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Inelastic scattering of slow positrons by helium, neon and argon atoms
Classified abstracts
5629-5638
the partial pressure or throughput of nitrogen in the system as shown using controlled leaks of both pure nitrogen and air. The nitrogen may destroy the columnar microstructure and the film perpendicular magnetic anisotropy which is due to the well-oriented hcp phase. This sensitivity to nitrogen in the background gases makes it necessary to achieve a low background pressure in the sputtering chamber if films with perpendicular magnetic anisotropy are to be obtained. T M Cougblin, J Vat Sci Technol, 20 (Z), 1982, 171-174. 31 5629. Pressure and angle of incidence effects in reactive planar magnetron sputtered En0 layers. (USA)
ZnO films have been prepared by rf sputtering a Zn target in a planar magnetron system with controlled Ar/O, gas mixtures. The films were deposited on unheated glass substrates which were either stationary in front of the target or in constant motion. Both the system pressure and plasma impedance changed when an oxide layer formed on the target surface. This occurred at an oxygen flow rate which increased almost linearly with rf power; at 500 W, the required flow rate was 9 ml min-’ and the pressure increased from 0.1 to 1.2 Pa due to the reduced oxygen gettering. High resistance ZnO films were deposited at oxygen flow rates above this threshold value. The target self-bias voltage increased by 30 V at this value; it is affected by both the system pressure and the power. The deposition rate increased linearly with power at approximately 0.03 @m/min)/(W/cm’) which appears to be typical of sputtering from a ZnO layer or target. For continuous substrate motion, the average rate was approximately 7% of this value. All the films were polycrystalline ZnO with a preferred orientation, the c axis of the hexagonal structure being within a small angle of the substrate normal; this orientation was improved by motion of the substrate past the target. Films deposited at pressures of approximately 0.4 Pa had a large internal stress, as revealed both by substrate bending and X-ray measurements. Increasing the pressure to 4.7 Pa decreased the stress by an order of magnitude. SEM analysis showed that this was associated with the development of a columnar structure. The refractive indices obtained from guided wave measurements were 1940~0.006 and 1.962 kO.003, which correspond to 97% of the single crystal values. The resistivity measured normal to the film plane was greater than 1O’R cm. The changes in film stress and structure are similar to effects in metal films. The electromechanical coupling coefficients obtained from SAW measurements are approximately half the best reported value. (Canada) S Maniv et al, .f Vat Sci Technol, 20 (2), 1982, 162-170.
33. NUCLEONICS 33 5630. Electron temperature
measurement
of cold plasma
in a strong
mnguetic field. (GB)
This paper shows how electron temperature and density in low pressure cold plasma (T.< 10 eV) can be measured directly from cyclotron resonance absorption measurements in a strong homogeneous magnetic field (cz20 T). For pressure below 0.5 torr, the cvclotron line width is Doppler broadened and the electron temperature is directly derived from this parameter. At high pressures the line width becomes collision broadened and the electron temperature is indirectly derived using the known energy dependence of the collision frequency. (France) A Dorelon et al, J Phys D: Appl Phys, 15 (4), 1982, 605-614. 33 5631. Beam-foil spectroscopy of Se IV, V and VI. (Canada) Six new transitions are assigned in Se V, resulting in the classification of three new levels: 4s4d ‘D, 4~5s ‘5, and 4s5p ‘P”. Lifetimes and multiplet$ values are presented for the 4s24d2D, 4s4p2 *P, 4s4p2 ‘S, and 4~42 ‘b terms of Se IV. the 4~5s 3S.4s4d “D. 4s4d and 4n2 ‘D. 4~40 ‘PO.and 40~ 3P terms of Se V and the 5s *s, 4d *D, and 4p *PO terms’of Sk VI. The cascade repopulation problems were analysed by using the ANDC method on the terms 4s4p ‘PO of Se V and 4p *PO of Se VI. J L Bahr et al, J Cen Phys, 60 (8), 1982, 1108-I 116. 33 5632. ACT-I: A steady-state torus for basic pLasma physics research. (USA) The construction and operation of a steady-state toroidal plasma device are described. The toroidal plasma can be maintained without any rotational transform and the plasma quality is significantly better than that in linear devices. It opens up new areas for basic plasma physics research. Examples of experiments on wave propagation, heating and _ _current generation are presented. K L Wong et al, Rev Sci Instrum, 53 (4), 1982, 409416. 418
