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The influence of substrate temperature on the optical properties of ion-assisted reactively evaporated vanadium oxide thin films
Classified abstracts 64854493
invoked to explain the resistance changes in these films. It was found that the magnitude of the electric field (9 V/cm) did not influence the postdeposition coalescence but did affect the initial resistance of the film. Films studied under relative humidity conditions of greater than 85% showed an interesting crossover of the functional dependence of the film resistance on time consistent with earlier findings in this laboratory. Repeated deposition studies revealed that the agglomeration rate fell drastically beyond a particular deposition cycle indicating that the percolation threshold had been reached with the occurrence of large scale coalescence (LSC). M S Murali Sastry et al, Vacuum, 38, 1988, 21~5. 20 6485. Measurements of vapour stream density with the electron emission method A method of measuring vapour stream density in vacuum evaporation systems, based on the change in electron emission properties of a metallic thermocathode, is presented. The measuring gauge and supply-control system are described in detail. The experimental calibration characteristics and response times for Ti, Ni and Cr are presented for gauges fitted with W, Re and Ir cathodes. Simple construction, high sensitivity, small dimensions of the vapour detector and its self-cleaning ability make the method useful for control of vacuum evaporation processes of many substances. W Slrwko et al, Vacuum, 37, 1987, 739 745. 20 6486. Optical response of switching SmS in thin films prepared by reactive evaporation We describe a simple technique for fabrication of samarium monosulfide films using reactive evaporation and unheated substrates, resulting in films which consist of highly ordered SmS grains in an amorphous dielectric matrix. Mechanical polishing of the films results in a semiconductormetal transition in a fraction of the grains, with an associated large change in the optical response. The films are stable in the switched state, and may be locally annealed back to the semiconducting state using a laser, thus suggesting application in optical data storage. The optical properties in both states are successfully modeled using a Bruggeman effective medium theory and experimentally determined values of the input parameters. C F Hiekey and U J Gibson, J appl Phys, 62, 1987, 3912-3916. 20 6487. Intrinsic stress and structural properties of mixed composition thin films Intrinsic stress and microstructure of mixed composition films were investigated for several binary systems o f l R optical materials. These properties were measured for the entire range of compositions and for mixing obtained by codeposition and by layering of alternate pure components. The variation of stress with composition was observed to be significantly different, depending on the method of mixing. Microstructural analysis revealed a corresponding difference in the grain structure of the films. Low compressive stress films were obtained by coevaporation of high tensile stress materials. These can be used to produce thick and mechanically stable gradient-index optical coatings. Haluk Sankur et al, Appl Optics, 27, 1988, 1564-1567. 20 6488. Characterization of phosphate crystal nucleation and growth on coldrolled steel The formation of a dense, phosphate crystal coating on a steel surface is of prime importance in paint technology to prevent corrosion and to provide a proper substrate for paint adhesion. Crystal nucleation and growth, from an immersion phosphating bath, was examined in detail by infrared spectroscopy, scanning electron microscopy, x-ray diffraction, and electron spectroscopy. The application of high-spatial-resolution Auger electron spectroscopy, which probes individual crystals and substrate regions between crystals, was especially useful and yielded new information on the growth of phosphate coatings. In the system studied, the 15-nm-thick native oxide layer is removed in the first 5 s of immersion as the iron surface dissolves in the bath. Phosphate crystals are identified as nearly all phosphophyllite [ZnzFe(PO4)z'4H20], but with surfaces enriched in Ni and depleted in Zn. No precursor species form prior to the phosphophyllite growth, in contrast to observations on other phosphating systems. The combined application of our instrumental characterization techniques, together with our experimental protocol, is
a powerful method for examining the initial steps in the formation of many surface coating materials. Stephen W Gaarenstroom and Robert A Ottaviani, J Vac Sci Technol, A6, 1988, 966-970. 20 6489. The influence of substrate temperature on the optical properties of ion-assisted reactively evaporated vanadium oxide thin films The properties of vanadium dioxide (VO2) films bombarded with oxygen ions during deposition are examined as a function of substrate temperature. Electrical and optical properties of the as-deposited films are discussed. After annealing to the VO2 form, these films exhibit phase transition temperatures reduced from a nominal 67°C, the lowest thus far in this series being 38°C. Rutherford backscattering analysis indicates low-level tungsten contamination of the films, presumably from the ion gun filaments. The contaminant has a role in properties modification but does not provide a complete explanation for our observations. F C Case, J Vac Sci Technol, A6, 1988, 2010-2014. 