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847. Oxygen adsorption on tantalum and the effects of thermal desorption
Classified Classified
abstracts
846-960
abstracts on this page 846-855
Editor’s note The label immediately following the title of each item denotes country or origin of publication, that at the end of each abstract indicates country of origin of work (where known).
I.
General
vacuum
12. MEASUREMENT
science
and engineering
18. GASEOUS
OF LOW PRESSURES
12 846. Unity of measurements of pressure and hardness. (USSR) Metrological works in the fields of measurement of pressure and hardness are discussed. It is recommended that metrological work be divided into four regions: measurement of residual pressure from 0 to 16 x lo-’ Pa, measurement of absolute pressure from lo-* to 1 x lo5 Pa, barometry 0.57-1.0 x lo5 Pa and measurement of pressure differences from 0 to lo5 Pa. E F Dolinskiy et al, Izmerit Tekh, No 5, May 1972, 15-18 (in Russian). 16. GASES AND SOLIDS 16 847. Oxygen adsorption on tantalum and the effects of thermal desorption (Czechoslovakia) Oxygen adsorption on faces of single crystal tantalum is studied at 300 K using an electron emission microscope with a base pressure of 1 x 10m9 torr. Operation of the oxygen gun was monitored by an omegatron mass spectrometer. It is found that the average value of work function reaches 6.4 eV at maximum oxygen coverage. Oxygen is predominantly adsorbed on the (112) and (001) faces and it does not penetrate the crystal volume. On the (111) and (011) faces, the structure of tantalum changes with oxygen volume penetration. At large coverages the (101) and (110) faces appear. (Bulgaria) N Drandarov and V Kanev, Proc 5th Czech Conf Electron Vacuum Phys, Czech Acad Scienc Brno 1972, III b-2 (in Russian). 16 848. Investigation of the sorption process of oxygen on tungsten by the method of ionization of molecular beams. (USSR) Kinetics of oxygen adsorption on tungsten is investigated at residual pressure of lo- lo torr using the method of ionization of molecular beam. Optically polished tungsten polycrystalline discs with predominant (100) orientation, cleaned in vacuum of 10m9 torr at 2800 K, were used as target adsorbents. A two-stage adsorption mechanism is presented. The first stage of oxygen adsorption from the molecular beam is characterized by localized adsorption at which the adsorption probability is equal to unity at free adsorption centres (tungsten atoms) and equal to zero on occupied centres. The adsorption rate continuously decreases as the coverage degree increases. At the second stage, the adsorption probability is equal to unity and the mechanism of nonlocalized adsorption takes place. Physically adsorbed molecules migrate on surface until they find a free site for chemisorption. Ya P Zingerman, Fiz Tverd Tela, 14 (l), 1972, 285-288 (in Russian). 16 849. Barium adsorption on platinum. (USSR)
Barium adsorption on platinum and work function of the film system obtained are investigated in a field electron microscope. Surface of the emission point was cleaned by prolonged heating in vacuum of 1 to 2 x 10e9 torr at 1450°C. Barium coverage arising from migration of adsorbed atoms at 1050 K reduces the work function to 3.1 + 0.1 eV. This value remains constant after increase of coverage. This result is explained by reactive diffusion of barium in platinum and by formation of an intermetallic compound. The activation energy of barium surface diffusion on platinum in the region of (111) faces is measured to be 1.0 f 0.2 eV. Yu V Zubenko, Fiz Tverd Tela, 14 (I), 1972, 454-457 (in Russian).
and
ELECTRONICS
18 850. Low-energy study of Of + N2 + NO+ + N*. (USA) Laboratory-energy distributions of NO+ were measured for the above reaction with a merging-beams apparatus over a range of interaction energy W from 0.05 to 15 eV. Absolute and relative cross sections as a function of internal energy of the reactants (N2 was always in the ground electronic state), information on the partition of available energy into translational and internal energy of the products, and some information on the angular scattering of NO+ in the centre-of-mass were obtained from the measured distributions. The results verify some previously observed flowing-afterglow data which indicate a large enhancement of the reaction cross section at thermal energies due to vibrational excitation of N,. The mergingbeams apparatus is described in detail. R H Neynabee and G D Magnuson, J Chem Phys, 58 (lo), 15th May 1973,4586-4598.
