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Thin-film thickness monitor range extender
Classified abstracts 1542-1 551 30 1542. Thermal and nonthermal switching in a-CdAs2 thin-film sandwich structures: The effect of bias rate. (USA) Thin-film devices incorporating a-CdAs2 which display currentcontrolled negative differential resistance (CNDR) under quasistatic bias conditions are described. By biasing devices with short rapid rise-time pulses, threshold switching is observed to set in at much higher voltages than needed for quasistatic CNDR. The transition region between these extremes has been studied by biasing the devices with an adjustable power ramp whose slope was varied over many orders of magnitude. Under ramp bias, the devices show C N D R with a turnover voltage approaching the quasistatic value for bias times to turnover of 0.1 sec or longer. More rapid bias rates result in C N D R with a strongly increasing turnover voltage with increasing bias rate. Analysis of the temperature of the device during ramp bias indicates that the turnover mechanism is Joule-heat induced for bias times of 0.5 sec or longer, "electronic" for bias times of 10 -3 sec or less, and of mixed origin in between. D D Thornburg, J Appl Phys, 46 (I0), 1975, 4526-4530. 3O 1543. A method of formation of thin oxide films on silicon in a microwave magnetoactive oxygen plasma. (GB) The possibility of formation of thin oxide films on silicon in a microwave magnetoactive oxygen plasma at pressures of 5 × 10-s-! Tort is described, and the corresponding experimental results are presented. (Czechoslovakia) L B~rdo~ et al, JPhys D: ApplPhys, 8 (16), 1975, LI95-L197. 30 1544. Thin-film thickness monitor range extender, (USA) A simple thin-film thickness monitor mechanical range extender is described which permits rapid in vacuo switching from reduced to full deposition rate sensitivity. F C Wilson et al, Rev Scient Instrum, 46 (11 ), 1975, 1593-1594. 3O 1545. Self-heating effects in thin-film type-I superconductors (USA) We have investigated the current-induced electrical resistance for zero applied magnetic field in long superconducting strips of tin 100-200 /zm wide and up to a few ~m thick. We observe self-heating effects similar to those reported recently by Skocpol, Beasley, and Tinkham (SBT) for "one-dimensional" tin microbridges with dimensions much smaller than those of our samples. Our results agree well with the onedimensional SBT hotspot model for long microbridges. In the presence of an inductive load, relaxation oscillations can be observed resulting from the negative differential resistance region in the V-I characteristic. R P Huebener, JApplPhys, 46 (11), 1975, 4982-4985. 3O 1546. CulnS2 thin films: Preparation and properties. (USA) The growth and electrical properties of CulnS2 thin films are described. Two deposition schemes, single- and double-source methods, are reported. Data are presented indicating the effects of film and substrate temperature on the electrical characteristics (mobility, resistivity, and carrier concentration) o[bthe films. Both n- and p-type films are reported, and the effects of sulfur concentrations are discussed. Some postdeposition annealing effects are also detailed. L L Kazmerski et al, J Appl Phys, 46 (I I ), 1975, 4865-4869. 3O 1547. Trap-perturbed emission-limited current in amorphous selenium fium~. (USA) The photoinduccd discharge characteristics for positivcly charged amorphous selenium films were studied under constant light intensities chosen to give discharge times comparable to release times of holes from deep traps (approximately 7 sec). Hole mobilities, lifetimes, and field-dependent quantum efficiencics were measured by means of a pulsed-light technique. A modified light-discharge technique was used to measure trap release times. The discharge rate as a function of surface potential is explained semiquantitatively in terms of a uniform space-charge model which includes the effects of decreased electron-hole generation rate because of trapped space charge, reduced carrier range because of capture of holes by traps, and the release and transport of holes captured at earlier times in the discharge period. J IBerg and N C Miller, J ApplPhys, 46 (11), 1975, 4812-4818. 1 28
30 1548. Electron transport properties of copper films. II. Thermoelectric power. (USA) Thermoelectric power (TEP) of as-deposited and annealed polycrystalline and epitaxially grown copper films of thickness 100-5000 A has been measured. The TEP increases with the film thickness to reach a saturation value at about 3000 A. The thickness dependence decreases markedly with increasing annealing temperature and also with increasing temperature of deposition. The saturation value of the TEP of as-deposited films is about 1.5 times the bulk value of copper and decreases rapidly with annealing to approach the singlecrystal bulk value. In sharp contrast to the behavior of the TEP, the resislivily and its temperature coefficient and the carrier concentration of the same copper films exhibit little size effects and insignificant changes due to annealing for thicknesses larger than 1030 A. The observed thickness dependence of the TEP of unannealed and annealed films shows no agreement with the Fuchs-Sondheimer (F-S) theory. Further, there is no correlation between the thickness dependence of the TEP and the temperature coefficient of resistivity as expected on the basis of the F-S theory. Since the thickness variation of the TEP changes markedly with annealing, the observed dependence is not a genuine mean free path effect. The observed linear dependence of the TEP on the inverse of the film thickness (as expected from the F-S theory) is totally accidental and, therefore, physically meaningless values of U = (8 In/0 InE)EF are obtained from the slopes of the lines. Arguments have been advanced to suggest that the observed thickness dependence of the TEP can be understood only in terms of the effect of a large thickness-dependent concentration of structural defects frozen in the metal films. The defect-induced changes in the TEP would be caused by the distortions in the Fermi surface and, hence, changes in the energy dependence of the mean free path or relaxation time at the Fermi surface. (India) A P Thakoor et al, J ApplPhys, 46 (1 I), 1975, 4777-4783. 30 1549. Density and electrical conductivity of an abnormal fcc phase observed in rare earth metal films. (GB) Abnormal fcc monocrystalline films of all stable lanthanides were obtained by epitaxial growth. Electron-diffraction patterns allowed us to determine the film density. The observed influence of average thickness and surface roughness on electrical resistivity led us to an estimate of the values of some bulk-metal charge-transport parameters. The data thus got were compared with those for normalstructure materials. (Italy) C Reale, Vacuum, 25 (9/10), 1975, 403-405.
