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A source of highly spin-polarized slow electrons based on the ‘Fano effect’ on caesium atoms
Classified abstracts
5669-5678
doped n+ layers with peak carrier concentrations of 8 x 10” cme3 and 7 x lo*’ cm-’ for (100) and (111) samples were obtained, respectively, after electron beam irradiation. The effect of additional thermal treatment on electrical behaviours and crystalline quality of electron-beam annealed samples has been investigated. Carrier concentration decreased with increasing additional annealing temperature up to 800°C and it increased above 8oo”C, where the system approached a thermal equilibrium and at the same time thermal diffusion of As occurs. Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM) observations revealed that no residual damage remained after electron beam irradiation but dislocation loops were formed during the course of additional thermal annealing. (Japan) Y Yatimoto et al, J Appl Phys, 53 (1). 1982, 276-283. 35 5669. So and Te doping of molecular beam epitaxial GaAs using a SnTe source (USA)
Secondary ion mass spectroscopy and free electron concentration measurements have been used to study the incorporation of Sn and Te in MBE GaAs when SnTe is used as the source of these impurities. The probability of incorporation of Sn and Te approaches unity for substrate temperatures (T,)S 550°C and decreases to less than 0.1 for T,>,6oo”C. This decrease is attributed to desorption of SnTe from the GaAs surface. A SnTe ‘pair’ incorporation mechanism is proposed which dominates over the entire substrate temperature range studied. However, dissociation of SnTe molecules on the GaAs surface, with subsequent surface accumulation of Sn and Te, becomes non-negligible for T,L58o”C. A model is presented which explains these as well as other features of the experimental data. Douglas M Collhts et al, J Appl Phys, 53 (4), 1982, 3010-3018. 35 5670. Laser treatment of a oomubstitutioaal alloy Cr implanted in alumimun. (USA) A nonsubstitutional alloy of 7 atm% Cr implanted in single-crystal aluminium has been irradiated with Q-switched ruby laser pulses up to 6 J cm-*. Liquid phase epitaxy, resulting in enhanced substitutionality without any Cr redistribution, is observed up to 2 J cm-* for a laser pulse duration of 25 ns. At higher energy densities and with shorter pulses, 12-ns duration, convection effects are observed to inhibit liquid phase epitaxy. The surface retlectance appears to reduce due to high implantation dose. (Italy) G Battagiin et al, J Appl Phys, 53 (4), 1982, 32243230. 35 5671. Compressive strength and outgassing characteristics of concrete for large vacuum-system construction. (USA) Concrete enclosures can be used for vacuum-system construction. However, limited information exists on the beahviour of concrete in vacuum. For this reason, concrete testing was performed recently at the Los Alamos National Laboratory to obtain data on outgassing and compressive strength of concrete in vacuum. The results of the experimental programme will be presented to support the major conclusion that concrete is suitable for high-vacuum systems without degradation of strength and should be considered for large vacuum-system construction. H S Cullingford et al, J Vat Sci Technol, 20 (4), 1982, 1043-1047.
