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947. Emission properties of thin film tunnel cathodes
Classified
abstracts
936-947
16 936. Electron impact desorption of carbon monoxide from tungsten. (Italy)* It has been established that CO is adsorbed on tungsten in at least three different states of binding. By measurement of desorbed ion currents, the ion energy distribution was derived and used to estimate the relative populations in the adsorbed states. Desorption crosssections are in reasonable agreement with values from the work of others, but show significant difference between the values for CO cross-sections on tungsten and molybdenum. It is considered that the experimental evidence indicates a larger electron impact desorption cross-section for molybdenum than for tungsten, despite the similarity in crystal structure. (Canada) P A Redhead, Nuovo Cimento Suppl, 5 (2), 1967, 586-597. 16 937. Instructions between low-energy electrons and adsorbed carbon monoxide. (Italy)* Desorption from carbon monoxide adlayers on molybdenum were investigated using a resonant-ion mass spectrometer device employing 5 grids and allowing direct mass analysis of desorbed ions. At CO pressures of 1O-4 newtons/ma, Of and CO+ ions were clearly recognized in the spectrum arising from 100 eV electron bombardment. Measurements of the energy losses of 20 eV impinging electrons and surface potential measurements were consistent with previous data obtained on the adsorption kinetics of CO on transition metals. (France) D ADegras and J Lecante, Nuovo Cimento Suppl, 5 (2), 1967,598 -605. 16 938. Interaction of electrons with adsorbed water. (Italy)+ The effects of low-energy electron bombardment of polycrystalline nickel and tungsten ribbons, during exposure to water, was investigated by the dynamic sorption method. Mass spectrometric measurements indicated that the water disappears and molecular hydrogen and oxygen are desorbed. The results for tungsten indicate that atomic oxygen is also evolved. The investigational method allows study of electronic desorption under steady-state conditions and measurement of the adsorption properties of the metals. Water pressure ranged from 10-O to 1O-Btorr and electron current densities from 1O-5 to lO-p A/cm?. The metal ribbon temperature rose to 200°C after bombardment with 10-a A/cm2 at 400 V and all measurements were performed at this temperature. (Germany) A Klopfer, Nuovo Cimento Suppl, 5 (2), 1967, 606-611. 16 : 18 939. Thermoelectron emission from tungsten in a stream of Ba and Cs atoms. (USSR) A method is described for the investigation of thermoelectron emission from a metal simultaneously under the action of two streams of neutral atoms. In this way, the emission from tungsten for barium streams of 5 x 10ia to 1Ol6 at/cm%ec and caesium streams of 4 x 1Ol5 to 5x 10” at/cm%ec was determined. The emission proaerties of tungsten are primarily determined by the barium atoms and only a weak caesium influence was observed. V G Baxanov et al, Fiz Tverd Telu, 10 (2), Feb 1968, 507-512 (in Russian). 16 940. Study of potassium ion adsorption on molybdenum surfaces. (USSR) By means of a modulated atomic beam, the desorption temperatures for positive potassium ions from polycrystalline molybdenum surfaces were determined. They were found to increase linearly from 1.82 eV at 950°K to 2.1 eV at 1200°K. N G Ban’kovskiy et al, Fiz Tverd Tela, 10 (l), Jan 1968, 153-158 (in Russian). 17. THERMODYNAMICS 17 941. Study of thermal dissociation of alkaline-earth oxides ln high vacuum. (USSR) BaO and SrO samples were heated at 1O-s torr and the components of evaporation were analyzed by a mass spectrometer. For barium oxide, the predominant component is BaO with an evaporation rate of about 2x lo-* g.cm-2sec-1 at 1300°K. Quantities of evaporated Ba and 0, are only of several per cent of the BaO and the ratio of evaporated Ba molecules to 0, molecules is about 2 at 1150°K. At higher temperatures the BaO sample is enriched by barium as 426
