478. Kinetics of oxygen chemisorption on iridium

Classified abstracts 472--480 denum filament, recrystallized by heating in vacuum with the (100) face exposed, was used in the experiments. Heating of the filament above 1900°K results in the complete removal of adsorbed particles from the surface, and atomically clean surfaces with a secondary ion current of only Mo + are obtained. The oxygen pressure was varied in the range 5 x 10 -s to 1 x 10 -9 torr. Increase of oxygen pressure results in a decrease of the latent period (the time interval between beginning of oxygen adsorption and the moment of oxide formation on molybdenum surface), a decrease in the time necessary for formation of an equilibrium oxide layer on the surface, and an increase in oxide concentration. State of the surface film, composition, and oxide concentrations are reproducible and reversible with varying temperature and oxygen pressure. This effect indicates that the oxide film is formed by a layer of surface oxides. V Ya Kolot et al, Fiz Tverd Tela, 13 (6), 1971, 1521-1524 (in Russian). 16 472. Oxygen interaction with (0001) rhenium face. (USSR) Interaction of oxygen with the closest packed (0001) face of rhenium single crystal was investigated by the methods of low-energy electron diffraction and work function changes of the surface. Changes of the work function of surface at oxygen adsorption were determined from displacement of volt-ampere characteristics in the retarding-field region. The experiments were performed in a sealed device, attaining 1 × 10-9 torr after evacuation and evaporation of titanium and molybdenum getters. Oxygen adsorption on rhenium at room temperature results in a 0.9 eV increase in the work function and in the appearance of diffraction patterns corresponding to the (2 × 2) structure. Heating the adsorbed layers to 300°C reduces the work function and enhances the intensity of additional reflexions. A comparison of measurements of work function of the system substrate-film, structure of surface, and intensity of reflexions is made over a broad temperature interval and at different degrees of coverage. It is shown that formation of the (2 × 2) structure occurs with the introduction of oxygen atoms into the surface layer of rhenium and with its reconstruction. D A Gorodetskiy and A N Knysh, Fiz Tverd Tela, 13 (9), 1971, 25212526 (in Russian). 16 473. Thermodynamics of monoatomic adsorbed films. (USSR) Two models of monoatomic films adsorbed on crystalline surfaces are considered. In the first model it is supposed that atoms are adsorbed at fixed positions of two types differing in adsorption energy; interaction of adsorbed atoms has the form of attraction at a distance. In the other model, all position of atom arrival are equivalent (interaction of adsorbed atoms has the form of dipole-dipole repulsion). The effect of mutual depolarization is taken into account. Using a self-consistent field method, equations of state of monolayers and curves of loss of stability are obtained. The existence of three phases in the first model and of two phases in the second model is shown. The phase transitions between these phases are of the first kind. The results of calculations are compared with published experimental data. The applicability of the SCF method is evaluated. The analysis o f these models leads to qualitative conclusions on the thermodynamics of certain types of films and on the phase transitions in them. L A Bolshov, Fiz Tverd Tela, 13 (6), 1971, 1679-1684 (in Russian). 16 474. Kinetics of carbon monoxide sorption by bulk titanium. (USSR) The sorption kinetics of carbon monoxide by bulk titanium, in the temperature range 400 to 700°C and pressure range of 5 × 10 -~ to 5 x 10 -5 torr, are presented. Values of the basic constants in the equation describing kinetics of sorption process are determined. Approximative calculations of the carbon monoxide sorption by bulk titanium in dependence on temperature, pressure and sorption time are proposed. S P Zholobov et al, Electronic Technology, Scient-Techn Collect, Receiving Tubes, No 1, 1971, 20-28 (in Russian). 16 475. Sorption kinetics of oxygen-containing gases at low pressures. (USSR) On the basis of analysis of interaction of surface and bulk phenomena, an adsorption-diffusion model of sorption of oxygen containing gases is presented. The model explains the known kinetic characteristics of sorption in all stages, and it gives boundary conditions of transition from one stage of sorption to another. A method of approximative calculation of sorption rates in electro-vacuum