36. PARTICLE BEAMS AND SOURCES 36 5672. A kollow catkode arc as a bigk intensity beam soarce for ground state and metastabk
noble gas atoms in the eV translational energy range. (GB)
The medium density plasma column (nz lo*’ m-“) close to the exit of the cathode of a hollow cathode arc is highly ionized, with ion and electron temperatures ‘&zOS-1.5 eV and T,z 3 eV, respectively. By sampling this plasma with an orifice in the end anode (at a floating potential) a high intensity beam with a broad velocity distribution is obtained for the noble gas atoms Ne, Ar and Kr, both in the ground state and in metastable states n*. Typical centre-line intensities for argon are I(O)=2 x 10” s-l sr-l, T=2 x lo4 Kand 1(0),.=2x 1Ol4 s-l sr-‘, 7’,‘,.=3x lo4 K. These values are in good agreement with model calculations of the process of molecular beam sampling, which are discussed in this paper. The source is of a simple design and easy to operate. The life time of the tungsten (or tantalum) hollow cathode is typically 40 h for argon and krypton. The shortest life time is for neon with a tungsten cathode, due to the high operating temperature Ts 3000 K of the cathode tip. (The Netherlands) P G A Theuws et al, J Phys E: Sci Instrum, 15 (5), 1982, 573-579. 422
36 5673. The 118e of a retarding field electron spectrometer ia h-atom collision experiments. (GB) A spectrometer is described which consists of retarding field grids and a post-monochromator, and which is constructed to detect electrons emitted into the backward hemisphere in ion-atom collisions. The construction is such that the impinging ion beam passes through the spectrometer before colliding with the target foil. The experimental line width (fwhm) of monochromatic electrons is 68 eV in the energy range 15&800 eV. An account of the performance of the spectrometer in ion-atom collision experiments is given. (The Netherlands) W Duinker and J VP Eck, J Phys Ec Sci Instrum, 15 (5), 1982, 525-529. 36 5674. Optimization of low-perveance eJectron gun by experimental and numerical methods (GB) The paper presents a proposed method for improving the electron gun used for microscopes or similar electron beam devices. The electron gun has been divided into two zones: the high perveance cathode zone and the low perveance lens zone. The tinal virtual crossover of the gun is thus the image of the exit pupil of cathode zone. This image is produced by the action of the lens zone. The basic assumption of this approach is that the electron brightness doe-s not depend significantly on the lens zone electron+ptical parameters. Based on this assumption the optimization of the electrodes has been carried out. This has been done experimentally in the cathode zone and by means of numerical calculations in the lens zone. Results obtained for the scanning electron microscope gun are presented as an example of this approach. (Poland) Zbigaiew Mate&a and Witold Slhwko, J Phys E: Sci Irutrum, 15 (4), 1982, 444-447. 36 5675. An alkaliiioo gun for ose in collision experiments. (GB) A detailed description of a low-energy (255OOeV) alkali-ion gun is reported. Performances are compared with computer-aided design and theory. Using a ‘Li-ion emitter, currents up to lo-’ A at 500 eV ion energy were obtained. The angular spread was 8” (fwhm) at an ion energy of 25 eV. (Italy) G Conforti et al, J Phys E: Sci Instrum, 15 (8), 1982, 827-830. 36 5676. H- beam emittance measarements for the Penning and the asymmetric, grooved magnetron surf&e-plasma sources (USA) Beam intensity and emittance measurements show that the H- beam from our Penning surface-plasma source (SPS) has twice the intensity and ten times the brightness of the H- beam from an asymmetric, grooved magnetron SPS. H- ion temperatures of 5 eV for the Penning SPS and 22 eV for the asymmetric, grooved magnetron are deduced by using a simple emittance theory and the present emittance measurements. H Vernon SmithJr and Paul Allison, Reo Sci Instrum, 53 (4), 1982,405-408. 36 5677. A source of highly spi~polarixed slow electrons based on tbe ‘Faso effect’ on cat&m atoms, (GB) The source of spin-polarized electrons recently used in a ‘triple-scattering experiment’ in Miinster is described in detail. The polarized electrons are generated by the photoionization of caesium atoms with circularly polarized uv radiation from a high-pressure mercury discharge lamp (Fano effect). Electron intensities of 5 nA with polarization of 84% have been routinely obtained during continuous runs of up to 200 h in the kinetic energy range between 17 and 5OOeV with an energy spread of I 1.5 eV. The polarization and intensity fluctuation was f 1% and k 10% in 10 h, respectively. (West Germany) R M6lhkamp and U Heinzmann, J Phys E: Appl Phys, 15 (6), 1982, 692-696. 36 5678. Repetitive operation of an inductivelydriven
electron-keam diode.
