195. Investigation of current rise on pulsed breakdown of millimeter vacuum gaps

Classified

abstracts

186-195

dependence on various evaporation conditions, are investigated. The thermal annealing of films is studied. M V Kurik and G A Sandul, (/krain Fiz Zh, 15 (3), 1970, 391-394 (in

adatom gas are analyzed, and features of the ensemble coalescence of the charged grains are considered. Ya E Geguzin et al, Fiz Tverd Tela, 12 (7), July 1970, 195331962 (in

Ukrainian).

Russian).

186. Electrical characteristics sapphire. (USSR)

of the surface of single-crystal

30 films on

Surface characteristics of hetero-epitaxial single-crystal silicon films of n-p type, obtained by evaporation in vacuum at 1 x lo+ torr on sapphire, are investigated with the aid of measurements of local contact potential difference, field effect, and photoconductivity. The band bending and surface trap concentration are estimated. V S Lisenko et al, ilkrain Fir Zh, 15 (3), 1970,409-414 (in Ukrainian). 30 187. Optical properties of PbCl, thin films.

(USSR) Optical properties of thin PbCI, films prepared by evaporation in vacuum at IO+ torr on quartz substrates are investigated. Experimental results are discussed. N L Kramarenko et al, Ukrain Fiz Zh, 15 (3), 1970, 415-420 (in Ukrainian). 30 188. Electron gun for evaporation

of thin films.

(Yugoslavia) The design of an electron gun, used for the vacuum deposition of thin films of metals, alloys, semiconductors or dielectrics, is described. Simplicity and high efficiency of the electron beam power used for deposition are the most important characteristics of the design. A ring cathode is used as an electron source. High voltage of up to 10 kV is applied for focusing the electron beam to a target diameter of 1 mm. At the highest electron beam current of 250 mA, it is possible to obtain deposition temperatures up to 3800°C. Electron gun characteristics are determined. B Navinsek, Elektrotehniski Vestnik, 37 (l-3), 1970, 9-l 1 (in Slovenian). 189. Arrangement beam. (USSR)

for ionization

of material

evaporated

30 by electron

A vacuum system is described, in which a discharge in metal vapour is used to enhance the degree of ionization. The arrangement consists of a discharge chamber and electron beam evaporator. The metal vapour is ionized by the electron beam used for evaporation and by accelerated secondary electrons emitted on metal bombardment. A Penning discharge is used to enhance the metal vapour ionization. The system is pumped to 5 x 1O-Etorr and during evaporation the pressure is kept below 1.5 x 10v5 torr. Characteristics of this system for copper as evaporation material are given. The copper vapour plasma can also be observed visually. Typical dependencies of the collector and discharge currents on time are given. Discharge power dissipated on the cathode is small with respect to the electron beam power. The deposition rate is therefore determined by electron beam parameters. It is shown that at deposition rate below 100 A/set the arrangement allows deposition of films uniformly bombarded by ions, on a substrate of a few centimetres diameter, with ion current density of 50 to 100 /LA/cm2, and the ratio of ion to atom current of 0.5 per cent. The copper films, 0.3 to 0.7 ,um thick, have 2 to 3 times higher adhesion to substrate in comparison with those prepared without discharge. The ion source can also be used for obtaining ohmic contacts to GaAs. V P Belevskiy and V M Koptenko, Prib Tekh Eksper, Nr 4, July-Aug 1970, 188-190 (in Russian). 190. Limiting of tunnel current in Me-D-Bi,,Sb, centres localized near the interface D-Bit,:,Sb,.

junctions

30 by capture

(USSR) Metal-dielectric-BiSb junctions are studied. W-shaped tunnelling conductance curve of these junctions is attributed to the presence of bismuth in the material of the upper electrode. The bismuth atoms produce local energetic states near the surface of the dielectric layer, penetrating into it during vacuum evaporation. 0 0 Galkin and 0 M Ianatev. Ukrain Fiz Zh. 15 (3). 1970. 436-438 _ I

.,.

