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A study of surface stoichiometry and thermionic emission using LaB6.
Classified abstracts 4342-4351 model is self-consistent and requires no experimentally determined parameters. L Bromberg and L D Smullin, J uppl Phys, 50 (4), 1979, 2634-2637. 4342. Study of collective ion acceleration in vacuum. (USA) Theoretical and experimental studies of the collective acceleration of ions by a linear electron beam in an evacuated drift tube are presented. A one-dimensional theoretical model of the collective acceleration process that predicts accelerated proton energies of many times the electron-beam energy is presented. The formation of a virtual cathode downstream of the anode-cathode gap is discussed, and the subsequent movement of the virtual cathode downstream as the anode plasma expands allows for enhanced acceleration of ions trapped in the potential well of the virtual cathode. Experiments reported indicate that effective electron beam propagation and effective collective acceleration occurs when a plasma source initially well confined to the anode is present. W W Destler et al, J upp. Pllys, 50 (5), 1979, 3015-3022. 12 4343. Hydrogen content and density of plasma-deposited amorphous silicon-hydrogen. (USA) The hydrogen concentration and density of amorphous semiconducting films prepared by glow-discharge decomposition of silane have been measured as a function of deposition temperature. An inductively coupled as well as a capacitively coupled plasma-decomposition system was used. For samples prepared by the capacitively coupled system, the hydrogen content decreased from 26 to 8 at.“,‘, and the density increased from 1.9 to 2.27 g cm-’ as the substrate temperature was increased from 25 to 450°C. H Fritzsche et al, J appl Phys, 50 (5), 1979, 3366-3369. 4344. Propagation of power pulses in magnetically insulated vacuum transmission lines. (USA) The propagation of a 1.8 MV 80 kA power pulse in a 10 m long 41.6 R impedance coaxial vacuum transmission line has been investigated experimentally. The onset of magnetic insulation has been correlated to attainment of the critical current. Measurements of boundary (cathode) current suggest that 50-60!/, of the current flows in space charge in the axial direction between the conductors. The pulse sharpens as it propagates and attains a stationary shape. Pulse rise times of 4 ns were observed. Propagation velocities equal to 0.7 c have been measured. Power and energy transports as high as 90 and 70% have been observed. The peak power density in the transmission line was 2 x lo9 W cme2. M S Di Capua and D C Pellinen, J appl Phys, 50 (5), 1979, 3713-3720. 12 4345. A study of surface stoicbiometry and thermionic emission using LaB6. (USA) The variables which influence the surface composition of vaporizing compounds have been studied using the behaviour of LaB6 as an example. The thermionic work function of LaB6 has been determined as a function of surface stoichiometry. A nearly constant value of 2.93 eV for the effective work function was observed from the LaBs + LaB, boundary up to approximately LaBs.os. A further increase in boron content caused a steep increase reaching 3.40 eV at the LaB6 + LaB9 boundary at 1500 K. The interior composition which produces a surface composition having a high emission flux and the lowest attrition rate is in the high boron regionnear LaBs,s, not at the stoichiometric composition. E K Storms and B A Mueller, J uppl Phys, 50 (5), 1979, 3691-3698. 4346. Secondary electron emission from vanadate-phosphate glasslst (USA) Secondary electron emission from V,O,-P,O, glasses has been investigated for a range of primary energies between 90 eV and 5.5 keV. The sample compositions studied cover the useful range for these materials. from 50 to 95 mot% VZOs. The measurements were carried out on specimens freshly cleaved in ultra-high vacuum. Accurate data for these materials have not previously been available. (-1 E A Flinn and M Salehi, J appl Phys, SO (5), 1979, 3674-3676. 238
