Polysilane conducting properties

Subsequent studies illustrated the complexity of the phase transitions in di-alkyl polysilanes and the dramatic effects these have on the optical and conductive properties. A general conclusion that could be reached was that the mobility of charge invariably decreases in going from the crystal to the liquid crystal phase, and if subsequent higher temperature liquid crystal phase transitions occur, these result... 

The polysdanes are normally electrical insulators, but on doping with AsF or SbF they exhibit electrical conductivity up to the levels of good semiconductors (qv) (98,124). Conductivities up to 0.5 (H-cm) have been measured. However, the doped polymers are sensitive to air and moisture thereby making them unattractive for practical use. In addition to semiconducting behavior, polysilanes exhibit photoconductivity and appear suitable for electrophotography (qv) (125—127). Polysdanes have also been found to exhibit nonlinear optical properties (94,128). 

Polysilanes can be regarded as one-dimensional analogues to elemental silicon, on which nearly all of modern electronics is based. They have enormous potential for technological uses [1-3]. Nonlinear optical and semiconductive properties, such as high hole mobility, photoconductivity, and electrical conductivity, have been investigated in some detail. However, their most important commercial use, at present, is as precursors to silicon carbide ceramics, an application which takes no advantage of their electronic properties. 

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. 

Silicon-based polymers form a dimensional hierarchy from disilanes, to crystal silicon, and through polysilanes, ladder polymers, siloxenes, polysilane alloys, clusters, and amorphous silicons and include unsaturated systems, such as polysilenes, hexasilabenzenes, and so on. Their properties depend basically on the network dimensions and can vary from conducting (metallic) and semiconducting to insulating. 

The electronic properties of the polysilanes in discussion which might also be a reason for the differences in their behavior as HTLs the workfunctions and the hole conductivity are currently under investigation. 

Even a preliminary investigation of the properties of some inorganic pol5miers reveals that some of them have unexpected properties. Polythi-azyl is an anisotropic electrical conductor and shows conductivity that is comparable to metals. At 0.26 K this polymer becomes superconducting [4, 5]. Polysilanes which contain catenated silicon atoms in a polymeric chain have several unusual properties. These polymers have a o-electron delocalization. They are radiation sensitive and many of them are thermo-chromic. Many members of this family also show nonlinear optical behavior [17, 19]. 

Addition of flexible side chains to the stiff 7r-conjugated polymer backbone of the host polymer has proven to be an extremely effective procedure for obtaining tractable and fusible materials. This approach is not limited to conducting polymers but has also attracted considerable attention in more conventional rigid-rod-like polymers [96-99] including various polyimides and polyamides and in other novel polymers such as the polysilanes [100]. Not only does this modification enable the utilization of conventional polymer processing methods, it can also, in some cases, create new materials that exhibit enhanced electronic properties in comparison to the linearly unsubstituted parent polymer. These side-chain-substituted conducting polymers also exhibit properties that do not exist in the unsubstituted hosts discussed in... 

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