Single layer films and a multilayer structure of SRO (Silicon Rich Oxide) have been prepared by LPCVD (Low Pressure Chemical Vapour Deposition) and characterized by FTIR., SIMS, XPS, TEM and AFM measurements. The stacked structure is composed of alternating layers of SRO with high Si content and SRO with low Si content. The layered structure is confirmed by SIMS and TEM measurements. The composition of the materials is discussed. Besides Si nano-crystals, the existence of agglomerates of silicon oxide with structure close to fused silica and the existence of oxynitrides is evidenced in the films with high Si content. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Structural characteristics of a multilayer of silicon rich oxide (SRO) with high Si content prepared by LPCVD

1.06 – Whiskers and Particulates

In this chapter an overview of whisker, platelet, and particulate reinforcements for composites with actual or potential use in structural, thermal, or electronic applications are presented. The reinforcements can be used in different reinforcing phase, such as, polymer, ceramic or metal matrix. Enhancement in mechanical, magnetic, thermal, electrical, or other properties can be achieved with the use of reinforcing materials. Whiskers, particulates and flakes are advantageous in terms of processing and cost than that of continuous fiber. Whiskers have superior specific mechanical properties for elevated temperature performance than that of fibers. Particulates are comparatively cheap and can produce isotropic properties.

Whiskers and Particulates

The existence of bulk oxygen in the lattice of silicon nitride is studied. In the study, silicon nitride, primarily ?-phase, is prepared by different methods and either powder or whiskers obtained, depending upon the method of preparation. On characterizing the samples, it is observed that they have almost identical XRD patterns, whereas there IR absorption spectra shows significant differences. This prompted another investigation and its results are presented.

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Bulk oxygen in α-silicon nitride and its effect on IR absorption

The preparation of high-purity silicon nitride powder (useful as high-temperature ceramic material) from silicon tetrachloride has been studied. Zinc was chosen for reduction to Si, which involved vapour reaction in a two-zone horizontal furnace. The silicon nitride whiskers formed were characterized by x-ray diffraction (XRD) and electron microscopy. The whiskers were very thin (approx 0.5 mu m, length gt; 1 cm) at low reaction temperature (950 deg C). In situ nitration with increased nitrogen flow was tried without success, although 0.1 mu m whisker thickness was obtained, and dry ammonia gas was then used for separate nitration at 1200-1300 deg C. XRD and infrared absorption data revealed alpha -Si sub 3 N sub 4 as the product (thickness 0.5, length approx 12 mu m). Such whisker-like particles with uniform aspect ratio may also be useful in ceramic composites.

/pdf/preparation-and-nitridation-of-silicon-whiskers-48pegtxjsh.pdf

P. S. Lakshminarasimham

Papers

Preparation and nitridation of silicon whiskers

Bulk oxygen in α-silicon nitride and its effect on IR absorption