oxygen evaporates more rapidly until some equilibrium state is reached. Strontium oxide is evaporated much more slowly with basic components Sr and 0, but the character of the process is the same as for BaO. G Ya Pikus et al, Fiz Tverd Telu, 10 (l), Jan 1968, 125-134 (in Russian). 17 942. Electronographic study of a thermally treated corundum surface. (USSR) The influence of therma treatment on a corundum surface Iayer damaged by mechanical processing was investigated by means of electronography. Corundum was baked at 1O-6 torr or in inert atmosphere at temperatures of up to 2100°C. Comparing difraction pictures with the curves of evaporation at different temperatures it is shown that the basic process occurring during thermal treatment is recrystallization of the damaged layer, and not evaporation. S A Semiletov et al, Fiz Tverd Tela, 10 (l), Jan 1968, 71-76 (in Russian). 18. GASEOUS ELECTRONICS 18 : 16 Field emission studies of oxygen, hydrogen and nitrogen by a molybdenum tip. See abstract number 930. 18 : 16 Thermoelectron emission from tungsten in a stream of Ba and Cs atoms. See abstract number 939. 18 : 16 943. Inert gas ion bombardment induced work function changes In polycrystalline tungsten and gold ribbon. (Great Britain) Polycrystalline tungsten and gold ribbon targets were bombarded with low-energy (100 eV-600 eV) inert gas ions of helium, argon and krypton. The thermionic work function of the target was monitored before and after bombardment by a retarding potential field method in a diode valve with the target as the anode. Work function recovery was monitored during post-bombardment stop annealing studies. Bombardment-induced work function increases of several tenths of an electron volt in tungsten were recovered in annealing stages corresponding to surface vacancy migration and gas release from the surface regions. Smaller work function reductions in gold targets were annealed in stages corresponding to damage diffusion, normal diffusion and gas diffusion processes. R P W Lawson and G Carter, Vacuum, 18 (4), April 1968.205-211. 18 944. Discrimination and amplification of difference frequency in a plasma waveguide, by an electron beam. (USSR) Discrimination and amplification of difference frequency is theoretically analyzed for plasma excited in a waveguide by the passage of an electron beam through a neutral gas. N Ya Kotsarenko and A M Fedorchenko, Rudiotekh Elektron, 12 (12), 1967, 2162-2170 (in Russian) 18 945. Determination of the effective emitting surface of an oxide cathode. (USSR) By a method employing a longitudinal magnetic field for measurement of the effective emitting surface of oxide cathodes, it was found that for porous oxide coatings with a small accelerating voltage near to the surface, the emission may be 4 times higher than that from non-porous cathodes with the same work function. This effect is caused by extraction of electrons from the pores. The possibility of emission current control outside of the space-charge limited region by a small accelerating voltage in the vicinity of the cathode surface, is discussed. M V Krasin’kova et al, Radiotekh Elektron, 12 (12), 1967, 2197-2206 (in Russian). 946. The work function of alloys of rhenium with scandium. (USS: Thermionic emission work functions of 3.0 eV and 3.35 eV were measured for rhenium-scandium alloys containing 0.8 and 5 per cent of scandium respectively. A minimal value of 2.85 eV was determined at 30 per cent scandium. Below 1600°K no influence of temperature was observed. A A Gugnin and 0 Kb Khamidov, Radiotekh Elektron, 12 (12), 1967, 2270 (in Russian). 18 947. Emission properties of thin film tunnel cathodes. (USSR) Thin film systems of Cr-SiO$-Al and Ni-Al,O,-Au were prepared by
Classified
abstracts
949-961
pyrolytic dissociation of organic compounds under vacuum and their emission properties were measured. For voltages of 0 to 10 V, characteristics with a region of N-type negative resistance were found. The higher-voltage regions may be described by the exponential law. V F Korzo and P S Kiev, Radiotekh Elektron, 12 (12). 1967, 22732274 (in Russian). 18 948. On some peculiarities of the transfer of rotational and vibrational energies ln ion-molecular collisions. (USSR) Nitrogen at a pressure of 2 x 10-l to 5 x 1O-i torr was bombarded by Li+, Na+, KC, He+, Ne+ and Ar+ ions with energies of 0.7 to 25 keV and the distribution of Na+ ions in an excited state was investigated to explain the mechanism of the energy transfer in ion-molecular collisions. G N Polyakova et al, Zh Eksper Teor Fir, 54 (2), Feb 1968. 374-383 (in Russian). 18 : 31 949. On triggered discharge in a vacuum gap switching pulse currents up to 150 kA with a frequency of 1 MHZ. (USSR) A vacuum switch is described which is used for obtaining current pulses by means of discharging a capacitor with a voltage of 60 kV in damping oscillations with a frequency of 1.25 MHz and peak current of 165 kA. The influence of the method of triggering the discharge on the delay time is discussed. P N Dashuk et al, Izv VUZ Fiz, 11 (l), 1968, 11-16 (in Russian). 