31. S P U T T E R I N G 31 1550. Inexpensive de sputtering system for scanning electron microscopy. (USA) A simple, easy to construct dc gold sputtering system suitable for coating nonconducting scanning electron microscope (SEM) samples is described. Gold foil is used for the target cathode and air for the ionizing gas. Components are readily.available and can be assembled in less than a day. R B Bolon, Rev Scient h~strum, 46 (10), 1975, 1421-1422. 31 1551. Application of ion etching to produce finest structures of thin films. r.f. cathode sputtering is used for ion etching of fine structures in gold and copper layers of 3 to 6 p.m thickness. In the ion etching process the sample to be etched is sputtered over its whole surface while the desired structure is covered by a mask produced by photo]itography. For ion etching of gold layers up to 3 /~m thickness photoresist can be directly used as the mask. For ion etching of 3 to 6 ~.m gold and copper layers metal masks, particularly titanium masks, are suitable. The metal masks are produced by chemical etching or by the lift-off technique. For ion etching with photoresist masks the process parameters must be carefully optimized in view of the sensitivity of the photoresists to increased temperature and reactive residual gases. Ion etching with metal masks is comparatively less critical and, when using titanium, it offers the advantage that by adding oxygen to the sputter gas the titanium etching rate can be
30 1548. Electron transport properties of copper films. II. Thermoelectric power. (USA) Thermoelectric power (TEP) of as-deposited and annealed polycrystalline and epitaxially grown copper films of thickness 100-5000 A has been measured. The TEP increases with the film thickness to reach a saturation value at about 3000 A. The thickness dependence decreases markedly with increasing annealing temperature and also with increasing temperature of deposition. The saturation value of the TEP of as-deposited films is about 1.5 times the bulk value of copper and decreases rapidly with annealing to approach the singlecrystal bulk value. In sharp contrast to the behavior of the TEP, the resislivily and its temperature coefficient and the carrier concentration of the same copper films exhibit little size effects and insignificant changes due to annealing for thicknesses larger than 1030 A. The observed thickness dependence of the TEP of unannealed and annealed films shows no agreement with the Fuchs-Sondheimer (F-S) theory. Further, there is no correlation between the thickness dependence of the TEP and the temperature coefficient of resistivity as expected on the basis of the F-S theory. Since the thickness variation of the TEP changes markedly with annealing, the observed dependence is not a genuine mean free path effect. The observed linear dependence of the TEP on the inverse of the film thickness (as expected from the F-S theory) is totally accidental and, therefore, physically meaningless values of U = (8 In/0 InE)EF are obtained from the slopes of the lines. Arguments have been advanced to suggest that the observed thickness dependence of the TEP can be understood only in terms of the effect of a large thickness-dependent concentration of structural defects frozen in the metal films. The defect-induced changes in the TEP would be caused by the distortions in the Fermi surface and, hence, changes in the energy dependence of the mean free path or relaxation time at the Fermi surface. (India) A P Thakoor et al, J ApplPhys, 46 (1 I), 1975, 4777-4783. 30 1549. Density and electrical conductivity of an abnormal fcc phase observed in rare earth metal films. (GB) Abnormal fcc monocrystalline films of all stable lanthanides were obtained by epitaxial growth. Electron-diffraction patterns allowed us to determine the film density. The observed influence of average thickness and surface roughness on electrical resistivity led us to an estimate of the values of some bulk-metal charge-transport parameters. The data thus got were compared with those for normalstructure materials. (Italy) C Reale, Vacuum, 25 (9/10), 1975, 403-405.
31. S P U T T E R I N G 31 1550. Inexpensive de sputtering system for scanning electron microscopy. (USA) A simple, easy to construct dc gold sputtering system suitable for coating nonconducting scanning electron microscope (SEM) samples is described. Gold foil is used for the target cathode and air for the ionizing gas. Components are readily.available and can be assembled in less than a day. R B Bolon, Rev Scient h~strum, 46 (10), 1975, 1421-1422. 31 1551. Application of ion etching to produce finest structures of thin films. r.f. cathode sputtering is used for ion etching of fine structures in gold and copper layers of 3 to 6 p.m thickness. In the ion etching process the sample to be etched is sputtered over its whole surface while the desired structure is covered by a mask produced by photo]itography. For ion etching of gold layers up to 3 /~m thickness photoresist can be directly used as the mask. For ion etching of 3 to 6 ~.m gold and copper layers metal masks, particularly titanium masks, are suitable. The metal masks are produced by chemical etching or by the lift-off technique. For ion etching with photoresist masks the process parameters must be carefully optimized in view of the sensitivity of the photoresists to increased temperature and reactive residual gases. Ion etching with metal masks is comparatively less critical and, when using titanium, it offers the advantage that by adding oxygen to the sputter gas the titanium etching rate can be