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3087. Cataphoretic distributions of Zn and F in a ZnF2He positive-column discharge
Classified abstracts 3087-3096 method. The measured velocity distribution of the fast neutral atoms is described by the sum of two MaxwelI-Boltzmann distributions with temperatures on the order of 0.25 and 1 eV, respectively. This bimodal distribution is attributed to an overpopulation of the high-energy tail of the ion velocity distribution. The measured intensities of the fast neutrals vary between 5 ,~ 10 t'~ and 7 . 10 ~'~ (molecules- t sr- ~). (Netherlands) P G A Theuws et al, J Appl Phys, 48 (6), 1977,2261-2269. 12 3087. Cataphoretic distributions of Zn and F in a ZnFz-He positivecolumn discharge. (USA) Measurements of the longitudinal distributions of Zn and F atoms in a positive-column helium discharge tube have been made using ZnF2 as a source in a conventional appendage reservoir. It has been shown that while the cataphoresis of Zn* ions is mainly responsible for determining the Zn longitudinal distribution, the cataphoresis of F - ions probably formed by capture of free electrons from the discharge by F atoms strongly influences the distribution of F atoms. The application of metal-fluoride-noble-gas discharges to further metal-vapor laser reserach is discussed. M Cem Gokay and L A Cross, J Appl Phys, 48 (6), 1977, 2294-2296. 12 3088. Dissociation of fluorine by electron impact. (USA) Using a previously developed F-atom diagnostic technique, the efficiency of F2 dissociation by an electron beam or an electronbeam-sustained discharge was systematically studied. By monitoring the transient concentration of ions generated during the electronbeam-sustained discharge, we have determined the F - ÷ F 2 + ion-ion recombination and F2 dissociative attachment rate constants at various E/P conditions. The dissociative attachment rate constant of F2 at an average electron energy of 1 eV was found to be about (2.3±0.3) >: 10 -9 cm3/molecule sec-K and increased with decreasing electron energy. The F - + F 2 + - - 3 F recombination rate constant at an E/P of 18 kV/cm/atm was found to be about (1.5±0.2)× 10 - s cm3/molecule see-= and also increases with decreasing F/P values. The sustained-discharge enhancement of F-atom production from these experiments in F2 is small, ~1.7. Hao-Lin Chen et al, J Appl Phys, 48 (6), 1977, 2299-2305. 12 3089. Magnetic constriction effects in high-current vacuum arcs prior to the release of anode vapor. (USA) A model is developed describing the interelectrode plasma generated by a multi-cathode-spot cathode as a conducting fluid flowing from the cathode to the anode. The model is analyzed numerically for a sample physical situation consisting of a 3-kA Cu vapor arc between 25-mm-diam electrodes separated by 9 mm, in which case the mass density and fluid velocity are found to be 5 x 10 - s kg/m 3 and 7 x 103 m/s, respectively. The fluid flow is analyzed and a constriction caused by the magnetic pinch force is found to develop near the anode. A constriction in the current flow is also calculated, caused primarily by the Hall current. (Israel) R L Boxman, J Appl Phys, 48 (6), 1977, 2338-2345. 12 3090. Measurements with double probes in organic vapor for understanding the glow-discharge polymerization processes. (USA) Effects of contamination on the double-probe characteristics in nitrogen glow discharge are studied by using defined films polymerized in styrene glow discharge. As the contamination of the film is increased in thickness, the current-voltage (Ij-V~) curve of the probe shifts along the Va axis and all the parameters employed for estimating electron temperature are varied. An equivalent circuit of the film allows one to interpret neither of these parameters but the shift of curve. The limit of the film thickness is also determined within which the probe characteristic is scarcely affected. On the assumption that this limit can be applied to the organic vapor, the electron temperature in the positive'column of glow discharge in styrene vapor at 1 torr is estimated at 22,000 K by a quick performance of the double-probe measurement. (Japan) Shinji Yamaguehi et al, J Appl Phys, 48 (6), 1977, 2363-2369. 12 3091. Spread of total energy dislxibufion of thermal field-emitted electrons from LAB6. (GB) The spread of the total energy distribution of thermal field-emitted electrons from LaB6 is calculated and compared with that from W.
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The results show that the energy spread of electrons emitted from LaBs has a maximum at a certain temperature, and that the spread of those from W is smaller than those from LaBs. This suggests that a low work-function material does not necessarily show a good performance for a temperature field-emitted electron source. (Japan) Hiroshi Adachi et al, J Phys D: Appl Phys, 10 (8), 1977, L I 13-L I 15. 12 3092. rf discharge plasma conditions ill a plasma processing apparatus. (GB) Measurements were made of specimen support, wall and probe potentials in a plasma, as typically used for plasma enhanced reactions, excited by an rf supply (27 MHz, 80 V peak to peak). The rf power was coupled to the reaction chamber with various electrode arrangements. The results show that the specimen support and metal strips placed along the chamber wall develop a potential which is always negative with respect to plasma potential, but positive or negative to ground depending on various types of rf electrode arrangement. Electron and ion currents were found to diminish when a floating metal screen insulated from ground was placed around the specimen support. However when the metal screen was grounded the ion current at the support decreased but electron current, in general, increased. Double probe measurements were made to estinaate electron energy in an rf discharge. S M Ojha, I/actium, 27 (2), 1977, 65-67. 12 3093. Ultraviolet spectral elticiencies of surface-spark discharges with emphasis on the iodine photodissociation laser pumpband. (USA) Spectroscopic studies of the uv emission from surface-discharge sparks across AI.,O3, BN, ZnO, ZrO2, BaTiO3, ZnO-AzO3, and Cr203-AI203 substrates have been performed in He, N2, CO2, At, SF6, and Ar ÷ i-C3FTI gases at pressures of 1-I0 atm. Considerable differences were found in the performance of the various substrates; based on absolute measurements which are believed to be conservative, an electrical-to-optical conversion efficiency of 9.4~1.1% for uv emission in the 2500-2900-A iodine-laser pumpband was obtained from discharges across a Cr_,O3-AI203 substrate in Ar gas. Pumpband energy densities of several J/cm z are readily attainable. R E Beverly et al, Appl Opt, 16 (6), 1977, 1572-1577.