950. The influence of neutral gas temperature on the parameters of ionixation waves in neon. (Czechoslovakia) Experiments were carried out in which the neutral gas in the positive column of a dc glow discharge in neon was cooled to 77°K. The effect of the cooling on the group velocity, phase velocity, frequency and relaxation time of p, r and s waves and on the lifetime of metastable atoms in the ionization waves was investigated. K Masek and V Perina, Czech .I Phys, B18 (3), 1968, 363-375 (in English). 18 : 31 951. Ascertaining the causes of undesirable thermal emission. (Czechoslovakia) Possible causes of thermal emission of the electrode material used in the construction of high power transmitting tubes was experimentally investigated. Polishing of MO parts in solution of CrO,+H,PO, may be recommended but impurity residues from various alkaline baths and especially from atmosphere containing alkaline earth carbonates strongly influence the thermionic emission of MO and W grids. For tubes with thoriated tungsten cathodes, zirconium silicide antiemission coating was successfully employed but tubes with tungsten cathodes must be baked at 1450°C under vacuum or in pure hydrogen. P Schneider and P Hix, Slabopr Obzor, 29 (3), March 1968, 158-162 (in Czech). 18 952. Study of field dependent secondary electron emission from MgO porous layers. (USSR) Anomalous secondary electron emission from MgO layers was investigated at room and liquid nitrogen temperatures. The noninertial component of the emission is independent of temperature changes but the field dependent emission is higher at higher temperatures and sharply increases with increase of emitter-to-collector voltage. N L Yasnopol’skiy and A E Shabel’nikova, Fiz Tverd Tela, 10 (1), Jan 1968, 103-107 (in Russian). 18 953. On the sputtering mechanism of solids. (USSR) Comparing measured values of the sputtering coefficients of polycrystalline Zr and ZrC and of MO, W and MO-W alloy bombarded by 5 to 17 keV Ar+ ions at 6x 1O-a torr, it is shown that the same mechanism of sputtering operates for the pure metals and for their carbides or alloys. This fact cannot be explained by the theory of focusons but is accommodated by the Lehman theory of cascades of collisions. B M Gurmin et al, Fiz Tverd Tela, 10 (2). Feb 1968, 411-414 (in Russian). 954. Elastic retlection of electrons from silicon single crystals. (USS: After baking at 1250°C at 5 x lo-’ torr and at 1100°C at 5 x 10-O torr the coefficient of electron elastic reflection was measured for primary energies of 20 to 1000 eV. Two peaks were found at 45 and at 75 eV
and at higher energies the value of the coefficient decreases. A 30-hour adsorption of residual gases at 1 x lo-’ torr increases the coefficient values at peaks by about 33 per cent without effect on the character of the dependence. A R Shul’man et al, Fiz Tverd Tela, 10 (2), Feb 1968, 655-656 (in Russian). 18 955. Current growth in sparks in the p&e breakdown of short wcuurn gaps. (USSR) A theory explaining the mechanism of the current growth stage of vacuum breakdown is presented and experimentally verified. The effect of increasing the delay time at higher overvoltages in the same gap is discussed in detail. G A Mesyats and D I Proskurovskly, Zzv VUZ Fir, 11 (l), 1968,81-85 (in Russian). 18 956. Exoelectron emission of germaninrn and silicon. (USSR) The possibility of exploitation of the effect of exoemission for the investigation of microdefects on Ge and Si surfaces is discussed. V I Kryuk et al, Zzv VCJZFiz, 11 (l), 1968, 118-122 (in Russian). 18 957. Angular dependence of energy spectra of secondary ions scattered by the surface of single crystals. (USSR) Molybdenum single crystal faces (100) and (110) were bombarded by positive potassium ions with energies of 25 to 5000 eV and the energy spectra of secondary ions were measured. The characteristics are connected with multiple collisions of incident ions with crystal atoms and the decrease of the scattering angle leads to an increase in the number of repeatedly colliding ions. U A Arifov and A A Aliev, Zh Eksper Teor Fiz, 54 (2). Feb 1968,354361 (in Russian). 