Sublimation sources

The nature of the adsorption sites for CO on Cgo gave rise to yet another work, in which Lubezky et al. [71] used LiF/Cgo and NaCl/Cgo mixed films as adsorbent in an attempt to obtain spectra of CO adsorbed on individual C q molecules which might be present in the films as a result of their simultaneous deposition from two separate sublimation sources. The results obtained with the LiF/Cgo films fulfilled their expectations apart from two bands ascribable to CO adsorption on LiF, a third band at 2130 cm could be ascribed to CO adsorption on Cgg. This clearly showed that CO adsorbs on top of individual Cgo molecules dispersed in the LiF matrix. With NaCl/C Q, however, no IR bands for CO adsorbed on C q were found. Isosteric heat calculations revealed that the isosteric heat of CO on NaCl (18.8 kj/mol) is considerably higher than that on single Cgg molecules (11.7 kJ/mol). Therefore, preferential adsorption is thought to take place on NaCl, which would explain the absence of bands for CO adsorbed on Cjo-... 

The film growth and electrical measurements were performed in the ultra high vacuum (UHV) chamber with a base pressure of MO Torr. It was equipped with LEED optics, evaporation unit with three sublimation sources (Si, Cr, Fe) and manipulator with samples holder and a quartz thickness sensor. In situ electrical measurements were conducted using automated UHV Hall installation [2], The p-type (lOQ cm) Si(lll) wafers were used as substrates. The native oxide and... 

Growth experiments were carried out in two ultra high vacuum (UHV) cambers with sublimation sources of Si, Fe and Cr and quartz sensors of film thickness. Optical properties of the samples were studied in UHV chamber VARIAN (210 10Torr) equipped with differential reflectance spectroscopy (DRS) facilities. The samples surface was studied in the second UHV chamber (1 -10 9 Torr) equipped with LEED optics. Si(100) and Si(l 11) wafers were used as substrates for different series of the growth experiments. For the growth of silicide islands, metal films of 0.01-1.0 nm were deposited onto silicon surface. Silicon overgrowth with the deposition rate of 3-4 nm/min was carried out by molecular beam epitaxy (MBE) at 600-800 °C for different substrates. The samples were then analyzed in situ by LEED and ex situ by HRTEM and by... 

Sublimation sources have the advantage that the vaporizing material does not melt and flow. Examples of vaporization from a solid are sublimation from a chunk of pure material, such as chromium, and sublimation from a solid composed of a subliming phase and a nonvaporizing phase, e.g. Ag 50% Li for lithium vapor and Ta 25% Ti alloy wire (KEME P ) for titanium vapor. Heating may be by resistive heating, direct contact with a hot surface, radiant heating from a hot surface, or bombardment by electrons. 

Sublimation source (vaporization) A vaporization source for heating materials, such as chromium, that sublime rather than evaporate. The subUmation source can function best by ensuring good thermal contact between the heater and the solid. Examples Electroplated chromium on a tungsten heater heating by radiation in an oven-like structure direct e-beam heating of the surface of a solid. 

Thermal Theory. The thermal approach to flame retardancy can function in two ways. Eirst, the heat input from a source may be dissipated by an endothermic change in the retardant such as by fusion or sublimation. Alternatively, the heat suppUed from the source maybe conducted away from the fibers so rapidly that the fabric never reaches combustion temperature. 

Hexamethylenetetramine. Hexa, a complex molecule with an adamantane-type stmcture, is prepared from formaldehyde and ammonia, and can be considered a latent source of formaldehyde. When used either as a catalyst or a curative, hexa contributes formaldehyde-residue-type units as well as benzylamines. Hexa [100-97-0] is an infusible powder that decomposes and sublimes above 275°C. It is highly soluble in water, up to ca 45 wt % with a small negative temperature solubiUty coefficient. The aqueous solutions are mildly alkaline at pH 8—8.5 and reasonably stable to reverse hydrolysis. 

Most tanks store Hquid rather than gases or soHds. Characteristics and properties such as corrosiveness, internal pressures of multicomponent solutions, tendency to scale or sublime, and formation of deposits and sludges are vital for the tank designer and the operator of the tank and are discussed herein. Excluded from the discussion are the unique properties and hazards of aerosols (qv), unstable Hquids, and emulsions (qv). A good source of information for Hquid properties for a wide range of compounds is available (2). 

Intermolecular potential functions have been fitted to various experimental data, such as second virial coefficients, viscosities, and sublimation energy. The use of data from dense systems involves the additional assumption of the additivity of pair interactions. The viscosity seems to be more sensitive to the shape of the potential than the second virial coefficient hence data from that source are particularly valuable. These questions are discussed in full by Hirschfelder, Curtiss, and Bird17 whose recommended potentials based primarily on viscosity data are given in the tables of this section. 

Values were reproduced from a tabulation by J. R. Goates and J. B. Ott in Chemical Thermodynamics An Introduction, Harcourt Brace, Jovanovich. Inc., New York, 1971, pp. 137— 139. References to the original sources for these data are given there. b Normal sublimation point. 

Purification of the radioactive tracer was modified to include a fractional sublimation before a single extraction—recrystallization cycle to conserve the tracer material. Microgram samples were prepared in melting point capillaries for assay by mass spectroscopic analysis (Table III), made by direct probe injection of the sample into the ion source (18). The probe was heated rapidly to 200°C, and mass spectra were obtained during vaporization of the sample. Tri-, tetra-, and pentachlorodibenzo-p-dioxins vaporized simultaneously with no observed fractionation. 

If lead nitrate is used rather than the chloride or acetate as the source of divalent lead, the crude dicyclopentadienyllead may explode violently during purification by high-vacuum sublimation at 100-130°C. 

The procedure of Lifson and Warshel leads to so-called consistent force fields (OFF) and operates as follows First a set of reliable experimental data, as many as possible (or feasible), is collected from a large set of molecules which belong to a family of molecules of interest. These data comprise, for instance, vibrational properties (Section 3.3.), structural quantities, thermochemical measurements, and crystal properties (heats of sublimation, lattice constants, lattice vibrations). We restrict our discussion to the first three kinds of experimental observation. All data used for the optimisation process are calculated and the differences between observed and calculated quantities evaluated. Subsequently the sum of the squares of these differences is minimised in an iterative process under variation of the potential constants. The ultimately resulting values for the potential constants are the best possible within the data set and analytical form of the chosen force field. Starting values of the potential constants for the least-squares process can be derived from the same sources as mentioned in connection with trial-and-error procedures. 

Cl2Ga(N3)] air sensitive, sublimes at 70-100 °C in vacuum UHV-CVD Heteroepitaxial growth on Si and sapphire substrates at 650-700 °C, 1 1 films, no need for additional N source 293... 

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