Semiconductors polysilane

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). 

A rapidly increasing number of publications on polysilanes documents current interest in these polymers (JJ. Polysilanes are potentially applicable in microlithography as high resolution UV-resists (2J, imageable etch barriers ), or contrast enhancement layers (4). They have been successfully used as precursors to Si-C fibers (5J and ceramic reinforcing agents ((L). Polysilanes have also initiated polymerization of vinyl monomers (J ). Doping of polysilanes have increased their conductivity to the level of semiconductors (8). Very recently polysilanes were used as photoconductors (9) and non-linear optical materials (10b... 

Despite the success of the disorder model concerning the interpretation of data on the temperature and field dependence of the mobility, one has to recognize that the temperature regime available for data analysis is quite restricted. Therefore it is often difficult to decide if a In p vs or rather a In p vs representation is more appropriate. This ambiguity is an inherent conceptual problem because in organic semiconductors there is, inevitably, a superposition of disorder and polaron effects whose mutual contributions depend on the kind of material. A few representative studies may suffice to illustrate the intricacies involved when analyzing experimental results. They deal with polyfluorene copolymers, arylamine-containing polyfluorene copolymers, and c-bonded polysilanes. 

The polysilanes are nurtnally electrical insulators, but on doping with AsF or SbFs they exhibit electrical conductivity up lo the levels of good semiconductors. 

Atomic force microscopy, polysilanes, 3, 599 Atomic layer epitaxy, for semiconductor growth, 12, 11 Atom transfer radical polymerization type reactions, isotope labeling studies, 1, 567... 

Tacticity is required for the synthesis of crystalline thin polysilane films used for optical and semiconductor devices. Modern synthetic routes allow control over the conformation and tacticity of polysilane molecules used as precursors for thin layers of photoresists, photoconductors and nonlinear optical phases in complex semiconductor and (opto)electronic devices. These properties can be exploited only if the synthesis method ensures a minimal level of contamination, especially with oxygen and metals, and special care is taken to limit electronic-grade polysilanes to a level of contamination on the order of a few ppm in the case of oxygen and in the ppb range for metals. The reactivity of polysilane toward oxygen has forced placing the devices in a helium environment during measurement procedures.36... 

Polysilanes Porous Inorganic Materials Semiconductor Nanocrystal Quantum Dots Short-lived Intermediates Silicon Inorganic Chemistry. 

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 ... 

Two types of new silicon-branched organosilicon polymers, linear and ladder polysilane structures, were produced from dihalo- and tetrahalodisilane, respectively, via alkali-metal-mediated reactions. Further investigations disclosed that the polymers may he useful as photoresists, semiconductors, ceramic precursors, and composite materials in high-technology fields. 

Silicon-backbone materials include silane oligomers, polysilanes, silicon clusters, and amorphous and crystalline silicons. These materials have been investigated independently in two different fields. Crystalline and amorphous silicon are studied in the field of solid-state physics (i), whereas polysilanes and related molecules are studied in the field of organosilicon chemistry (2). Crystalline silicon (c-Si) and amorphous hydrogenated silicon (a-Si H) are well known as two of the most useful semiconductors for electronic and optical devices. Polysilanes have been investigated for application as SiC ceramic binders (3) and photoresists (4). The methods of synthesizing... 

The band gap decreases on going from the unsubstituted polysilane to the dimethyl-substituted polysilane from 3.52 to 2.64 eV, in line with previous semiempirical studies 11, 12), Local-density functional methods typically underestimate the band gap in insulators and semiconductors by 30-50% (20). For poly(dimethylsilane), with an experimentally indicated gap... 

The band gap in polysilanes approaches 4 eV compared to nearly 8 eV in satur.iied carbon. skelcion.s. The polysilanes arc insulators in pure form but often can be doped to give semiconductors. 

Poly silanes 12 which can be obtained by cocondensation of (7,8-diphenylfluoranthene-8-)methyl-dichlorosilane with dichlorodimethylsilane, dichloro-methyl-phenylsilane, or dichlorodiphenylsilane in toluene show an increase in conductivity to the level of semiconductors, after doping with strong electrophiles. The charge-transfer complexes are formed by mixing the polysilanes and electron acceptors, such as antimony pentafluoride, tetracyanoethylene or chlora-nil. The UV absorptions of these complexes shift to... 

Polysilanes have been investigated as the raw materials of new ceramics, photoresist polymers for high resolution lithography, semiconductors, electro-conductive polymers, etc. [46]. Polydimethylsilane is prepared by adding di-chlorosilane to the dispersed minute particles of sodium in toluene solution. 

Abstract The linear and nonlinear optical properties of polysilanes, and in particular poly(di-n-hexylsilane), have been investigate by vacuum UV spectroscopy and by two-photon induced processes. The electronic structure of the polymer inferred from these measurements is consistent with models which view the polymer as a one-dimensional semiconductor quantum wire. The exciton related optical nonlinearities are also large enough to allow polysUanes to be considered for various nonlinear switching applications. 

Some recent studies of the electronic properties of poly silanes have suggested that the first UV transition is not a band-to-band transition, but is instead excitonic in nature [13,16,17,18].These predict that the onset of band-to-band transitions must therefore be at higher energies, with an exciton binding energy of an eV or more, as is common for Frenkel excitons in molecular systems. Since the vacuum ultraviolet (VUV) specmim has not been measured until now, the question of whetha- a one-dimensional semiconductor band gap model or a molecular orbital model is appropriate for the polysilanes has been unresolved. 

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