Takashi Goto

State of boron in chemical vapour-deposited SiC-B composite powders

Etude de letat du bore dans les poudres SiC-B, preparees par depot chimique en phase vapeur a partir de (CH 3 ) 2 SiCl 2 , B 2 H 6 et H 2 a 1673 K et 0,1 MPa

Dielectric properties of chemically vapour-deposited Si3N4

The dielectric properties of chemically vapour-deposited (CVD) amorphous and crystalline Si3N4 were measured in the temperature range from room temperature to 800° C. The a.c. conductivity (σa.c.) of the amorphous CVD-Si3N4 was found to be less than that of the crystalline CVD-Si3N4 below 500° C, but became greater than that of the crystalline CVD-Si3N4 over 500° C due to the contribution of d.c. conductivity (σd.c.). The measured loss factor (ɛ″) and dielectric constant (ε′) of the amorphous CVD-Si3N4 are smaller than those of the crystalline CVD-Si3N4 in all of the temperature and frequency ranges examined. The relationships ofε″ αωn-1, (ε′-ε′∞) αωn-1 andε″/(ε′-ε′∞) = cot (nπ/2) (were observed for the amorphous and crystalline specimens, where ω is angular frequency andn is a constant. The values ofn of amorphous and crystalline CVD-Si3N4 were 0.8 to 0.9 and 0.6 to 0.8, respectively. These results may indicate that the a.c. conduction observed for both of the above specimens is caused by hopping carriers. The values of loss tangent (tanδ) increased with increasing temperature. The relationship of log (tanδ) ∝T was observed. The value of tanδ for the amorphous CVD-Si3N4 was smaller than that of the crystalline CVD-Si3N4.

As‐grown superconducting Bi(‐Pb)‐Sr‐Ca‐Cu‐O films by electron cyclotron resonance plasma sputtering

Bi(‐Pb)‐Sr‐Ca‐Cu‐O thin films were prepared on MgO(100) single‐crystal substrates by electron cyclotron resonance (ECR) plasma sputtering at substrate temperatures from room temperature to 590u2009°C. Pb‐doped superconducting as‐grown films were obtained above 560u2009°C. The Tc values of the Pb‐doped films prepared at 570–590u2009°C were 58–64 K which increased with increasing substrate temperature. Pb‐undoped as‐grown films obtained at 590u2009°C showed superconduction (Tc =30 K), but the films obtained below 580u2009°C were semiconductors. The grain sizes and contents of the 37 A phase (110 K phase) were increased by the Pb doping into the as‐grown Bi‐Sr‐Ca‐Cu‐O films.

Preparation of titanium carbide plates by chemical vapour deposition

Thick titanium carbide (TiCx) plates were prepared by chemical vapour deposition using TiCl4, CCl4 and H2 as source gases at deposition temperatures (Tdep) of 1573 to 1873 K, total gas pressures (Ptot) of 4 and 40 kPa, and source gas molar ratio (CCl4/(TiCl4 + CCl4)) (mc) of 0.13 to 0.91. The effects of deposition conditions on the microstructure, preferred orientation, deposition rate, lattice parameter and composition were investigated.A plate-like TiCx was obtained at mc less than 0.5. The (110) plane was preferably oriented parallel to the deposition surface at Tdep of 1673 to 1873 K. The deposition rates showed a strong mc dependence and the maximum rate was found at mc = 0.3 to 0.5. The activation energies for the formation of TiCx plates were 86 kJ mol−1 at Ptot = 4 kPa and 95 kJ mol−1 at Ptot= 40 kPa. When mc values were in the range of 0.13 to 0.51, the lattice parameter increased with an increase in mc and decreased with an increase in Tdep. The lattice parameter was almost constant beyond mc = 0.72 at all Tdep. The atomic ratio (C to Ti) for TiCx varied from 0.6 to 1.0 with deposition conditions.

Preparation of Superconducting YBa2Cu3O7-x Films by ECR Plasma Sputtering

Y-Ba-Cu-O films were prepared on (100)MgO single crystal substrates by ECR plasma sputtering. As-deposited films without substrate heating were amorphous and electrically insulating. The amorphous film was crystallized to YBa2Cu3O7-x by postannealing at 930°C for 1 min in O2 gas, and the Tc of the postannealed film was 70.5 K. The film prepared at the substrate temperature of 650°C was crystalline YBa2Cu3O7-x and the Tc of the film without any postannealing was 73 K.

Chemical Vapor Deposition of Silicon Borides

Monolithic SiB 4±x and SIB6 plates about 1 nm in thickness were prepared by CVD using SiCl 4 , B 2 H 6 and H 2 gases as source materials. The CVD-SiB 4±x , plates have nonstoichiometric compositions between B/Si=3.1 and 5.0. The lattice parameters of the CVD-SiB 4±x , plates are a=0.633 nm and c=1.262 to 1.271 nm. The density of the CVD-SiB 4±x ranges from 2.39 to 2.45 g/cm 3 . The CVD-SiB 6 plates have a constant composition of B/Si=6.0. The lattice parameters of the CVD-SiB 6 plates are a=1.444 nm, b=1.828 nm, c=0.9915 nm, and their density Is 2.42 g/cm 3 . These measured densities are both almost in agreement with theoretical values. The electrical conductivity, Seebeck coefficient, Hall mobility and thermal conductivity of the CVD-SiB 4±x and CVD-SiB 6 plates were examined in the temperature range from 300 to 1000K. The conduction mechanism Is discussed and their figure of merit values for thermoelectric materials are evaluated.

Microhardness of non-stoichiometric TiCx, plates prepared by chemical vapour deposition

Abstract The relationship between Vickers microhardness and non-stoichiometric composition of titanium carbide (TiCx) plates was investigated. TiCx plates having a composition range from x = 0.57 to 1.0 were prepared by chemical vapour deposition using TiCl4, CCl4 and H2 as source gases at total gas pressures (Ptot) of 4 and 40 kPa and deposition temperatures (Tdep) of 1573 to 1873 K. The microhardness increased from about 2000 to 3000 kg mm−2 with increasing x independent of Tdep, but this change depended on Ptot. The TiCx plates prepared at Ptot = 4 kPa showed slightly higher hardness values than those prepared at Ptot = 40 kPa. The relationship between Ptot and microhardness was explained by the difference in grain sizes. The grain sizes of deposits prepared at Ptot = 4kPa were about half the size of those prepared at Ptot = 40 kPa.