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12. Gaseous interactions with solids
Cla~sifiqd abstracts 6 2 6 7 - 6 2 7 5 11 6267. An axial-emission magnetron ionization gauge The axial-emission ionization gauge (AEG) has been modified to form an axial-emission magnetron ionization gauge (AEMG) by adding an axial magnetic field to the electrode construction of the AEG. This modification results in a much lower limiting measurable pressure. A E M G gives performances like that of Lafferty's hot-cathode magnetron ionization gauge ( L H M G ) but the ratio of the X-ray photocurrent to the anode current 1~,:1, is smaller by more than two orders, so its lower limit is lower than that of L H M G . The upper limit of measurable pressure can be extended to 1 . 3 3 x 1 0 - : Pa (1 ×10 - ' t t o r r ) by operating the A E M G without the magnet. Since the electrode construction of A E M G is very simple, it is easy to de-gas and this is of benefit to its operation under extremely high vacuum. J Z Chen et al, J l,'ac Sci Technol, A3, 1985, 14-17. 11 6268. Sensitivity of hot cathode ionization gauges As a part of an experimental programme of some years duration we have attempted to characterize several hot cathode ionization gauge types in the high vacuum range by the uniformity, linearity and stability of their nitrogen sensitivity. Results for six commonly used types are summarized here. Of the gauges tested, the most promising overall performance was obtained from tubulated Bayard-Alpert gauges with two tungsten filaments mounted 180¢ apart about the grid. Conventional triode gauges with tungsten filaments came close to this level of performance and have superior high pressure linearity. C R Tilford, J Vac Sci Technol, A3, 1985, 546-550. I1 6269. Depressurization as a means of leak checking large vacuum vessels A c o m m o n problem associated with large vacuum vessels used in magnetic confinement fusion experiments is that leak checking is hampered by the inaccessibility to most of the vacuum vessel surface. This inaccessibility is caused by the close proximity of magnetic coils, diagnostics and, for those vessels that are baked, the need to completely surround the vessel with a thermal insulation blanket. These obstructions reduce the effectiveness of the standard leak checking method of using a mass spectrometer and spraying a search gas such as helium on the vessel exterior. Even when the presence of helium is detected, its entry point into the vessel cannot always be pinpointed. This paper will describe a method of o~ ercoming this problem. By slightly depressurizing the vessel, an influx of helium through the leak is created. The leak site can then be identified by personnel within the vessel using standard sniffing procedures. There are two conditions which make this method of leak checking practical. First. the vessel need only be depressurized 2 Ib in.-~, thus allowing personnel inside to perform the sniffing operation. Second, the sniffing probe used lLeybold--Heraeus "Quick Test') could detect a change in helium concentration as small as 100 ppb, which allows for faster scanning of the vessel interior. Use of this technique to lind an elusive 10 "-~ tort Is -~ leak in the Doublet I11 tokamak vacuum vessel will be presented. R W Callis et al, J Vac Sci Technol, A3, 1985, 538 541. 11 6270. Measurement and calibration techniques used in computer partial pressure analysis The uses of residual gas analysers (RGA's) in computer controlled analytical studies and process monitoring applications are discussed in this paper. The relative merits are compared for the two most commonly used RGAs, which are the magnetic sector and the quadrupole mass analyscr. Methods of installing RGAs in vacuum systems and computer interfacing techniques are described. Measurement and calibration methods are outlined for applications where it is desirable to characterize either partial pressures or gas evolution rates. Interpretation of RGA spectra and limitations imposed by analytical errors are also discussed. 1) J Mitchell, J Vac Sci Technol, A3, 1985, 527-532. 11 6271. Sensitivity of the Contra-Flow leak detector at high test pressures The Contra-Flow leak detection tachnique consists of letting the tracer gas lhelium) diffuse upstream through the high vacuum pump toward the mass spectrometer sensor. The test object can remain at relatively high total pressure, as high as the tolerable foreprcssure of the high vacuum pump. Because this environment is not in the molecular flow regime, the relationship of detection sensitivity to p u m p performance parameters is sufficiently different from those of conventional leak detectors to warrant an investigation. Comparative tests were made with both types of detectors over a wide range of test pressures using water vapour, air.