18 958. Studies of the nitrogen afterglow. I. Surface catalytic efllciency and diiusion-controlled decay of atomic nitrogen. (USA) The temporal behavior of the afterglow light intensity in decaying nitrogen plasmas, as well as that of the number density of N+, NI+, N3+ and N,+ ions was studied in the pressure range of about 0.1 to 1.7 torr. Analysis of the light intensity decay curves gave values of the surface catalytic efficiency yN for the recombination of nitrogen atoms at the plasma boundary. The use of a quadrupole mass spectrometer ensured that the data related to pure nitrogen as well as to extremely clean surfaces. Values of YNfor molybdenum sputtered on a clean glass surface decreased with pressure from a value of 0.22 at 0.09 torr to 0.04 at 1.35 torr. R E Land and H J Oskam, .I Chem Phys, 48 (1). 1st Jan 1968,109-l 15. 18 959. calculation of three-body ionic recombination rate. (USA) The three-body ionic recombination rate at low densities is calculated for a slightly ionized gas by considering that the relaxation of the energy of molecules occur by a “diffusion” process. The effective conductivity in the equivalent diffusion equation is the second moment of the energy transfer. The moments are derived in closed form using classical mechanics and enable the recombination rate constant to be obtained. Good agreement with experimental data is found. S A Landon and J C Keck, J Chem Phys, 48 (l), 1st Jan 1968.374-380. 18 960. Energy dependence for single and double ionization by electron impact between 250 and 2200 eV. (USA) Studies have been made of Rb, Zn. Mg, NHs, NO, Nt. CO, COS, CS, and H,S. The results show that the direct double-ionization cro-L section (simultaneous ejection of two electrons) can be written as a-E-t, where E is the energy of incident ions. When doubly charged ions are formed by the Auger effect, there is a departure from E-l dependence. The experiments show that molecular ions COS++ C&++, Has++ and NH,++ can be formed by the Auger effect. The single-ionization cross section is shown to satisfy the usual dependence Cc-E-l log BE. The equipment and techniques used are described in a previous publication to which reference is made. F Fiquet-Fayard et al, J Chem Phys, 48 (1), 1st Jan 1968,478-482. 18 961. Threshold electron impact excitation of atoms and molecules: detection of triplet and temporary negative ion states. (USA) A technique which utilizes SF, as a scavenger of low-energy electrons is employed to study the “threshold” excitation spectra of He, N., HCl, H,O, D,O and a number of aromatic molecules. For electrons 427
abstracts
936-947
16 936. Electron impact desorption of carbon monoxide from tungsten. (Italy)* It has been established that CO is adsorbed on tungsten in at least three different states of binding. By measurement of desorbed ion currents, the ion energy distribution was derived and used to estimate the relative populations in the adsorbed states. Desorption crosssections are in reasonable agreement with values from the work of others, but show significant difference between the values for CO cross-sections on tungsten and molybdenum. It is considered that the experimental evidence indicates a larger electron impact desorption cross-section for molybdenum than for tungsten, despite the similarity in crystal structure. (Canada) P A Redhead, Nuovo Cimento Suppl, 5 (2), 1967, 586-597. 16 937. Instructions between low-energy electrons and adsorbed carbon monoxide. (Italy)* Desorption from carbon monoxide adlayers on molybdenum were investigated using a resonant-ion mass spectrometer device employing 5 grids and allowing direct mass analysis of desorbed ions. At CO pressures of 1O-4 newtons/ma, Of and CO+ ions were clearly recognized in the spectrum arising from 100 eV electron bombardment. Measurements of the energy losses of 20 eV impinging electrons and surface potential measurements were consistent with previous data obtained on the adsorption kinetics of CO on transition metals. (France) D ADegras and J Lecante, Nuovo Cimento Suppl, 5 (2), 1967,598 -605. 16 938. Interaction of electrons with adsorbed water. (Italy)+ The effects of low-energy electron bombardment of polycrystalline nickel and tungsten ribbons, during exposure to water, was investigated by the dynamic sorption method. Mass spectrometric measurements indicated that the water disappears and molecular hydrogen and oxygen are desorbed. The results for tungsten indicate that atomic oxygen is also evolved. The investigational method allows study of electronic desorption under steady-state conditions and measurement of the adsorption properties of the metals. Water pressure ranged from 10-O to 1O-Btorr and electron current densities from 1O-5 to lO-p A/cm?. The metal ribbon temperature rose to 200°C after bombardment with 10-a A/cm2 at 400 V and all measurements were performed at this temperature. (Germany) A Klopfer, Nuovo Cimento Suppl, 5 (2), 1967, 606-611. 