Selected Properties of Semiconductor Solid

In this brief review we illustrated on selected examples how combinatorial computational chemistry based on first principles quantum theory has made tremendous impact on the development of a variety of new materials including catalysts, semiconductors, ceramics, polymers, functional materials, etc. Since the advent of modem computing resources, first principles calculations were employed to clarify the properties of homogeneous catalysts, bulk solids and surfaces, molecular, cluster or periodic models of active sites. Via dynamic mutual interplay between theory and advanced applications both areas profit and develop towards industrial innovations. Thus combinatorial chemistry and modem technology are inevitably intercoimected in the new era opened by entering 21 century and new millennium. 

Modern technological developments and many fields of pure and applied research depend on the quantitative information about the spatial element distribution in thin solid layers and thin-film systems. For example, without the use of thin films the experimental studies on the physics of semiconductor are very difficult. Similarly the diffusion processes in solids, sandwich-like thin films structures in microelectronics, anti-reflecting or selectively transparent optical films, catalysts, coatings, composites - all rely on material properties on an atomic scale. The development of these new materials as well as the understanding of the basic physical and chemical properties that determine their specific characters are not possible without the knowledge of their compositional structure, in particular in the interface regions. 

Crystalline silicon is the most widely used semiconductor material today, with a maiket share of above 90%. Because of its indirect electronic band structure, however, the material is not able to emit light effectively and therefore carmot be used for key applications like light-emitting diodes or lasers. Selected one- or two-dimensional silicon compounds like linear or branched polysilylenes [1] or layered structures like siloxene [2], however, possess a direct band gap and therefore exhibit intense visible photoluminescence. Siloxene, a solid-state polymer with a sheet-like layered structure and an empirical formula Si H (OH) , in particular, is considered as an alternative material for Si-based liuninescent devices. Detailed studies of stmctural and photophysical properties of the material, however, are strraigly impeded by its insolubility in organic solvents. 

Solvent Effects, Crystal Fields. - This report is concerned with molecular properties and full coverage of intermolecular effects and solid state susceptibilities is not attempted. The papers reviewed in this section have been selected because they contain material closely related to the calculated properties of individual molecules. For example, calculations based on the electronic band structures of semiconductors etc. are excluded, but a few papers relating molecular crystal susceptibilities to the molecular hyperpolarizabilities are included. 

The refractive index and other optical properties for metals, semiconductors, and certain other compounds can be found in the tables Optical Properties of Selected Elements and Optical Properties of Selected Inorganic and Organic Solids in Section 12 of this Handbook. 

Ba " ", Cs, NH4", Ag" ") and anions (NOi j Cl , HCOi ). Solid-state ISEs (coated wire electrodes) have also been developed in which the sensitive membrane is coated directly onto a metal wire, usually a silver-silver halide. While these have the advantage of being small and easy to fabricate, they have been noted for their unpredictable properties and suffer from lifetime and stability problems. More sophisticated approaches involve the use of semiconductor planar fabrication technologies to deposit ion-sensitive layers onto semiconductor substrates to produce ion-selective field-effect transistors. These are conceptually very attractive but it has proven very difficult to produce devices as good as the equivalent ISE. 

Solid surfaces covered by arrays (forests) of whiskers are black bodies because of multiple reflections of the photons in the labyrinth maze structure [4041]. A spectrum selectivity related to topical properties of the material is inherent in arrays of semiconductor whiskers. The transmitted part is characteristic of silicon absorption starting at a wavelength of 1.1 pm. The reflected part changes montonically. The calculated absorption was 93.0% at 1.00 pm, 86.8% at 1.34 pm, 84,5% at 1.55 pm, and 79.8 at 2.00 pm [40]. 

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