33 5633.100 temperature and tbe density distributiou in tbe coroua of a dense z pirub. (USA)
Magnetic field measurements, which are performed at a dynamic z-pinch experiment, yield the ion temperature of the dense plasma column. The value of the ion temperature is consistent with results obtained from the speed of signal propagation, from the equilibrium of the pressure of the plasma boundary and from a consideration of the balance of energy. From an analysis of the speed of compressional Alfvtn waves in the region between the wall and the compressed plasma channel, the density outside the dense column is derived. The electron density in the corona is about three orders of magnitude smaller than in the core. (West Germany) K H Finken and U Ackermann, J Appl Phys, 53 (l), 1982, 226229. 33 5634. Tramient conditiom in inductively heated plasma: thermodynamic equiRbiurn and temperature meamremettts. (Canada) A study has been made on transient extinction conditions in an inductively heated argon plasma. It was observed that local thermodynamic equilibium (LTE) conditions do exist between the metastable 3P2 level and upper energy levels, so that during the decay time it is possible to determine a meaningful temperature, using the 3P2 level as fundamental level and the partition functions being calculated accordingly. Together with the temperature determination, a concentration distribution of argon metastables was obtained. Studies of this type are useful for the investigation of quenching processes in plasmas, affecting favourably chemical reactions or solid-gas interactions, thus leading to enhanced catalytic effects or modifications of solid particle structures which are liable to generate new electrical, thermal, etc. properties of interest. Paul Meubus, Can J Phys, 60 (6), 1982, 886-892. 33 5635. Iaelastic seatterlng of slow positrons by belium, neon and argon atoms. (Canada) Measurements of the excitation and ionization of helium, neon and argon by positrons of energies between threshold and 50 eV, utilizing time-offlight energy loss spectrometry, are reported. Scattering into forward angles up to 60” is observed and the measurements suggest that sharp forward lobes exist in the angular distributions of positrons scattered following atomic excitation. Multiple scattering corrections to the measurements are described. Comparison is made with the inelastic scattering of electrons by the same atoms, and connections drawn between the present results and those of the recent complementary studies of Griffith et al and Charlton et al. (USA) P G Coleman et al, Can .I Phys, 60 (4), 1982, 584590. 33 5636. Low-energy positrouhydrogen molecule scattering. (Canada) The method of Hara using two centre formalism has been employed to investigate positron-hydrogen molecule scattering at low incident energies. Two model potentials have been used to see the importance of the choice of effective potential. It has ken found that the total cross sections are sensitive to the details of the effective potential. The present results are in qualitative agreement with measured values and other existing theoretical predictions. (India) Sukanya Sur and A S Ghosb, Can J Phys, 60 (4). 1982, 597-600. 33 5637. Positron diffusion in krypton and xenon. (Canada) The equations describing diffusion of positrons in krypton and xenon are solved with the best theoretical scattering and annihilation data available to date to obtain the time variation of thi positron annihilation rate. The theoretical shoulder lengths obtained with the data of McEachran et al agree well with the experimental values given by the University College London group, while the shoulder lengths obtained with the data of Schrader are much larger. The present results allow for an assessment of the accuracy of the existent low energy e+Kr and e+Xe elastic cross sections. (Romania) R I Cftmpeanu, Can .I Phys, 60 (4), 1982, 615617. 33 5638. Radial variation of excited atom demities in an argon plasma column produced by a microwave surface wave. (Canada) The radial variations of radiative and metastable atom densities in an argon plasma column produced by a microwave surface wave are obtained. A large variety of radial profiles is observed as a function of wave frequency (300-1000 MHz), gas pressure (SC200 mtorr), tube diameter (17.534 mm) and axial magnetic field. The results differ significantly from those reported for the dc positive column, where the radial distributions keep approximately the same J, Bessel-like profile. M Moisan et al, Can J Phys, 60 (3), 1982, 379-382.