nitrogen and argon to simulate various test object pressure conditions. The results reveal that at test pressures above approximately one pascal the Contra-Flow method provides at least ten times higher sensitivity. Exposure of the test object to mechanical pump oil vapour can be prevented by a continuous stream of a helium-free gas or by the use of zeolite traps. The latter do not absorb helium significantly but produce a great effect on the residual gas composition. M H Hablanian, Vacuum, 35, 1985, 119--123.
12. G A S E O U S I N T E R A C T I O N S W I T H SOLIDS 12 6272. A comparison of the outgassing characteristics of several solar absorbing coatings An investigation has been conducted of the room temperature outgassing characteristics of several optically black solar absorbing coatings. The coatings were deposited either electrochemically, by spraying, or by brushing onto aluminium or stainless steel substrates. Vacuum outgassing rates and residual gas evolution have been studied for exposure times on the order of 100 h. Representative outgassing values are given for the following coating,"substrate combinations: anodized and black dyed aluminium, etched electroless nickel on aluminium, black chrome on aluminium and on stainless steel, and black paint on aluminium. The results confirm that the outgassing rates of these coatings can be expressed as an exponential decay function [ref 1: B B Dalton, Transactions of the 8th National Symposium. Pergamon, New York, p 42 (1962)] of the form 9, = At -~, where the outgassing rate at a specific time g, is a product of the outgassing rate after 1 h exposure to vacuum A and the time t raised to the inverse power of re. In the case of the anodized aluminium, m was found to be approximately equal to 0.5. For the other materials, m was found to be about equal to 1.0. E D Erikson et al, J Vac Sci Technol, A3, 1985, 1711 --1714. 12 6273. Technique for in vacuo passivation of ZrAI alloy bulk getters We have developed a method for passivating previously activated ZrA1 alloy bulk getters. Such passivation is essential for avoiding embrittlement of the getters during discharge cleaning operations in tokamak fusion devices. The method consists of exposing the getters (at room temperature) to a controlled a m o u n t of oxygen, followed by pulse discharge cleaning to restore the vacuum vessel walls to clean conditions. We have tested this method on the T o k a m a k Fusion Test Reactor (TFTR) and present measurements of the decrease in the hydrogen and oxygen pumping speeds as functions of the quantity of oxygen adsorbed. These measurements are in good agreement with previous laboratory results. Using this method followed by 20 h of pulse discharge cleaning, we have reduced the getter pumping speed by more than a factor of 2 × [ 0 3 and have recovered the same clean vacuum conditions as existed prior to the oxygen exposure. J L Cecchi et al, J Vac Sci Technol, A3, t985, 487-490. 12 6274. Design considerations for simple gas dosets in surface science applications The flux distributions and enhancement factors for various gas doser designs typically used in surface science applications and chemisorption studies have been calculated and compared. The following conclusions, which will aid the experimentalist in the choice of closer design, can be made. ( 1) The enhancement factor expected for a given doser can easily be derived from Fig. 2. (2) The optimum doser design is a multichannel array with a radius slightly larger than that of the sample, and a distance from the sample < 10% of the sample diameter. (Complications of this design are discussed.) (3) Because of space requirements, the sample-doser distance must sometime be >_40% oftbe sample diameter, in which cases it is better to use a cosine emitter. A good, very simple doser design is described that consists of a small cosine emitter with a sample-doser distance of 1/2 the sample diameter. This provides an enhancement factor > 50% of the optimum theoretical enhancement, with only slight ( __+15%) flux gradients. (4) For a given doser distance, a needle doser provides the largest enhancement factor, but always has a cery strong gradient in flux across the sample. C T Campbell and S M Valone, J ~'ac Sci Technol. A3, 1985, 41)8 -,J,l I. 12 6275. Kinetics of charge trapping in dielectrics Transient electronic conduction in thermally grown SiO,, has been shown to be limited by space-charge evolution. The space charge originates from
41
