Effusion cells

For comparison, Battles et al. (15) determined the partial heats of sublimation of Pu02(g) and Pu0(g) above PuOi.33 over the temperature range 1937 to 2342 K by means of mass spectrometric measurements with Iridium effusion cells. The absence of Iridium oxides or Iridium species In the vapor phase Indicated that Iridium was nonreducing toward plutonia. The partial heats of sublimation calculated from the slopes of the temperature dependency data yielded values of 127.1 1.2 and 138.8 1.6 kcal/mol for Pu0(g) and Pu02(g) ... 

Spectrometric measurements, mass, with irridium effusion cells, heats... 

Finally, it should be mentioned that the unstable species may be generated in a matrix by co-condensation of metal atoms evaporated from the effusion cells and stable molecules diluted with an excess of inert gas. Equation (3) represents an example. 

Simpler methods of generation of intermediates in the gas phase are the thermal ones. The thermal reactions are carried out either in Knudsen effusion cells under equilibrium conditions or in flow reactors at very low pressure. Effusion cells are widely applied for the evaporation of monomeric... 

Matrix Raman spectroscopy allows detection of some additional vibrations which are inactive in IR spectra (e.g. symmetrical vibrations vi in AB3 molecules having 3 symmetry) or which tie in the far infrared region. In practice, matrix-isolated organic intermediates have not been studied by Raman spectroscopy the main objects of these investigations are inorganic molecules (AICI3, PbS, Gep2, SiO, etc.) which are evaporated from solids in effusion cells. 

Figure 10.10 Schematic representation of a Knudsen effusion cell.

Knudsen cells (effusion cells) are exclusively used for vapor pressure measurements (see vapor pressure) in the pressure range from 1 torr to 10-6 torr. In the low temperature range (—20° — +400 °C) pyrex glass cells are applicable. Especially the vapor pressures of dyes, organic compounds can be measured in such cells, because metal cells may sometimes cause catalytic decompositions of the investigated materials. 

Fig. 34. Vapor pressure of benzoic acid measured on a thermobalance with Knudsen effusion cell...

A sketch of the polished Dural effusion cell used in Ref 17 is shown in Fig 3. Two such cells were used with knife edge orifices of diameter 0.602 1.012mm and length of 0.1104 and 0.1132mm, respectively... 

In molecular beam epitaxy (MBE) [317], molecular beams are used to deposit epitaxial layers onto the surface of a heated crystalline substrate (typically at 500-600° C). Epitaxial means that the crystal structure of the grown layer matches the crystal structure of the substrate. This is possible only if the two materials are the same (homoepitaxy) or if the crystalline structure of the two materials is very similar (heteroepitaxy). In MBE, a high purity of the substrates and the ion beams must be ensured. Effusion cells are used as beam sources and fast shutters allow one to quickly disrupt the deposition process and create layers with very sharply defined interfaces. Molecular beam epitaxy is of high technical importance in the production of III-V semiconductor compounds for sophisticated electronic and optoelectronic devices. Overviews are Refs. [318,319],... 

The CdS/ZnO interface is of particular importance in Cu(In,Ga)Se2 thin film solar cells because it is used in the standard cell configuration (Fig. 4.2). A first experimental determination of the band alignment at the ZnO/CdS interface has been performed by Ruckh et al. [102]. The authors have used ex-situ sputter-deposited ZnO films as substrates. The interface formation was investigated by stepwise evaporation of the CdS compound from an effusion cell. Photoelectron spectroscopy revealed a valence band offset of A Vb = 1.2eV. An identical value of 1.18eV has been derived using first-principles calculations [103]. With the bulk band gaps of CdS and ZnO of 2.4 and... 

Figure 3. Improved effusion cell for vapor pressure measurement...

Knudsen Effusion cell Knudsen Effusion cell... 

With tantalum effusion cells, the results of Ackermann et al. (16) are virtually identical with the earlier work of Phipps et al. (19) (1593-2063 K) and yielded total vapor pressure values of plutonium-bearing species which were considerably higher (by approximately a factor of ten) than those obtained with the less reducing tungsten (as well as Re and Ir) cells. Ackermann et al. (16) correlated the vapor pressure results obtained with tantalum effusion cells with the univariant diphasic system consisting of Pu203(s)-PuOi,51(s) as the condensed phases and PuO(g) as the primary gaseous species. 

J) 10 W cm the species were the most stable cluster ions with the highest intensities in LIMS. The influence of laser power density is illustrated in Figure 9.56 At low laser power density small clusters (C3) are observed to have the highest intensity. The abundance distribution in laser evaporation is similar to that observed from thermal vaporization in Knudsen effusion cells with the following abundance sequence (C3 > C2 > >> C5 > 4)." By increasing the laser power... 

To examine the processes of cluster formation in the gas phase a Knudsen Cell has been used. A mixture of ZnO and graphite powders was positioned inside the effusion cell. The carbothermal reaction between ZnO and graphite was used to create zinc vapor. The effusion cell was heated up to a temperature above 1000°C. 

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