5629-5638
the partial pressure or throughput of nitrogen in the system as shown using controlled leaks of both pure nitrogen and air. The nitrogen may destroy the columnar microstructure and the film perpendicular magnetic anisotropy which is due to the well-oriented hcp phase. This sensitivity to nitrogen in the background gases makes it necessary to achieve a low background pressure in the sputtering chamber if films with perpendicular magnetic anisotropy are to be obtained. T M Cougblin, J Vat Sci Technol, 20 (Z), 1982, 171-174. 31 5629. Pressure and angle of incidence effects in reactive planar magnetron sputtered En0 layers. (USA)
ZnO films have been prepared by rf sputtering a Zn target in a planar magnetron system with controlled Ar/O, gas mixtures. The films were deposited on unheated glass substrates which were either stationary in front of the target or in constant motion. Both the system pressure and plasma impedance changed when an oxide layer formed on the target surface. This occurred at an oxygen flow rate which increased almost linearly with rf power; at 500 W, the required flow rate was 9 ml min-’ and the pressure increased from 0.1 to 1.2 Pa due to the reduced oxygen gettering. High resistance ZnO films were deposited at oxygen flow rates above this threshold value. The target self-bias voltage increased by 30 V at this value; it is affected by both the system pressure and the power. The deposition rate increased linearly with power at approximately 0.03 @m/min)/(W/cm’) which appears to be typical of sputtering from a ZnO layer or target. For continuous substrate motion, the average rate was approximately 7% of this value. All the films were polycrystalline ZnO with a preferred orientation, the c axis of the hexagonal structure being within a small angle of the substrate normal; this orientation was improved by motion of the substrate past the target. Films deposited at pressures of approximately 0.4 Pa had a large internal stress, as revealed both by substrate bending and X-ray measurements. Increasing the pressure to 4.7 Pa decreased the stress by an order of magnitude. SEM analysis showed that this was associated with the development of a columnar structure. The refractive indices obtained from guided wave measurements were 1940~0.006 and 1.962 kO.003, which correspond to 97% of the single crystal values. The resistivity measured normal to the film plane was greater than 1O’R cm. The changes in film stress and structure are similar to effects in metal films. The electromechanical coupling coefficients obtained from SAW measurements are approximately half the best reported value. (Canada) S Maniv et al, .f Vat Sci Technol, 20 (2), 1982, 162-170.
33. NUCLEONICS 33 5630. Electron temperature
measurement
of cold plasma
in a strong
mnguetic field. (GB)
This paper shows how electron temperature and density in low pressure cold plasma (T.< 10 eV) can be measured directly from cyclotron resonance absorption measurements in a strong homogeneous magnetic field (cz20 T). For pressure below 0.5 torr, the cvclotron line width is Doppler broadened and the electron temperature is directly derived from this parameter. At high pressures the line width becomes collision broadened and the electron temperature is indirectly derived using the known energy dependence of the collision frequency. (France) A Dorelon et al, J Phys D: Appl Phys, 15 (4), 1982, 605-614. 33 5631. Beam-foil spectroscopy of Se IV, V and VI. (Canada) Six new transitions are assigned in Se V, resulting in the classification of three new levels: 4s4d ‘D, 4~5s ‘5, and 4s5p ‘P”. Lifetimes and multiplet$ values are presented for the 4s24d2D, 4s4p2 *P, 4s4p2 ‘S, and 4~42 ‘b terms of Se IV. the 4~5s 3S.4s4d “D. 4s4d and 4n2 ‘D. 4~40 ‘PO.and 40~ 3P terms of Se V and the 5s *s, 4d *D, and 4p *PO terms’of Sk VI. The cascade repopulation problems were analysed by using the ANDC method on the terms 4s4p ‘PO of Se V and 4p *PO of Se VI. J L Bahr et al, J Cen Phys, 60 (8), 1982, 1108-I 116. 33 5632. ACT-I: A steady-state torus for basic pLasma physics research. (USA) The construction and operation of a steady-state toroidal plasma device are described. The toroidal plasma can be maintained without any rotational transform and the plasma quality is significantly better than that in linear devices. It opens up new areas for basic plasma physics research. Examples of experiments on wave propagation, heating and _ _current generation are presented. K L Wong et al, Rev Sci Instrum, 53 (4), 1982, 409416. 418
