Measurement of grain-boundary diffusion at low temperature by the surface-accumulation method. II. Results for gold-silver system. (USA)

Classified abstracts 4374-4383 The change of gauge sensitivity with temperature increase is found to be negative and very small; this change is probably explicable by small pressure changes due to thermal transpiration of the gas. K J Close et al, Vacuum, 29 (617), 1979, 249-250. 22 4374. The use of an oscillating vane gauge to determine gas composition of binary gas mixtures. (GB) A description is presented of a continuously driven oscillating vane gauge, which can be used to determine the composition of binary gas mixtures. Consideration is given to operation not only in the molecular and viscous pressure range but also in the intermediate 10-100 mtorr range. (Australia) F H Dyksterhuis, Vacurtm, 29 (4/5), 1979, 149-154.

23. PLUMBING,

VACUUM

VALVES,

BAFFLES

AND TRAPS

23 4375. Pressure-made soft-metal vacuum seals for glass and ceramics. (GB) Indium and aluminum are used as soft-metal pressure sealants for glass-to-glass and glass-to-ceramic interfaces and, in addition, between a wide range of dissimilar materials having unlike thermal coefficients of expansion. The metals form a true seal, being molecularly bonded to the base materials and provide electrical conductivity through the vacuum enclosure. Aluminium seals are made just below the softening point of ‘hard’ glass. R C Neuhauser, Vucuum, 29 (6/T), 1979, 231-235. 23 4376. Capillary array: a new type of window for the vacuum ultraviolet. (USA) Experiments with optical radiation often require separation of a region of relatively high pressure from a lower-pressure region while allowing transmission of radiation between regions. When work is done with vacuum ultraviolet radiation (VUV), the problem is made more difficult by the small number of transparent materials, there being no bulk materials which transmit at shorter wavelengths than the 1050 8, cutoff of LiF. In this paper we report the successful use of glass capillary arrays combined with differential pumping to sustain large pressure differences with excellent transmission of radiation throughout the VUV region. T B Lucatorto et al, Appl Opt, 18 (14), 1979,2505-2509.

24. LEAK

DETECTORS

AND

LEAK

DETECTION

24 4377. The influence of virtual leaks on the pressure in high and ultrahigh vacuum systems. (GB) It is found that the least upper bound to the pressure in a vacuum system with a virtual leak is Q&et& Where Q0 (torr 0.1) is the quantity of gas trapped at t = 0, e = 2.718, to(s) is the time from the start of the pumpdown and S (I s-‘) is the real pumping speed. (USA) D Edwards Jr, Vucuum, 29 (4/5), 1979, 169-172.

25. HEATING

EQUIPMENT

AND THERMOMETERS

25 4378. Temperature measurements on thin vapour-deposited films. (GB) A method for precise temperature measurements on thin vapourdeposited films has been developed for magneto-optical Kerr studies of the critical magnetic behaviour of thin nickel films. The combination of a bulk platinum resistor and a thin-film Au-Pt thermocouple eliminates errors which usually occur if only one of these probes is used. The accuracy and stability of the method are determined by the resistor, whereas the thermocouple used as a zero indicator in a feedback circuit extends the applicability of the resistor to measurements on thin films. Local temperature changes down to lo-’ K can be measured reliably, e.g. at the film spot where a laser beam is reflected. (Germany) S Schwa& J Phys E: Sci Instrum, 12 (5), 1979,436-438.

III.

