Katsuki Kitahama

Synthesis of diamond by laser-induced chemical vapor deposition

Diamond has been obtained by ArF excimer laser‐induced chemical vapor deposition. The reaction was carried out by use of C2H2 diluted with H2 as a source gas and at the pressure range of 8–75 Torr. The products were characterized by scanning electron microscopy and reflection electron diffraction. Deposits prepared in the temperature range of 40–800 °C, which were measured by the thermocouple attached to the substrate, show several lines of diamond in the reflection electron diffraction photographs. The fact that the laser beam must be concentrated for the diamond formation to occur strongly suggests that the reaction proceeds through a multiple photon process.

Optimization of single crystal preparation of Bi2Sr2CaCu2Ox superconductor by the travelling solvent floating zone method

Optimization of single crystal preparation of the Bi2.2(Sr, Ca)2.8Cu2.0Oy superconductor by the travelling solvent floating zone method has been performed with the intention of obtaining large single crystals and improving the superconductive transition temperature, Tc. The composition ratio, Sr/Ca, and the oxygen partial pressure of growth atmosphere, PO2 , were varied in the crystal growth. A single crystal typically obtained was a thin plate of the dimensions of 5×50×2 mm3. The thickness of the crystal was the largest in the crystal growth at Sr/Ca=1.4, while no distinct change was observed in the resulting crystals in the range of 22~100 kPa. Electric and magnetic properties, the formal charge of copper ions and existence of ion defects are discussed.

Reinvestigation of the carbon films prepared by ArF excimer laser‐induced chemical vapor deposition

It has already been reported by the authors [K. Kitahama, K. Hirata, H. Nakamatsu, S. Kawai, N. Fujimori, T. Imai, H. Yoshino, and A. Doi, Appl. Phys. Lett. 49, 634 (1986)] that the formation of diamond was confirmed in an ArF excimer laser‐induced chemical vapor deposition experiment using acetylene as a carbon source. However, a careful reexamination of the reflection electron diffraction photographs afterward reveals that the deposit is something other than diamond. Raman spectra of the deposit were compared with those of other homologous substances. It is concluded that the structure of the deposit consists of individual graphite layers which are randomly translated parallel to the layers and rotated about the normal of the layers, although separations between individual graphite layers are kept constant. The structure is identical with that of the material known as a ‘‘heat‐treated carbon black.’’

Layer-by-layer epitaxial growth of a Bi2Sr2CuO6 thin film on a Bi2Sr2CaCu2O8 single crystal

The epitaxial growth of a Bi2Sr2CuO6 (2201) thin film on a Bi2Sr2CaCu2O8 (2212) single crystal has been performed using computer‐controlled laser molecular beam epitaxy. The surface of the 2212 single crystal used as the substrate is smooth and invariant under the growth condition at 640 °C in NO2 pressure of 1×10−5 mbar. The growth process of the 2201 film has been observed by in situ reflection high‐energy electron diffraction (RHEED), and the layer‐by‐layer growth of the 2201 phase is confirmed by the oscillation of RHEED intensities. During the growth, a modulated surface structure which is characteristic of the Bi cuprate crystals is always present.

Solid-state polymerization of pentoxane (─CH2─O─)5

Abstract In the course of systematic study of the solid-state polymerization of the cyclic oligomers of formaldehyde (─CH2─O─)m, it was found that pentoxane (─CH2─O─)5 undergoes polymerization in the solid state to form polyoxymethylene (─CH2─O─)n by X-irradiation. The present article contains (a) the molecular and crystal structure determination of pentoxane, (b) the determination of the relative crystal orientation of pentoxane and the resultant polyoxymethylene, and (c) some discussions on the role played by the crystal structure of pentoxane in the solid state polymerization comparing with the cases of trioxane and tetraoxane. Pentoxane forms an orthorhombic crystal. The crystallographic data are a = 8.194 A, b = 10.691 A, c = 7.682 A, D14 2h - Pbcn, four molecules in the unit cell. The relative crystal orientation of pentoxane and polyoxymethylene was determined using X-ray diffraction from single crystals of pentoxane which were partially converted into polyoxymethylene by X-irradiation. The polyoxy...

Preparation of Li-containing Bi2Sr2CaCu2O8 single crystals and their Li solubility limit

Abstract With the aim of substituting Cu with Li in the Bi 2 Sr 2 CaCu 2 O 8 crystal, preparation of single crystals by a traveling solvent floating zone method has been undertaken and single crystals with maximum dimensions 30×4×0.2 mm 3 have successfully been obtained. The presence of Li in the crystal structure and the solubility limit of as much as 13% in the molar ratio Li/(Li+Cu) were confirmed by chemical analyses. Although the location of Li in the crystal structure and the precise oxygen content remain unclear, the crystals show a small elevation of superconductive transition temperature, up to T c = 93 K, with increase in Li content. Some typical data of magnetic susceptibility and conductivity are also presented.

Tunneling spectra of Au / Bi2Sr2CuO8 thin film / Bi2Sr2CaCu2O8 single crystal junctions with well defined interface

Abstract Reproducible tunneling spectra of Bi 2 Sy 2 CaCu 2 O 8 single crystals have been obtained using well defined Au / Bi 2 Sr 2 CuO 8 film / Bi 2 Sr 2 CaCu 2 O 8 single crystal junctions which are prepared by laser molecular beam epitaxy. The total shape of the spectra is BCS like and temperature dependence of the gap energy (42meV at 10 K) agrees with the weak-coupling BCS curve. The value of 2D/kT=5.8 obtained here, however, is larger than that predicted by the BCS weak-coupling theory.

1.1 substitution to BlSrCaCuO superconductor

Abstract Li doped Bi 2 Sr 2 CaCu 2 O x single crystals have been obtained by the floating zone method from the starting materials in which less than 20% of Cu atoms are replaced by Li atoms. A single crystal typically obtained is in dimensions 20 × 2 × 0.1 mm 3 . Although the location of Li atoms in the crystal structure remains unclear, incorporations of Li atoms into the crystals as much as 5∼18% in Li/Cu ratios were confirmed by ICP analysis. Inclusion of Li atoms into the structure raises the T c by several degrees, and the highest T c (=93 K ) was attained for the crystal of the highest Li content.

Synthesis and NMR study of solid electrolytes in the system Li3NLiCl

Abstract Syntheses have been carried out in the whole range of the system Li 3 NLiCl. The cubic antifluorite-type structure is possessed in the composition range 2Li 3 N·3LiCl9Li 3 N·11LiCl. Other than these, the new phase Li 9 N 2 Cl 3 was found, which did not crystallize in the cubic system. The 7 Li relaxation was studied for the antifluorite-type compounds and for the Li 11 N 3 Cl 2 . The activation energies for the Li + hopping motion were obtained: E a = 0.19−0.21 eV for the cubic compounds, and 0.33 eV for the Li 11 N 3 Cl 2 . The ionic conductivities for all compounds were measured using the pulsed-current method. The new phase of Li 9 N 2 Cl 3 showed the highest ionic conductivity in this series of compounds.

Preparation of Bi2Sr2CuO6 single crystals by the traveling solvent floating zone method

Abstract Preparation of single crystals of the type, Bi2Sr2CuO6 have been undertaken by the traveling solvent floating zone method. Since the polycrystalline material is obstainable as a single phase only at a non-stoichiometric composition, crystal growth throughout this study was concentrated to the composition, Bi2.4Sr1.6CuOx, which yielded a cleaved fragment of the single crystal in dimensions 40 × 6 × 1 mm3. The crystal melts incongruently at around 875†C and exhibits no superconductive behavior above 4.1 K.