12 4347. The effect of alumina inclusions on the breakdown and emission properties of copper surfaces in vacuum. (USA) We have studied electrical breakdown in vacuum for copper electrodes which have been intentionally contaminated by adding l/2% by weight of alumina powder having a size of 500, 50 or 5 pm. Electron emission, pulse breakdown and scanning electron microscopy have been used to evaluate the dielectric characteristics of the surfaces. Comparison of these results with those obtained using a zone-refined copper surface indicate an initial degradation of about 30% for the surface containing 50 pm particles and little effect for the surface containing 500 pm particles. All surfaces conditioned to about the same voltage. Breakdown to all samples containing particles was clearly associated with metal-insulator boundaries. G A Farrall et al, J uppl Phys, 50 (5), 1979, 3608-3614. 12 4348. Energy loss and escape depth of hot electrons from shallow p-n junctions in silicon. (USA) The emission of electrons from a reverse-biassed p-n located below and parallel to an rr-type emitting surface has been investigated experimentally. By sputter thinning the rl-layer, followed by annealing and CS-0 treatments all in vacuum, we have been able to measure the energy distributions of emitted electrons at several different n-layer thicknesses, allowing direct application of a theoretical treatment due to Baraff. The surface barrier of w I.1 CV enables us to sample electrons having an average energy of about 3.0 eV above the conduction-band minimum. At these energies, considerably below those studied by most others, we find the mean free path for optical phonon emission, L,,, IO be I41 A, for ionization, I.,. to be 8526 A, and the total attenuation length, L,, to be 359 A. I Shahriary, et al, J uppl Phys, 50 (3), 1979, 1428-1438. 12 4349. Prebreakdown discharges in mercury-rare-gas mixtures. (USA) We have examined the properties of mercury-rare-gas discharges operated at low fields whcrs volume ionization is negligible. The discharge current is due to thcrnmionically produced electrons and is limited by the electron mobility. The mixtures consisted of mercury and either Ar, Kr or Xe at 30-760 torr. Temperatures were varied from 50 to 250°C. Uv and visible radiation production, as well as electrical propcrtics, were measured and compared to theoretical calculations. The measured positive volt-ampere characteristics agree well with theory. The calculated efficiency for excitation of Hg 3P1 in these discharges is greater than SOS:, over a wide range of conditions. The low measured radiation production efficiency (less than 5 “/‘,) is consistent with model calculations which include quenching of the ‘PI by Hg and the rare gas to the ‘P,, state and its subsequent decay by the formation of mercury excimers. W D Partlow and L E Kline, J uppl Phys, 50 (3), 1979, 1250-1255. 4350. Positive-ion drift velocities and Townsend primary ionization coefficients in ethane. (GB) Positive-ion drift velocities have been measured in ethane gas, using the pulsed Townsend discharge technique, over the range 40 I E/p I 1400 V cm-’ torr-‘. For 40 < E/p <_ 825 V cm-’ torr-’ positive-ion drift velocities were determined by the balanced-pulse technique, and in the range 490 _< E/p < 1400 V cm-’ torr-’ by the positive-ion successor interval method. The experimental ion drift velocity was found to exhibit a linear dependence on E/p at low E/p changing to a square-root dependence at high E/p. Townsend primary ionization coefficients have also been determined from balanced pulse measurements over the range 40 I E/p I 825 V cm-’ torr-‘. Experimental values of u/p are in moderate agreement with Townsend conductivity determinations, being lower at low E/p and higher at high E/p. In the range 100 2 E/p 2 250 V cm-‘ torr-’ agreement is good. The effect of space-charge field distortion on the CLcoefficient, and hence the balanced pulse, is discussed. It is found that space-charge field distortion can produce different effects on the G( coefficient in the pulsed and steady-state Townsend discharges. M P Watts and A E D Heylen, J Phys D: Appl Phys, 12 (5), 1979, 695-702. 12 4351. Plasma oxidation of silicon in a microwave discharge and its specificity. (GB) The paper analyses conditions of oxide formation on silicon in a microwave plasma. Experimentally it is shown that oxide films can
