Precursor stocking

Selenium precursor stock solution was prepared by adding 0.32 mmol of selenium powder to 20 mL deionised water in a three-necked flask. Sodium borohydride (0.81 mmol) was carefully added to this mixture and the flask was immediately purged with nitrogen gas to create an inert environment. The mixture was then stirred for 2 h, at room temperature. The entire selenium dissolves in water giving rise to a colourless selenium solution. The cadmium solution was prepared by adding 0.32 mmol of CdCb powder in 20 mL of deionised water. The zinc solution was prepared by dissolving 0.32 mmol ZnCb in 20 mL of... 

After the precursor stock solution is prepared, various techniques can be used to coat the substrate, depending on the solution viscosity, required film thickness and coverage. The most common methods in the semiconductor industry are spin- and dip-coating. Other processes that are used for deposition include spray coating and stamping. A summary of the uses, limitations, and advantages of the various thin film deposition methods is reported in Table 2.2. 

The synthetic approach is very simple and does not require any special set up. In a typical room temperature reaction, 1.0 mL aqueous solution of cadmium chloride was added to 20 mL aqueous solution of soluble starch in a 50 mL one-necked round-bottom flask with constant stirring at room temperature. The pH of the solution was adjusted from 6 to 11 using 0.1 M ammonia solution. This was followed by a slow addition of 1.0 mL colourless selenide ion stock solution. The mixture was further stirred for 2 h and aged for 18 h. The resultant solution was filtered and extracted with acetone to obtain a red precipitate of CdSe nanoaprticles. The precipitate was washed several times and dried at room temperature to give a material which readily dispersed in water. The same procedure was repeated for the synthesis of PVA and PVP - capped CdSe nanoparticles by replacing the starch solution with the PVA and PVP polymers while the synthesis of elongated nanoparticles was achieved by changing the Cd Se precursor ratio from 1 1 to 1 2. The synthesis of polymer capped ZnSe nanoparticles also follows the same procedure except that ZnCb solution was used instead of CdCb solution. 

The p-xylylene species plays a central role in the coating process itself as well as in the making of the dimers which are used as feed-stocks for the coating process. Polymers and dimers have both been made from precursor p-xylene compounds (4) featuring a variety of X and Y leaving groups. 

Modification by acetylacetone is a powerful route, that allows precursor solutions to be stabilized. Interaction of titanium alkoxides with acetylacetone was extensively studied and reviewed in [1391,86]. Study ofreactions, occurring on interaction of Zr(OPrn)4 and Ti-Zr alkoxide mixture with acetylacetone, was performed in [1448] and allowed the authors to simplify the technique for preparation of precursor solution for PZT films application and to overcome the requirement of prolonged refluxing, which certainly decreases reproducibility. After dissolution of titanium and zirconium alkoxides in methoxyethanol, acetylacetone is added to form stable zirconium and titanium stock solutions. The introduction of acetylacetone allowed aqueous lead acetate (and lanthanum acetate for PLZT films) solutions to be added to mixed titanium and zirconium solutions. No reaction steps involving elevated temperatures or distillation or long reaction times are required. The solution could be used both immediately on mixing or after storage for several months. Such solutions were successfully used for application of ferroelectric films. 

A liquid-handling robot was customized for both sol-gel [46] and evaporative wafer-based syntheses [44]. The appropriate precursors are mixed from stock solutions into micro-titer plates and then volumetrically transferred to the support wafers. Key variables in these syntheses are the drying environment and drying temperature and post treatments. The liquid or gel is dried under controlled conditions and then thermally processed in a tube furnace exposed to desired process gases. After synthesis is complete, the wafers are analyzed by XRD, SEM, and XRF to monitor structural phases, morphologies, and compositions respectively. 

A rapid semiautomated microdilution method for the microbiological assay of the chloroquine has been developed by Desgardins (26). Antimalarial activity of chloroquine may be studied against cultured Plasmodium falciparum, microplates are used to prepare serial dilution of the drug. Parasites obtained from continuous stock cultures are subcultured in the micro-plates for 42 h. Inhibition of uptake of a radio labeled nucleic acid precursor by parasites serves as the indicator of antimicrobial activity. 

In November 2006, the Government of the Russian Federation issued a decision requiring importing and exporting companies to submit reports on their trade in narcotic drugs, psychotropic substances and precursor chemicals and requiring manufacturers, producers and retailers to submit reports on the respective quantities produced, manufactured, supplied, sold and in stock. 

Preparation of Preceramic Polysilazanes. At MIT (Massachusetts Institute of Technology), our initial research on silicon-based preceramic polymers was aimed at developing a precursor for silicon nitride. To this end, we studied the ammonolysis of dichlorosilane, H2SiCl2 (ii). This reaction had already been carried out on a millimolar scale in the gas phase and in benzene solution by Stock and Somieski in 1921 (12). We found that this reaction gave a much better yield of soluble ammonolysis product when it was carried out in more polar solvents such as dichloromethane or diethyl ether (ii). 

Roundabouts, or traffic circles, function as hubs to facilitate traffic flow. The citric acid cycle is the biochemical hub of the cell, oxidizing carbon fuels, usually in the form of acetyl CoA, as well as serving as a source of precursors for biosynthesis. [(Above) Chris Warren/Intemational Stock.]... 

One can easily summarize the requirements that should be fulfilled before the titanium-based ceramic materials can be obtained through an aqueous solution synthesis method. First, the precursor compound should possess good solubility in water, and preferably it should be stable over a wide pH range. In ideal case such compound should be a weighing form for titanium however, from the practical considerations it is sufficient to have a stock solution stable for a reasonably long period of time. Second, the reagent should be non-toxic, relatively cheap and its impact on the environment should be small. Its composition and chemistry should be simple and the reactions with other cations that will be introduced to the system must be well-predictable. The tendency to form precipitates with many cations, like in the case of oxalate ions, must be avoided. Finally, from an industrial point of view, the overall process should be cost effective and environmentally benign. 

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