Precursors evaporation

Two methods for the evaporation of precursors may be employed - resistance heating and electron beam collision. The first method employs a simple alumina crucible that is heated by a W filament. Temperatures as high as 1,800°C may be reached inside the chamber, which is enough for some metals or metal salts to vaporize. Deposition rates for this method are 1-20 A s . The use of an electron beam to assist in the precursor evaporation results in temperatures on the order of 3,000°C, being more suited for the deposition of refractory metals/alloys and metal oxides such as alumina, titania, and zirconia. Since the temperature of the chamber interior is much higher than the walls, the gas-phase ions/atoms/molecules condense on the sidewalls as well as the substrate this may lead to film contamination as the nonselective coating flakes off the chamber walls. 

Precursor Evaporation temp. (°C) Deposition temp. (°C) Carrier gas Reactor pressure (Torr) Substrate Film composition... 

CVD precursor Evaporation Deposition Deposition Carrier Reactor temp. temp. rate gas pressure... 

Scholle P.A., Ulmer D.S. Melim L.A. 1992 - Late-stage calcites in the Permian Capitan Formation and its equivalents, Delaware Basin margin, west Texas and New Mexico evidence for replacement of precursor evaporates. Sedimentology, 39 207-234. 

Dry-Throwaway Processes. Dry-throwaway systems were the precursor of processes that removed SO2 iu the ductwork, eg, the BCZ and IDS processes. Here, however, the device is a spray chamber similar to the wet scmbbers such as the three modules of the Colstrip iastallation (Fig. 12). Into the upper portion of the chamber a slurry or clear solution containing sorbent is sprayed. Water evaporates from the droplets, the sorbent reacts with SO2 both before and after drying, and the dry product is removed ia a downstream baghouse or ESP (72). Unfortunately, dry scmbbiag is much less efficient than wet scmbbiag and lime, iastead of the much less expensive limestone, is required to remove SO2 effectively. Consequentiy, a search has been conducted for more reactive sorbents (72—75). 

Coppet(II) oxide [1317-38-0] CuO, is found in nature as the black triclinic tenorite [1317-92-6] or the cubic or tetrahedral paramelaconite [71276-37 ]. Commercially available copper(II) oxide is generally black and dense although a brown material of low bulk density can be prepared by decomposition of the carbonate or hydroxide at around 300°C, or by the hydrolysis of hot copper salt solutions with sodium hydroxide. The black product of commerce is most often prepared by evaporation of Cu(NH2)4C02 solutions (35) or by precipitation of copper(II) oxide from hot ammonia solutions by addition of sodium hydroxide. An extremely fine (10—20 nm) copper(II) oxide has been prepared for use as a precursor in superconductors (36). 

Extraction and purification (Shimomura, 1991b). The luciferin precursors PS-A and PS-B are extracted from the dried fruiting bodies of Panellus stipticus (5 g) with methanol, and the extract is evaporated under reduced pressure to remove most of the methanol. The residue (pH 6.3) is diluted with a small amount of water and extracted with ethyl acetate, and the extract is evaporated to dryness. The precursors in the residue are purified by three steps of silica gel chromatography and one step of HPLC, while monitoring the absorbance of eluate at 220-230 nm. The procedure is summarized below ... 

The relatively high volatility of Tg[CH = CH2]8 has enabled it to be used as a CVD precursor for the preparation of thin films that can be converted by either argon or nitrogen plasma into amorphous siloxane polymer films having useful dielectric propertiesThe high volatility also allows deposition of Tg[CH = CH2]g onto surfaces for use as an electron resist and the thin solid films formed by evaporation may also be converted into amorphous siloxane dielectric films via plasma treatment. ... 

Usually noble metal NPs highly dispersed on metal oxide supports are prepared by impregnation method. Metal oxide supports are suspended in the aqueous solution of nitrates or chlorides of the corresponding noble metals. After immersion for several hours to one day, water solvent is evaporated and dried overnight to obtain precursor (nitrates or chlorides) crystals fixed on the metal oxide support surfaces. Subsequently, the dried precursors are calcined in air to transform into noble metal oxides on the support surfaces. Finally, noble metal oxides are reduced in a stream containing hydrogen. This method is simple and reproducible in preparing supported noble metal catalysts. 

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