T. Numata

Structural transformations at room temperature adsorption of In on Si(111)√3 × √3-In surface: LEED-AES-STM study

Abstract Low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and scanning tunnelling microscopy (STM) have been used to study the evolution of the surface structure upon room temperature deposition of In onto In-predeposited Si(111)√3 × √3-In surface. The sequential formation of the Si(111)2 × 2 and Si(111)√7 × √3 surface phases has been detected and coverage ranges of their existence have been determined. STM observations have revealed that the Si(111)2 × 2-In phase has a honeycomb-like atomic structure with depressions in T 4 positions. The structural model built of In trimers has been proposed. The “low-temperature” Si(111)√7 × √3-In phase shows up in STM images as parallel rows of protrusions and its structure has been found to differ from the structure of the known “high-temperature” Si(111)√7 × √3-In phases. The inheritance of the defects at the structural transition from √3 × √3 structure to 2 × 2 structure has been discussed.

The role of Si atoms in In/Si(111) surface phase formation

Abstract The deposition of In onto the surface appears to result, depending on the temperature, in the formation of three different reconstructions, Si(111)-(2 × 2)-In (20–100°C), Si(111)-(4 × 1)-In (∼200°C) and (∼450°C). The formation of each surface phase has been determined to be controlled by the mobility of the top Si atoms. At the to (2 × 2) transition, the bulk-like termination of the Si(111) substrate is preserved. At the formation of the Si(111)-(4 × 1)-In phase, Si atoms reorder via a bond-switching process. The formation of the phase involves surface Si mass transport. The applicability of the results obtained to other submonolayer adsorbate/Si systems is discussed, and the criterion for revealing the surface phases with a reconstructed substrate is formulated.

STM observation of the atomic hydrogen adsorption on the Si(111)4 × 1-In surface

Abstract We have used scanning tunneling microscopy and low-energy electron diffraction to study early stages of atomic hydrogen interaction with Si(111)4 × 1-In surface at temperature 300°C. Indium rows of the 4 × 1-In structure were removed during interaction with atomic hydrogen and Si(111)4 × 1-H and Si(111)1 × 1-H coexisting regions were observed. This 4 × 1-H region was ascribed to the substrate reconstruction in accordance with the previous observations. Thus the substrate reconstruction for the Si(111)4 × 1-In was directly observed and evidenced. These results are interpreted on the basis of the recently proposed dimerized chain models for the Si(111)3 × 1 Ag and alkali metals reconstruction.

Si(111) 2 × 2–In ↔ Si(111)√ 3 ×√ 3–In Scanning Tunneling Microscope Tip-Induced Structural Transformation

We have found STM tip-induced 2 ×2–In → √3×√3–In and √3×√3–In → 2 ×2–In structural transformations on a Si(111) surface at room temperature, relatively low bias voltages and large tip-sample separations. The processes were found to be reversible depending on the tip bias voltage polarity. Our results can be explained by STM tip-induced diffusion of In atoms on the √3×√3–In and 2 ×2–In surfaces.

Structural transformations of the Si(111)2 × 2-In surface induced by STM tip and thermal annealing

Abstract We have investigated In deposition on to Si (111) 3 × 3 - In surface by using low-energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). A 2 × 2 structure was formed at 50–100°C. Indium deposition at around 200°C on the 3 × 3 surface or thermal annealing of the 2 × 2 surface resulted in the 4 × 1 structure formation but not through a 31 × 31 phase, as takes place at higher temperatures. The difference between low and high temperature surface phase formation is discussed. We have found that the 2 × 2 structure converts into the 3 × 3 one during STM observation. This process was explained by STM-induced In atoms diffusion and/or desorption. Possible atomic arrangement of the 2 × 2-In reconstruction was proposed.

Atomic-hydrogen-induced self-organization processes of the In/Si(111) surface phases studied by scanning tunneling microscopy

Abstract We have investigated the initial processes of the interaction of atomic hydrogen with the 4×1 and the 31 × 31 surface phases in the In/Si(111) system at substrate temperature around 300°C using scanning tunneling microscopy. It has been revealed that the atomic-hydrogen-induced self-organization processes of these surface phases are strongly dependent on the substrate Si reconstruction. The adsorption of atomic hydrogen on the 4×1-In surface, which has a reconstruction of 2 ML of Si layers, involves removal of In atoms from the surface but no Si movement, resulting in the formation of hydrogen-terminated bared zigzagging Si chains with the preservation of the 4×1 periodicity. On the other hand, the adsorption of atomic hydrogen on the 31 × 31 surface, which has a reconstruction of 1 ML of Si layer, exhibits peculiar self-organization processes depending on the hydrogen exposure: at the initial stage of the hydrogen exposure only the half-unit of the 31 × 31 lattice is preferably attacked by hydrogen atoms with the preservation of the 31 × 31 periodicity, while upon prolonged hydrogen exposure, the 31 × 31 periodicity is destroyed as a result of the movement of the Si reconstructed layer, forming hydrogen-terminated quasi-1D Si chains. These results suggest the possibility of atomic-hydrogen-induced self-organization of substrate Si atoms.

New structural model for the Si(111)4×1–In reconstruction

Abstract A new π-bonded-chain-stacking-fault (π-SF) model is proposed for the Si(111)4×1–In surface structure. The model incorporates 4×1 Si(111) substrate reconstruction consisting of the sixfold Si rings in the faulted–unfaulted sequence connected through fivefold and sevenfold Si rings. Indium atoms (0.75 monolayer) reside above sixfold and fivefold Si rings, while sevenfold Si rings form π-bonded chains between In ridges.

STM observation of Ag clustering on hydrogen-terminated Si(100) surfaces

Abstract The effect of hydrogen termination on Si(100)-2 × 1 surfaces upon Ag deposition at room temperature (RT) and high temperature (350°C) has been investigated by a scanning tunneling microscopy. The results are also compared with those on clean Si(100)-2 × 1 surfaces. When Ag was deposited at RT, small Ag clusters formed on the hydrogen-terminated surface, in contrast that scattered and relatively individual Ag atoms formed on a clean Si(100)-2 × 1 surface. As increasing the substrate temperature, the size of Ag clusters became larger and the shape gradually changed to rectangular, whose edges were parallel to [011] and [01 3 ] directions. Structural models for these surfaces are also proposed.