Akira Kawazu

In situ growth of Bi-Sr-Ca-Cu-O thin films by molecular beam epitaxy technique with pure ozone

Thin films of Bi-Sr-Ca-Cu-O have been grown in situ on SrTiO3 (001) substrates using a molecular beam epitaxy technique with a pure ozone source. This allows us to grow highly oriented films at substrate temperature of 700°C without heat treatment in oxygen. One of the films showed a superconducting transition at 10.0 K.

Evaporation Rate and Saturated Vapor Pressure of Functional Organic Materials

The evaporation rate and saturated vapor pressure (p) for functional organic materials have been evaluated by thermogravimetry in vacuum. A series of metal phthalocyanines (M-Pc) such as Cu-Pc, Ni-Pc, Pb-Pc and TiO-Pc, Tris(8-hydroxy-quinoline) aluminum complex ( Alq3), fullerene (C60) and tetrathiafulvalene (TTF), tetracyanoquinodimethane (TCNQ) and TTF-TCNQ are examined, together with the relationship between p and the enthalpy of evaporation.

Observation of step bunching on vicinal GaAs(100) studied by scanning tunneling microscopy

Similar step bunchings which consist of 7–9 single steps were observed by scanning tunneling microscopy on both vicinal GaAs(100) surfaces grown by metalorganic chemical‐vapor deposition (MOCVD) and annealed in AsH3 atmosphere. Growth parameters, including deposition rate, layer thickness, V/III ratio, and growth temperature, did not affect the morphology of the step bunching. These results indicate that step bunching is induced during the annealing process and its surface morphology is preserved during MOCVD growth for a wide range of growth parameters.

Growth of Bismuth Layers on Si(100) Surfaces

The adsorption of bismuth on Si(100) surfaces is studied by quadrupole mass spectrometry, LEED and AES. Two adsorption states are observed: one is a two-dimensional (first) phase with saturation coverage and the other a bulk-like (second) phase without saturation coverage. When the two-dimensional phase of Bi was formed at a high substrate temperature, the LEED patterns from the Si surfaces showed an Si(100)2×1 structure with weak fractional order spots. In the Auger amplitude vs. deposition time curves, break points were observed at the completion of the first-phase adsorption. These points shift towards the higher coverage side with decreasing substrate temperature during deposition in accordance with the increase in the amount of adsorbed bismuth atoms.

Kinetics of deposition of bismuth film by a molecular beam method

Abstract The growth processes of bismuth films on Si(111) surfaces were studied using quadrupole mass spectrometry, AES, and LEED. At higher substrate temperatures, the adsorption occurs only in a tightly bound state. The LEED pattern from these surfaces shows a Si(111) √3 × √3−30° -Bi structure. At lower temperatures, the orientation relationship of Bi(0001) ∥ Si(111) was observed for thick films.

Structure and electrical properties of thin bismuth films

Abstract The resistivity of thin Bi films on silicon was measured for films of various thicknesses. The experimentally obtained thickness dependence of the resistivity was compared with the result of a numerical calculation based on the equation which was proposed by Mayadas and Shatzkes. At 290 K the experimental curve fitted the numerical one with surface and grain boundary reflection coefficients of 0.6 and 0.12 respectively.

Growth Mechanism of Thin Films of A Charge Transfer Complex, TTF-TCNQ, Formed on Alkali Halide

Abstract A charge transfer complex of tetrathiafulvalene and tetracyano-quinodimethane (TTF-TCNQ) is vacuum-deposited onto air-cleaved (001) planes of alkali halides, NaCl, KC1 and KBr. The molecular orientation in thin films and surface morphology are characterized by transmission electron microscopy (TEM), and scanning tunneling microscopy (STM) and atomic force microscopy (AFM) to confirm the fine structure and dependence of nucleation and crystal growth on the kinds of substrate.

Phase Transition between c (4×2) and p (2×2) Structures of the Si(100) Surface at 6 K Caused by the Fluctuation of Phase Defects on Dimer Rows due to Dimer Flip-Flop Motion

Dimers of the Si(100) surface previously observed at 120–140 K, which partially appeared to be symmetric, were frozen at 6 K, and an atomically resolved structural change between c(4×2) and p(2×2) arrangements of the Si(100) surface was observed for the first time by scanning tunneling microscopy. The observed change was due to the fluctuation of phase defects of a new type on dimer rows, which have a structure similar to that of the type-C defect. Dimer flip-flop motion at the phase boundary which induces the apparent phase transition, and creation and annihilation of the anti-phase domain were clearly observed.

Structural studies of Al/Si(111) surfaces by LEED

Al-adsorbed Si(111) surfaces were studied by observing patterns, line profiles and intensity versus energy (I-V) curves of low-energy electron diffraction (LEED). Four different surface structures, i.e., √3×√3, √7×√7, incommensurate and α-phase 7×7 structures were observed as a function of Al coverage and the substrate temperature. Dynamical LEED analysis Si(111)√3×√3 R30 o surface, appearing after the deposition of Al of about 1/3 monolayer at the substrate temperature of 650 o C, shows adsorption of Al atoms above the second layer Si atoms (T 4 site).

Development of an ultrahigh vacuum atomic force microscope for investigations of semiconductor surfaces

A new atomic force microscope (AFM) adapted for ultrahigh vacuum operation is described. This AFM utilizes the optical beam deflection method to detect the cantilever displacement. Both the laser diode and the photodiode sensor are contained within the vacuum chamber. An inchworm motor mechanism is used for the tip–sample approach. Up to eight cantilevers are stored in the chamber and can be used without breaking vacuum. The vacuum system is equipped with a sample heater, an evaporation cell, a gas inlet valve, and a low‐energy electron diffraction system, for observing semiconductor surfaces. Imaging of a graphite surface and a clean Si (111) surface with step structures have been obtained.