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devices, during their manufacture and use, is presented which is based on the considered sorption model. C P Zholobov, Electronic Technology, Scient-Techn Collect, Receiving Tubes, No 1, 1971, 3-10 (in Russian). 16 476. Influence of carbon concentration in titanium on the sorption of carbon monoxide. (USSR) The experimental data on the dependence of the carbon monoxide sorption rate on the carbon concentration in titanium, are presented. The sorption rate was measured by the method of pressure drop on a calibrated capillary connecting the working volume with the gas inlet system. It is shown that the sorption rate of carbon monoxide by titanium at investigated temperatures considerably depends on the volume concentration of carbon in titanium. At carbon content of 0.05 weight per cent in titanium, the original sorption rate remains unchanged. I G Domakhin et al, Electronic Technology, Scient-Techn Collect, Receiving Tubes, No 1, 1971, 110-115 (in Russian). 16 477. The problem of the coefficient of thermal accommodation. (USSR) In the preparation of films from various materials for microelectronics, it is necessary to vary the deposition rate of materials over a broad range. It is useful to know the value of the thermal accommodation coefficient and its dependence on the evaporation conditions: the deposition rate and the surface temperature. When the deposition rate is reduced below the critical value, evaporation of the previously deposited film takes place. In the deposition of materials, the substrates are heated from 400 to 500°C depending on the deposition rate. It is necessary to take account of the surface temperature in calculations of film thickness. M M Nekrasov and A G Zaporozhets, Problems of Microelectronics, Collect, Kiev Naukovaya Dumka 1971, 179-181 (in Russian). 16 478. Kinetics of oxygen chemisorption on iridium. (USSR) Using the flash filament method together with a time-of-flight mass spectrometer, the kinetics of oxygen interaction with iridium is investigated. Textured iridium filaments with predominantly (111) face surfaces were used in the experiments. Cleaning from carbon impurity was by heating the filaments at 1900°K in an oxygen partial pressure of 3 × 10-" torr for several hours. The pressure of residual gases in the experimental device was about 10-9 torr. It is shown that oxygen is adsorbed on iridium in the atomic form in two adsorption states and it is thermally desorbed in the form of molecules. The activation energies of oxygen desorption and the pre-exponential factors in the kinetic equation of desorption are determined for both adsorption states. Dependence of the sticking coeffÉcient of oxygen on iridium on the degree of coverage is also obtained. A model of twophase adsorption is presented which enables one to explain the complex character of the experimental dependence of the sticking coefficient on the degree of coverage. V N Ageev and N I Ionov, Zh Tekh Fiz, 41 (10), Oct 1971, 2196-2202

(in Russian). 16 479. Simultaneous sorption of He and H2 by layers of condensed gases at 4.2°K. (USSR) The simultaneous sorption of helium and hydrogen by layers of condensed argon and nitrogen was investigated at 4.2°K in the pressure range 10-3 to 10 -9 torr. Sorption isotherms of helium and hydrogen by argon and nitrogen layers are measured for the case when the layers previously absorbed a determined quantity of hydrogen or nitrogen. It is found that the helium capacity of a layer is reduced with increasing amount of previously absorbed hydrogen. The curves of equilibrium of phases of helium and hydrogen are constructed from the results of measurements. It is shown that during simultaneous sorption, a region of helium and hydrogen concentrations exists, for which the equilibrium helium pressure is below 10-s torr which is important for practical application of condensed gas sorption of helium. Substitution of helium from the layer by hydrogen is observed at 4.2°K and 10-3 to 10-" torr. V B Yuferov and P M Kohzev, Zh Tekh Fiz, 40 (12), 1970, 2598-2600

(in Russian). 16 480. Rare gas diffusion in alkali metal iodides. (Germany) Xenon-133 diffusion coefficients were measured in single crystals of KI, RbI and CsI over the temperature range of 150 to 500°C. Xenon was incorporated in the crystals both by doping with precursor 1133