Classified abstracts 6276-6284 trapping of the injected species. It induces a field which affects the emission of charges as the injecting electrode. The trapping of charge has been analysed on the basis of three, essentially different, mechanisms: (1) first order trapping, (2) first order trapping which takes into account that trapped charges repel injected charges, and (3) trapping which increases d u r i n g injection due to the generation of states. It is shown that implementation of the three trapping mechanisms yields a current vs injected charge plot which is given in the asymptotes by simple logarithmic functions. Intersection of the asymptotes directly yields the value of the capture cross section. From the slopes of the asymptotes the surface density0es) of the trap(s) can be calculated. The method can be used without, a priori, assuming either the injection mechanism or the trapping mechanism. From the relative position of the intersection points the applicable mechanism can be derived, however. For thermal SiO 2 on Si we determined, by this method, values of trap densities and capture cross sections which are typical for water-related traps. Furthermore, we derived that trapping mechanism {2) fits our data best. D R Wolters and d J van der Schoot, J appl Phys, 58, 831-837. 12 6276. Empirical determination of adsorption isotherm for nitrogen on glass for various conditions of vacuum and near-ambient temperature We have measured the adsorption isotherm of nitrogen on glass in the ranges 10 - 2_i0- 3 tort and - 78- 0:C and compared it with Hobson's theory. Gao Ben-hui et al, Vacuum, 35, 1985, 9-11. 12 6277. Diffusion of hydrogen in metals The present status of our understanding of the diffusion of hydrogen in metals, both experimental and theoretical, is reviewed. Discussions are focused on the mechanism of diffusion of hydrogen isotopes H, D and T in fcc and bcc metals; the positive m u o n (~÷) is referred to where appropriate. An up-to-date compilation of diffusion data as a function of temperature and isotope mass has been made, and a clear distinction in general diffusion behaviour in fcc and bcc metals is noted. Subsequently. the results obtained from the Gorsky effect, nuclear magnetic resonance and quasi-elastic neutron scattering that provide information on elementary j u m p processes are discussed. A conceptual framework of the q u a n t u m diffusion of light interstitials in metals is given, including the recent K o n d o theory that emphasizes the crucial importance of particle-conduction electron interactions in the diffusion process, especially at low temperatures. It is shown with the help of recent estimates ofthe tunnelling matrix element that the overall feature ofdiffusion of hydrogen isotopes in bcc metals as well as ,u ÷ in fcc metals can be explained consistently within the frame presented here. Finally, receht advances in the diffusion studies on hydrogen in bcc metals are described. They include a re-analysis of quench-recovery experiments that manifested nearly athermal diffusion of H, D and T in Ta at low temperatures, and an enormous enhancement of the diffusivity under stress (superdiffusion) observed for H and D in V. Y Fukai and II Sugimoto, Adr" Phys, 34, 1985, 263--326. 12 6278. The effect of a depth dependent diffusion coefficient on the trapping of mobile particles near a solid surface A diffusion model is presented which allows an experimental test for the existence of an anisotropic region at a crystal surface induced by the asymmetry of the vacuum-crystal interface. The model is a generalization of that developed by van G o r k u m and Kornelsen which assumed a diffusion coefficient independent of position in the crystal. The model was modified by assuming that the anisotropy can be described by a variable diffusion coefficient very near ttte surface. It is shown that if such an anisotropic region exists, the fraction of trapped particles f should increase with the temperature at v, hich the crystal is held during diffusion. If the region does not exist, the fraction of trapped particles should not depend on the crystal temperature. An attempt was made to measure the dependence of f on temperature for He trapping at very shallow HeV traps in Mo (1001. The results indicate that even at the depth of the shallowest traps in Mo 11130) ( < 5 .~,), no significant anisotropic diffusion of the helium occurs. M Fontalne and E V Kornelsen, Rad Effects, 90, 1985, 111-125. 12 6279. Irregularities in helium release rates from metal ditritldes Helium release rates from erbium and zirconium ditritide films were measured with 3-s time resolution. All films exhibited some variability in 3He release rates on this time scale, but the nonuniformity of the release rate was greatest for samples undergoing the transition into accelerated release, which occurs when the occluders approach the m a x i m u m 42