20 6490. Columnar structure of obliquely deposited iron films prepared at low substrate temperatures The columnar grain structure of obliquely deposited iron films prepared at various substrate temperatures was investigated. The substrate temperature T~ was varied from 77 to 473 K. The incidence angle was 60 ° and the pressure during evaporation was 4.0 × 10 -3 Pa. The results obtained are as follows. (1) At high temperatures (T 0 > 240 K) the inclination angle of the columnar grains deviates from the value of 41 ° predicted by the well-known tangent rule but at low temperatures (Ts ~< 240 K) it closely approaches the predicted value. (2) There is a particular temperature near 270 K below which the columnar grains are extremely narrow and have no crystallographic preferred orientation. K Hara and M Kamiya, Thin Solid Films, 158, 1988, 239-244. 20 6491. Diffusion in InP using evaporated ZnaP2 film with transient annealing A new diffusion technique in InP using a Zn3P2 layer as the diffusion source with rapid thermal annealing is evaluated, and a number of interesting features are discussed. A p+ layer can only be achieved at temperatures ranging between 500 and 550°C with a 15-s minimum diffusion time. Diffusivity is calculated and it is comparable with that of furnace diffusion. However, in order to form a shallow layer, there should not be any high temperature treatment or any other cause for the redistribution of Fe or dopant. Annealing at 850°C for 15 s prior to diffusion moves the carrier profile from 3000 to 6000 A, deep, and the second diffusion front extends to 2.4/am for the semi-insulating InP substrate. Similar results are obtained on MOCVD grown semi-insulating Fe :InP epiwafer. Diffusion performed on samples without preannealing resulted in two diffusion fronts and a 2.8-pm deep second diffusion front is observed for a diffusion performed on a preannealed epiwafer. Kon-Wei Wang et al, J appl Phys, 63, 1988, 2104-2109. 21. SPUTTERING 21 6492. Synthesis and properties of thin film polymorphs of molybdenum trioxide Thin film polymorphs of molybdenum trioxide have been synthesized by reactive r.f. sputtering in an atmosphere of argon plus oxygen. Films deposited on thermally insulated substrates are polycrystalline and exhibit preferred orientation. Depending on the oxygen partial pressure Po2 during sputtering, the films crystallize in either the thermodynamically stable ~-MoO3 form (Po2 ~ 50%) (unique two-dimensional layered structure) or the newly discovered, metastable monoclinic /?-MOO3 phase (Po2 ~ 10%) (three-dimensional ReO3-related structure). Metastable // films convert thermally to the ~t phase and the transformation appears topotactic. In contrast, films deposited on cooled substrates are amorphous. A correlation between the particular phase formed and adatom mobility is noted. P F Carcia and E M McCarron III, Thin Solid Films, 155, 1987, 53~53. 21 6493. Deposition of Si,C,_,:films by reactive r.f. sputtering Tbe preparation of thin SixC 1 x : H films at low temperatures by reactive r.f. sputtering in acetylene argon gas using pure silicon wafers as target material was investigated. Optimum conditions for SiC deposition were 493
invoked to explain the resistance changes in these films. It was found that the magnitude of the electric field (9 V/cm) did not influence the postdeposition coalescence but did affect the initial resistance of the film. Films studied under relative humidity conditions of greater than 85% showed an interesting crossover of the functional dependence of the film resistance on time consistent with earlier findings in this laboratory. Repeated deposition studies revealed that the agglomeration rate fell drastically beyond a particular deposition cycle indicating that the percolation threshold had been reached with the occurrence of large scale coalescence (LSC). M S Murali Sastry et al, Vacuum, 38, 1988, 21~5. 20 6485. Measurements of vapour stream density with the electron emission method A method of measuring vapour stream density in vacuum evaporation systems, based on the change in electron emission properties of a metallic thermocathode, is presented. The measuring gauge and supply-control system are described in detail. The experimental calibration characteristics and response times for Ti, Ni and Cr are presented for gauges fitted with W, Re and Ir cathodes. Simple construction, high sensitivity, small dimensions of the vapour detector and its self-cleaning ability make the method useful for control of vacuum evaporation processes of many substances. W Slrwko et al, Vacuum, 37, 1987, 739 745. 20 6486. Optical response of switching SmS in thin films prepared by reactive evaporation We describe a simple technique for fabrication of samarium monosulfide films using reactive evaporation and unheated substrates, resulting in films which consist of highly ordered SmS grains in an amorphous dielectric matrix. Mechanical polishing of the films results in a semiconductormetal transition in a fraction of the grains, with an associated large change in the optical response. The films are stable in the switched state, and may be locally annealed back to the semiconducting state using a laser, thus suggesting application in optical data storage. The optical properties in both states are successfully modeled using a Bruggeman effective medium theory and experimentally determined values of the input parameters. C F Hiekey and U J Gibson, J appl Phys, 62, 1987, 3912-3916. 20 6487. Intrinsic stress and structural properties of mixed composition thin films Intrinsic stress and microstructure of mixed composition films were investigated for several binary systems o f l R optical materials. These properties were measured for the entire range of compositions and for mixing obtained by codeposition and by layering of alternate pure components. The variation of stress with composition was observed to be significantly different, depending on the method of mixing. Microstructural analysis revealed a corresponding difference in the grain structure of the films. Low compressive stress films were obtained by coevaporation of high tensile stress materials. These can be used to produce thick and mechanically stable gradient-index optical coatings. Haluk Sankur et al, Appl Optics, 27, 1988, 1564-1567. 