Vacuum

30. EVAPORATION

applications AND DEPOSITION

IN VACUO

30 4379. Thin film coatings: algorithms for the determination of refiectance and transmittance, and their derivatives. (USA) The paper deals with the specular optical properties of thin dielectric or metallic multilayer coatings. Recurrent formulas are given for reflectance, transmittance, and their derivatives with respect to thicknesses, indices, incidence, and wavelength. Because of its simplicity and flexibility, the proposed method is particularly well fitted for use in a digital computer and for optimization programs. (France) H Dupoisot and J Morizet, Appl Opt, 18 (15), 1979,2701-2704. 30 4380. Normal conductivity and superconductivity of an Al-type iodine phase. (GB) A metallic Al-type iodine modification exhibiting soft superconductivity was quench-deposited on CaO or SrO. The normal resistivity, superconducting transition temperature and critical magnetic field decrease with increasing thickness. On heating, the ordinary nonmetallic diatomic structure is restored. (Italy) C Reale, Vacuum, 29 (617), 1979, 245-248. 30 4381. Thin film optical coatings. 7. Two-layer coatings close to antireflection. (USA) This paper examines the residual reflection of two-layer coatings close to antireflection. Residual reflection can be induced either by fluctuations or errors in the thickness of the layers. Fluctuations in thickness, resulting from insufficiently accurate measuring equipment, lead to the notions of stability and tolerances. When reflection is substantial, a method of calculation is proposed for determining thicknesses effectively deposited. (France) J Mouchart et al, Appl Opt, 18 (8), 1979, 12261232. 30 4382. Neutral density filters by co-evaporated Ag and SiOl films for near ir radiation. (USA) Optical properties of Ag and SiOl co-evaporated films were studied in the visible and near ir regions, and a novel neutral density filter for near ir radiation has been proposed. The films, which contain 56 vol.% Ag. exhibit almost wavelength-independent optical transmittance in the longer than 1 pm wavelength region. Neutral density filters, which have desired optical transmittance, can be obtained by controlling the co-evaporated film thickness. A Shibukawa, Appl Opt, 18 (9), 1979, 1460-1462. 30 4383. Measurement of grain-boundary diffusion at low temperature by the surface-accumulation method. II. Results for gold-silver system. (USA) Grain-boundary diffusion rates in the gold-silver system were measured at relatively low temperatures by the surface-accumulation method which was analysed in Part I. The specimen was a polycrystalline gold film possessing columnar grains on which a silver layer was initially deposited epitaxially on one surface. During subsequent low-temperature annealing lattice diffusion was frozen out, and diffusion then occurred along the grain boundary and freesurface short circuits. The silver. therefore, diffused into the film from the silver layer along the boundaries, eventually reaching the opposite surface where it accumulated and was measured by Auger spectroscopy. The silver layer acted as an effective constant silver source, and grain-boundary diffusivities were calculated from the accumulation data. However, the exact location of the effective constant source in the silver layer could not be determined and this led to an uncertainty in the values of the grain-boundary diffusivities of a factor of 10. Lower- and upper-bound values were therefore described by D,(lower bound) = 7.8 x lo-’ exp(-0.62eV/kT) and &(upper bound) = 7.8 x 10es x exp( -0.62eV/kT)cm2 s-’ in the temperature range 30-269°C. An examination of available grainboundary diffusion data (including the present) suggests a tendency for the observed activation energy to decrease with decreasing temperature, and this was ascribed to a spectrum of activated jumps in the grain boundary and/or a spectrum of boundary types in the specimen employed. The constant source behaviour was tentatively ascribed, at least in part, to a grain-boundary ‘Kirkendall effect’ resulting from the faster diffusion of silver than gold. The work 241

Classified abstracts 4384-4393 indicates a need for increased understanding of the details of grainboundary diffusion in alloys. J C Hwang et al, J uppl Phys, 50 (3), 1979, 1349-1359. 30 4384. Theoretical model of thin-film deposition profile with shadow effect. (USA) A theoretical model and a computational algorithm are presented for the shadow deposition of thin films through a generalized mask of finite dimensions in a vacuum environment. The computer model enables a theoretical study of the deposited film thickness profile from extended sources with shadow effect. Numerical evaluation of the masked deposition profile has been carried out to illustrate the film-profile dependences on several basic mask parameters. Using computer-aided design procedures, a deposition mask has been successfully constructed for the fabrication of precisely shaped thin film Luneburg lenses for guided optical wave applications. S K Yao, J appl Phys, 50 (5). 1979, 3390-3395. 30 4385. Optical and electrical properties of evaporated amorphous silicon with hydrogen. (USA) The optical and electrical properties of evaporated amorphous silicon with hydrogen have been studied under various deposition conditions. Infrared measurements indicate that the hydrogen content of the films are comparable to a-Si: H films produced by other techniques. The optical-absorption coefficient below the band gap of w 1.55 eV was measured to be u 100 cm-’ for samples made at deposition temperatures of -275-325°C. For these samples the photoresponse at room temperature and the temperature dependence of the conductivities were studied. Dark conductivities were found to be thermally activated for T > 300 K with activation energies of -0.75 eV. We found type-l photoconductivity and investigated its dependence on the light intensity. When samples were heated to -175°C in a vacuum and then exposed to air, they exhibited timedependent increases in the dark conductivity and photoconductivity. Thiseffect was reversible by a reanneal in a vacuum. High-temperature anneals to -450°C increased the optical absorption below 1.4 eV and decreased the photoresponse significantly. A K Ghosh et al, J appl Phys, 50 (5). 1979, 3407-3413. 30 4386. Infrared quenching of photocapacitance in evaporated ZnS: Ag thin films. (USA) The deep centres in evaporated ZnS:Ag thin films have been characterized by observation of the infrared quenching of photocapacitance using Schottky barriers. The photoionization energy of holes for transitions from Ag centres to the valence band edge is determined to be 0.56 eV at 300 K. The spectral distribution of the photoionization cross-section of holes is obtained theoretically. It has been found that the magnitude of the photocapacitance quenching depends linearly on the intensity of the infrared illumination in the low-intensity range. The concentration profile of Ag impurities has been measured and is almost uniform throughout the depletion layer in the films.

