Precursor films

The microscopic complexity of the contact angle is illustrated in Fig. X-14, which shows the edge of a solidified drop of glass—note the foot that spreads out from the drop. Ruckenstein [176] discusses some aspects of this, and de Gennes [87] has explained the independence of the spreading rate on the nature of the substrate as due to a precursor film present also surrounding a nonspread-... 

It is generally believed that in the first stage of a passivation reaction—just below —a precursor film is fonned... 

When spontaneous spreading occurs, the bulk of the advancing liquid is preceded by a precursor film, usually a few millimeters in width and a few hundred nanometers or less in thickness [58], as pictured in Fig. 12. The observed dynamic contact angle is that which is made by the bulk liquid against the precursor film, and it itself depends on the rate of the advance of the nominal interline. The relationship between the rate of spontaneous spreading, i.e. the rate of movement of the nominal interline normal to itself, (/, and the dynamic contact... 

Figure 3. Scanning electron micrographs of palladium features on quartz substrate as a function of laser power (measured on target) and scan speed. Palladium acetate precursor film thickness is 1.5 pm (cw Ar+ laser - 5145A line, spot size —0.8 pm FWHM).

Precursor Film Substrate T at 10 2 torr (°C) Growth rate ( im h ) Characteristic... 

Figure 3.2. Film formation using a dimensional reduction approach involves three steps 1) breaking up the insoluble extended inorganic framework (a) into more soluble-isolated anionic species, which are separated by some small and volatile cationic species (b). 2) Solution-processing thin films of the precursor (b). 3) Heating the precursor films such that the cationic species and corresponding chalcogen anions are dissociated, leaving behind the targeted inorganic semiconductor (c).

Despite facile formation of p-type ZnTe from the precursor, films of ZnTe formed from a drop cast precursor solution had a small grain structure (using conditions that we have so far explored), which limited prospective TFT device performance. Note that we expect a similar chemistry to that for ZnTe to also be operative for selected other metal telluride precursors. In contrast to the ZnTe films, well-crystallized films of In2Te3 have been formed using... 

Nonvacuum electrodeposition and electroless deposition techniques have the potential to prepare large-area uniform precursor films using low-cost source materials and low-cost capital equipment. Therefore, these techniques are very attractive for growing CIGS layers for photovoltaic applications. 

Figure 7.6. SEM of the electrodeposited CIGS precursor film (a) surface morphology and (b) cross section. 

The electrodeposited precursor films prepared in our laboratory that produced high-efficiency devices were Cu-rich films. These precursor films required additional In, Ga, and Se, deposited by PVD, to adjust their final composition to Culni xGaxSe2. During this second step, the substrate temperature was maintained at 560 °C 10 °C. Figure 7.7 presents the Auger analysis of the final absorber and shows nonuniform distribution of Ga in the absorber and more Ga near the surface. This result is primarily from the second-stage PVD addition. The Ga hump is not helpful for hole collection. The device efficiencies are expected to increase by optimizing the Ga distribution in the absorber layers. The optimized layers should have less Ga in the front and more Ga on the back, which facilitates hole collection. 

The electrodeposited precursor films, annealed in air at 870 °C in the presence of a TBSBCCO pellet, produce a biaxial textured Tl-1223 phase, as confirmed by an XRD pole-figure measurement. The omega and phi scans indicate full-width at half-maximum (FWHM) values of only 0.92° and 0.6°, respectively, which indicates a very high-quality film. The superconductive transition temperature of the Tl-1223 film, determined resistively, was about 110 K. Figure 7.11... 

The electrodeposited Bi2Sr2CaiCu2Ox (BSCCO) precursor films were obtained by co-electrodeposition of the constituent metals using nitrate salts dissolved in DMSO solvent. The electrodeposition was performed in a closed-cell configuration at room temperature ( 24°C). The cation ratios of the electrodeposition bath were adjusted systematically to obtain BSCCO precursor compositions. A typical electrolyte-bath composition for the BSCCO films consisted of 2.0-g Bi(N03)3-5H20,1.0-g Sr(N03)2, 0.6-g Ca(N03)2-4H20, and 0.9-g Cu(N03)2-6H20 dissolved in 400 mL of DMSO solvent. The substrates were single-crystal LAO coated with 300 A of Ag. 

Bhattacharya, R. N. Batchelor, W. Ramanathan, K. Contreras, M. A. Moriarty, T. 2000. The performance of CuIn1 xGaxSe2-based photovoltaic cells prepared from low-cost precursor films. Solar Energy Mater. Solar Cells 63 367-374. 

Three kinds of PAV films was prepared using methoxy pendant precursors. The chemical structures and synthetic route of the PAV films used in this study are shown in Fig. 19. The details of synthesis of the methoxy pendant precursors have been described in refs. 29 and 30. The precursors were soluble in conventional organic solvents, for example, chloroform, dichloromethane, benzene and so on. The precursor polymer thin films were spin-coated on fused quartz substrates from the chloroform solutions. The precursor films were converted to PAV films by the heat-treatment at 250 0 under a nitrogen flow with a slight amount of HC1 as a catalyst. This method provided high performance PAV films with excellent optical quality. 

Thin-film dielectrics (Ba0 92Ca108)(Ti0 92Zr0 08)O3 for the thin-film capacitors were prepared using Ba, Ca, and Zr ethoxides and Ti isopropoxide in refluxed methoxyethanol solutions as precursors. Films were deposited on a usual platinized Si substrate. Crystalline thin films after heat treatment at 800°C demonstrated dielectric permittivity of 1200, dielectric loss of0.5%, nonlinear coefficient a = 0.92, and break-down voltage of980 V [1595],... 

Figure 7.15 Liquid spreading on a solid surface with a precursor film. ...

For systems which spread spontaneously it is well-known that a spreading drop forms a thin (< 0.1 pm) primary or precursor film [279-282], Its thickness and extension are determined by surface forces. In the precursor film, energy is dissipated by viscous friction. The liquid transport in the precursor film is driven by the disjoining pressure in the precursor film which sucks liquid from the wedge of the drop. 

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