quantities of helium that they can retain. The 3He release rate variability appeared to be associated with the spontaneous release of helium in bursts of about 109 atoms. The release of bursts 0f helium was als0 stimulated by vibrating or flexing the film substrates. Although these effects are not expected based on the diffusion of isolated helium atoms of the lattice, the effects of temperature on helium release rates were consistent with the diffusion model. These observations lead to the conclusion that two distinct mechanisms are responsible for the release of helium from the metal ditritide films. D J Mitchell and J L Provo, J appl Phys, 57, 1985, 1855-1860. 13. M A T E R I A L S A N D T E C H N I Q U E S IN V A C U U M 13 6280. A simple proeedure for high precision orientation of single crystal surfaces A simple method for very accurate alignment of single crystals by means of the Laue method is described. The improved preparation technique allows the surface orientation accuracy of + 0 . 1 % , within the required orientation, to be maintained throughout the subsequent preparation steps. The final result is judged from thermal energy helium diffraction experiments. U Linke and B Poelsema, J Phys E: Sci Instrum, 18, 1985, 26-27. 13 6281. U H V universal manipulator with direct cooling An ultrahigh-vacuum compatible sample manipulator which incorporates rotation and a Dewar for sample cooling is described. The rotation is accomplished using a differentially pumped rotary seal made of two Teflon O rings and the temperature of the sample can be controlled from 30 K to over 1600 K. N J Wu, Rev Sci lnstrum, 56, 1985, 752-754. 13 6282. Ultrahigh-vacuum double-axis goniometer for angle-resolved spec-
troscopies
Described here is a double-axis goniometer currently used in angleresolved neutral atom beam scattering. A special feature is the decoupling of the two rotation axes. An additional design concept is flexibility; the device can be adapted to almost all existing uhv systems, independent of port position and size, and of chamber diameter. K M Martini, Rec Sci lnstrum, 56, 1985, 240-241.
II. Thin f i l m t e c h n o l o g y 20. E V A P O R A T I O N 20 6283. Transmission electron microscopy of electron-beam.evaporated arsenic trisulfule films Transmission electron microscopy in conjunction with X-ray photoelectron spectroscopy (XPS) was used to study the possible microstructural changes occurring in electron-beam-evaporated arsenic trisulphid¢ thin films, when deposited on a sodium chloride substrate from room temperature to 250~C. These films were found to be amorphous up to 150°C, while a transition from the a m o r p h o u s to the polycrystalline phase was observed to take place at 200'~C. The electron-diffraction results showed that the crystallized sulfur-rich phase was predominantly As2S ~, along with As2S 3. The XPS spectrum showed shifts in binding energy values for As towards higher energies. A shift of 0.9 eV for the As {3d) spectrum was attributed to the transition from the As2S.~ to the As2S ~ phase occurring at ~ 200~C. Amarjit Singh, J appl Phys, 58, 1985, 309-312. 2O 6284. Metalizing system for coating an astronomical telescope mirror A vacuum metallizing system developed for coating a 2.12 m astronomical telescope mirror is described. The 3 m din chamber, installed at 2800 m altitude at the Mexican National Astronomical Observatory at San Pedro Mfirtir, Baja California, was developed with uniquely economical equipment and simplicity of design to facilitate ease of operation, safe handling of the mirror and reliability in this remote location. In order to meet strict performance specifications within a very limited budget, nontraditional equipment suppliers and fabricators were used. The project design and administration philosophy are described. M Roth F and E B Grapero J Vac Sci Technol, A3, 1985, 512-515.
nitrogen and argon to simulate various test object pressure conditions. The results reveal that at test pressures above approximately one pascal the Contra-Flow method provides at least ten times higher sensitivity. Exposure of the test object to mechanical pump oil vapour can be prevented by a continuous stream of a helium-free gas or by the use of zeolite traps. The latter do not absorb helium significantly but produce a great effect on the residual gas composition. M H Hablanian, Vacuum, 35, 1985, 119--123.
