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702. Efficient electron emitter employing hollow cathode discharge
Classified
abstracts
701-712
18 701. The combination of Auger spectroscopy and characteristic loss spectroscopy for the elements V to Co. (Germany) Splitting of the M,,, characteristic loss peak has been observed following oxidation of clean Cr and V surfaces, but not after oxidation of Fe and Co, although in all four cases the Auger spectra were characteristic for an oxidized surface. In addition, even when the Cr Auger spectrum indicated a clean surface, the M,,, loss peak was found to have a position and width different from those expected for a clean metal. The results are explained on the assumption of different ranges for electrons of different origins. The characteristic loss electrons do have a significantly greater range than Auger electrons of the same energy and of course a very much greater range than the lowenergy Auger electrons. When a clean surface of Fe or Co is exposed to oxygen at room temperature, a monolayer of oxide is formed at the surface, and the resulting Auger spectrum is similar to that of a bulk oxide. The characteristic loss spectrum is, however, unaffected. Cr and V, on the other hand, oxidize more readily at room temperature, resulting presumably, in a thicker oxide layer at the surface. J P Coad and J C Riviere, Ph_~sStat Sol (a), 7 (2), Ocr 1971, 571-575. 18 702. Efficient electron emitter employing hollow cathode discharge. (USSR) A special gas-discharge system is described which employs a hollow cathode of MO tube 20 mm in length and 8 mm in diameter as an efficient electron emitter. The minimum pressure at which discharge could be maintained was 2.5 torr. A method for the transport of a high-density electron current, without significant losses, through regions with a discrete pressure drop from 0.4 to lOma torr, is presented. The maximum density of the electron current was 300 A/cm2 with an electron energy spread of 0 to 60 eV. V A Popov et al, Izv AN SSSR Ser Fiz, 35 (2), 1971, 327-329 (in Russian). 18 703. Intensities of Auger and photoelectron spectra. (USSR) Intensities of Auger and photoelectron spectra of elemental emitters in a bulk polycrystalline target and of a surface monolayer deposited on a bulk substrate are calculated for ionization by X-ray photons and electrons with energies of 1 to 50 keV. A G Stadnikov and A P Nikolskiy, Izv AN SSSR Ser Fiz, 35 (2), 1971, 33CL333 (in Russian). 18 704. Model of the oxide cathode with surface donor centres. (USSR) An analysis of data on nature of chemical bond and electron state of donor centres in crystals of alkaline-earth metal oxides is presented. A new model of thermionic emission in ionic crystals is given. Surface donor centres close to the vacuum level are formed on the surface of an oxide cathode as a result of vacuum treatment including thermal, chemical and current activation. B P Nikonov, Izv AN SSSR Ser Fiz, 35 (2), 1971,270-278 (in Russian). 18 705. Investigation of influence of surface states on thermionic properties of alkaline-earth metal oxides. (USSR) influence of surface states generated by barium deposition on the thermionic properties of alkaline-earth metal oxides is investigated in an experimental device at 1 x IO-” torr. A linear dependence of the emission current on the concentration of surface donor centres of two types, 1 .O and 1.4 eV below the vacuum level, is found. K S Beynar and B P Nikonov, Izv AN SSSR Ser Fiz, 35 (2), 197 1,286290 (in Russian). 18 706. Thermionic parameters of (111) and (110) faces of single crystal W covered with Ge film. (USSR) Thermionic parameters of spherical tungsten single crystals are investigated in a sealed device at 1 x IO-* torr during deposition of Ge on W crystal. It is shown that during adsorption of Ge on (111) and (110) faces of single crystal W the density of the thermionic current decreases due to a considerable decrease in the thermionic constant of the Richardson equation. V Kh Burkhanova and N A Gorhatyy, Izv AN SSSR Ser Fiz, 35 (2), 197 I, 291-292 (in Ru.wan). 18 707. The problem of instability of the electron emission from thin dispersed gold films activated by barium oxide (Au-BaO). (USSR) Causes of instability of the emission current of hot electrons from a
