Papers by Bernard Gallois
Materials and Processing Report, 1989
MRS Proceedings, 1989
Superconducting thin films of YBa2Cu307‐x were grown on MgO (100) and YSZ(IOO) substrates without... more Superconducting thin films of YBa2Cu307‐x were grown on MgO (100) and YSZ(IOO) substrates without post‐annealing by metal organic chemical vapor deposition using vertical, high‐speed (1100 rpm) rotating disk reactor. The source materials were Y(tmhd)3, Ba(tmhd)2, and Cu(tmhd)2, which were kept at 135 °C, 240 °C, and 120 °C respectively. The precursors were transported using nitrogen as the carrier gas and introduced separately into the cylindrical stainless steel reaction chamber, which was maintained at 60 torr. The oxygen partial pressure was 30 Torr. The substrates were heated resistively at 800°C. After growth, the films were cooled down at a rate of 5 °C/min under 1 atmospheric pressure of pure oxygen. The X‐ray diffraction pattern of the films showed primarily an orientation of c‐axis perpendicular to the substrates, with weak peaks of (hoo) corresponding to a‐axis orientation. Scanning Electron Microscopy of the films showed a well‐developed a‐axis and c‐axis plate‐like struc...
Le Journal de Physique Colloques, 1989
The SAGE Encyclopedia of Food Issues
MRS Proceedings, 1995
Theoretical works have indicated that carbon nitride, in a β-C4N4 phase, would have optical and m... more Theoretical works have indicated that carbon nitride, in a β-C4N4 phase, would have optical and mechanical properties comparable to or exceeding those of diamond. In this effort, the formation of carbon nitride thin films was investigated using a Plasma Assisted Ion Beam Deposition (PAIBD). In this technique, a C- ion beam combined with a N2 or NH3 RF plasma source is used to synthesize carbon nitride films. These films were investigated as a function of both C- ion beam energy and the power of the plasma source. The C- ion energy was found to be a key parameter in the formation of carbon nitride. The films were evaluated by a variety of diagnostic techniques including Raman, AES, XRD and FTIR. Analysis confirms high nitrogen concentration in the synthesized films and the major portion of carbon being single bonds in the sp3 bond configuration, which is a characteristic of the tetrahedral -C3N4 phase. Tribology tests confirmed that the friction coefficient and the wear rate are comp...
MRS Proceedings, 1997
ABSTRACTSpecular laser reflectance (He-Ne laser) has been used to monitor in-situ and in real tim... more ABSTRACTSpecular laser reflectance (He-Ne laser) has been used to monitor in-situ and in real time the growth rate and the index of refraction of oxide films during chemical vapor deposition. This technique has been implemented on an inverted vertical stagnation-flow reactor equipped with a solid-source delivery system. Yttria deposited on silicon has been chosen as a starting material to characterize the reactor and the precursor delivery system capabilities. The experimental reflectance curves have been fitted to a simple three-layer (gas/film/substrate) model allowing the determination of the growth rate and of the refractive index. The growth rate has been studied as a function of various key processing parameters: the source feeding rate, the powder packing density, the oxygen partial pressure and the total pressure. The change in reflectivity has also been recorded during pulsed-delivery growth. Nanometer-scale resolution is obtained which demonstrates that this method can be ...
TiCxNy coatings were grown on graphite substrates in a computer-controlled, hot-wall chemical vap... more TiCxNy coatings were grown on graphite substrates in a computer-controlled, hot-wall chemical vapour deposition (CVD) reactor, using gas mixtures of TiCl4–CH4–N2–H2 at a total pressure of 10.7 kPa (80 torr) and at a temperature of 1400 K. Growth rate, composition, morphology and crystallographic texture of the TiCxNy coatings were investigated as a function of the CH4/CH4+N2 ratio in the range
MRS Proceedings, 1994
Solid solutions of lead zirconate titanate (PZT) and lead magnesium niobate (PMN) doped with bari... more Solid solutions of lead zirconate titanate (PZT) and lead magnesium niobate (PMN) doped with barium/strontium were developed for use in miniature electrostrictive actuators. The microstructural features of the materials were determined by high-resolution transmission electron microscopy (HREM) and by x-ray diffractometry. The response and the strain hysteresis were measured by applying a sinusoidal or a rectangular voltage pulse. Pulses of variable amplitude and width were applied to the elements to study the switching behavior of 90° domain walls in the materials and to elucidate the initial zero-position “walk off” mechanism. The strain hysteresis or remanent strain of PZT decreased with increasing PMN concentration. A barium-doped PZT (Ba-PZT) composition containing 4 mole% of PMN exhibited ferroelectric relator behavior with a field-induced strain much larger than those of lead magnesium niobate (PMN) electrostrictive materials and a small remanent strain hysteresis.