12 4347. The effect of alumina inclusions on the breakdown and emission properties of copper surfaces in vacuum. (USA) We have studied electrical breakdown in vacuum for copper electrodes which have been intentionally contaminated by adding l/2% by weight of alumina powder having a size of 500, 50 or 5 pm. Electron emission, pulse breakdown and scanning electron microscopy have been used to evaluate the dielectric characteristics of the surfaces. Comparison of these results with those obtained using a zone-refined copper surface indicate an initial degradation of about 30% for the surface containing 50 pm particles and little effect for the surface containing 500 pm particles. All surfaces conditioned to about the same voltage. Breakdown to all samples containing particles was clearly associated with metal-insulator boundaries. G A Farrall et al, J uppl Phys, 50 (5), 1979, 3608-3614. 12 4348. Energy loss and escape depth of hot electrons from shallow p-n junctions in silicon. (USA) The emission of electrons from a reverse-biassed p-n located below and parallel to an rr-type emitting surface has been investigated experimentally. By sputter thinning the rl-layer, followed by annealing and CS-0 treatments all in vacuum, we have been able to measure the energy distributions of emitted electrons at several different n-layer thicknesses, allowing direct application of a theoretical treatment due to Baraff. The surface barrier of w I.1 CV enables us to sample electrons having an average energy of about 3.0 eV above the conduction-band minimum. At these energies, considerably below those studied by most others, we find the mean free path for optical phonon emission, L,,, IO be I41 A, for ionization, I.,. to be 8526 A, and the total attenuation length, L,, to be 359 A. I Shahriary, et al, J uppl Phys, 50 (3), 1979, 1428-1438. 12 4349. Prebreakdown discharges in mercury-rare-gas mixtures. (USA) We have examined the properties of mercury-rare-gas discharges operated at low fields whcrs volume ionization is negligible. The discharge current is due to thcrnmionically produced electrons and is limited by the electron mobility. The mixtures consisted of mercury and either Ar, Kr or Xe at 30-760 torr. Temperatures were varied from 50 to 250°C. Uv and visible radiation production, as well as electrical propcrtics, were measured and compared to theoretical calculations. The measured positive volt-ampere characteristics agree well with theory. The calculated efficiency for excitation of Hg 3P1 in these discharges is greater than SOS:, over a wide range of conditions. The low measured radiation production efficiency (less than 5 “/‘,) is consistent with model calculations which include quenching of the ‘PI by Hg and the rare gas to the ‘P,, state and its subsequent decay by the formation of mercury excimers. W D Partlow and L E Kline, J uppl Phys, 50 (3), 1979, 1250-1255. 4350. Positive-ion drift velocities and Townsend primary ionization coefficients in ethane. (GB) Positive-ion drift velocities have been measured in ethane gas, using the pulsed Townsend discharge technique, over the range 40 I E/p I 1400 V cm-’ torr-‘. For 40 < E/p <_ 825 V cm-’ torr-’ positive-ion drift velocities were determined by the balanced-pulse technique, and in the range 490 _< E/p < 1400 V cm-’ torr-’ by the positive-ion successor interval method. The experimental ion drift velocity was found to exhibit a linear dependence on E/p at low E/p changing to a square-root dependence at high E/p. Townsend primary ionization coefficients have also been determined from balanced pulse measurements over the range 40 I E/p I 825 V cm-’ torr-‘. Experimental values of u/p are in moderate agreement with Townsend conductivity determinations, being lower at low E/p and higher at high E/p. In the range 100 2 E/p 2 250 V cm-‘ torr-’ agreement is good. The effect of space-charge field distortion on the CLcoefficient, and hence the balanced pulse, is discussed. It is found that space-charge field distortion can produce different effects on the G( coefficient in the pulsed and steady-state Townsend discharges. M P Watts and A E D Heylen, J Phys D: Appl Phys, 12 (5), 1979, 695-702. 12 4351. Plasma oxidation of silicon in a microwave discharge and its specificity. (GB) The paper analyses conditions of oxide formation on silicon in a microwave plasma. Experimentally it is shown that oxide films can