gap system containing gold film activated by BaO are considered. Evaporation of the dispersed gold film and activation of its surface by several BaO monolayers was performed in a sealed device at residual gas pressure below 10e7 torr. It is found that the decrease of the power fed to the film due to an increase in its resistance forms the main cause of the emission current decay. A S Sukhariev and S V Zagrebneva, Izv AN SSSR Ser Fiz, 35 (2), 1971, 298-301 (in Russian). 18 708. Secondary electron emission of W and MO single crystals. (USSR) A systematic experimental study of secondary emission characteristics of W and MO single crystals at low and elevated temperatures is carried out in sealed devices at residual gas pressures below 1O-8 torr. Experimental results are discussed. M V Gomoyunova and B Z Aliev, izv AN SSSR Seu Fiz, 35 (2), 1971, 231-236 (in Russian). 18 709. Positive surface ionization of atoms of alkali metals and their halide compounds. (USSR) Positive surface ionization of K atoms and KCI, KI and CsCl molecules on the (100) face of W is investigated in sealed devices at pressures below 1 x 1Om8 torr. Two maxima are found on the plot of the ion current vs the density of ionizing molecular flow of alkali halide compounds, while only one maximum is observed on the plot of alkali atoms. An explanation of this phenomena is presented. E F Chaykovskiy et al, Zzv AN SSSR Ser Fiz, 35 (2), 1971, 373-378 (i/r Russian). 18 710. Some characteristics and emission mechanism of a zirconium carbide thermionic cathode. (USSR) ZrC offers potential use as cathode material in thermionic energy converters and magnetohydrodynamic generators due to its stability at high temperatures. ZrC was prepared by reduction of ZrO by charcoal mixed in stoichiometric composition in argon atmosphere at 2600’ C. It is found that pure ZrC has an effective work function 4.05 eV at temperature of 1800°K in vacuum. In argon ambient up to lo-” torr the emission current does not change. In potassium and caesium vapours the emission current from ZrC increases considerably. Emission properties with additions of MO and Ti and with deposited metallic films of Zr on the cathode surface are also investigated. Theoretical analysis and the experimental data on the thermionic emission from ZrC in vacuum, argon and alkali metal vapours indicate that the emission mechanism is of a metallic character and is governed by a Zr film on the surface of ZrC. Kh S Kan and B S Kulvarskaya, Zzv AN SSSR Ser Fiz, 35 (2), 1971, 279-285 (in Russian). 18 711. Field electron emission of monocrystalline lanthanum hexaboride. (USSR) Field electron emission of LaB, is investigated in the range - 196 to 5OO’C. The experiments were performed in a glass sealed field electron microscope containing also a manometric system and tantalum getter. LaB, tius with curvature radius of 5OCO to 7000 8, were prepared by electrol;tic etching. A residual gas pressure of lo-” torr was attained in the device after careful degassing and getter evaporation. Influence of the residual gases on the operation of a LaB, field emitter was investigated at lo-’ to 1Oms torr. The residual gas contained mainly nitrogen as was confirmed from the tungsten emission patterns. It is found that the field emission current is markedly reduced at lo-’ torr. Simultaneously with the emission current decrease a decrease in the brightness of emission patterns of the LaB, single crystal is observed. All the experimental data can be explained by the existence on the surface of free lanthanum atoms not bound to the LaB, lattice. G A Kudintseva et al, Izv AN SSSR Ser Fiz, 35 (2), 1971, 293-297 (in Russian). 18 712. Secondary emission and elastic reflection of electrons from single crystals. (USSR) The angular dependencies of the coefficients of secondary emission, inelastically and elastically reflected electrons are investigated over a wide range of energies from a few tens to a few thousand evofprimary electrons. The influence of target temperature and energy spectra of secondary electrons at various incidence angles of the primary electrons are investigated for single crystal molybdenum, tungsten 241
