Amorphous silicon boron nitride

During their genesis all precursor derived ceramics pass through an amorphous state which in certain cases is stable up to the respective decomposition temperature. The propensity to crystaUize is strongest for the binary silicon and boron nitrides and carbides, while in particular quaternary materials out of the Si/B/N/C system show the strongest resistance towards crystallization. It is interesting to note that in any case investigated, so far, the amorphous multinary ceramics decompose into the binary border phases upon crystallization - crystalline ternary silicon boron nitrides or carbides are not known to date cf. [9]. 

Boron-containing nonoxide amorphous or crystalline advanced ceramics, including boron nitride (BN), boron carbide (B4C), boron carbonitride (B/C/N), and boron silicon carbonitride Si/B/C/N, can be prepared via the preceramic polymers route called the polymer-derived ceramics (PDCs) route, using convenient thermal and chemical processes. Because the preparation of BN has been the most in demand and widespread boron-based material during the past two decades, this chapter provides an overview of the conversion of boron- and nitrogen-containing polymers into advanced BN materials. 

The multilayer nanocomposite films containing layers of quasi-spherical Fe nanoparticles (d — 5.8 nm) separated by dielectric layers from boron nitride (BN) are synthesized by the repeated alternating deposition of BN and Fe onto a silicon substrate [54]. In this work the authors managed to realize the correlation in the arrangement of Fe nanoparticles between the layers the thin BN layer deposited on the Fe layer has a wave-like relief, on which the disposition of Fe nanoparticles is imprinted as a result, the next Fe layer deposited onto BN reproduces the structure of the previous Fe layer. Thus, a three-dimensional ordered system of the nanoparticles has been formed on the basis of the initial ordered Fe nanoparticle layer deposited on silicon substrate [54]. The analogous three-dimensional structure composed of the Co nanoparticles layers, which alternate the layers of amorphous A1203, has been obtained by the PVD method [55]. 

Up to now, most work on cBN deposition has been done using single crystal silicon substrates. Those films grow in a typical phase sequence which has been shown for the first time by Kester et al. [37] in 1993 and since then confirmed by many groups At first an amorphous layer at the interface to the substrate is formed which is usually referred to as aBN. This layer probably contains also some silicon from the substrate and is due to ion-induced intermixing. After that a turbostratic boron nitride (tBN) layer is formed. Turbostratic boron nitride is a BN form consisting of nearly parallel hBN-like layers which, however, do not have defined three-dimensional orientation. The distance of these layers is a few percent enlarged in comparison to the hBN crystal (see e.g. [1]). Under deposition conditions which... 

Non-oxide preceramic polymers which are expected to yield, under convenient thermal and chemical conditions, boron-containing amorphous or crystallized ceramics including boron nitride (BN), boron carbide (B C), boron carbonitride (B-C-N), and boron silicon carbonitride Si-B-C-N. 

While metallic solids are deposited by reactions that involve metallic intermediates and ionic solids result from ionic reactions, the solids with covalent bonds grow by means of radical surface reactions. Examples of such materials are diamond, amorphous diamond-like carbon, silicon, and silicon carbide. Diamond and diamond-like carbon can be deposited if hydrocarbon and hydrogen radicals are available at the growing surface. Silicon carbide and boron nitride growth has also been modeled in terms of radical reactions at the surface. 

This includes single crystal silicon [15], germanium [22] and alumina [10] fibers. Polycrystalline fibers can grow either by a VLS or a VS phase transformation when the incident laser power (focal temperature) is intermediate, and supports the growth of a fiber with a semisolid tip. This includes polycrystalline silicon [15], boron [5] and silicon carbide fibers [23]. Amorphous fibers are obtained by a VS phase transformation when the incident laser (focal temperature) is low, and supports the growth of a fiber with a hot but solid tip. This includes amorphous silicon [15], boron [12], carbon [13] [16], silicon carbide [23], and silicon nitride [17] fibers. 

A boron nitride film is applied between the transparent conductive SnOg layer and the amorphous silicon layer in photoelectric solar cells, thus preventing Sn and O diffusion [101]. 

Matsunaga, K., Iwamoto, Y. (2001). Molecular dynamics study of atomic structure and diffusion behavior in amorphous silicon nitride containing boron. Journal of the American Ceramic Society, 84(10), 2213-2219. doi 10.1111/j.l 151-2916.2001. tb00990.x. 

The synthesis of processable precursors for Si-B-N-C ceramics became a goal of intensive investigations as soon as the outstanding thermal and mechanical properties of this system were reported [1,2]. The amorphous phase of Si-B-N-C ceramics can show excellent thermal stability up to 2000 °C without mass loss or crystallization. The role of boron is believed to be to increase the high-temperature stability and to prevent the crystallization and decomposition of silicon nitride above 1500 °C. Primarily, the atomic ratio and chemical environment of boron in Si-B-N-C precursors seem to affect the thermal behavior of resulting ceramic materials. 

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