Masamichi Yoshimura

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).

Observation of thin film of one‐dimensional organic conductor tetrathiofulvalene tetracyanoquinodimethane by means of atomic force microscopy

Thin films of the charge transfer complex of tetrathiofulvalene tetracyanoquinodimethane (TTF‐TCNQ) deposited on KC1 and KBr were studied by atomic force microscopy (AFM). Structures corresponding to the molecular arrangement of the crystallographic ab‐plane were observed in the molecular‐scale AFM images. Large‐scale imaging (15×15 μm) revealed that the films consist of rectangular islands whose longer sides (corresponding to the highly conductive b‐axis) orient in the [110] or [110] direction of the KC1 and KBr(001) surfaces. A small number of islands rotated 32° from the [110] direction were also observed on the KBr substrate. The arrangement of these islands can be explained by considering the adsorption of a TCNQ molecule to the metastable state.

The surface structure of an organic conductor (BEDT-TTF) 2KHg(SCN)4 observed by scanning tunneling microscopy

Abstract The bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) molecules in the surface cation layer of the (BEDT-TTF)2KHg(SCN)4 crystal were observed by scanning tunneling microscopy (STM). The obtained arrangement of BEDT-TTF was in good agreement with that expected from the structure determined by X-ray diffraction. In addition, some subsidiary images were observed around the K and Hg ion positions. The STM image of the BEDT-TTF molecules was influenced by the structure of the anion layer on them, and they showed a strong bias dependence.

STM study of organic thin films of BEDT-TTF iodide

Thin films of α-BEDT-TTF iodide were studied and found to show a new structure besides its normal crystal structure; the periodicity in the direction of the a-axis is about two times as large as that of its crystal value. The appearance of this new structure is considered to be responsible for the anomalous metal-insulator transition reported previously. Similar structures were also observed for thin films of α1-BEDT-TTF iodide.

Structural studies of Al/Si(100) by LEED

The structures of Al-adsorbed Si(100) surfaces were studied by observing patterns, line profiles and intensity-versus-energy (l-V) curves of low-energy electron diffraction (LEED), Al-adsorbed 2 × 1, 2 × 2 and 2 × 3 structures were observed as a function of Al coverage and the substrate temperature. After deposition of less than 0.25 ML of Al below 300°C, we observed an Al-2 × 1 LEED pattern whose l-V curves were different from those of the clean Si(100)2 × 1 surface. For 0.5 ML deposition of Al, a 2 × 2 phase appeared at a substrate temperature of 100°C. At about 0.3 ML, a 2 × 3 structure was formed at 300°C, which was confirmed by observing the LEED pattern and line profiles. It was also found that the main features of l-V curves of the Al-2 × 2 surface and those of the In-2 × 2 surface are very much alike. This reflects the fact that their geometric structures are also alike.