2225. Interaction of metal layers with polycrystalline Si

Classified abstracts 2215-2225 effect of the high-frequency conductance of the space-charge region turns out to be quite small when the series-resistance effect is taken into account; the performance is then determined by a single transittime factor Ig(j~o) 12 and a series-resistance factor that is independent of transit time. The effect of tunnelling on the device performance is ,discussed briefly. Satisfactory detection and mixing performance seems feasible for the 10M0-/~m wavelength range. A van der Ziel, J Appl Phys, 47 (5), 1976, 2059-2068. 34 2215. Electron gun for generation of snbnanosecond electron packets at very high repetition rate. (USA) In order to create and study trapped particle modes in a plasma column, we have designed an electron gun which delivers packets with a duration shorter than 1 nsec at energies of about 100 eV, and with a repetition frequency of several hundred megahertz. This gun is made with parts of a classical disc-sealed microwave triode. This paper describes the gun itself and the pulse generator used to modulate it. Some results concerning trapped particle modes are shown in conclusion. (France) M Weinfeld and A Bouchoule, Rev Scient Instrum, 47 (4), 1976, 412417. 34 2216. Pulsed microsecond high-energy electron beam accelerator. (USA) Electron beams delivering up to 60 kA at 1.5 MV with pulse durations of 0.5-1.5/~sec were obtained by connecting a low-inductance Marx generator directly across a vacuum diode. Beams with up to 44 kJ and conversion efficiencies up to 51% from Marx energy into electron beam energy were obtained. T H Martin and R S Clark, Rev Scient Instrum, 47 (4), 1976, 460M63. 34 2217. On programmable control of electron-beam welding with space distributed weld. (USSR) Methods for the displacement of the electron beam focused to the surface of welded objects are discussed. Advantages of changing the focusing distance by changes in the focusing current are given. Expenditures necessary for control of focusing distance at welding of space distributed weld are analysed. E N Banya et al, Vestn Kiev Politekh Inst Set Automat Elektropriborostr, No 11, 1974, 137-139 (in Russian). 34 2218. Evaluation of resolution of a three-electrode spherical analyser for investigation of elastically reflected slow electrons. (USSR) Resolution of a three-electrode spherical analyser is calculated on the account of the defocusing action of entrance aperture, defocusing of electron beam at motion in the retarding field between the grid and the specimen and of the scattering action of grid cells. O M Artamonov et al, Uchen Zap LGU, No 370, 1974, 136-140 (in

Russian). 34 2219. Measurement of diffusion length of minority carriers with the aid of an electron beam. (USSR) A method is described for the measurement of small values of diffusion length is the order of tenth microns of minority charge carriers in semiconductors and for the investigation of local changes in diffusion length. The method is based on application of a fine electron beam in vacuum. V I Kononov et al, Coil of Works on Semicon Materials, Dev and Applic, Voronezh, 1973, 182-184 (in Russian). 35 2220. Grain size and film thickness of Nb3 Sn formed by solid-state diffusion in the range 650-800°C. (USA) A simple etching and replication technique for the determination of grain size in thin films of NbaSn has been established. The resulting data compares well with previous reports of grain size as a function of reaction temperature and of the pinning force FPmax as a function of grain size. The possibility of an optimum grain size for Fpmax is indicated. B J Shaw, JApplPhys, 47 (5), 1976, 2143-2145. 35 2221. Inhomogeneities in superconducting niobium surfaces. (USA) Inhomogeneities in superconducting Nb have considerable influence on ac losses in cables; they also give bad rf results. To study inhomogeneities near Nb surfaces, the magnetic induction profile B(x) and hence the critical current density.~(x) were determined as a function of distance x from the surface in samples which were mach-