abstracts
701-712
18 701. The combination of Auger spectroscopy and characteristic loss spectroscopy for the elements V to Co. (Germany) Splitting of the M,,, characteristic loss peak has been observed following oxidation of clean Cr and V surfaces, but not after oxidation of Fe and Co, although in all four cases the Auger spectra were characteristic for an oxidized surface. In addition, even when the Cr Auger spectrum indicated a clean surface, the M,,, loss peak was found to have a position and width different from those expected for a clean metal. The results are explained on the assumption of different ranges for electrons of different origins. The characteristic loss electrons do have a significantly greater range than Auger electrons of the same energy and of course a very much greater range than the lowenergy Auger electrons. When a clean surface of Fe or Co is exposed to oxygen at room temperature, a monolayer of oxide is formed at the surface, and the resulting Auger spectrum is similar to that of a bulk oxide. The characteristic loss spectrum is, however, unaffected. Cr and V, on the other hand, oxidize more readily at room temperature, resulting presumably, in a thicker oxide layer at the surface. J P Coad and J C Riviere, Ph_~sStat Sol (a), 7 (2), Ocr 1971, 571-575. 18 702. Efficient electron emitter employing hollow cathode discharge. (USSR) A special gas-discharge system is described which employs a hollow cathode of MO tube 20 mm in length and 8 mm in diameter as an efficient electron emitter. The minimum pressure at which discharge could be maintained was 2.5 torr. A method for the transport of a high-density electron current, without significant losses, through regions with a discrete pressure drop from 0.4 to lOma torr, is presented. The maximum density of the electron current was 300 A/cm2 with an electron energy spread of 0 to 60 eV. V A Popov et al, Izv AN SSSR Ser Fiz, 35 (2), 1971, 327-329 (in Russian). 18 703. Intensities of Auger and photoelectron spectra. (USSR) Intensities of Auger and photoelectron spectra of elemental emitters in a bulk polycrystalline target and of a surface monolayer deposited on a bulk substrate are calculated for ionization by X-ray photons and electrons with energies of 1 to 50 keV. A G Stadnikov and A P Nikolskiy, Izv AN SSSR Ser Fiz, 35 (2), 1971, 33CL333 (in Russian). 18 704. Model of the oxide cathode with surface donor centres. (USSR) An analysis of data on nature of chemical bond and electron state of donor centres in crystals of alkaline-earth metal oxides is presented. A new model of thermionic emission in ionic crystals is given. Surface donor centres close to the vacuum level are formed on the surface of an oxide cathode as a result of vacuum treatment including thermal, chemical and current activation. B P Nikonov, Izv AN SSSR Ser Fiz, 35 (2), 1971,270-278 (in Russian). 18 705. Investigation of influence of surface states on thermionic properties of alkaline-earth metal oxides. (USSR) influence of surface states generated by barium deposition on the thermionic properties of alkaline-earth metal oxides is investigated in an experimental device at 1 x IO-” torr. A linear dependence of the emission current on the concentration of surface donor centres of two types, 1 .O and 1.4 eV below the vacuum level, is found. K S Beynar and B P Nikonov, Izv AN SSSR Ser Fiz, 35 (2), 197 1,286290 (in Russian). 18 706. Thermionic parameters of (111) and (110) faces of single crystal W covered with Ge film. (USSR) Thermionic parameters of spherical tungsten single crystals are investigated in a sealed device at 1 x IO-* torr during deposition of Ge on W crystal. It is shown that during adsorption of Ge on (111) and (110) faces of single crystal W the density of the thermionic current decreases due to a considerable decrease in the thermionic constant of the Richardson equation. V Kh Burkhanova and N A Gorhatyy, Izv AN SSSR Ser Fiz, 35 (2), 197 I, 291-292 (in Ru.wan). 18 707. The problem of instability of the electron emission from thin dispersed gold films activated by barium oxide (Au-BaO). (USSR) Causes of instability of the emission current of hot electrons from a
