Takashi Kawano

Determination of effective energy loss functions and x-ray photoelectron spectroscopy source functions for Si 2p photoelectrons from clean Si(111), oxygen-adsorbed Si(111) and SiO2 surfaces

Effective energy loss functions for Si 2p photoelectrons were determined for the thermally cleaned Si(111), oxygen-adsorbed Si(111) and SiO2 surfaces by the analysis of the reflection electron energy loss spectroscopy (REELS) spectra using the extended Landau theory. The background subtraction of the Si 2p x-ray photoelectron spectroscopy (XPS) spectra using these effective energy loss functions has enabled the XPS source functions to be derived with considerable effectiveness. This result has indicated that the effective energy loss functions derived for the clean Si(111) surface are significantly affected by the oxygen adsorption and the XPS source functions from the clean and oxygen-adsorbed Si(111) surfaces show a small hump due to the chemical shift by the oxygen adsorption appearing at the tail of the lower kinetic energy side of the Si 2p peak from the oxygen-adsorbed Si surface. On the SiO2 surface, the analysis of the REELS spectrum has yielded the effective energy loss function reflecting the fi...

Oxygen nonstoichiometry effect on structural modulation in Bi-2212 cuprate superconductors

Abstract The X-ray diffraction patterns for Bi 2 Sr 2 Ca 1− x Y x Cu 2 O 8+ y sintered in air or Ar indicated that the reduction in the number of excess oxygen ions induced a structural change from orthorhombic to pseudotetragonal. When the oxygen contents decreased with the reducing treatment, the period of modulation in Bi 2 Sr 2 Ca 1− x Y x Cu 2 O 8+ y increased. This result supported the model of excess oxygen ions in the BiO sheet. However, it was difficult to understand the change of modulation period with increasing Y contents using the model of excess oxygen ions in the BiO layers. Also, it is included that the Y substitution for Ca and La substitution for Sr in the Bi 2 Sr 2 CaCu 2 O 8+ y system result in parallel effects for the modulation structure.

Characterization of Sc?O/W(100) Surface as Schottky Emitter: Work Function Change for Activation Processing

To elucidate the electron emissivity of the Sc–O/W(100) Schottky emitter, the Sc–O/W(100) surface, prepared by scandium deposition onto the W(100) surface followed by oxygen exposure and heating at an operating temperature of ~1400 K, was studied by ion scattering spectroscopy (ISS), Auger electron spectroscopy (AES) and measurement of the relative work function change. The results have revealed that heating of the oxygen adsorbed Sc/W(100) surface leads to the diffusion of the oxygen atoms into the substrate to locate very probably beneath the topmost scandium atoms. This relocation of the oxygen atoms forms an electric double layer, resulting in a significant decrease of the work function. The topmost surface composition of the Sc–O/W(100) system observed by ISS did not change during cooling the sample from ~1400 K to room temperature under the present conditions. The results of the present work strongly suggest that the surface properties of the Sc–O/W(100) system are very similar to those of the Zr–O/W(100) system at the operating temperature.

Unique source for scandium oxide layer deposition on tungsten for surface study of high electron emissivity

The objective was to prepare scandium oxide layers on tungsten for the surface study of Sc-O/W(100) emitters using two design types of a compact evaporator for Sc 2 O 3 and for metallic scandium deposition. Both of these evaporators were compatible with ultrahigh vacuum operation in a specimen chamber optimized for surface analytical measurements. The Sc 2 O 3 evaporator allowed Sc 2 O 3 to be deposited on a substrate while maintaining its stoichiometric composition. It was also demonstrated that scandium oxide layers could be prepared effectively on a substrate by deposition of metallic scandium followed by oxygen exposure.

Electrical conduction in superconductive Nd2− xCe xCuO4− y at high temperatures

The oxygen-partial-pressure dependence of resistivity indicated that the charge carriers in Nd 2-x Ce x CuO 4-y were electrons. According to the resistivity data of these compounds at temperatures above 770 K, Ce doping affected the relation between the oxygen deficiency and oxygen partial pressure in Nd 2 CuO 4−y : the doping of Ce worked to hinder the formation of oxygen vacancies in the lattice. Moreover, the carrier density after Ce doping was found to be much less than the value anticipated from the amount of the dopant

Correlation of Bi and Cu valencies with structural modulation in (Bi2−x Pbx Sr2CaCu2Oy

Abstract We investigated how the (Bi,Pb) and Cu valencies changed as the modulation structure varied with the substitution of Pb for Bi in (Bi 2−x Pb x )Sr 2 CaCu 2 O y . The Cu valency remained almost constant being independent of the Pb content. Meanwhile as Pb content increased, the (Bi, Pb) valency monotonically decreased and, on the contrary, the modulation period increased. This result is explained by the excess oxygen ions model in the Bi(Pb)-O layers.

Electrical properties of Nd1.85Ce0.15CuO4−y at high temperatures

The temperature dependence of electrical resistivity of Nd1.85Ce0.15CuO4−y was measured with oxygen partial pressure fixed at 2.08×10−1, 1.8×10−2, 8.1×10−4, and 3.3×10−6 atm. The oxygen partial pressure dependence of resistivity indicated that the charge carriers in Nd1.85Ce0.15CuO4−y were electrons. The temperature dependence of resistivity exhibited a linear metallic behavior at high temperatures and a semiconductorlike behavior at low temperatures, having a minimum at an intermediate temperature. Difficulties are pointed out in obtaining a unified view for the mechanism of normal electrical conduction in Nd1.85Ce0.15CuO4−y .

Preparation of “124” superconductors using only alkoxides

Abstract The “124” phase (YBa 2 Cu 4 O 8 ) is synthesized at a low temperature of 700°C in O 2 gas flow (PO 2 =1 atm) by means of a sol-gel method using only alkoxides. The prepared Cu-butoxide for the present synthesis is soluble up to 36 mMol/l in butanol and hydrolyzable. The sample sintered at 760°C exhibits superconductivity with the zero-resistance temperature (Tc R=0 ) at 78K.

Superconducting properties of Bi2(LaxLn1−x)yCa3−yCu2Oz (Ln=Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm)

Abstract Oxide superconductors, Bi2(LaxLn1−x)yCa3−yCu2Oz (Ln=Y or rare-earth element), have been synthesize d by doping an additional rare-earth element in the BiLaCaCuO compounds. The zero resistivity superconducting transition temperature of the sample with x=0.5 and y=0.5 increased by about 20 K to be 45 K when compared with the BiLnCaCuO (Ln =La, Nd and Pr) superconductors.

Study on Zr-Si/W(100) Surface at High Temperatures by Reflection High Energy Electron Diffraction

Reflection High Energy Electron Diffraction study has revealed that a Zr–Si/W(100) surface has an island structure at the operating temperature of ~1300 K. The structure hardly changes when the sample temperature is lowered to room temperature. This result has confirmed the previous work that the Zr–Si/W(100) system does not undergo phase transition as does the Zr–O/W(100) system at ~1000 K. The surface properties of the Zr–Si/W(100) system, so long as surface characterization is concerned, hardly change in the range of sample temperature between operating temperature and room temperature.