Polycrystalline breakdown

Carbon deposits have been grown on heated polycrystalline iron specimens in a gas reaction cell in a scanning electron microscope. The complete range of deposits formed from methane at temperatures between 620°C and 850°C have been surveyed, from the first appearance of solid carbon on the surface to the final structural breakdown of the metal. Four characteristic morphologies have been identified. 

The additional enhancement provided by coadsorbed halide ions on a colloidal silver surface has been pointed out [401]. As an explanation, morphological changes effected by the strongly adsorbed anions have been invoked. The photo-driven CT that is assumed to proceed from filled metal states near the Fermi level of the metal to the first and second excited state in the case of pyrazine adsorbed on polycrystalline gold has been invoked as the cause for the breakdown of Raman selection rules upon adsorption (i.e. the activation of originally Raman-forbidden vibrational modes) [314]. 

The interface layer formed in the CVD process between the silicon substrate and the SIPOS film can lead to unstable I-V characteristics or to an electric breakdown in high-voltage planar devices. The modified ATR method was applied to study this interfacial layer between a Si substrate and polycrystalline Si [77], IR reflectance spectra were recorded in p- and 5-polarized radiation at 80°. The normalized reflectance spectra R = Rp/Rs were compared to the spectra of a test (reference) structure with a known thickness of Si02 and were calcnlated by the three-phase model, with an absorbing layer characterized by a complex dielectric constant and two transparent silicon layers with real dielectric constants. The analysis of the vlo band at 1210 cm revealed that the interface layer is comprised of silicon oxides, mainly Si02, with a thickness of 0.7 nm [77]. 

Sapphire fibers are hard, strong and scratch resistant to most materials and provide excellent wear surfaces. They can withstand higher pressures than polycrystalline alumina since they lack the grain boundary interface breakdown of the latter. Sapphire fibers transmit ultraviolet, visible, infrared and microwaves and serve as excellent wave guides between 10.6 and 17 microns, and offer durable and reliable IR transmission. By virtue of their high thermal conductivity they can be rapidly heated and cooled. 

Within single crystals and ceramic crystallites, respectively, the dipole moments of neighbouring domains are either perpendicular or anti-parallel to each other. For polycrystalline materials the orientation of the crystallites and thus of the domains is randomly distributed. In the original state these materials do not exhibit a macroscopic polarization and thus no piezoelectric effect. However, the latter can be induced by applying a static electric field below the Curie temperature where the domains of uniform dipole moments arrange towards the polarization field (paraelectric polarization). The field strength applied should be between the saturation and the breakdown range. Due to this polarization the ferroelectric material becomes piezoelectric. 

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