II. V a c u u m
a p p a r a t u s and auxiliaries
20. PUMPING SYSTEMS 20 3094. A cryopumped aerodynamic molecular beam apparatus. (GB) The use of cryopumping simplifies the design and construction of an aerodynamic molecular beam system, since the very fast pumping speeds attainable enable a high vacuum to be maintained even in the presence of heavy gas loads. A molecular beam facility, pumped exclusively by 4.2 K cryosurfaces, is described. B A Hands and P D Bentley, Vocttttm, 27 (2), 1977, 53-59.
21. PUMPS AND P U M P FLUIDS 21 3095. Geometry and properties of the plasma in a quadrupole ion pump. (USA) The diameter of the plasma in a quadrupole ionization gauge and quadrupole ion pump has been measured as a function of pressure. The radio-frequency quadrupole systems are tuned in such a way that electrons remain on stable trajectories in the center of the tube. Being emitted at one end, the electrons encounter an inverted field at the other end so that they travel on spiral paths back and forth until they collide with the rest gas molecules, producing ions which are collected as an ion current i + at a cylinder surrounding the four hyperbolically shaped quadrupole electrodes. The inverse pressure relationship pi +4~a = const can be explained with the experimental result showing the plasma diameter d being inversely proportional to the square root of the pressure p: d = aop- t~2. (Brazil) H Sehwarz, J Vac Sci Technol, 14 (2), 1977, 731-733. 21 3096. Performance of the modified orbitron pump. (USA) The conventional orbitron pump is modified to improve the speeds for inert gases. Pumping speed measurements were made on the
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The results show that the energy spread of electrons emitted from LaBs has a maximum at a certain temperature, and that the spread of those from W is smaller than those from LaBs. This suggests that a low work-function material does not necessarily show a good performance for a temperature field-emitted electron source. (Japan) Hiroshi Adachi et al, J Phys D: Appl Phys, 10 (8), 1977, L I 13-L I 15. 12 3092. rf discharge plasma conditions ill a plasma processing apparatus. (GB) Measurements were made of specimen support, wall and probe potentials in a plasma, as typically used for plasma enhanced reactions, excited by an rf supply (27 MHz, 80 V peak to peak). The rf power was coupled to the reaction chamber with various electrode arrangements. The results show that the specimen support and metal strips placed along the chamber wall develop a potential which is always negative with respect to plasma potential, but positive or negative to ground depending on various types of rf electrode arrangement. Electron and ion currents were found to diminish when a floating metal screen insulated from ground was placed around the specimen support. However when the metal screen was grounded the ion current at the support decreased but electron current, in general, increased. Double probe measurements were made to estinaate electron energy in an rf discharge. S M Ojha, I/actium, 27 (2), 1977, 65-67. 12 3093. Ultraviolet spectral elticiencies of surface-spark discharges with emphasis on the iodine photodissociation laser pumpband. (USA) Spectroscopic studies of the uv emission from surface-discharge sparks across AI.,O3, BN, ZnO, ZrO2, BaTiO3, ZnO-AzO3, and Cr203-AI203 substrates have been performed in He, N2, CO2, At, SF6, and Ar ÷ i-C3FTI gases at pressures of 1-I0 atm. Considerable differences were found in the performance of the various substrates; based on absolute measurements which are believed to be conservative, an electrical-to-optical conversion efficiency of 9.4~1.1% for uv emission in the 2500-2900-A iodine-laser pumpband was obtained from discharges across a Cr_,O3-AI203 substrate in Ar gas. Pumpband energy densities of several J/cm z are readily attainable. R E Beverly et al, Appl Opt, 16 (6), 1977, 1572-1577.
II. V a c u u m
a p p a r a t u s and auxiliaries
20. PUMPING SYSTEMS 20 3094. A cryopumped aerodynamic molecular beam apparatus. (GB) The use of cryopumping simplifies the design and construction of an aerodynamic molecular beam system, since the very fast pumping speeds attainable enable a high vacuum to be maintained even in the presence of heavy gas loads. A molecular beam facility, pumped exclusively by 4.2 K cryosurfaces, is described. B A Hands and P D Bentley, Vocttttm, 27 (2), 1977, 53-59.
21. PUMPS AND P U M P FLUIDS 21 3095. Geometry and properties of the plasma in a quadrupole ion pump. (USA) The diameter of the plasma in a quadrupole ionization gauge and quadrupole ion pump has been measured as a function of pressure. The radio-frequency quadrupole systems are tuned in such a way that electrons remain on stable trajectories in the center of the tube. Being emitted at one end, the electrons encounter an inverted field at the other end so that they travel on spiral paths back and forth until they collide with the rest gas molecules, producing ions which are collected as an ion current i + at a cylinder surrounding the four hyperbolically shaped quadrupole electrodes. The inverse pressure relationship pi +4~a = const can be explained with the experimental result showing the plasma diameter d being inversely proportional to the square root of the pressure p: d = aop- t~2. (Brazil) H Sehwarz, J Vac Sci Technol, 14 (2), 1977, 731-733. 21 3096. Performance of the modified orbitron pump. (USA) The conventional orbitron pump is modified to improve the speeds for inert gases. Pumping speed measurements were made on the