MRS Proceedings, 1991
Specific compositions of boron-carbon-silicon ceramics exhibit improved abrasive wear and good th... more Specific compositions of boron-carbon-silicon ceramics exhibit improved abrasive wear and good thermal shock resistance, but require bulk sintering at temperatures in excess of 2100K. The formation of such phases by chemical vapor deposition was investigated in the temperature range of 1073K–1573K. Methyltrichlorosilane (CH3SiCl3), boron trichloride, and methane were chosen as reactant gases, with hydrogen as a carrier gas and diluent. The coatings were deposited in a computer-controlled, hot-wall reactor at a pressure of 33 MPa (200 Torr).Below 1473K the coatings were amorphous. At higher temperatures non-equilibrium reactions controlled the deposition process. The most common coating consisted of a silicon carbide matrix and a silicon boride, SiB6, dispersed phase. Multiphase coatings of B+B4C+SiB6 and SiC+SiB6+SiB14 were also deposited by controlling the partial pressure of methane and boron trichloride. Non-equilibrium thermodynamic analysis qualitatively predicted the experimen...
Journal of Crystal Growth, 1991
Highly c-axis oriented, highly dense, low carbon YBa 2Cu 3°x superconducting thin films have been... more Highly c-axis oriented, highly dense, low carbon YBa 2Cu 3°x superconducting thin films have been formed in-Situ at a reduced substrate temperature as low as 570°Cby a novel plasma enhanced metalorganic chemical vapor deposition process. Superconducting YBa2Cu3Othin films, having a zero resistance transition temperature of 82 K and critical current density of iO~A/cm
Le Journal de Physique IV, 1993
Texture analyses were performed on the chemically vapor deposited monolithic TiN, Tic, TiCxN, coa... more Texture analyses were performed on the chemically vapor deposited monolithic TiN, Tic, TiCxN, coatings and graded TiN/TiC coatings by wide film Debye-Scherrer X-ray diffraction technique. The preferred orientations of the coatings were investigated as a function of coating thickness and input gas composition. The growth of TiN and Tic coatings was initiated as randomly oriented crystallites which subsequently grew into large columnar grains with a <110> preferred orientation. The textures of Tic coatings with the same thickness changed from the <110> orientation to the <loo> orientation with decreasing hydrogen concentration in the gas phase. TiCxN coatings exhibited a preferred orientation of <Ill> up to the C$~/CH,+N, ratio of 0.14 above which a strong <loo> texture developed. The texture analyses on the graded TiN/TiC coatings showed that the Tic top layers were oriented in a <loo> direction perpendicular to the sample surface.
Diamond and Related Materials, 1992
,\ capacidvely coupled RF plasma-assisted chemical vapor deposition reactor was used to synthesiz... more ,\ capacidvely coupled RF plasma-assisted chemical vapor deposition reactor was used to synthesize diamond. A diamond phase Isp 3 C C bondsl was detected in the deposits by Raman scattering spectroscopy. Its concentration, measured by core electron energy loss spectroscopy (CEELS), was estimated to be about 40";. The amount of hydrogen in the deposits measured by hydrogen profiling i3> helium ions was of the order of 1% regardless of the growth conditions. These results suggested a possibility of diamond synthesis ~> it capacitivcly coupled RF PACVD technique.
Ceramics International, 1996
Abstract Pyrolytic carbon coatings were deposited on a graphite substrate by chemical vapour depo... more Abstract Pyrolytic carbon coatings were deposited on a graphite substrate by chemical vapour deposition technique from impinging jets of ethylene gas. The growth and structure of the coatings were investigated as a function of gas flow velocity. The deposition rate of the coatings increased linearly with the square root of gas velocity or flow rate of ethylene. This behaviour was explained by a mass-transport theory. The coatings exhibited cone-like morphology at low gas velocities and cauliflower-like morphology at high gas velocities. Textural analyses revealed that all the coatings were preferentially oriented in the 〈001〉 direction perpendicular to the substrate.