12. G A S E O U S I N T E R A C T I O N S W I T H SOLIDS 12 6272. A comparison of the outgassing characteristics of several solar absorbing coatings An investigation has been conducted of the room temperature outgassing characteristics of several optically black solar absorbing coatings. The coatings were deposited either electrochemically, by spraying, or by brushing onto aluminium or stainless steel substrates. Vacuum outgassing rates and residual gas evolution have been studied for exposure times on the order of 100 h. Representative outgassing values are given for the following coating,"substrate combinations: anodized and black dyed aluminium, etched electroless nickel on aluminium, black chrome on aluminium and on stainless steel, and black paint on aluminium. The results confirm that the outgassing rates of these coatings can be expressed as an exponential decay function [ref 1: B B Dalton, Transactions of the 8th National Symposium. Pergamon, New York, p 42 (1962)] of the form 9, = At -~, where the outgassing rate at a specific time g, is a product of the outgassing rate after 1 h exposure to vacuum A and the time t raised to the inverse power of re. In the case of the anodized aluminium, m was found to be approximately equal to 0.5. For the other materials, m was found to be about equal to 1.0. E D Erikson et al, J Vac Sci Technol, A3, 1985, 1711 --1714. 12 6273. Technique for in vacuo passivation of ZrAI alloy bulk getters We have developed a method for passivating previously activated ZrA1 alloy bulk getters. Such passivation is essential for avoiding embrittlement of the getters during discharge cleaning operations in tokamak fusion devices. The method consists of exposing the getters (at room temperature) to a controlled a m o u n t of oxygen, followed by pulse discharge cleaning to restore the vacuum vessel walls to clean conditions. We have tested this method on the T o k a m a k Fusion Test Reactor (TFTR) and present measurements of the decrease in the hydrogen and oxygen pumping speeds as functions of the quantity of oxygen adsorbed. These measurements are in good agreement with previous laboratory results. Using this method followed by 20 h of pulse discharge cleaning, we have reduced the getter pumping speed by more than a factor of 2 × [ 0 3 and have recovered the same clean vacuum conditions as existed prior to the oxygen exposure. J L Cecchi et al, J Vac Sci Technol, A3, t985, 487-490. 12 6274. Design considerations for simple gas dosets in surface science applications The flux distributions and enhancement factors for various gas doser designs typically used in surface science applications and chemisorption studies have been calculated and compared. The following conclusions, which will aid the experimentalist in the choice of closer design, can be made. ( 1) The enhancement factor expected for a given doser can easily be derived from Fig. 2. (2) The optimum doser design is a multichannel array with a radius slightly larger than that of the sample, and a distance from the sample < 10% of the sample diameter. (Complications of this design are discussed.) (3) Because of space requirements, the sample-doser distance must sometime be >_40% oftbe sample diameter, in which cases it is better to use a cosine emitter. A good, very simple doser design is described that consists of a small cosine emitter with a sample-doser distance of 1/2 the sample diameter. This provides an enhancement factor > 50% of the optimum theoretical enhancement, with only slight ( __+15%) flux gradients. (4) For a given doser distance, a needle doser provides the largest enhancement factor, but always has a cery strong gradient in flux across the sample. C T Campbell and S M Valone, J ~'ac Sci Technol. A3, 1985, 41)8 -,J,l I. 12 6275. Kinetics of charge trapping in dielectrics Transient electronic conduction in thermally grown SiO,, has been shown to be limited by space-charge evolution. The space charge originates from
41