ined, annealed, and chemically polished or electro-polished and anodized. With identical samples the magnetization and 18-kHz penetration depths were also measured as a function of dc magnetic field, applied parallel to the surface. These measurements on Nb samples, which were all exposed to air, indicate that two superconducting phases exist near the surface. One of them has an Hc2 much higher (50%) and the other somewhat higher (10%) than He2 in the bulk. In addition, strong pinning exists near the surface as evidenced by Jc higher than 106 A/cm z. These effects were found, although to a somewhat lesser extent, even after uhv annealing. The high He2 values and strong pinning near the surface, even above the bulk Hc 2, can be explained by the presence of inhomogeneities there. (Germany) A D Gupta ct al, J Appl Phys, 47 (5), 1976, 2146-2153. 35 2222. Narrow Bloch walls in the RCod-type rare-earth-cobalt compounds. (USA) For compounds of the type YCodxNis _ 5x the saturation moment and Curie temperature were determined. For large Co concentrations the rigid-band approach applies. The magnetic splitting of the 3d band collapses near x = 0.2. Magnetic isotherms were studied at 4.2 K as a function of concentration. The form of the virgin magnetization curve, the presence of large intrinsic coercive forces, and the observation of pronounced thermomagnetic history effects suggest the presence of narrow Bloch walls of only a few interatomic distances in these compounds. It is argued that the presence of narrow Bloch wails is the primary reason for the high coercive forces observed usually in solid pieces of materials of the type RCodxCu5_ 5x. (Netherlands) K H J Buschow and M Brouha, J Appl Phys, 47 (4), 1976, 1653-1656. 35 2223. The role of grain-boundary structure in shock-induced spallation of molybdenum. (USA) Grain boundaries and grain-boundary ledge structures are shown to have a controlling influence on intergranular spallation in molybdenum resulting from shock-wave rarefraction interactions. The structure of grain boundaries and their relationship to spall fracture are examined in detail utilizing the techniques of transmission and scanning electron microscopy, and are shown to be conducive to microcrack nucleation, coalescence, and propagation along the boundary planes. Grain boundaries possessing a high degree of complex structure such as dislocations and ledges are shown to vary significantly in effective dislocation density from the grain matrices, and this phenomenon coupled with the ability of ledges to nucleate cracks appears to account for intergranular spallation in molybdenum shock loaded to pressures of 150 and 250 kbar. L E Murr, J Appl Phys, 47 (4), 1976, 1364--1369. 35 2224. Sharpening of metal tips by heat treatment in vacuum. (GB) It is well known that a metal tip blunts if it is heated in vacuum. According to our hypothesis, a sharpening may occur in the case of an evaporation of the tip material. To test this, molybdenum tips were heated in vacuum. A typical result: at 2400 K, the tip radius decreases from 8 /zm to 0.3 /~m thus confirming the hypothesis. Measured and calculated final radii agree roughly. The pure material evaporation can be replaced by a surface reaction followed by the evaporation of the reaction products. This is shown on tungsten tips heated (1750 K) in the presence of oxygen (0.5 m torr). The evaporation of tungsten oxides results in a sharpening to a radius to 0.05 tzm. Under special conditions, in connection with the formation of solid drops, radii down to 0.01 t~m are obtained. (France) Vu Thien Binh et al, J Phys E: Scient Instrum, 9 (5), 1976, 377-381

(in French). 35 2225. Interaction of metal layers with polycrystalline Si. (USA) Solid-phase reactions of metal films deposited on 0.5-/zm-thick polycrystalline layers of Si grown by chemical vapour deposition at 640°C were investigated by MeV 4He backscattering spectrometry, glancing angle X-ray diffraction, and SEM observations. For the metals A1, Ag, and Au, which form simple eutectics, heat treatment at temperatures below the eutectic results in erosion of the poly-Si layer and growth of Si crystallites in the metal film. Crystallite formation is observed at T ~ 550°C for Ag, T >~ 400°C for AI, and T ~> 200°C for Au films. For the metals Pd, Ni, and Cr, heat treatment results in 497

