Oxynitride properties

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. 

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. 

Phosphorus oxynitride, PON, is a useful starting product, as a phosphorus and nitrogen source, to prepare various nitridooxophos-phates, in particular phosphorus oxynitride glass compositions (211). Moreover, it shows as a material excellent chemical stability with potential applications in several domains. In microelectronics, for example, PON has been used to form by evaporation insulating films for the passivation of III-V InP substrates and the elaboration of MIS (metal-insulator-semiconductor) structures (190, 212-215). PON could have also valuable properties in flame retardancy (176,191,216). 

Nitrides and oxynitrides represent a relatively new class of catalytic material. Justin Hargreaves and D. McKay (University of Glasgow, UK) show that these materials have only recently been explored for reactions (e.g., photocatalysis) beyond those that take advantage of their acid-base properties and their ability to mimic Pt-based catalysts. Tuning the acid-base properties of nitrides is possible by incorporating oxygen within their structure. 

Amongst other systems reported for the Knoevenagel condensation reaction have been, nitrogen incorporated ZSM-5 and high surface area silicon oxynitride." The ZSM-5 based -system potentially combines tuneable acid/ base properties with shape selectivity leading to the potential of selective conversion and/or unusual reaction pathways. 

Siaions consist of three-dimensional arrays of (Si—Al) (O.N)4 tetrahe-dra. These oxynitrides are traditionally fabricated with silicon nitride An example is beta-sialon, where the O and Si are partially replaced by N and Al, respectively. Advanced sialons are now being researched to enhance fracture toughness and iinpioved cieep properties,... 

C02 laser pyrolysis of reactant gases has been used to produce a wide variety of dispersed, single crystal nanoparticles (average size 2 to 20 nm). This chapter discusses the production of nitrides (oxynitrides) and carbides (oxycarbides) of Group 6B elements (Mo and W) and Fe by this technique. The emphasis is on the characterization of the atomic order in the particle and the chemical state of the particle surface. The catalytic properties of these particles for coal liquefaction and heteroatom removal from model compounds is also addressed briefly. 

The possibility of the incorporation of oxygen into the particle is particularly relevant for the carbides and nitrides of molybdenum and tungsten which possess a high affinity for this element.13,23 The oxygen may come from the carbonyl precursor, and result in oxycarbide or oxynitride formation in the core of the nanoparticle itself.16 Exposure to the ambient can also result in the formation of surface oxycarbides and oxynitrides with catalytic properties different from those of the pure nitride or carbide phase.15,24-26 However, heat treatment of these nanoparticles with a mixture of methane/hydrogen or ammonia/hydrogen should convert the surface to a pure nitride or carbide form. 

This model goes a long way towards explaining most experimental results reported in the literature for ISFETs with oxide or nitride surfaces. Unfortunately, the properties of these materials prepared in different laboratories are very different. It is known that silicon nitride (really silicon oxynitride SisNztOx) forms an oxygen-rich layer at the surface, whose thickness depends on the deposition conditions. This passivation layer forms rapidly (in a matter of hours) and is very stable, even under continuous exposure to aqueous electrolyte. The hydration of this layer seems to fit the requirements and predicted behavior of the Sandifer model. Consequently, ISFETs that have been exposed to aqueous solution for more than one hour show no adsorption effects which would be expected from the SBT model. 

Oxynitride glasses may be heat treated to form glass-ceramics, effectively multi-phase composites. The process involves heat treatment at two different temperatures, firstly to induce nucleation, then to allow crystal growth of the nuclei. The crystalline phases formed depend on both the composition of the parent glass and the temperatures used for heat treatment. The extent of their formation and growth, the relative amounts and distributions of different phases (including residual glass) and their characteristics will determine the overall properties of the particular composite. The formation of these types of materials and their properties is outlined below. 

Other investigations have incorporated SiC nano-phase inclusions into oxynitride glass matrices in order to form composites with improved mechanical properties. 

SiC particle reinforced oxynitride glass composites have been investigated and found to have higher values of mechanical properties which are related to the volume fraction of SiC inclusions, provided that SiC-glass reactions can be avoided. These composites have been shown to be suitable for viscoplastic forming. 

X-Ray Absorption Near-Edge Structure and Optical Properties of Hafnium Oxynitride Thin Films... 

Hafnium oxynitride (Hf-O-N) thin films have attracted interest because of their unique properties, particularly their high dielectric constant, relatively large... 

Silicon nitride, oxynitride and silicon aluminium oxynitride (SiAlON) compounds are of considerable technical interest as advanced ceramics because of their stability and chemical inertness at elevated temperatures, and their excellent mechanical properties. Si MAS NMR has proved to be useful in studying various aspects of these compounds, including their formation and structure, the processes by which they are... 

The last three chapters summarize unique structural and chemical features of a variety of glasses. They also provide an overview of the important aspects of the glass systems. Chapters 12 and 13 discuss respectively oxide and chalcogenide glasses particularly in view of their chemistry, structure and a number of special phenomena associated with them. In chapter 14, synthesis, structure and properties of halide, oxyhalide, oxynitride and metallic glasses are discussed. Some aspects of glass-like carbon have also been presented. 

Practical interest in nitrides is mainly focussed in their use as tough ceramics such as sialons and interstitial nitride coatings on metals [368,369]. Silicon oxynitride glasses are of importance in fiber optics as their refractive indices depend on the nitrogen content. There are surely other interesting properties awaiting exploration. 

The topics of subsequent sections are the different materials used for thin films, specifically, silicon oxide (Section 5.5.3), silicon nitride (Section 5.5.4), poly-silicon (Section 5.5.5), and other materials, such as metals and silicon oxynitride, as well as novel thin film materials that may appear in future sensor designs (Section 5.5.6). In these sections, we adhere to the following structure first, the basic deposition process is briefly described, followed by the common function of the layer in sensor design. Subsequently, we discuss in detail the important material properties. 

Silicon oxynitrides (SiOxNy) are thin films that are basically a mixture of silicon oxide and silicon nitride, produced in a CVD-process by adding nitrous oxide (N20) to the gases used for silicon nitride deposition. By changing the oxide-to-ni-tride ratio, the properties of these films can be modified towards improved thermal and moisture stability and lower stress compared to pure silicon oxide or silicon nitride thin films [32]. At low oxygen concentrations (0/(0+ N) <0.3), oxynitride layers have good diffusion barrier characteristics [33] and oxidation resistance. 

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