33 5633.100 temperature and tbe density distributiou in tbe coroua of a dense z pirub. (USA)
Magnetic field measurements, which are performed at a dynamic z-pinch experiment, yield the ion temperature of the dense plasma column. The value of the ion temperature is consistent with results obtained from the speed of signal propagation, from the equilibrium of the pressure of the plasma boundary and from a consideration of the balance of energy. From an analysis of the speed of compressional Alfvtn waves in the region between the wall and the compressed plasma channel, the density outside the dense column is derived. The electron density in the corona is about three orders of magnitude smaller than in the core. (West Germany) K H Finken and U Ackermann, J Appl Phys, 53 (l), 1982, 226229. 33 5634. Tramient conditiom in inductively heated plasma: thermodynamic equiRbiurn and temperature meamremettts. (Canada) A study has been made on transient extinction conditions in an inductively heated argon plasma. It was observed that local thermodynamic equilibium (LTE) conditions do exist between the metastable 3P2 level and upper energy levels, so that during the decay time it is possible to determine a meaningful temperature, using the 3P2 level as fundamental level and the partition functions being calculated accordingly. Together with the temperature determination, a concentration distribution of argon metastables was obtained. Studies of this type are useful for the investigation of quenching processes in plasmas, affecting favourably chemical reactions or solid-gas interactions, thus leading to enhanced catalytic effects or modifications of solid particle structures which are liable to generate new electrical, thermal, etc. properties of interest. Paul Meubus, Can J Phys, 60 (6), 1982, 886-892. 33 5635. Iaelastic seatterlng of slow positrons by belium, neon and argon atoms. (Canada) Measurements of the excitation and ionization of helium, neon and argon by positrons of energies between threshold and 50 eV, utilizing time-offlight energy loss spectrometry, are reported. Scattering into forward angles up to 60” is observed and the measurements suggest that sharp forward lobes exist in the angular distributions of positrons scattered following atomic excitation. Multiple scattering corrections to the measurements are described. Comparison is made with the inelastic scattering of electrons by the same atoms, and connections drawn between the present results and those of the recent complementary studies of Griffith et al and Charlton et al. (USA) P G Coleman et al, Can .I Phys, 60 (4), 1982, 584590. 33 5636. Low-energy positrouhydrogen molecule scattering. (Canada) The method of Hara using two centre formalism has been employed to investigate positron-hydrogen molecule scattering at low incident energies. Two model potentials have been used to see the importance of the choice of effective potential. It has ken found that the total cross sections are sensitive to the details of the effective potential. The present results are in qualitative agreement with measured values and other existing theoretical predictions. (India) Sukanya Sur and A S Ghosb, Can J Phys, 60 (4). 1982, 597-600. 33 5637. Positron diffusion in krypton and xenon. (Canada) The equations describing diffusion of positrons in krypton and xenon are solved with the best theoretical scattering and annihilation data available to date to obtain the time variation of thi positron annihilation rate. The theoretical shoulder lengths obtained with the data of McEachran et al agree well with the experimental values given by the University College London group, while the shoulder lengths obtained with the data of Schrader are much larger. The present results allow for an assessment of the accuracy of the existent low energy e+Kr and e+Xe elastic cross sections. (Romania) R I Cftmpeanu, Can .I Phys, 60 (4), 1982, 615617. 33 5638. Radial variation of excited atom demities in an argon plasma column produced by a microwave surface wave. (Canada) The radial variations of radiative and metastable atom densities in an argon plasma column produced by a microwave surface wave are obtained. A large variety of radial profiles is observed as a function of wave frequency (300-1000 MHz), gas pressure (SC200 mtorr), tube diameter (17.534 mm) and axial magnetic field. The results differ significantly from those reported for the dc positive column, where the radial distributions keep approximately the same J, Bessel-like profile. M Moisan et al, Can J Phys, 60 (3), 1982, 379-382.