Modulated film

Electrodeposition of composition-modulated films was first performed by Brenner in 1939 (1) by employing two separate baths for the two components and a periodic immersion of the deposit in the two baths. This is too cumbersome a method to be adopted in practice. Deposition from a single bath with the presence of salts of the two components of the multilayer is what is desired, but there was a serious problem with the deposition of two metals from one bath. Specifically, whereas a layer of the more noble member can be deposited by choosing the potential to be between the reduction potentials of the two metals, one can expect that when the potential is set to a value appropriate for reduction of the less noble member, both will be deposited, resulting in an alloy layer rather than a pure metal. Thus, to nobody s surprise, even as recently as 1983, Cohen et al. (2), were able to deposit only a layered structure of alloys rather than pure metals. In addition they cast doubt on the possibility that a modulation cycle (the thickness of the basic layers, the periodic repetition of which... 

Uq = shear module, quartz Uf = shear module, film... 

Electrodeposition of composition-modulated films was first performed by Brenner in 1939 (1) by employing two separate baths for the two components and a periodic immersion of the deposit in the two baths. This is too cumbersome a method to be adopted in practice. Deposition from a single bath with the presence of salts of the two components of the multilayer is what is desired. 

Fig. 2. Schematic examples of various types of multiiiQreis or compositionally modulated films (CMF).

Co/Gd) films. T. Nakamura et al. (1987) have carried out syntheses of amorphous (Co/Gd) sputtered films with anisotropy modulated superstructures. Webb et al. (1985) have investigated the structural and magnetic properties of such specimens. The modulated films were sputtered onto a thin Cr layer deposited previously itself onto oriented substrates. From XRD it is observed that the longer sequences exhibit both fee and hep Co structures, whereas smaller sequences are amorphous. Deposition... 

In order to make a multipurpose plant even more versatile than module IV, equipment for unit operations such as soHd materials handling, high temperature/high pressure reaction, fractional distillation (qv), Hquid—Hquid extraction (see Extraction, liquid-liquid), soHd—Hquid separation, thin-film evaporation (qv), dryiag (qv), size reduction (qv) of soHds, and adsorption (qv) and absorption (qv), maybe iastalled. 

If the index of refraction of a thin material were modulated in Heu of its absorption, the resultant transmittance function for a gra ting prepared as in the absorption case is given by equation 9 where n is the average index of the thin film. An is the amphtude of the index perturbation, and T is the thickness of the film. 

Because membranes appHcable to diverse separation problems are often made by the same general techniques, classification by end use appHcation or preparation method is difficult. The first part of this section is, therefore, organized by membrane stmcture preparation methods are described for symmetrical membranes, asymmetric membranes, ceramic and metal membranes, and Hquid membranes. The production of hollow-fine fiber membranes and membrane modules is then covered. Symmetrical membranes have a uniform stmcture throughout such membranes can be either dense films or microporous. 

Hollow-fiber designs are being displaced by spiral-wound modules, which are inherently more fouling resistant, and require less feed pretreatment. Also, thin-film interfacial composite membranes, the best reverse osmosis membranes available, have not been fabricated in the form of hoUow-fine fibers. 

The birefringent (BR) modulator makes use of polarized light and tensorial nature of the electrooptic coefficient. For example, poled organic polymer films are characterized by two nonzero components for the electrooptic tensor and parallel and orthogonal to the poling direction,... 

Amorphous Silicon. Amorphous alloys made of thin films of hydrogenated siUcon (a-Si H) are an alternative to crystalline siUcon devices. Amorphous siUcon ahoy devices have demonstrated smah-area laboratory device efficiencies above 13%, but a-Si H materials exhibit an inherent dynamic effect cahed the Staebler-Wronski effect in which electron—hole recombination, via photogeneration or junction currents, creates electricahy active defects that reduce the light-to-electricity efficiency of a-Si H devices. Quasi-steady-state efficiencies are typicahy reached outdoors after a few weeks of exposure as photoinduced defect generation is balanced by thermally activated defect annihilation. Commercial single-junction devices have initial efficiencies of ca 7.5%, photoinduced losses of ca 20 rel %, and stabilized efficiencies of ca 6%. These stabilized efficiencies are approximately half those of commercial crystalline shicon PV modules. In the future, initial module efficiencies up to 12.5% and photoinduced losses of ca 10 rel % are projected, suggesting stabilized module aperture-area efficiencies above 11%. 

As with ah thin-film PV technologies, the projected manufacturing costs of a-Si H ahoy PV modules fah rapidly with annual manufacturing volume, ie, MWp /yr. The primary driver of this volume cost reduction is the volume—cost relationship of commercially available thin-film processing equipment. Thin-film coating machines often have capacities equivalent to 3—5 yr, so that manufacturing economies of scale are more fully realized at the... 

The key determinants of future cost competitiveness of a-Si H PV technology are a-Si H deposition rates, module production yields, stabilized module efficiencies, production volume, and module design. Reported a-Si H deposition rates vary by more than a factor of 10, but most researchers report that the high quaUty films necessary for high stabilized efficiencies require low deposition rates often due to high hydrogen dhution of the Si (and Ge) source gases (see Semiconductors, amorphous). 

Small-area thin-film CdTe solar cells have been fabricated with sunlight-to-electricity conversion efficiencies near 16%, comparable to crystalline siUcon solar cells in large-scale manufacturing. Large-area monolithic integrated CdTe modules have been fabricated with efficiencies of ca 10%, comparable to crystalline siUcon modules commercially available. 

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