(in Ukrainian). 191. Diffusional

coalescence

of metal grains on nonmetal

30 substrates.

(USSR) Diffusional coalescence kinetics of gold grains deposited by a molecular beam on NaCl crystal surface is investigated using an electron microscope. It is found that electrically charged centres on the substrate considerably influence the coalescence kinetics, Equilibrium conditions of the charged metallic grains with a two-dimensional 146

192. Technology for the batch manufacture circuits. (Poland)

30 hybrid thin film micro-

Vacuum evaporation technology for hybrid thin film microcircuits, manufactured in small batches, is described. Properties of the variable masking method are tested and compared with those of sequence processing. Technological processes including ion etching, evaporation of Ni-Cr alloy as resistors, SiO as dielectrics and protective layers, Al as capacitor electrodes and Au as contact material, are described together with pressure behaviour. A Jurewicz, Elektronika,

11 (3), 1970, 107-l 11 (in Polish).

30 193. Peculiarities of tbe angular distribution of sputtered material from single crystals bombarded by ions. (USSR)

The angular distribution of sputtered material under ion bombardment in a broad range of incidence angle, was investigated for single crystals. Single crystals of gold and gold-copper alloy, cut at the (110) and (100) planes, were bombarded by argon ions with energy of 70 keV. Target temperature measured by a thermocouple were 400470°K during ion bombardment. Sputtered material was deposited on a semicylindrical collector made of polyethylene film, 40 microns thick. A pressure of 3 to 6 x lo-’ torr in the working region during ion bombardment was maintained by a powerful pumping system with nitrogen traps. Sputtering patterns were evaluated by visual observation, optical density measurement of deposits by a microphotometer, or radiographic analysis. Target material release in the directions (llO), (lOO), (211), (310), (Ill), (312), (411), (210), (332) and (521) was observed and bands representing tracks of the (111) and (100) planes were found. Relative suppression of material release in the high index directions and at ion incidence angles approximating to the transparent directions in the crystal, was observed. It is concluded that the high energy of the bombarding ions, the high incidence angles, the relatively low mass of the ions with respect to the target atoms, and the use of the cylindrical collector, form the causes of the patches of sputtered material observed with higher indices. V E Dubmskiy and S Ya Lebedev, Fiz Tverd Tela, 12 (7), Ju/y 1970, 1906-1911 (in Russian). 31. EVACUATION

AND SEALING

194. Investigation of structure of electron beams emitted from cathode torch in the initial phase of vacuum breakdown. (USSR)

31 a

Investigation of erosion traces on an anode surface in the initial state of vacuum breakdown was carried out using the method of discharge interruption. A pulse generator produced pulses with amplitude of 35 kV, pulse length of 100 nsec and pulse front of 1 nsec. Interruption of the vacuum discharge was obtained using a vacuum discharge tube with dielectric. Copper, aluminium and molybdenum electrodes were tested. The relationship between the character of the erosion traces on the anode and anode surface structure, was determined by thermal etching of the anode surface in vacuum or by chemical etching. Investigations were carried out in a uniform field with a vacuum gap of 0.35 mm. Two types of erosion traces on the anode were observed: one type has a form of circle; the other type has the shape of a torch. It was found that the erosion traces are due to the electron beams emitted from cathode torches formed at burst microedges. The erosion traces of the torch type are formed, when the electron beams emitted from the cathode torches are overlapped. It is concluded that the cause of formation of many shallow craters on the anode is the nonuniformity of anode surface properties. G P Bazhenov et al, 1zv VUZ Fiz, Nr 8, 1970, 87-90 (in Russian). 195. Investigation of current rise on pulsed breakdown vacuum gaps. (USSR)

31 of millimeter

To elucidate the mechanism of vacuum breakdown and also to explore the possibility of utilizing the initial state of vacuum breakdown in the technique of direct action nanosecond accelerators, the time characteristics of vacuum breakdown of gaps of a few mm were investigated. Experiments were performed in vacuum at 1 x 10m5torr, reached with the aid of a mechanical pump, an oil diffusion pump and two thermoelectric traps. The vacuum discharge chamber has a coaxial structure. The dependence of the rise-time of the spark on the