16 : 18 939. Thermoelectron emission from tungsten in a stream of Ba and Cs atoms. (USSR) A method is described for the investigation of thermoelectron emission from a metal simultaneously under the action of two streams of neutral atoms. In this way, the emission from tungsten for barium streams of 5 x 10ia to 1Ol6 at/cm%ec and caesium streams of 4 x 1Ol5 to 5x 10” at/cm%ec was determined. The emission proaerties of tungsten are primarily determined by the barium atoms and only a weak caesium influence was observed. V G Baxanov et al, Fiz Tverd Telu, 10 (2), Feb 1968, 507-512 (in Russian). 16 940. Study of potassium ion adsorption on molybdenum surfaces. (USSR) By means of a modulated atomic beam, the desorption temperatures for positive potassium ions from polycrystalline molybdenum surfaces were determined. They were found to increase linearly from 1.82 eV at 950°K to 2.1 eV at 1200°K. N G Ban’kovskiy et al, Fiz Tverd Tela, 10 (l), Jan 1968, 153-158 (in Russian). 17. THERMODYNAMICS 17 941. Study of thermal dissociation of alkaline-earth oxides ln high vacuum. (USSR) BaO and SrO samples were heated at 1O-s torr and the components of evaporation were analyzed by a mass spectrometer. For barium oxide, the predominant component is BaO with an evaporation rate of about 2x lo-* g.cm-2sec-1 at 1300°K. Quantities of evaporated Ba and 0, are only of several per cent of the BaO and the ratio of evaporated Ba molecules to 0, molecules is about 2 at 1150°K. At higher temperatures the BaO sample is enriched by barium as 426
oxygen evaporates more rapidly until some equilibrium state is reached. Strontium oxide is evaporated much more slowly with basic components Sr and 0, but the character of the process is the same as for BaO. G Ya Pikus et al, Fiz Tverd Telu, 10 (l), Jan 1968, 125-134 (in Russian). 17 942. Electronographic study of a thermally treated corundum surface. (USSR) The influence of therma treatment on a corundum surface Iayer damaged by mechanical processing was investigated by means of electronography. Corundum was baked at 1O-6 torr or in inert atmosphere at temperatures of up to 2100°C. Comparing difraction pictures with the curves of evaporation at different temperatures it is shown that the basic process occurring during thermal treatment is recrystallization of the damaged layer, and not evaporation. S A Semiletov et al, Fiz Tverd Tela, 10 (l), Jan 1968, 71-76 (in Russian). 18. GASEOUS ELECTRONICS 18 : 16 Field emission studies of oxygen, hydrogen and nitrogen by a molybdenum tip. See abstract number 930. 18 : 16 Thermoelectron emission from tungsten in a stream of Ba and Cs atoms. See abstract number 939. 18 : 16 943. Inert gas ion bombardment induced work function changes In polycrystalline tungsten and gold ribbon. (Great Britain) Polycrystalline tungsten and gold ribbon targets were bombarded with low-energy (100 eV-600 eV) inert gas ions of helium, argon and krypton. The thermionic work function of the target was monitored before and after bombardment by a retarding potential field method in a diode valve with the target as the anode. Work function recovery was monitored during post-bombardment stop annealing studies. Bombardment-induced work function increases of several tenths of an electron volt in tungsten were recovered in annealing stages corresponding to surface vacancy migration and gas release from the surface regions. Smaller work function reductions in gold targets were annealed in stages corresponding to damage diffusion, normal diffusion and gas diffusion processes. R P W Lawson and G Carter, Vacuum, 18 (4), April 1968.205-211. 18 944. Discrimination and amplification of difference frequency in a plasma waveguide, by an electron beam. (USSR) Discrimination and amplification of difference frequency is theoretically analyzed for plasma excited in a waveguide by the passage of an electron beam through a neutral gas. N Ya Kotsarenko and A M Fedorchenko, Rudiotekh Elektron, 12 (12), 1967, 2162-2170 (in Russian) 18 945. Determination of the effective emitting surface of an oxide cathode. (USSR) By a method employing a longitudinal magnetic field for measurement of the effective emitting surface of oxide cathodes, it was found that for porous oxide coatings with a small accelerating voltage near to the surface, the emission may be 4 times higher than that from non-porous cathodes with the same work function. This effect is caused by extraction of electrons from the pores. The possibility of emission current control outside of the space-charge limited region by a small accelerating voltage in the vicinity of the cathode surface, is discussed. M V Krasin’kova et al, Radiotekh Elektron, 12 (12), 1967, 2197-2206 (in Russian). 