust the 0/N ratio of these oxynitride solids and thus to tune the acid-base properties. The aluminophosphate oxynitrides are active in Knoevenagel condensation, but a basicity range can not yet determined. Supporting Pt or Pt/Sn on AlPONs allows to prepare catalysts that are highly active and selective in dehydrogenation reactions. 

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. 

Martinez-Ferrero, E., Sakatani, Y., Boissire, C., Grosso, D., Fuertes, A., Fraxedas, J., and Sanchez, C. (2007) Nanostructured titanium oxynitride porous thin films as efficient visible-active photocatalysts. Advanced Functional Materials, 17 (16), 3348—3354. 

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