Classified

abstracts

196205

gap distance was determined for electrodes of aluminium, copper and molybdenum. It was found that the time for a current rise to 10 per cent above the level at the beginning of the pulse is determined by the average electric field intensity. The rise-time of the spark current depends linearly on the gap distance. General agreement between the time characteristics of vacuum breakdown for small and long vacuum gaps indicates the same breakdown initiating mechanism. Vacuum breakdown initiation of long gaps is determined by the formation of cathode torches. It is conclud-d that the motion of the anode torch is not sufficient for pulsed discharge initiation in vacuum. The vacuum breakdown is initiated only in the case, when efficient electron sources are formed on the cathode surface and these electron sources are cathode torches. S P Vavilov and G A Mesyats, Izv VUZ Fiz, Nr 8, 1970, 90-94 (in

set and amplitude of 200 kV, a high velocity oscillograph, and x-ray detector were used to investigate the vacuum discharge time characteristics. It was found that with increasing excess voltage on the vacuum gap, the time of voltage collapse on discharge is diminished. The length of x-ray pulses emitted at breakdown of the vacuum gap is decreased from 45 to 8 nsec with excess voltage increase. It is concluded that in two-electrode vacuum gaps of 1 to 2 mm distance at excess voltage of 1.5 to 3.2, the most probable mechanism of vacuum breakdown is initiated by field emission. N V Belkin and E A Avilov, Zh Tekh Fiz, 40 (8), Aug 1970, 1723-l 724 (in Russian). 31 201. Investigation of breakdown in argon and helium due to picosecond

31 1%. Investigation of high voltage pulsed discharge development in long tubes during the formation uhase. (USSR) Investigation of high voltage pulse> discharge development in long tubes filled with hydrogen to a pressure of 0.4 to 5 torr is carried out during the formation phase. The experimental results are discussed. V V Belous and V N Kostin, Izv VUZ Fir, Nr 8, 1970, 128-133 (in

ruby laser light pulse. (USSR) The threshold flux for breakdown in argon and helium at pressures from 1 torr, induced by a 50 picosecond ruby laser pulse, is investigated. Results show that pressure ranges exist, in which breakdown occurs either as a result of the avalanche mechanism or as a result of multiphoton ionization of gas atoms in the field of the strong light wave. The two mechanisms can be distinguished by their different dependence on gas pressure. I K Krasyuk et al, Zh Eksper Teor Fir, 58 (5), May 1970, 1606-1608

Russian).

(in Russian).

Russian).

31 197. Controlled gas discharge device with cold hollow cathode. (USSR)

A device for commutation of high pulsed currents in high voltage equipment is described. Application of a hollow cold cathode of metal, together with a new design of the starting electrode, in this gas discharge device, working at a hydrogen pressure of 0.3 torr, allowed decrease of the starting power to 10ms wattsec for commutation of a pulsed current of 16 kA. Life characteristics of this device were tested. I I Aksenov et al, Prib Tekh Eksper, Nr 4, July-Aug 1970, 18&185 (in Russian).