(Japan)

superposed upon an expansion velocity u. In the particular experimental condition with rapid short circuit, the interaction was realized by electrons of low energy. The maximal temperature obtained with a thin 25 pm tantalum anode was of the order of 20 eV and hydrodynamic speed 1.4 cm ps-‘. The characteristics of the electron beam generator used were 600 kV, 200 kA, and 60 ns. (France) C Peugnet et al, J appl Phys, 50 (4), 1979, 2936-2939. 30 4389. Properties of high sensitivity GaP/In,Ga, -.P/GaAs:(Cs-0) transmission photocathodes. (USA) Negative electron affinity (NEA) GaAs photocathodes were vapour grown on GaP/In,Ga,-,P substrates with 0.4 < x < 0.65. The dependence of cathode sensitivity, electron diffusion length, cathode back-interface recombination velocity, and surface-escape probability on buffer-layer composition was determined. The optimal In,Ga,-,P composition for these samples was in the range of 52-55% InP. Indium unintentionally introduced into the GaAs causes a shift in the In,Ga, -*P composition for good lattice match. SIMS and AES measurements were made to obtain the chemical and electronic structure of the epitaxial layers. The photosensitivity dependence on both Zn doping concentration and cathode thickness are presented. The highest transmission mode photosensitivity measured was 740 pA/lm. D G Fisher and G H Olsen, J uppl Phys, 50 (4), 1979, 2930-2935. 30 4390. Vacuum coating of reflectors of small radius of curvature aided by gas scattering. (Germany) In the production of cold mirrors as used in 8 mm film projectors a large number of approximately hemispherical substrates (r z 20 mm) has to be coated simultaneously with several optically active layers. The optical thickness of each layer must be uniform within a few per cent both radially and with respect to rotational symmetry. An approximate calculation shows that this aim can be attained when use is made of the scattering of the evaporant at the atoms or molecules of an inert gas. The reflectors are mounted on discs rotating in a planetary movement so that the axis of each reflector is always pointing to the evaporator source. The system of interference layers produced that way is at least as much resistant to climatic stresses as are dielectric layers produced by orthodox high vacuum evaporation. K Steinfelder et al, Vakrrrrm, 28 (2), 1979, 48-53 (in Germon). 30 4391. Properties of TilN layers produced by ion-plating. (Germany) Constant substrate temperatures up to about 450°C can be attained in an ion plating plant fitted with a Piercetype electron gun only by appropriate adjustment of the discharge parameters without the use of a separate heat source. By reactive evaporating of titanium in a residual gas atmosphere of 8 x lo-’ mbar argon and 2.5 x 10e2 mbar nitrogen at a substrate temperature of 400°C the maximum microhardness HVO.OIN of 20,000 N x mm-’ is attained at a condensation rate of 20 pm x min-I. SEM investigations have shown that the layer consists almost entirely (except for 1%) of Ti,N. I Badny and G Kienel, Vukuum, 28 (6), 1979, 168-172 (in German).

30 4387. Formation of iridium silicides from Ir thin films on Si substrates. (USA) The formation of iridium silicides from the interaction of iridium films with single-crystal silicon substrates has been studied from 350 to 1000°C. Three distinct ohases. IrSi. , IrSi, _.,*I?). . _. and IrSi,.“, were identified. Different modes of formation were observed and investigated. IrSi and IrSi,.,s form in layers parallel to the substrate at temperatures from 350 to 900°C. The growth of IrSi, from nuclei that spread laterally occurs at about lOOo”C, where possible the kinetics were systematically studied. S Peters-son et al, J uppl Phyx, 50 (5), 1979, 3357-3365. 30 4388. Simultaneous measurement of the temperature and the hydrodynamic speed of a thin foil submitted to an intense electronic energy deposition. (USA) We have determined the temperature and hydrodynamic speed of a thin tantalum anode heated by a pinched relativistic electron beam. These measurements were simultaneously realized by analysing the speed distribution of thermal ions emitted by the plasma. The plasma ions can be represented by a Maxwellian velocity distribution

30 4392. Antireiiection coatings on plastic substrates. (Germany) The most well known anti-reflection coating on mineral glasses is a MgF, layer. This coating cannot be applied to plastic substrates even when a barrier layer between substrate and MgF, is used. A double layer system, consisting of ZrO, and a borosilica glass, is described which meets most of todays requirements for application on spectacle and magnification lenses as well as on lenses for cameras. The described double layer allows a low substrate temperature and can even be applied to temperature sensitive plastics such as PMMA. The evaporation is accomplished by an electron beam source with a special crucible. G Kienel and B Heinz, Vakuum, 28 (4), 108-112 (in German). 30 4393. Thick metallic films obtained by ion-plating. (France) An ion-plating deposition system using an electron beam evaporation source was developed to obtain adherent, thick and uniform thickness coatings on substrates with various configuration. Al, Sm, Y and W coatings were obtained with thicknesses between 80 and 2.000 pm. A Brothier et al, Vide, 34 (196), 1979, 109-I 11 (in French).

T Suda et al, J uppl Phys, 50 (5), 1979, 3638-3643.

242