Classified abstracts 6276-6284 trapping of the injected species. It induces a field which affects the emission of charges as the injecting electrode. The trapping of charge has been analysed on the basis of three, essentially different, mechanisms: (1) first order trapping, (2) first order trapping which takes into account that trapped charges repel injected charges, and (3) trapping which increases d u r i n g injection due to the generation of states. It is shown that implementation of the three trapping mechanisms yields a current vs injected charge plot which is given in the asymptotes by simple logarithmic functions. Intersection of the asymptotes directly yields the value of the capture cross section. From the slopes of the asymptotes the surface density0es) of the trap(s) can be calculated. The method can be used without, a priori, assuming either the injection mechanism or the trapping mechanism. From the relative position of the intersection points the applicable mechanism can be derived, however. For thermal SiO 2 on Si we determined, by this method, values of trap densities and capture cross sections which are typical for water-related traps. Furthermore, we derived that trapping mechanism {2) fits our data best. D R Wolters and d J van der Schoot, J appl Phys, 58, 831-837. 12 6276. Empirical determination of adsorption isotherm for nitrogen on glass for various conditions of vacuum and near-ambient temperature We have measured the adsorption isotherm of nitrogen on glass in the ranges 10 - 2_i0- 3 tort and - 78- 0:C and compared it with Hobson's theory. Gao Ben-hui et al, Vacuum, 35, 1985, 9-11. 12 6277. Diffusion of hydrogen in metals The present status of our understanding of the diffusion of hydrogen in metals, both experimental and theoretical, is reviewed. Discussions are focused on the mechanism of diffusion of hydrogen isotopes H, D and T in fcc and bcc metals; the positive m u o n (~÷) is referred to where appropriate. An up-to-date compilation of diffusion data as a function of temperature and isotope mass has been made, and a clear distinction in general diffusion behaviour in fcc and bcc metals is noted. Subsequently. the results obtained from the Gorsky effect, nuclear magnetic resonance and quasi-elastic neutron scattering that provide information on elementary j u m p processes are discussed. A conceptual framework of the q u a n t u m diffusion of light interstitials in metals is given, including the recent K o n d o theory that emphasizes the crucial importance of particle-conduction electron interactions in the diffusion process, especially at low temperatures. It is shown with the help of recent estimates ofthe tunnelling matrix element that the overall feature ofdiffusion of hydrogen isotopes in bcc metals as well as ,u ÷ in fcc metals can be explained consistently within the frame presented here. Finally, receht advances in the diffusion studies on hydrogen in bcc metals are described. They include a re-analysis of quench-recovery experiments that manifested nearly athermal diffusion of H, D and T in Ta at low temperatures, and an enormous enhancement of the diffusivity under stress (superdiffusion) observed for H and D in V. Y Fukai and II Sugimoto, Adr" Phys, 34, 1985, 263--326. 12 6278. The effect of a depth dependent diffusion coefficient on the trapping of mobile particles near a solid surface A diffusion model is presented which allows an experimental test for the existence of an anisotropic region at a crystal surface induced by the asymmetry of the vacuum-crystal interface. The model is a generalization of that developed by van G o r k u m and Kornelsen which assumed a diffusion coefficient independent of position in the crystal. The model was modified by assuming that the anisotropy can be described by a variable diffusion coefficient very near ttte surface. It is shown that if such an anisotropic region exists, the fraction of trapped particles f should increase with the temperature at v, hich the crystal is held during diffusion. If the region does not exist, the fraction of trapped particles should not depend on the crystal temperature. An attempt was made to measure the dependence of f on temperature for He trapping at very shallow HeV traps in Mo (1001. The results indicate that even at the depth of the shallowest traps in Mo 11130) ( < 5 .~,), no significant anisotropic diffusion of the helium occurs. M Fontalne and E V Kornelsen, Rad Effects, 90, 1985, 111-125. 12 6279. Irregularities in helium release rates from metal ditritldes Helium release rates from erbium and zirconium ditritide films were measured with 3-s time resolution. All films exhibited some variability in 3He release rates on this time scale, but the nonuniformity of the release rate was greatest for samples undergoing the transition into accelerated release, which occurs when the occluders approach the m a x i m u m 42
