Chemical solution deposition processing stages

Figure 2.1. Processing stages in chemical solution deposition of thin films. Controllable parameters are shown on the left dependent processes are shown in italics. [Reprinted from Ref. 16 with the permission of the publisher, Taylor Francis, Ltd. R. W. Schwartz et al., Sol-gel processing of PZT thin films a review of the state-of-the-art and process optimization strategies, Int. Ferro., 7,259, (1995).]...

Two different stages for silver deposition on platinum can be described one at 1.1 V vs. RHE responding to a silver-platinum alloy electrodissolution (overlapped with the oxygen electroadsorption at free platinum sites) and the other at 0.65 V due to the silver oxidation (from the onset of the bulk deposition process) deposited on the former surface alloy [88,89]. The former process splits into two peaks when the potentiostatic ageing is performed. The spectroscopic techniques such as XPS and ARXPS (angle resolved x-ray photoelectron spectroscopy) were used to determine the chemical composition of the silver films on the platinum in an acid solution [92], The technique was not able to discern between the presence of silver oxides and sulfates, only an energy shift of the clean silver 3d5/2 band at a upd level of —0.5 eV was detected. 

The wet synthesis of CdS nanoparticles used in this work is based on the reaction between a dissolved cadmium salt (CdCl2) and a S-containing compound (thiourea (NH2)2CS) in an aqueous solution. Chemical deposition of CdS nanoparticles in the CdCl2 - NH3 - NaOH - (NH2)2CS - H2O bath was described elsewhere [3]. In the present work all the baths had the same composition and were prepared from solutions of cadmium chloride CdCl2 (0.005 mold-1), ammonia NH3-H2O (1.5 moll"1), sodium hydroxide NaOH (0.074 mold-1) and thiourea (NH2)2CS (0.025 mol-F1) using distilled water. The synthesis temperature was varied from 294 to 325 K. The primary concentrations of the precursors have been chosen according to the thermodynamic analysis [4]. A supersaturation of the solution with Cd(OH)2 takes place in the baths. It means that the mechanism of the cadmium sulfide formation could involve the stage of Cd(OH)2 formation. When the deposition process of CdS particles in the solution completed, the residue was filtered at an ambient pressure and dried at room temperature. 

Chemical reduction is used extensively nowadays for the deposition of nickel or copper as the first stage in the electroplating of plastics. The most widely used plastic as a basis for electroplating is acrylonitrile-butadiene-styrene co-polymer (ABS). Immersion of the plastic in a chromic acid-sulphuric acid mixture causes the butadiene particles to be attacked and oxidised, whilst making the material hydrophilic at the same time. The activation process which follows is necessary to enable the subsequent electroless nickel or copper to be deposited, since this will only take place in the presence of certain catalytic metals (especially silver and palladium), which are adsorbed on to the surface of the plastic. The adsorbed metallic film is produced by a prior immersion in a stannous chloride solution, which reduces the palladium or silver ions to the metallic state. The solutions mostly employed are acid palladium chloride or ammoniacal silver nitrate. The etched plastic can also be immersed first in acidified palladium chloride and then in an alkylamine borane, which likewise form metallic palladium catalytic nuclei. Colloidal copper catalysts are of some interest, as they are cheaper and are also claimed to promote better coverage of electroless copper. 

---