18 851. Separation of plasma cluster moving at an angle with respect to the axis of a coaxial source. (USSR) It is experimentally shown that in a large vacuum chamber separation of a plasma cluster moving at an angle with respect to the axis of a coaxial plasma source is possible. Parameters of this cluster do not differ from those of a cluster moving along the axis of the source. A G Flelikov et al, Zh Tekh Fir, 42 (6). June 1972, 1325-1327 (in Russian). 18 852. Spectral investigation of field electron emission of CdS single
crystals in impulse and stationary regimes. (USSR) Comparative investigations of spectra1 characteristics of field photoelectron emission of CdS single crystals have been performed in impulse and stationary regimes. All experiments have been performed in vacuum of less than 10m9 torr at room temperature. B V Novikov et al, Fiz Tverd Tela, 14 (l), 1972, 19-23 (in Russian). 18 853. The heats of evaporation of atoms and ions of alkali metals and
their ionization coefficients on the surface of silicon single crystals. (USSR) The heats of evaporation of atoms and ions of Cs, K and Na and their ionization coefficients on (111) face of single crystal silicon are measured. E F Chaykovskiy and L I Kaysheva, Zh Tekh Fiz, 42 (6), June 1972, 1315-1316 (in Russian). 18 854. Influence of the space charge of relativistic electrons on field
electron emission. (USSR) Field cathodes can be used as sources of electrons for powerful and stable electron beams with currents of 10“ to lo6 A and electron energy up to several tens of MeV. Influence of the space charge of relativistic electrons on the field electron emission into vacuum is considered. Calculations are performed for the case of a spherical diode. L M Baskin et al, Zh Tekh Fiz, 42 (6). June 1972, 1282-1287 (in Russian). 18 855. Motion of plasma clusters in a multipole magnetic field of toroidal
configuration. (USSR) The processes .accompanying motion of plasma clusters in octupole magnetic field of toroidal configuration are investigated. It is found that plasma flux can be purified from natural gas and heavy ion 463
abstracts
846-960
abstracts on this page 846-855
Editor’s note The label immediately following the title of each item denotes country or origin of publication, that at the end of each abstract indicates country of origin of work (where known).
I.
General
vacuum
12. MEASUREMENT
science
and engineering
18. GASEOUS
OF LOW PRESSURES
12 846. Unity of measurements of pressure and hardness. (USSR) Metrological works in the fields of measurement of pressure and hardness are discussed. It is recommended that metrological work be divided into four regions: measurement of residual pressure from 0 to 16 x lo-’ Pa, measurement of absolute pressure from lo-* to 1 x lo5 Pa, barometry 0.57-1.0 x lo5 Pa and measurement of pressure differences from 0 to lo5 Pa. E F Dolinskiy et al, Izmerit Tekh, No 5, May 1972, 15-18 (in Russian). 16. GASES AND SOLIDS 16 847. Oxygen adsorption on tantalum and the effects of thermal desorption (Czechoslovakia) Oxygen adsorption on faces of single crystal tantalum is studied at 300 K using an electron emission microscope with a base pressure of 1 x 10m9 torr. Operation of the oxygen gun was monitored by an omegatron mass spectrometer. It is found that the average value of work function reaches 6.4 eV at maximum oxygen coverage. Oxygen is predominantly adsorbed on the (112) and (001) faces and it does not penetrate the crystal volume. On the (111) and (011) faces, the structure of tantalum changes with oxygen volume penetration. At large coverages the (101) and (110) faces appear. (Bulgaria) N Drandarov and V Kanev, Proc 5th Czech Conf Electron Vacuum Phys, Czech Acad Scienc Brno 1972, III b-2 (in Russian). 16 848. Investigation of the sorption process of oxygen on tungsten by the method of ionization of molecular beams. (USSR) Kinetics of oxygen adsorption on tungsten is investigated at residual pressure of lo- lo torr using the method of ionization of molecular beam. Optically polished tungsten polycrystalline discs with predominant (100) orientation, cleaned in vacuum of 10m9 torr at 2800 K, were used as target adsorbents. A two-stage adsorption mechanism is presented. The first stage of oxygen adsorption from the molecular beam is characterized by localized adsorption at which the adsorption probability is equal to unity at free adsorption centres (tungsten atoms) and equal to zero on occupied centres. The adsorption rate continuously decreases as the coverage degree increases. At the second stage, the adsorption probability is equal to unity and the mechanism of nonlocalized adsorption takes place. Physically adsorbed molecules migrate on surface until they find a free site for chemisorption. Ya P Zingerman, Fiz Tverd Tela, 14 (l), 1972, 285-288 (in Russian). 16 849. Barium adsorption on platinum. (USSR)
