Fabrication processes film coating

Copper Sulfide—Cadmium Sulfide. This thin-film solar cell was used in early aerospace experiments dating back to 1955. The Cu S band gap is ca 1.2 eV. Various methods of fabricating thin-film solar cells from Cu S/CdS materials exist. The most common method is based on a simple process of serially overcoating a metal substrate, eg, copper (16). The substrate first is coated with zinc which serves as an ohmic contact between the copper and a 30-p.m thick, vapor-deposited layer of polycrystaUine CdS. A layer is then formed on the CdS base by dipping the unit into hot cuprous chloride, followed by heat-treating it in air. A heterojunction then exists between the CdS and Cu S layers. 

Either particulate sol or polymeric sol has been used for thin film coatings. The polymeric sol was fabricated by partial hydrolysis of corresponding metal alkoxide. If the rate of hydrolysis or condensation is very fast, then some kinds of organic acids, beta-dicarbonyls, and alkanolamines have been used as chelating agent in sol-gel processes to control the extent and direction of the hydrolysis-condensation reaction by forming a strong complex with alkoxide. [2]. 

If suitable equipment for processing the polymer melt is not available, or if the polymer will not melt, or melts only with decomposition, the processing may be carried out from solution. This technique, however, is limited to the fabrication of films, membranes, fibers, coatings, and adhesives. 

Figure 15.24 shows the fabrication process of the optical filter on a fluorinated polyimide substrate. First, the low-thermal-expansion-coefficient PMDA/TFDB poly(amic acid) solution was spin-coated onto a Si substrate and baked. Then alternate TiO2 and SiO2 layers were formed on the polyimide film by ion-assisted deposition. The multilayered polyimide film was diced and peeled off from the Si substrate. In this way, thin optical filters on a fluorinated polyimide substrate are easily fabricated. 

The sol-gel process involves the transition of a system from a liquid "sol" (mostly colloidal) into a solid "gel" phase (11). By applying this methodology, it is possible to fabricate ceramic or glass materials in a wide variety of forms ultrafine or spherical-shaped powders, thin film coatings, ceramic fibers, microporous inorganic membranes, monolithic ceramics and glasses, or extremely porous aerogel materials. 

Calendering and extrusion lines (Chapter 5) produce film, sheet, and for applying plastic coatings to textiles, paper, or other supporting material. Table 9.1 provides comparison in fabricating PVC film. The extrusion process provides flexibility, when compared to calendering, that includes ease of changing product thicknesses, widths, materials, and provides for short production runs. 

In GLC, separation occurs based on differences in partitioning of the sample components between the carrier gas and the liquid phase. A wide selection of liquid phases makes GLC a versatile separation technique. Further, the liquid phase can be a polymer or a chemically bonded phase. In all cases, the liquid phase is film coated or chemically bonded onto a solid support surface or a column wall. Liquid-bonded phases overcome the problem of leakage of the stationary phase material into the carrier. They are used commonly in LC also, and the process to fabricate... 

Polymer-coated hollow-fibers with a length of 1-2 m and iimer diameters of 0.32-1 mm are fabricated by modifying the process of coating the silver and polymer films. Firstly, a thin film of silver is deposited on the iimer surface of the... 

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