Vacuum evaporation method

Techniques such as vacuum evaporation method, melting process in a glass matrix, and so on [88], basically fundamental fabrication techniques for inorganic NPs and semiconductor quantum dots, would not be expected to be applied to organic and polymer compounds and materials because of their thermal instability [89, 90]. In contrast, the so-called reprecipitation method [1-4] is a useful and convenient procedure to prepare organic and polymer NCs. This method has been further improved as the supercritical reprecipitation method [1-3,28,29], reprecipitation-microwave irradiation method [1-3, 30-34], and inverse-reprecipitation method [1-3, 27, 42, 43], being closely related to the physicochemical properties of the target compound and materials. 

Compared with other methods, vacuum evaporation produces coatings that have a most satisfactory corrosion resistance, e.g. 0.005 mm of evaporated Cd gives a degree of protection to steel similar to that afforded by 0.01 mm of electrodeposited Cd. Cadmium coatings on ferrous and other substrates can meet authoritative specifications concerning corrosion... 

In Section 13.2, we introduce the materials used in OLEDs. The most obvious classification of the organic materials used in OLEDs is small molecule versus polymer. This distinction relates more to the processing methods used than to the basic principles of operation of the final device. Small molecule materials are typically coated by thermal evaporation in vacuum, whereas polymers are usually spin-coated from solution. Vacuum evaporation lends itself to easy coaling of successive layers. With solution processing, one must consider the compatibility of each layer with the solvents used for coating subsequent layers. Increasingly, multilayered polymer devices arc being described in the literature and, naturally, hybrid devices with layers of both polymer and small molecule have been made. 

The later publication [1] reveals that the title compound is in fact a relatively stable compound. The previously attempted preparation of the then unknown compound from trichloroacetonitrile, sodium azide and ammonium chloride (0.14 0.42 0.2 mol) by an analogous established method [2], but at lower initial temperature because of the exothermic reaction, gave, after vacuum evaporation of solvent, an oily product. When sampled with a pipette, this evolved gas and then exploded violently. It was thought that an azidomethyltetrazole may have been formed by displacement of chloro-substituent(s) by the excess azide employed [3], An alternative hypothesis which involved isomerisation of the title compound to the open chain azidoazomethine [4] was discounted, because no trace of this could be detected [1]. 

Ethylbenzene, Thallium triacetate Ucmura, S. et al., Bull. Chem. Soc., Japan., 1971, 44, 2571 Application of a published method of thallation to ethylbenzene caused a violent explosion. A reaction mixture of thallium triacetate, acetic acid, perchloric acid and ethylbenzene was stirred at 65°C for 5 h, then filtered from thallous salts. Vacuum evaporation of the filtrate at 60°C gave a pasty residue which exploded. This preparation of ethylphenylthallic acetate perchlorate monohydrate had been done twice previously and uneventfully, as had been analogous preparations involving thallation of benzene, toluene, three isomeric xylenes and anisole in a total of 150 runs, where excessive evaporation had been avoided. 

Gel filtration with Sephadex was used by Ghassemi and Christman [426] to make separations by molecular size on water samples concentrated by vacuum evaporation. Fluorescence was also used as one method for following the fractionation. Molecular size was also used by Gjessing [427] but with pressure dialysis as the method of separation. A similar method of concentration and separation was used by Brown [428] to follow the dispersion of these materials as fresh and salt water mixed in the Baltic Sea. 

Property measurements of fullerenes are made either on powder samples, films or single crystals. Microcrystalline C6o powder containing small amounts of residual solvent is obtained by vacuum evaporation of the solvent from the solution used in the extraction and separation steps. Pristine Cgo films used for property measurements are typically deposited onto a variety of substrates (< . , a clean silicon (100) surface to achieve lattice matching between the crystalline C60 and the substrate) by sublimation of the Cr,o powder in an inert atmosphere (e.g., Ar) or in vacuum. Single crystals can be grown either from solution using solvents such as CS and toluene, or by vacuum sublimation [16, 17, 18], The sublimation method yields solvent-free crystals, and is the method of choice. 

The extracts from the reaction are combined and shaken up with a little anhydrous magnesium sulfate (120 grams) and filtered. The filtrate is evaporated to dryness in the rotary vacuum evaporator, care being taken not to heat the extracts or the residual syrup above 55° C. A good mechanical vacuum pump and effective cold traps in the line are necessary to remove the residual dimethylformamide from the residue. A brown to black bubbly residue should remain when evaporation is complete. This residue contains the amide product and considerable impurities. A general method of purifying the amide follows. 

In the Langmuir free-evaporation method, the sample is suspended freely in a vacuum system with no container sunounding it. As very low levels of vapour pressure can be measured it has advantages over the Knudsen method where the lower limit is about 10" atm. (Kubaschewski et al. 1993). It is therefore more usefril in materials with high sublimation energies and therefore inherently low vapour pressiues. It has a further advantages in that there is no container with which to react, but there are more significant problems associated with temperature measurement. 

In all vacuum coating methods layers are formed by deposition of material from the gas phase. The coating material may be formed by physical processes such as evaporation and sputtering, or by chemical reaction. Therefore, a distinction is made between physical and chemical vapor deposition ... 

One technique which has produced thin, but not epitaxial films of BaPbj.xBixOg, and which shows good promise is the use of laser evaporation methods (40). Since the compound is efficiently transported stoichiometrically from the target to the substrate at a high rate and does not require a vacuum, this method may be superior to sputtering techniques. 

Model metal catalysts can be prepared by vacuum evaporation of the metal on supports and this method offers a simple and convenient way of investigating surface reactions between metals and gases. Some selected examples of support preparations are as follows. 

Small metal particles can also be obtained by vacuum evaporation in low pressure inert gases (16). Magnetic particles of metals such as iron, cobalt, nickel, and alloys of these metals can be prepared by this method. Though the amounts of particles obtainable by this method are limited, the particles are clean as compared with particles precipitated from solutions. They are mainly used for studies of physical properties of fine particles. 

S. Phenyldiazomethane (Vacuum pynolyzxa method). In a 200-mL, singlenecked, round-bottomed flask is placed 13.71 g (0.05 mol) of benzaldehyde tosylhydrazone. A 1.0 M solution (51 mL) of sodium methoxide in methanol (0.051 mol) (Note 2) is added via syringe and the mixture is swirled until dissolution is complete (Note 3). The methanol is then removed by rotary evaporator. The last traces of methanol are removed by evacuation of the flask at 0.1 mm for 2 hr. The solid tosylhydrazone salt is broken up with a spatula and the flask is fitted with a vacuum take-off adaptor and a 50-mL receiver flask. The system is evacuated at 0.1 nm and the receiver flask is cooled in a dry ice-acetone bath to about -50°C. The flask containing the salt is immersed in an oil bath and the temperature is raised to 90°C (use a safety shield). At this temperature, red phenyldiazomethane first begins to collect in the receiver flask. The temperature is raised to 220°C over a 1-hr period (Note 4). During this time red phenyldiazomethane collects in the receiver flask (Note 5). The pressure increases to 0.35 mm over the course of the pyrolysis. On completion of the pyrolysis the pressure drops to less than 0.1 mm. 

---