(USA)
Recovery of a pulsed electron beam diode operating in the 50 A crne2 range has been studied using an inductive storage source producing two - 150 kV pulses with pulse-to-pulse separation ranging from lc5OOys. The diode cannot instantaneously support a second voltage pulse because of the short circuit provided by the interelectrode plasma associated with the first pulse. The properties of this plasma, including its eITectivelifetime, have been studied. The diode is observed to recover for pulse separation times >, 100 ps. The results can be extended to repetitively pulsed electron beam generation as needed in many physics
5669-5678
doped n+ layers with peak carrier concentrations of 8 x 10” cme3 and 7 x lo*’ cm-’ for (100) and (111) samples were obtained, respectively, after electron beam irradiation. The effect of additional thermal treatment on electrical behaviours and crystalline quality of electron-beam annealed samples has been investigated. Carrier concentration decreased with increasing additional annealing temperature up to 800°C and it increased above 8oo”C, where the system approached a thermal equilibrium and at the same time thermal diffusion of As occurs. Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM) observations revealed that no residual damage remained after electron beam irradiation but dislocation loops were formed during the course of additional thermal annealing. (Japan) Y Yatimoto et al, J Appl Phys, 53 (1). 1982, 276-283. 35 5669. So and Te doping of molecular beam epitaxial GaAs using a SnTe source (USA)
Secondary ion mass spectroscopy and free electron concentration measurements have been used to study the incorporation of Sn and Te in MBE GaAs when SnTe is used as the source of these impurities. The probability of incorporation of Sn and Te approaches unity for substrate temperatures (T,)S 550°C and decreases to less than 0.1 for T,>,6oo”C. This decrease is attributed to desorption of SnTe from the GaAs surface. A SnTe ‘pair’ incorporation mechanism is proposed which dominates over the entire substrate temperature range studied. However, dissociation of SnTe molecules on the GaAs surface, with subsequent surface accumulation of Sn and Te, becomes non-negligible for T,L58o”C. A model is presented which explains these as well as other features of the experimental data. Douglas M Collhts et al, J Appl Phys, 53 (4), 1982, 3010-3018. 35 5670. Laser treatment of a oomubstitutioaal alloy Cr implanted in alumimun. (USA) A nonsubstitutional alloy of 7 atm% Cr implanted in single-crystal aluminium has been irradiated with Q-switched ruby laser pulses up to 6 J cm-*. Liquid phase epitaxy, resulting in enhanced substitutionality without any Cr redistribution, is observed up to 2 J cm-* for a laser pulse duration of 25 ns. At higher energy densities and with shorter pulses, 12-ns duration, convection effects are observed to inhibit liquid phase epitaxy. The surface retlectance appears to reduce due to high implantation dose. (Italy) G Battagiin et al, J Appl Phys, 53 (4), 1982, 32243230. 35 5671. Compressive strength and outgassing characteristics of concrete for large vacuum-system construction. (USA) Concrete enclosures can be used for vacuum-system construction. However, limited information exists on the beahviour of concrete in vacuum. For this reason, concrete testing was performed recently at the Los Alamos National Laboratory to obtain data on outgassing and compressive strength of concrete in vacuum. The results of the experimental programme will be presented to support the major conclusion that concrete is suitable for high-vacuum systems without degradation of strength and should be considered for large vacuum-system construction. H S Cullingford et al, J Vat Sci Technol, 20 (4), 1982, 1043-1047.