31 198. Materials for ignitron igniters. (Poland) An analysis of results obtained by various authors on materials for ignitron igniters is presented. Original results containing the examination of 35 high melting compounds are reported. Semiconducting materials B-BN-C prepared from pure materials and MoS&-S&N, prepared from materials with technical purity have been found to be the best igniter materials from the viewpoint of ignition parameter stability. Ignition power of these igniters is considerably less than 1.5 kW. These materialsarestableat temperatures of 1000°C in vacuum at pressure of lo-” torr for 12 hours and at pressure of IO+ torr for 6 hours. T W Duhowik, Elektronika, 11 (2), 1970, 81-86 (in Polish). 31 199. High power gas-discharge-controlled valves with cold cathode for commutation of high pulsed currents. (USSR) Results of an investigation of high power, gas-discharge-controlled valves, with cold cathode, for the commutation of high pulsed currents of 100 kA, are described. The valves are based on the principle of arc discharge extinction at low pressure of 10-l to 10m3torr with the current crossing zero. Discharge initiation is performed by a special sparking arrangement. Hydrogen gas phase pressure of 4 to 8 x 10e2 torr is important only in the initial state of discharge development, the subsequent discharge is maintained in metal vapour. With a current density decrease to 50-100 A/cm*, the metal vapour pressure is close to the initial state, and the gas phase of hydrogen or argon in deionization increases the breakdown strength of the valve. The design of a valve with plane electrodes and a short arc, without special gas filling, having initial pressure of 5 x 1OM8 torr, and allowing reliable commutation of millisecond pulsed currents of 50 kA at inverse voltage of 5 kV, is described. M Yu Geltsel and A A Podminogin, Zh Tekh Fiz, 40 (8), Aug 1970, 1707-1717 (in Russian). 31 ZOO.Some time characteristics of vacuum breakdown on pulsed voltage application with nanosecond front. (USSR) Vacuum breakdown of the gap of two-electrode, sealed x-ray tubes with plane anodes and hemispherical or disc cathodes was investigated after conditioning by at least 500 switchings. Tantalum anodes and a hemispherical tungsten cathode or a steel disc cathode were used. The cathode-anode distance was l-2 mm. The working surfaces of the cathode and anode were covered by shallow craters and edges. A pulse generator producing voltage pulses with a front of 5 x lO-8

31 202. Chemical composition of plasma in flowing CO, lasers and its role

in inverted population generation. (USSR) It is known that the chemical composition of sealed CO, laser gas changes during operation, due to electrical discharge. Using the method of infrared light absorption, it is shown that in flowing CO, lasers the degree of dissociation of the CO, is significant and that it varies from 10 to 70 per cent depending on the gas throughput velocity, discharge current, gas pressure, and discharge tube diameter. The dependence of the CO, molecule concentration in the outlet of the discharge tube on the gas throughput velocity permits determination of the dissociation rate dependence on the time of discharge action. Investigation of kinetics of CO, molecule dissociation in the plasma of CO, flowing laser indicates the need to take account of the changed chemical composition of gas when calculating the population inversion. The calculation of population inversion is performed taking account of the real gas composition and the electron velocity distribution function. The role of the different gas components of the laser mixture on the population inversion is determined. The dissociation rate in discharge as dependent on the total pressure of the laser mixture was determined for different discharge currents. E N Lotkova et al, Zh Tekh Fiz, 40 (7), Jdy 1970, 1402-1409 (in Russian). 31 203. Vacuum arrangement for testing luminescent screens and cathode

ray tubes before sealing off. (Poland) Special vacuum equipment for testing luminescent screens andcathode ray tubes before sealing them off, is described. It enables visual observation of the quality of luminescent screens excited by an electron beam. The vacuum system, containing a diffusion pump, maintains a working pressure of 5 x 10e5 torr in the tested tube. The vacuum tight connection of the vacuum system to the tested tube is described in detail. M Domanski et al, Elektronika, 11 (3), 1970, 97-103 (in Polish). 32. NUCLEONICS

32 204. Pulsed neutron source. (USSR) A pulsed, low-voltage, neutron generatoris described, which is intended for fast neutron spectrometry by the time of flight method. The high frequency deuterium ion source, focusing and modulating arrangement, accelerator and titanium-tritium target for neutron production, are discussed. The neutron source is evacuated by a forepump and oil diffusion pump with cold trap, to a working pressure of 5 x lo-” torr. M E Gurtovoy et al, Prib Tekh Eksper, Nr 4, July-Aug 1970,24-28 (in Russian). 32 205. Shortened gas target with charge exchange.

(USSR) A charge exchange gas target, consisting of thin tubes, is described. This modification enables considerable shortening of target length due to enhancement of the diffusion resistance. A gas target of this type with a length of 45 mm, tube dimensions of 0.75 x0.9 mm, and pressure in the centre of target of 3 x 10ea torr, corresponds to a 147