Applications of Polysilanes

Polysilanes have many applications [1-5]. These are based on the ability of some members of their family to serve as precursors to silicon carbide. Other applications of polysilanes stem from their interesting electronic and photophysical properties. 

---

Manufacture of P-Silicon Carbide. A commercially utilized application of polysilanes is the conversion of some homopolymers and copolymers to silicon carbide (130). For example, polydimethylsilane is converted to the ceramic in a series of thermal processing steps. Silicon carbide fibers is commercialized by the Nippon Carbon Co. under the trade name Nicalon (see Refractory FIBERS). 

As explained in the introduction, the polysilanes (and related polygermanes and poly-stannanes) are different from all other high polymers, in that they exhibit sigma-electron delocalization. This phenomenon leads to special physical properties strong electronic absorption, conductivity, photoconductivity, photosensitivity, and so on, which are crucial for many of the technological applications of polysilanes. Other polymers, such as polyacetylene and polythiophene, display electron delocalization, but in these materials the delocalization involves pi-electrons. 

N. Matsumoto, H. Suzuki and H. Miyazaki, Electronic/optical properties and device applications of polysilanes , in Reference 4, pp. 531-552. 

The various photoprocesses are important for several potential applications of polysilanes. Because of their intense fluorescence they have been suggested as scintillation materials for radiation detection. The chain-breaking reactions mean that polysilanes can be degraded by UV light it is this property that makes them useful as photoresist materials. 

One application of polysilanes is in a bilayer construction, as shown in Figure 10. To cover existing topography on the wafer, a thin planarizing layer of a nonphotoactive polymer is deposited, followed by a very thin photoresist layer, about 0.5 to 0.2 pm in thickness. The wafer is exposed through a mask. 

Applications. Some applications of polysilanes include their use as semiconductors, photoresists, photoinitiators, nonlinear optical materials, and ceramic precursors (9). Their use as ceramic precursors can be illustrated by the following reactions ... 

In addition, mechanistic studies of the photochemical reactions are necessary to determine whether similar processes occur in the solid state. Polymer chain scission is usually the predominant process in the solid state, although cross-linking reactions become more important in the presence of pendant unsaturation. However, little is known about the nature of the intermediates produced in the solid state. Information of this type is important, because most of the applications of polysilane derivatives require the materials as solid films. 

Several other studies on Nicalon-based ceramic fibers have also been conducted in addition to the investigation of oxidation curing of PCS fibers and effect of oxygen in tensile strength of SiC fibers [51]. Similarly, studies dealing with the chemistry, characterization, modification, use, and applications of polysilanes and polycarbosUane are also available [52]. 

Other applications of polysilanes include their utility as photoinitiators for vinyl polymerization. This application is based on the phenomenon of generating silyl radicals upon photolysis. Although polysilanes are not efficient photoinitiators they have unique properties such as being not susceptible to oxygen. Many organic monomers such as acrylates, and styrene have been polymerized by this method [4]. 

Matsumoto N, Suzuki H, Miyazaki H (2000) Electronic and optical properties in device applications of polysilanes. In Jones RG, Ando W, Chojnowski J (eds) Silicon containing polymers. Kluwer Academic, Dordrecht, pp 531-552... 

Polysilanes were first synthesized in the early 1920s, but no investigation of their application was made until the late 1970s. The discovery of the two-step transformation of polydimethylsilane to P-SiC fibres by Yajima et al. [90] marked the beginning of interest in their properties and thus the application of polysilanes. After the discovery of the semiconducting behaviour of polymethylphenylsilane by West et al. [91], the cornerstone for the application of polysilanes in electronics was laid. 

The facile cleavage of Si-Si bonds by UV radiation is also made use of in the application of polysilanes as photoresists. This application has been weU studied [107-110]. The technology covers a wide range from the structuring of metal films to the fabrication of micro lenses. 

Polysilanes can be part of the active layer or, such as in multi-layered OLEDs, serve as a hole transporting layer. There are a number of publications describing polysilanes as a photoactive layer or as a hole transporting material in organic solar cells but in most of them polysilanes are merely mentioned as a general example of an organic semiconductor. They are, for example, not specified in the published examples of patents and are only included to widen the scope of the claims. Only the publications mentioned below cover the application of polysilanes in organic photovoltaics in more detail. 

---