946. The work function of alloys of rhenium with scandium. (USS: Thermionic emission work functions of 3.0 eV and 3.35 eV were measured for rhenium-scandium alloys containing 0.8 and 5 per cent of scandium respectively. A minimal value of 2.85 eV was determined at 30 per cent scandium. Below 1600°K no influence of temperature was observed. A A Gugnin and 0 Kb Khamidov, Radiotekh Elektron, 12 (12), 1967, 2270 (in Russian). 18 947. Emission properties of thin film tunnel cathodes. (USSR) Thin film systems of Cr-SiO$-Al and Ni-Al,O,-Au were prepared by
Classified
abstracts
949-961
pyrolytic dissociation of organic compounds under vacuum and their emission properties were measured. For voltages of 0 to 10 V, characteristics with a region of N-type negative resistance were found. The higher-voltage regions may be described by the exponential law. V F Korzo and P S Kiev, Radiotekh Elektron, 12 (12). 1967, 22732274 (in Russian). 18 948. On some peculiarities of the transfer of rotational and vibrational energies ln ion-molecular collisions. (USSR) Nitrogen at a pressure of 2 x 10-l to 5 x 1O-i torr was bombarded by Li+, Na+, KC, He+, Ne+ and Ar+ ions with energies of 0.7 to 25 keV and the distribution of Na+ ions in an excited state was investigated to explain the mechanism of the energy transfer in ion-molecular collisions. G N Polyakova et al, Zh Eksper Teor Fir, 54 (2), Feb 1968. 374-383 (in Russian). 18 : 31 949. On triggered discharge in a vacuum gap switching pulse currents up to 150 kA with a frequency of 1 MHZ. (USSR) A vacuum switch is described which is used for obtaining current pulses by means of discharging a capacitor with a voltage of 60 kV in damping oscillations with a frequency of 1.25 MHz and peak current of 165 kA. The influence of the method of triggering the discharge on the delay time is discussed. P N Dashuk et al, Izv VUZ Fiz, 11 (l), 1968, 11-16 (in Russian). 950. The influence of neutral gas temperature on the parameters of ionixation waves in neon. (Czechoslovakia) Experiments were carried out in which the neutral gas in the positive column of a dc glow discharge in neon was cooled to 77°K. The effect of the cooling on the group velocity, phase velocity, frequency and relaxation time of p, r and s waves and on the lifetime of metastable atoms in the ionization waves was investigated. K Masek and V Perina, Czech .I Phys, B18 (3), 1968, 363-375 (in English). 18 : 31 951. Ascertaining the causes of undesirable thermal emission. (Czechoslovakia) Possible causes of thermal emission of the electrode material used in the construction of high power transmitting tubes was experimentally investigated. Polishing of MO parts in solution of CrO,+H,PO, may be recommended but impurity residues from various alkaline baths and especially from atmosphere containing alkaline earth carbonates strongly influence the thermionic emission of MO and W grids. For tubes with thoriated tungsten cathodes, zirconium silicide antiemission coating was successfully employed but tubes with tungsten cathodes must be baked at 1450°C under vacuum or in pure hydrogen. P Schneider and P Hix, Slabopr Obzor, 29 (3), March 1968, 158-162 (in Czech). 18 952. Study of field dependent secondary electron emission from MgO porous layers. (USSR) Anomalous secondary electron emission from MgO layers was investigated at room and liquid nitrogen temperatures. The noninertial component of the emission is independent of temperature changes but the field dependent emission is higher at higher temperatures and sharply increases with increase of emitter-to-collector voltage. N L Yasnopol’skiy and A E Shabel’nikova, Fiz Tverd Tela, 10 (1), Jan 1968, 103-107 (in Russian). 18 953. On the sputtering mechanism of solids. (USSR) Comparing measured values of the sputtering coefficients of polycrystalline Zr and ZrC and of MO, W and MO-W alloy bombarded by 5 to 17 keV Ar+ ions at 6x 1O-a torr, it is shown that the same mechanism of sputtering operates for the pure metals and for their carbides or alloys. This fact cannot be explained by the theory of focusons but is accommodated by the Lehman theory of cascades of collisions. B M Gurmin et al, Fiz Tverd Tela, 10 (2). Feb 1968, 411-414 (in Russian). 954. Elastic retlection of electrons from silicon single crystals. (USS: After baking at 1250°C at 5 x lo-’ torr and at 1100°C at 5 x 10-O torr the coefficient of electron elastic reflection was measured for primary energies of 20 to 1000 eV. Two peaks were found at 45 and at 75 eV
