7456. Thin film growth of silver sulphide I: initial stages of heteroepitaxy on NaCl

Classified abstracts 7455-7464 dominant absorption process. The direct bandgap was found to lie in the region 4.1 _+0.1 eV. V Casey and M I Stephenson, J Phys D : Appl Phys, 23, 1990, 1212-1215. 20 7455. Structure and superconducting properties of YBa2Cn307 _ x films prepared by nitrogen laser evaporation and CO2 laser annealing in oxygen Superconducting YBa2Cu3OT_x thin films were obtained under high vacuum (10 -s torr) on substrates of polycrystalline A1203 sapphire, SrTiO3, and Si, having zero resistance at 81, 85, 87 and 79 K, respectively. A N2 laser of 3.5 J cm 2 energy density was used for the evaporation. The substrates were heated by a cw single-mode CO2 laser and the annealing was performed by the same laser in an O5 atmosphere. Local planar superconducting regions were obtained by focusing the radiation of the cw CO2 laser upon the films. The films were investigated by scanning electron microscope, X-ray microanalysis and X-ray diffraction. V Serbezov et al, J Appl Phys, 67, 1990, 6953-6957. 20 7456. Thin film growth of silver sulphide I: initial stages of heteroepitaxy on NaC! Thin films of Ag2S were prepared by co-evaporation from two separate sources on NaC1 substrate crystals. The initial growth stages were studied by transmission electron microscopy. Two different modifications were found depending on the deposited amounts of Ag2S but not on the substrate temperature. In the first stage the Ag2S islands show a triclinic structure and are fourfold azimuthally oriented to the substrate where their (I 10) contact plane is parallel to the NaCI(001) cleavage face. With increasing film thickness the newly observed triclinic modification is transformed in the monoclinic modification (acanthite) where the Ag2S islands change their orientation via (010) to (012). Independent of the phase transformation and the orientation change the AgzS islands preserve their fourfold orientation to.the substrate. The epitaxial relationships for the three orientations are presented. H Haefke et al, Thin Solid Films, 188, 1990, 133 142. 20 7457. Thin film growth of silver sulphide II. Structure models of epitaxial contact layers The change in the structure and the change in orientation of thin films of Ag2S grown on NaC1 substrates, described in detail in the first part of this work, were studied as a function of the film thickness. The structure of the newly found trielinic pseudocubic modification of Ag2S is discussed. Models for the contact layers are given for three different growth structures. The structure-geometrical analysis of the epitaxial relationships is applied to explain the mechanism of transformations in the Ag2S films. It was found that in the initial growth stage the structure type and film orientation of Ag2S are induced by the substrate structure. Above a nominal film thickness of about 2.0 nm, the epitaxial orientation is determined mainly by the charge distribution and compensation in the interface region. K Bozhiiov et al, Thin Solid Films, 190, 1990, 129-138. 20 7458. Structural investigations of evaporated GeSe films Depending on the technological procedure of vacuum sublimation, amorphous or polycrystalline films of germanium monoselenide were obtained. The film composition determined by Auger electron spectroscopy at the surface and in the depth proved to be stoichiometric. C M Vodenicharov and P K Petkov, Thin Solid Films, 190, 1990, 335339. 20 7459. Evaporation of polyethylene powder for its thin film growth The growth rate Vfof thin films prepared by heating polyethylene powder in a quartz crucible is determined as a function of the substrate-crucible distance and the crucible temperature. It is found that the value of Vr is proportional to the pressure in the vacuum system during heating, which changes intermittently owing to intermittent boiling and evacuation by pumping. Some comments are given concerning why Vf is not proportional to the vapour pressure of the powder. K Maid, Thin Solid Films, 188, 1990, 355-359.

20 7460. Transport properties of flash-evaporated (Bil ~Sbx)2Te3 films II: theoretical analysis An analysis of the temperature dependence of several transport properties, particularly the Seebeck and Hall coefficients, of thermoelectrically optimized p-type (Bi~_xSbx)2We3films is carried out in the interval from 80 to 350 K for x = 0.75 including a comparison with bulk material data. The model calculations are based on the solution of the homogeneous Boltzmann equation in a relaxation time approximation since the films exhibit an in some ways bulk-like behaviour, e.g. the Hall mobility is of the order of that of the bulk material. In the framework of a one-valenceband model, the analysis of both bulk and film data favours a non-parabolic dispersion relation for Bi05SbLsTe3. It is shown that acoustic intravalley scattering is the predominant scattering mechanism of the charge carriers in the thermoelectrically optimized films. U Dillner and F Vrlklein, Thin Solid Films, 187, 1990, 263 273. 20 7461. A ballistic deposition model for films evaporated over topography MgF2 films were evaporated at angles of incidence of 5 and 40 ° onto oxide lines 1.5 #m wide on a silicon wafer. The film properties observed by scanning electron microscopy studies of cleaved cross-sections were compared with those predicted by simulation by a ballistic deposition model. Good agreement was found for the surface profiles of the films, the orientation of the columnar microstructure and the location of porous low density regions. R N Tait ctal, Thin Solid Films, 187, 1990, 375 384.

21. SPUTTERING 21 7462. Thin film sputter deposition for hybrid applications In thin films hybrid technology for microwave and precision applications increasingly complex processes with high quality layers are required. Several sputter deposition processes will be discussed. It is shown that NiCr films with a low nickel content can be adjusted for a low TCR by means of reactive sputtering. NiCr-AI20~ cermet films, obtained with a parallel sputtering technique, can be produced with a low TCR value up to 2000 ~[]. A comparison between reactively rf sputtered Si3N4 and Ta205 capacitor layers shows that tantalum pentoxide is the superior material. Near bulk resistivity gold layers can be obtained at moderate temperatures if the self bias voltage of the magnetron is kept at a low value. P Muralt and J P Seidel, Vacuum, 41, 1990, 1400-1402. 21 7463. Growth and structural characterization of single-crystal (001) oriented Mo-V superlattices Dual target magnetron sputtering has been used to grow single-crystal Mo-V superlattic structures (SLS) with modulation wavelengths 2 ranging from 0.6 to 17.7 nm on (001) oriented MgO substrates held at temperatures Ts between 600 and 900°C. High resolution cross-sectional transmission electron microscopy (HRXTEM) images and comparisons between experimental and calculated X-ray diffraction (XRD) spectra show that SLS with an interface sharpness of + 1 monolayer ( + 0.15 nm) could be grown for )~ <~ 4.9 nm and Ts <~ 700°C whereas interdiffusion broadened the interfaces for higher T~ values. This interface sharpness was also verified by growing SLS with ~. = 0.6 nm (one unit cell of Mo and one of V) which exhibited strong superlattice satellites in both XRD and selected area electron diffraction (SAED), and contrast from the individual layers was also observed in HRXTEM images. For 2 > 4.9 nm, HRXTEM images showed non-uniform layers and the XRD peak width (FWHM) increased by 250%. J Birch et al, Vacuum, 41, 1990, 1231 1233. 21 7464. Structure and optical properties of Au-Cr sputtered films used in digital optical recording media A u ~ r thin films deposited by dc magnetron sputtering are investigated for application to optical data storage media. Depending on the composition, the optical and electrical properties are governed to a large extent by the structure and the grain size of the film and by the degree of oxidation of Cr. Films interesting for optical recording media show typically grain sizes less than 3 nm, a reflectance of 40% and an absorb669