Barium adsorption on platinum and work function of the film system obtained are investigated in a field electron microscope. Surface of the emission point was cleaned by prolonged heating in vacuum of 1 to 2 x 10e9 torr at 1450°C. Barium coverage arising from migration of adsorbed atoms at 1050 K reduces the work function to 3.1 + 0.1 eV. This value remains constant after increase of coverage. This result is explained by reactive diffusion of barium in platinum and by formation of an intermetallic compound. The activation energy of barium surface diffusion on platinum in the region of (111) faces is measured to be 1.0 f 0.2 eV. Yu V Zubenko, Fiz Tverd Tela, 14 (I), 1972, 454-457 (in Russian).
and
ELECTRONICS
18 850. Low-energy study of Of + N2 + NO+ + N*. (USA) Laboratory-energy distributions of NO+ were measured for the above reaction with a merging-beams apparatus over a range of interaction energy W from 0.05 to 15 eV. Absolute and relative cross sections as a function of internal energy of the reactants (N2 was always in the ground electronic state), information on the partition of available energy into translational and internal energy of the products, and some information on the angular scattering of NO+ in the centre-of-mass were obtained from the measured distributions. The results verify some previously observed flowing-afterglow data which indicate a large enhancement of the reaction cross section at thermal energies due to vibrational excitation of N,. The mergingbeams apparatus is described in detail. R H Neynabee and G D Magnuson, J Chem Phys, 58 (lo), 15th May 1973,4586-4598.
18 851. Separation of plasma cluster moving at an angle with respect to the axis of a coaxial source. (USSR) It is experimentally shown that in a large vacuum chamber separation of a plasma cluster moving at an angle with respect to the axis of a coaxial plasma source is possible. Parameters of this cluster do not differ from those of a cluster moving along the axis of the source. A G Flelikov et al, Zh Tekh Fir, 42 (6). June 1972, 1325-1327 (in Russian). 18 852. Spectral investigation of field electron emission of CdS single
crystals in impulse and stationary regimes. (USSR) Comparative investigations of spectra1 characteristics of field photoelectron emission of CdS single crystals have been performed in impulse and stationary regimes. All experiments have been performed in vacuum of less than 10m9 torr at room temperature. B V Novikov et al, Fiz Tverd Tela, 14 (l), 1972, 19-23 (in Russian). 18 853. The heats of evaporation of atoms and ions of alkali metals and
their ionization coefficients on the surface of silicon single crystals. (USSR) The heats of evaporation of atoms and ions of Cs, K and Na and their ionization coefficients on (111) face of single crystal silicon are measured. E F Chaykovskiy and L I Kaysheva, Zh Tekh Fiz, 42 (6), June 1972, 1315-1316 (in Russian). 18 854. Influence of the space charge of relativistic electrons on field
electron emission. (USSR) Field cathodes can be used as sources of electrons for powerful and stable electron beams with currents of 10“ to lo6 A and electron energy up to several tens of MeV. Influence of the space charge of relativistic electrons on the field electron emission into vacuum is considered. Calculations are performed for the case of a spherical diode. L M Baskin et al, Zh Tekh Fiz, 42 (6). June 1972, 1282-1287 (in Russian). 18 855. Motion of plasma clusters in a multipole magnetic field of toroidal
configuration. (USSR) The processes .accompanying motion of plasma clusters in octupole magnetic field of toroidal configuration are investigated. It is found that plasma flux can be purified from natural gas and heavy ion 463