Science and Technology of Thin Film Superconductors 2, 1990
Physical Concepts of Materials for Novel Optoelectronic Device Applications II: Device Physics and Applications, 1991
ABSTRACT MOCVD and PE-MOCVD are versatile growth techniques which are capable of producing high q... more ABSTRACT MOCVD and PE-MOCVD are versatile growth techniques which are capable of producing high quality YBCO superconducting films. The use of these methods to grow YBCO films with Tc in the range 88-90 K and Jc(77 K) repeatably in excess of 10 exp 6 A/sq cm is reported. This can be accomplished at substrate temperatures as low as 730 C, in the case of MOCVD, and 670 C for PE-MOCVD, through the use of N2O as the oxidant source gas. Growth at temperatures down to 570 C has been demonstrated but as the cost of Tc decreasing to 72 K. Still, these results are very promising for development of a low temperature process for the growth of YBCO which will be compatible with active device technologies.
Applied Physics Letters, Jan 1, 1991
Epitaxial YBa2Cu3O(7-x) superconducting thin films with a zero resistance transition temperatures... more Epitaxial YBa2Cu3O(7-x) superconducting thin films with a zero resistance transition temperatures of about 90 K have been prepared, in situ, on LaAlO3 by a plasma-enhanced metalorganic chemical vapor deposition process at a substrate temperature of 670 C in 1 torr partial pressure of N2O. The composition of the films was varied systematically to investigate the effect of changes in the Ba/Y and Cu/Y ratio on the film properties. The results indicated that superconducting current densities exceeding 10 to the 6th A/sq cm, measured at 77 K by a transport method, could be obtained on films with an anomalously wide range of film compositions. Excess Cu (up to 60 percent and deficiency in Ba (down to 30 percent) from their stoichiometric values did not significantly degrade the superconducting properties of the films. As the composition approached the Y-Ba-Cu ratio of 1-2-3, an improvement in surface morphology and a decrease in superconducting transition temperature were found.
Physica C-superconductivity and Its Applications, Jan 1, 1992
The microstructure and the superconducting properties of YBa2Cu3O7−x thin films prepared by plasm... more The microstructure and the superconducting properties of YBa2Cu3O7−x thin films prepared by plasma-enhanced metalorganic chemical vapor deposition have been investigated systematically as a function of metal composition. Yttria precipitates are not apparent on the surface of yttrium-rich films. They are densely distributed within the films, their average size is of the order of 5–10 nm and their density can be as high as 1024/m3. Excess copper leads to the precipitation of copper oxide (CuO) particles on the surface of the films, but they are not found in the bulk. High transition temperatures and high critical current densities have been obtained over a wide range of compositions. Transition temperatures higher than 86 K are always obtained when the Cu/Ba ratio is larger than the stoichiometric ratio of 1.5. Films with Cu/Ba ratio larger than 1.5 and a Ba/Y ratio less than 1.7 usually have a critical current density larger than 106 A/cm2 at 77 K and 0 T. The dependence of the critical current density on temperature follows a power law, JcA(1−T/Tc)n. The value of n is 2 for stoichiometric and barium-rich films and 1 for yttrium-rich films. The best films with transition temperatures of 90K, critical current densities in excess of 106 A/cm2 at 77.5 K, and smooth surfaces are observed when the Ba/Y ration is around 1.6 and the Cu/Ba ratio is around 1.8.
Applied Physics Letters, Jan 1, 1991
... CS Chern,a) J. Zhao, YQ Li,b) P. Norris, B. Kear,a) B. Gallois,b) and Z. Kalmana) EMCORE Corp... more ... CS Chern,a) J. Zhao, YQ Li,b) P. Norris, B. Kear,a) B. Gallois,b) and Z. Kalmana) EMCORE Corporation, 35 ... resistance and magnetic susceptibility versus temperature of the as-deposited films show metallic behavior in the normal state and sharp superconducting transitions with ...
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Papers by Bernard Gallois