gap system containing gold film activated by BaO are considered. Evaporation of the dispersed gold film and activation of its surface by several BaO monolayers was performed in a sealed device at residual gas pressure below 10e7 torr. It is found that the decrease of the power fed to the film due to an increase in its resistance forms the main cause of the emission current decay. A S Sukhariev and S V Zagrebneva, Izv AN SSSR Ser Fiz, 35 (2), 1971, 298-301 (in Russian). 18 708. Secondary electron emission of W and MO single crystals. (USSR) A systematic experimental study of secondary emission characteristics of W and MO single crystals at low and elevated temperatures is carried out in sealed devices at residual gas pressures below 1O-8 torr. Experimental results are discussed. M V Gomoyunova and B Z Aliev, izv AN SSSR Seu Fiz, 35 (2), 1971, 231-236 (in Russian). 18 709. Positive surface ionization of atoms of alkali metals and their halide compounds. (USSR) Positive surface ionization of K atoms and KCI, KI and CsCl molecules on the (100) face of W is investigated in sealed devices at pressures below 1 x 1Om8 torr. Two maxima are found on the plot of the ion current vs the density of ionizing molecular flow of alkali halide compounds, while only one maximum is observed on the plot of alkali atoms. An explanation of this phenomena is presented. E F Chaykovskiy et al, Zzv AN SSSR Ser Fiz, 35 (2), 1971, 373-378 (i/r Russian). 18 710. Some characteristics and emission mechanism of a zirconium carbide thermionic cathode. (USSR) ZrC offers potential use as cathode material in thermionic energy converters and magnetohydrodynamic generators due to its stability at high temperatures. ZrC was prepared by reduction of ZrO by charcoal mixed in stoichiometric composition in argon atmosphere at 2600’ C. It is found that pure ZrC has an effective work function 4.05 eV at temperature of 1800°K in vacuum. In argon ambient up to lo-” torr the emission current does not change. In potassium and caesium vapours the emission current from ZrC increases considerably. Emission properties with additions of MO and Ti and with deposited metallic films of Zr on the cathode surface are also investigated. Theoretical analysis and the experimental data on the thermionic emission from ZrC in vacuum, argon and alkali metal vapours indicate that the emission mechanism is of a metallic character and is governed by a Zr film on the surface of ZrC. Kh S Kan and B S Kulvarskaya, Zzv AN SSSR Ser Fiz, 35 (2), 1971, 279-285 (in Russian). 18 711. Field electron emission of monocrystalline lanthanum hexaboride. (USSR) Field electron emission of LaB, is investigated in the range - 196 to 5OO’C. The experiments were performed in a glass sealed field electron microscope containing also a manometric system and tantalum getter. LaB, tius with curvature radius of 5OCO to 7000 8, were prepared by electrol;tic etching. A residual gas pressure of lo-” torr was attained in the device after careful degassing and getter evaporation. Influence of the residual gases on the operation of a LaB, field emitter was investigated at lo-’ to 1Oms torr. The residual gas contained mainly nitrogen as was confirmed from the tungsten emission patterns. It is found that the field emission current is markedly reduced at lo-’ torr. Simultaneously with the emission current decrease a decrease in the brightness of emission patterns of the LaB, single crystal is observed. All the experimental data can be explained by the existence on the surface of free lanthanum atoms not bound to the LaB, lattice. G A Kudintseva et al, Izv AN SSSR Ser Fiz, 35 (2), 1971, 293-297 (in Russian). 18 712. Secondary emission and elastic reflection of electrons from single crystals. (USSR) The angular dependencies of the coefficients of secondary emission, inelastically and elastically reflected electrons are investigated over a wide range of energies from a few tens to a few thousand evofprimary electrons. The influence of target temperature and energy spectra of secondary electrons at various incidence angles of the primary electrons are investigated for single crystal molybdenum, tungsten 241