Classified abstracts 2226-2235 silicide formation. The same initial silicides (Pd2Si, NizSi, and CrSi2), are formed at similar temperatures on single-crystal substrates. K Nakamura et al, J Appl Phys, 47 (4), 1976, 1278-1283. 35 2226. Backscattering analysis of the composition of silicon-nitride films deposited by rf reactive sputtering. (USA) Amorphous silicon-nitride films prepared by rf sputtering of an 8in.dia silicon target in a nitrogen discharge have been analysed using 1.8-MeV-4He-ion backscattering to determine the dependence of film composition on the discharge pressure and rf power. Films with thicknesses between 1000 and 2200/~ were deposited on (111) silicon substrates at pressures ranging from 2 to 20 m torr and rf power densities between ~ 1 and 5 W/cm 2 of target area. The target-tosubstrate spacing was held constant at 5 cm. Film composition, measured as the silicon-to-nitrogen ratio (Ns~/NN), was found to be uniform through the film thickness (with a depth resolution of 350 A.) and across the substrate surface. However, films deposited in separate runs under closely controlled and nominally identical conditions exhibited variations in Nsf/NN of up to 8 %. The silicon-tonitrogen ratio (Ns~/Nr~) in the deposited films varied from approximately 0.60 to 0.80 over the range of power and pressure investigated. The observed dependence of composition on the nitrogen discharge pressure exhibited similar features at all power densities. At the lowest pressures employed (2-4 m torr) the films were always nitrogen rich as compared to the stoichiometric compound Si3N4. As the nitrogen pressure was increased up to ~ 8 - 1 0 m tort the films became progressively less nitrogen rich. Beyond this point the composition tended to a value (Ns~/NN) nearly independent of pressure, but dependent on the rf power density. The pressure dependence of composition is consistent with reaction occurring at the substrate. The tendency for films to become less nitrogen rich with increasing nitrogen pressure is attributed to a reduction in the flux of chemisorbable nitrogen species at the substrate as pressure is increased. C J Mogab and E Lugujjo, J Appl Phys, 47 (4), 1976, 1302-1309. 35 2227. Electrophysical properties of gadolinium oxide doped with magnesium oxide. (USSR) Using the method of measurement of electrical conductivity and thermal emf, the formation of solid solutions of gadolinium oxide with magnesium oxide is investigated at various oxygen partial pressures. It is found that electrical resistivity of the solid solution (GdzO3-0.5 tool per cent MgO) does not depend on the composition of equilibrium gas phase in the oxygen partial pressure range of 10 -~6 to I0 -5 atm. V V Lashneva ct al, Materials and Products Produced by Powder Metallurgy, Coil, Kiev, 1974, 75-80 (in Russian). 35 2228. Quantitative calculation of phosphorus evaporation from the melt at pulling of silicon single crystals by the Czochralski method. (USSR) Quantitative calculations of phosphorus evaporation from the melt at pulling of silicon single crystals by the Czochralski method in dependence on phosphorus vapour pressure above the melt, gas pressure in the system and temperature distribution are presented. The calculations are based on experimental data. S I Gashenko et al, Scient Rep ofScient Res and Develop lust of Rare Metal Industry, No 51, 1974, 62~59 (in Russian). 35 2229. Features of the shape and form of crystallization front of dislocation-free silicon single crystals grown in the (100) and (110) directions. (USSR) The side surface and the form of crystallization front of dislocationfree silicon single crystals, grown in vacuum by the Czochralski method in the (100) and (110) directions, are investigated. N I Bletskan and L E Berezenko, Scient Rep ofScient Res and Develop lnst of Rare Metal lndustry, No 51, 1974, 47-53 (in Russian). 35 2230. Investigation of high-temperature interaction of titanium with materials based on ZrO2. (USSR) A thermodynamic analysis of Ti interaction with ZrO2 has been made. The interaction was investigated at the melting temperature of titanium in a crucible of ZrO2 in a vacuum of 10 - 3 to 10 -4 torr. It is shown at temperatures above 2000 K the formation of TiO, ZrO and Zr in the gas phase is thermodynamically probable. Possibility of using ZrO2 as a material for titanium evaporators in vacuum is noted. V M Gropyanov et al, Neorg Mater, 11 (1), 1975, 105-107 (in Russian). 498