20 6488. Characterization of phosphate crystal nucleation and growth on coldrolled steel The formation of a dense, phosphate crystal coating on a steel surface is of prime importance in paint technology to prevent corrosion and to provide a proper substrate for paint adhesion. Crystal nucleation and growth, from an immersion phosphating bath, was examined in detail by infrared spectroscopy, scanning electron microscopy, x-ray diffraction, and electron spectroscopy. The application of high-spatial-resolution Auger electron spectroscopy, which probes individual crystals and substrate regions between crystals, was especially useful and yielded new information on the growth of phosphate coatings. In the system studied, the 15-nm-thick native oxide layer is removed in the first 5 s of immersion as the iron surface dissolves in the bath. Phosphate crystals are identified as nearly all phosphophyllite [ZnzFe(PO4)z'4H20], but with surfaces enriched in Ni and depleted in Zn. No precursor species form prior to the phosphophyllite growth, in contrast to observations on other phosphating systems. The combined application of our instrumental characterization techniques, together with our experimental protocol, is
a powerful method for examining the initial steps in the formation of many surface coating materials. Stephen W Gaarenstroom and Robert A Ottaviani, J Vac Sci Technol, A6, 1988, 966-970. 20 6489. The influence of substrate temperature on the optical properties of ion-assisted reactively evaporated vanadium oxide thin films The properties of vanadium dioxide (VO2) films bombarded with oxygen ions during deposition are examined as a function of substrate temperature. Electrical and optical properties of the as-deposited films are discussed. After annealing to the VO2 form, these films exhibit phase transition temperatures reduced from a nominal 67°C, the lowest thus far in this series being 38°C. Rutherford backscattering analysis indicates low-level tungsten contamination of the films, presumably from the ion gun filaments. The contaminant has a role in properties modification but does not provide a complete explanation for our observations. F C Case, J Vac Sci Technol, A6, 1988, 2010-2014. 20 6490. Columnar structure of obliquely deposited iron films prepared at low substrate temperatures The columnar grain structure of obliquely deposited iron films prepared at various substrate temperatures was investigated. The substrate temperature T~ was varied from 77 to 473 K. The incidence angle was 60 ° and the pressure during evaporation was 4.0 × 10 -3 Pa. The results obtained are as follows. (1) At high temperatures (T 0 > 240 K) the inclination angle of the columnar grains deviates from the value of 41 ° predicted by the well-known tangent rule but at low temperatures (Ts ~< 240 K) it closely approaches the predicted value. (2) There is a particular temperature near 270 K below which the columnar grains are extremely narrow and have no crystallographic preferred orientation. K Hara and M Kamiya, Thin Solid Films, 158, 1988, 239-244. 20 6491. Diffusion in InP using evaporated ZnaP2 film with transient annealing A new diffusion technique in InP using a Zn3P2 layer as the diffusion source with rapid thermal annealing is evaluated, and a number of interesting features are discussed. A p+ layer can only be achieved at temperatures ranging between 500 and 550°C with a 15-s minimum diffusion time. Diffusivity is calculated and it is comparable with that of furnace diffusion. However, in order to form a shallow layer, there should not be any high temperature treatment or any other cause for the redistribution of Fe or dopant. Annealing at 850°C for 15 s prior to diffusion moves the carrier profile from 3000 to 6000 A, deep, and the second diffusion front extends to 2.4/am for the semi-insulating InP substrate. Similar results are obtained on MOCVD grown semi-insulating Fe :InP epiwafer. Diffusion performed on samples without preannealing resulted in two diffusion fronts and a 2.8-pm deep second diffusion front is observed for a diffusion performed on a preannealed epiwafer. Kon-Wei Wang et al, J appl Phys, 63, 1988, 2104-2109. 21. SPUTTERING 21 6492. Synthesis and properties of thin film polymorphs of molybdenum trioxide Thin film polymorphs of molybdenum trioxide have been synthesized by reactive r.f. sputtering in an atmosphere of argon plus oxygen. Films deposited on thermally insulated substrates are polycrystalline and exhibit preferred orientation. Depending on the oxygen partial pressure Po2 during sputtering, the films crystallize in either the thermodynamically stable ~-MoO3 form (Po2 ~ 50%) (unique two-dimensional layered structure) or the newly discovered, metastable monoclinic /?-MOO3 phase (Po2 ~ 10%) (three-dimensional ReO3-related structure). Metastable // films convert thermally to the ~t phase and the transformation appears topotactic. In contrast, films deposited on cooled substrates are amorphous. A correlation between the particular phase formed and adatom mobility is noted. P F Carcia and E M McCarron III, Thin Solid Films, 155, 1987, 53~53. 21 6493. Deposition of Si,C,_,:films by reactive r.f. sputtering Tbe preparation of thin SixC 1 x : H films at low temperatures by reactive r.f. sputtering in acetylene argon gas using pure silicon wafers as target material was investigated. Optimum conditions for SiC deposition were 493