quantities of helium that they can retain. The 3He release rate variability appeared to be associated with the spontaneous release of helium in bursts of about 109 atoms. The release of bursts 0f helium was als0 stimulated by vibrating or flexing the film substrates. Although these effects are not expected based on the diffusion of isolated helium atoms of the lattice, the effects of temperature on helium release rates were consistent with the diffusion model. These observations lead to the conclusion that two distinct mechanisms are responsible for the release of helium from the metal ditritide films. D J Mitchell and J L Provo, J appl Phys, 57, 1985, 1855-1860. 13. M A T E R I A L S A N D T E C H N I Q U E S IN V A C U U M 13 6280. A simple proeedure for high precision orientation of single crystal surfaces A simple method for very accurate alignment of single crystals by means of the Laue method is described. The improved preparation technique allows the surface orientation accuracy of + 0 . 1 % , within the required orientation, to be maintained throughout the subsequent preparation steps. The final result is judged from thermal energy helium diffraction experiments. U Linke and B Poelsema, J Phys E: Sci Instrum, 18, 1985, 26-27. 13 6281. U H V universal manipulator with direct cooling An ultrahigh-vacuum compatible sample manipulator which incorporates rotation and a Dewar for sample cooling is described. The rotation is accomplished using a differentially pumped rotary seal made of two Teflon O rings and the temperature of the sample can be controlled from 30 K to over 1600 K. N J Wu, Rev Sci lnstrum, 56, 1985, 752-754. 13 6282. Ultrahigh-vacuum double-axis goniometer for angle-resolved spec-
troscopies
Described here is a double-axis goniometer currently used in angleresolved neutral atom beam scattering. A special feature is the decoupling of the two rotation axes. An additional design concept is flexibility; the device can be adapted to almost all existing uhv systems, independent of port position and size, and of chamber diameter. K M Martini, Rec Sci lnstrum, 56, 1985, 240-241.
II. Thin f i l m t e c h n o l o g y 20. E V A P O R A T I O N 20 6283. Transmission electron microscopy of electron-beam.evaporated arsenic trisulfule films Transmission electron microscopy in conjunction with X-ray photoelectron spectroscopy (XPS) was used to study the possible microstructural changes occurring in electron-beam-evaporated arsenic trisulphid¢ thin films, when deposited on a sodium chloride substrate from room temperature to 250~C. These films were found to be amorphous up to 150°C, while a transition from the a m o r p h o u s to the polycrystalline phase was observed to take place at 200'~C. The electron-diffraction results showed that the crystallized sulfur-rich phase was predominantly As2S ~, along with As2S 3. The XPS spectrum showed shifts in binding energy values for As towards higher energies. A shift of 0.9 eV for the As {3d) spectrum was attributed to the transition from the As2S.~ to the As2S ~ phase occurring at ~ 200~C. Amarjit Singh, J appl Phys, 58, 1985, 309-312. 2O 6284. Metalizing system for coating an astronomical telescope mirror A vacuum metallizing system developed for coating a 2.12 m astronomical telescope mirror is described. The 3 m din chamber, installed at 2800 m altitude at the Mexican National Astronomical Observatory at San Pedro Mfirtir, Baja California, was developed with uniquely economical equipment and simplicity of design to facilitate ease of operation, safe handling of the mirror and reliability in this remote location. In order to meet strict performance specifications within a very limited budget, nontraditional equipment suppliers and fabricators were used. The project design and administration philosophy are described. M Roth F and E B Grapero J Vac Sci Technol, A3, 1985, 512-515.