36 2231. Some properties of NbzC and VzC in the homogeneity region. (USSR) Using the methods of chemical, X-ray and metallographic analyses, it is found that the homogeneity regions of NbzC and VzC, prepared by direct synthesis in an electrovacuum furnace at a pressure of 1 × 10 ,4 torr, are NbCo.42-NbCo.so and VCo,41 VCo,49, respectively. G V Samsonov et al, Neor9 Mater, 11 (I), 1975, 62-65 (in Russian). 36. V A C U U M INSTRUMENTATION FOR SURFACE STUDIES 36 2232. Si depth profile and contaminants in Si-doped AI film. (USA) Si depth profiles and contaminants in Si-doped A1 films deposited on SiP2 by electron-gun evaporation at different base pressures have been measured. The experimental techniques employed were Auger electron spectroscopy combined with ion milling for chemical analysis and depth profling, and transmission electron microscopy for film structure studies. Auger analysis showed that at intended doping levels of 1 and 2 at. % (previously calibrated using atomic absorption spectrometry) the AI films contained 0.9 and 1.9 at. % Si, if the total Si content was averaged over the entire film thickness. However, most of the S8 had migrated to the AI/SiO2 interface after deposition at 300°C and formed precipitates which nucleated at or near the AI/SiO2 interface. The major film contaminants were C and O, whose concentrations were directly related to the pressure during deposition. The lowest detection limits with the Auger technique were ~0.01 at. % (100 ppm) for both C and O, attained using a 50t, A incident electron beam current and a scan time of <30 s per element. C C Chang et al, J Appl Phys, 47 (5), 1976, 1790-1794. 36 2233. Influence of surface roughness on the intensity of elastically scattered low-energy noble-gas ions. (USA) The influence of surface roughness on the intensity of elastically scattered low-energy noble-gas ions has been determined for surfaces whose surface displacements are normally distributed. This has been done by modelling the effect of shadowing on the scattered-ion intensity. The experimental results are in good agreement with the values predicted by the model. G C Nelson, J ApplPhys, 47 (4), 1976, 1253-1255. 36 2234. Charging of insulators by ion bombardment and its minimization for secondary ion mass spectrometry (SIMS) measurements. (USA) The generation of charge build-up, caused by bombardment of insulating samples with energetic particles, and its role in altering the relative secondary-ion currents and reducing their absolute values, sometimes even to zero, are discussed. Proposed methods for charge reduction by bombardment with negative ions or with neutral particles, or by use of an auxiliary electron beam or spray gun, are shown to be not useful in every experimental situation. A further method involving introduction of an auxiliary conducting electrode when using negative primary ions is considered mechanistically, and tested by placing tantalum diaphragms onto the surface of yttrium iron garnet (YIG). The final charging values and mass spectra thus obtained are compared to those measured when using bare and metallic grid-covered surfaces of the same YIG sample. The satisfactory results achieved with the diaphragm show that SIMS analyses of insulators can be performed in a simple, quick, and inexpensive manner. (Netherlands) H W Weruer and A E Morgan, J ApplPhys, 47 (4), 1976, 1232-1242. 36 2235. Alloys of Sn and Ge on Nb surfaces. (USA) An investigation of possible surface effects on the formation of the superconducting compounds Nb3Sn and Nb3Ge is reported. Lowenergy electron diffraction and Auger electron spectroscopy were used to determine the symmetries and approximate compositions of surface compounds formed by reactions of fractional monolayers of Sn and Ge with the Nb[100] and Nb[ll0] surfaces. A number of ordered surface structures were observed for each of these elements when reacted with Nb, but epitaxial growth of Nb3Sn or Nb3Ge was not observed. With deposition of sufficient Sn, a disordered growth of Nb3Sn crystallites was obtained at temperatures up to 950°C; however, deposits of Ge greater than about one atomic layer diffused