36. PARTICLE BEAMS AND SOURCES 36 5672. A kollow catkode arc as a bigk intensity beam soarce for ground state and metastabk
noble gas atoms in the eV translational energy range. (GB)
The medium density plasma column (nz lo*’ m-“) close to the exit of the cathode of a hollow cathode arc is highly ionized, with ion and electron temperatures ‘&zOS-1.5 eV and T,z 3 eV, respectively. By sampling this plasma with an orifice in the end anode (at a floating potential) a high intensity beam with a broad velocity distribution is obtained for the noble gas atoms Ne, Ar and Kr, both in the ground state and in metastable states n*. Typical centre-line intensities for argon are I(O)=2 x 10” s-l sr-l, T=2 x lo4 Kand 1(0),.=2x 1Ol4 s-l sr-‘, 7’,‘,.=3x lo4 K. These values are in good agreement with model calculations of the process of molecular beam sampling, which are discussed in this paper. The source is of a simple design and easy to operate. The life time of the tungsten (or tantalum) hollow cathode is typically 40 h for argon and krypton. The shortest life time is for neon with a tungsten cathode, due to the high operating temperature Ts 3000 K of the cathode tip. (The Netherlands) P G A Theuws et al, J Phys E: Sci Instrum, 15 (5), 1982, 573-579. 422
36 5673. The 118e of a retarding field electron spectrometer ia h-atom collision experiments. (GB) A spectrometer is described which consists of retarding field grids and a post-monochromator, and which is constructed to detect electrons emitted into the backward hemisphere in ion-atom collisions. The construction is such that the impinging ion beam passes through the spectrometer before colliding with the target foil. The experimental line width (fwhm) of monochromatic electrons is 68 eV in the energy range 15&800 eV. An account of the performance of the spectrometer in ion-atom collision experiments is given. (The Netherlands) W Duinker and J VP Eck, J Phys Ec Sci Instrum, 15 (5), 1982, 525-529. 36 5674. Optimization of low-perveance eJectron gun by experimental and numerical methods (GB) The paper presents a proposed method for improving the electron gun used for microscopes or similar electron beam devices. The electron gun has been divided into two zones: the high perveance cathode zone and the low perveance lens zone. The tinal virtual crossover of the gun is thus the image of the exit pupil of cathode zone. This image is produced by the action of the lens zone. The basic assumption of this approach is that the electron brightness doe-s not depend significantly on the lens zone electron+ptical parameters. Based on this assumption the optimization of the electrodes has been carried out. This has been done experimentally in the cathode zone and by means of numerical calculations in the lens zone. Results obtained for the scanning electron microscope gun are presented as an example of this approach. (Poland) Zbigaiew Mate&a and Witold Slhwko, J Phys E: Sci Irutrum, 15 (4), 1982, 444-447. 36 5675. An alkaliiioo gun for ose in collision experiments. (GB) A detailed description of a low-energy (255OOeV) alkali-ion gun is reported. Performances are compared with computer-aided design and theory. Using a ‘Li-ion emitter, currents up to lo-’ A at 500 eV ion energy were obtained. The angular spread was 8” (fwhm) at an ion energy of 25 eV. (Italy) G Conforti et al, J Phys E: Sci Instrum, 15 (8), 1982, 827-830. 36 5676. H- beam emittance measarements for the Penning and the asymmetric, grooved magnetron surf&e-plasma sources (USA) Beam intensity and emittance measurements show that the H- beam from our Penning surface-plasma source (SPS) has twice the intensity and ten times the brightness of the H- beam from an asymmetric, grooved magnetron SPS. H- ion temperatures of 5 eV for the Penning SPS and 22 eV for the asymmetric, grooved magnetron are deduced by using a simple emittance theory and the present emittance measurements. H Vernon SmithJr and Paul Allison, Reo Sci Instrum, 53 (4), 1982,405-408. 36 5677. A source of highly spi~polarixed slow electrons based on tbe ‘Faso effect’ on cat&m atoms, (GB) The source of spin-polarized electrons recently used in a ‘triple-scattering experiment’ in Miinster is described in detail. The polarized electrons are generated by the photoionization of caesium atoms with circularly polarized uv radiation from a high-pressure mercury discharge lamp (Fano effect). Electron intensities of 5 nA with polarization of 84% have been routinely obtained during continuous runs of up to 200 h in the kinetic energy range between 17 and 5OOeV with an energy spread of I 1.5 eV. The polarization and intensity fluctuation was f 1% and k 10% in 10 h, respectively. (West Germany) R M6lhkamp and U Heinzmann, J Phys E: Appl Phys, 15 (6), 1982, 692-696. 36 5678. Repetitive operation of an inductivelydriven
electron-keam diode.
(USA)
Recovery of a pulsed electron beam diode operating in the 50 A crne2 range has been studied using an inductive storage source producing two - 150 kV pulses with pulse-to-pulse separation ranging from lc5OOys. The diode cannot instantaneously support a second voltage pulse because of the short circuit provided by the interelectrode plasma associated with the first pulse. The properties of this plasma, including its eITectivelifetime, have been studied. The diode is observed to recover for pulse separation times >, 100 ps. The results can be extended to repetitively pulsed electron beam generation as needed in many physics