Thermal vaporization

Vacuum Deposition. Vacuum deposition, sometimes called vacuum evaporation, is a PVD process in which the material is thermally vaporized from a source and reaches the substrate without coUision with gas molecules in the space between the source and substrate (1 3). The trajectory of the vaporized material is therefore line-of-sight. Typically, vacuum deposition takes place in the pressure range of 10 10 Pa (10 10 torr), depending on the level of contamination that can be tolerated in the resulting deposited film. Figure 3 depicts a simple vacuum deposition chamber using a resistively heated filament vaporization source. 

The vapor pressure is an important property of the material to be thermally vaporized. In a closed container at equiUbrium, the number of atoms returning to the surface is the same as those leaving the surface, and the pressure above the surface is the equiUbrium vapor pressure. Vapor pressures are strongly dependent on the material and the temperature (Fig. 4). 

Fig. 5. Thermal vaporization sources (a) hairpin (b) spiral (c) basket (d) boat and (e) canoe, which ate all resistively heated sources and (f) focused...

Most elements thermally vaporize as atoms but some, such as Sb, C, and Se, have a portion of their vapor as clusters of atoms. For these materials, special vaporization sources, called baffle sources, can be used to ensure that the depositing vapor is in the form of atoms by causing the material to be vaporized from multiple hot surfaces before it leaves the source. 

At aU but the lowest bombarding energies, the flux of atoms that are sputtered from the surface leaves the surface with a cosine distribution (Fig. 6). The sputtered atoms have kinetic energies higher than those of thermally vaporized atoms, as well as a high energy tail in the energy distribution that can be several tens of eV. 

In the sputtering process, each surface atomic layer is removed consecutively. If there is no diffusion in the target, the composition of the vapor flux leaving the surface is the same as the composition of the bulk of the material being sputtered, even though the composition of the surface may be different from the bulk. This allows the sputter deposition of alloy compositions, which can not be thermally vaporized as the alloy because of the greatly differing vapor pressures of the alloy constituents. 

The simple d-c diode sputtering configuration has the advantage that (/) large areas can be sputtered rather uniformly over long periods of time (2) the target can be made conformal with the substrate (J) the target-to-substrate distance can be made smaU compared to thermal vaporization and (4) the... 

The anionic species ROCS2 resulted from O-alkyl(aryl) esters of the hypothetical dithiocarbonic acids, ROC(S)SH, better known as xanthates, are versatile ligands and they generate an extensive coordination chemistry. The interest for metal xanthates is stimulated by their potential use as single source precursors for nanoscopic metal sulfides in photochemical or thermal vapor deposition systems under mild conditions,218 221 e.g. for Zn,222 Cd,223 In,224... 

Hass-McBee A thermal, vapor-phase process for chlorinating aliphatic hydrocarbons. The chlorine and the hydrocarbon vapor are separately heated to >250°C and then mixed. Propane is thus converted to 1, 3-dichloropropane. Invented in 1934 by H. B. Hass and E. T. McBee at Purdue University. 

Thermal treatment. See Heat treatment copper-beryllium alloys, 3 654 nickel-beryllium alloys, 3 657-658 of macrofouling organisms, 26 150 Thermal vaporization sources, 24 727 Thermal vaporization rate, 24 725 Thermal waste treatment, 25 831-834, 843-845... 

Unfortunately, some of the analyzed molecules, as most biologically related molecules (e.g., amino acids), are solids with extremely low vapor pressures at room temperature and rapidly decompose when they are heated. For these molecules, which cannot be thermally vaporized, laser ablation or desorption have been alternatively used to produce neutral species in the gas phase.Both methodologies refer to laser-induced particle removal (laser sputtering) from a surface under the two extremes of massive and negligible rates of surface erosion, respectively. 

Alternate Sample Introduction — Obviously, elimination of the sample dissolution stage would greatly reduce analytical time, as it is the slowest step in the analytical scheme. Pulsed-laser vaporization using a CO2—TEA laser seems promising(63, 64). Another possibility is the introduction of a suitable prepared slurry of the sample into the nebullzer(65). Thermal vaporization studies using heated substrates such as tanta-lum(66), carbon filaments(67), or carbon rods(39) have been reported. Silvester(39) de fined the problems of vapor transport, carrier gas expansion, and solid phase chemistry associated with electrothermal sample introduction to an ICP. 

The LC-MS with a supersonic molecular beam (LC-SMB-MS) apparatus, which is schematically shown in Figure 8.13, is based on a modified homemade GC-MS with an SMB system that was previously described [76]. The heart and soul of this system is the soft thermal vaporization nozzle (STVN) chamber. The STVN accepts the liquid flow from the LC or the flow injection liquid... 

This smoke can be generated by mechanical atomization or thermal vaporization but it is very corrosive to skin and metals. This is a cheap and effective method of screening though its screening efficacy is about half or less than that of P. 

Less volatile but thermally stable compounds can be thermally vaporized in the direct inlet probe (DIP) situated close to the ionizing molecular beam. This DIP is standard equipment on most instruments. An electron-impact spectrum results. 

This device comprises a hydrophobic surface using the wettability pattern of hydrophilic stripes for a surface-guided flow, micro channels [102], As substrates, hydrophobic materials were employed. The hydrophilic stripes were generated by mask-through thermal vapor deposition of MgF2 on a silicone mbber or thiolated gold substrate. 

For concrete estimates of the parameters of a reaction (3.1) let us turn to diatomic molecules, such as Na2, K2, Te2, which have been studied most in experiments on optical pumping of molecules via depopulation. A number of data characterizing the states and transitions in these objects under conditions typical for such experiments are given in Table 3.7. These parameters are, to a certain extent, characteristic of diatomic molecules in thermal vapors of the first, sixth and seventh group of the periodic system of elements, such as alkali diatomics, S2, Se2,12, etc. These molecules may... 

Umeno T, Fukuda K, Wang H, Dimov N, Iwao T, Yoshio M. Novel anode material for lithium-ion batteries Carbon-coated silicon prepared by thermal vapor decomposition. Chem Lett 2001 30 1186-1187. 

The following discussion will be concerned primarily with applications of the ms/ms technique in the synfuel area. Attempts will be made to illustrate the unique capabilities of the ms/ms analysis with examples taken from our work on coal liquefaction products. Figure 5 shows the positive ion chemical ionization (PCI) mass spectrum of the coal liquid in question (SRC II mid heavy distillate, total bottoms). This spectrum is actually the normalized sum of approximately 500 individual mass spectra taken while the SRC II was thermally vaporized from a solids probe into the source of a mass spectrometer, and represents the molecular weight profile of this distillate fraction. Since isobutane Cl gives to a first approximation only protonated molecular ions (and no fragment ions), the peaks represent the individual components in the SRC II arranged incrementally by molecular weight. 

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