and at higher energies the value of the coefficient decreases. A 30-hour adsorption of residual gases at 1 x lo-’ torr increases the coefficient values at peaks by about 33 per cent without effect on the character of the dependence. A R Shul’man et al, Fiz Tverd Tela, 10 (2), Feb 1968, 655-656 (in Russian). 18 955. Current growth in sparks in the p&e breakdown of short wcuurn gaps. (USSR) A theory explaining the mechanism of the current growth stage of vacuum breakdown is presented and experimentally verified. The effect of increasing the delay time at higher overvoltages in the same gap is discussed in detail. G A Mesyats and D I Proskurovskly, Zzv VUZ Fir, 11 (l), 1968,81-85 (in Russian). 18 956. Exoelectron emission of germaninrn and silicon. (USSR) The possibility of exploitation of the effect of exoemission for the investigation of microdefects on Ge and Si surfaces is discussed. V I Kryuk et al, Zzv VCJZFiz, 11 (l), 1968, 118-122 (in Russian). 18 957. Angular dependence of energy spectra of secondary ions scattered by the surface of single crystals. (USSR) Molybdenum single crystal faces (100) and (110) were bombarded by positive potassium ions with energies of 25 to 5000 eV and the energy spectra of secondary ions were measured. The characteristics are connected with multiple collisions of incident ions with crystal atoms and the decrease of the scattering angle leads to an increase in the number of repeatedly colliding ions. U A Arifov and A A Aliev, Zh Eksper Teor Fiz, 54 (2). Feb 1968,354361 (in Russian). 18 958. Studies of the nitrogen afterglow. I. Surface catalytic efllciency and diiusion-controlled decay of atomic nitrogen. (USA) The temporal behavior of the afterglow light intensity in decaying nitrogen plasmas, as well as that of the number density of N+, NI+, N3+ and N,+ ions was studied in the pressure range of about 0.1 to 1.7 torr. Analysis of the light intensity decay curves gave values of the surface catalytic efficiency yN for the recombination of nitrogen atoms at the plasma boundary. The use of a quadrupole mass spectrometer ensured that the data related to pure nitrogen as well as to extremely clean surfaces. Values of YNfor molybdenum sputtered on a clean glass surface decreased with pressure from a value of 0.22 at 0.09 torr to 0.04 at 1.35 torr. R E Land and H J Oskam, .I Chem Phys, 48 (1). 1st Jan 1968,109-l 15. 18 959. calculation of three-body ionic recombination rate. (USA) The three-body ionic recombination rate at low densities is calculated for a slightly ionized gas by considering that the relaxation of the energy of molecules occur by a “diffusion” process. The effective conductivity in the equivalent diffusion equation is the second moment of the energy transfer. The moments are derived in closed form using classical mechanics and enable the recombination rate constant to be obtained. Good agreement with experimental data is found. S A Landon and J C Keck, J Chem Phys, 48 (l), 1st Jan 1968.374-380. 18 960. Energy dependence for single and double ionization by electron impact between 250 and 2200 eV. (USA) Studies have been made of Rb, Zn. Mg, NHs, NO, Nt. CO, COS, CS, and H,S. The results show that the direct double-ionization cro-L section (simultaneous ejection of two electrons) can be written as a-E-t, where E is the energy of incident ions. When doubly charged ions are formed by the Auger effect, there is a departure from E-l dependence. The experiments show that molecular ions COS++ C&++, Has++ and NH,++ can be formed by the Auger effect. The single-ionization cross section is shown to satisfy the usual dependence Cc-E-l log BE. The equipment and techniques used are described in a previous publication to which reference is made. F Fiquet-Fayard et al, J Chem Phys, 48 (1), 1st Jan 1968,478-482. 18 961. Threshold electron impact excitation of atoms and molecules: detection of triplet and temporary negative ion states. (USA) A technique which utilizes SF, as a scavenger of low-energy electrons is employed to study the “threshold” excitation spectra of He, N., HCl, H,O, D,O and a number of aromatic molecules. For electrons 427