H. Tani

Ag-induced structural transformations on Si(111): quantitative investigation of the Si mass transport

Abstract Using scanning tunneling microscopy, the Si mass transport taking place at the formation of the Si(111) 3 × 3 -Ag and Si(111)6×1-Ag surface phases has been studied. From the measurement of the area occupied by various structural domains and the quantitative consideration of the Si mass balance, the top Si atom density in the Si(111) 3 × 3 -Ag and Si(111)6×1-Ag phases has been evaluated to be 1 monolayer and 4/3 monolayers, respectively.

The growth of indium thin films on clean and hydrogen-terminated Si(100) surfaces

Abstract Using scanning tunneling microscopy and low-energy electron diffraction techniques, we have investigated the growth of indium thin films on clean and hydrogen-terminated Si(100) surfaces at room temperature. In this study, we found the ‘ antisurfactant ’ effect of atomic hydrogen on indium thin-film growth on the Si(100) surface. On a clean Si(100) surface, indium atoms form the mixed reconstruction phases of ( n ×3)-In at low coverage. With increasing coverage, indium atoms start to form flat, two-dimensional islands preferentially at step edges of the substrate. In contrast, indium thin films grown on a hydrogen-terminated Si(100) surface do not form any reconstruction phase at low coverage and indium atoms form small clusters of spherical shape, indicating a modified indium growth mode mediated by the hydrogen adlayer.

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.

Atomic Hydrogen Interaction with the Si(100)4×3-In Surface Studied by Scanning Tunneling Microscopy

Using scanning tunneling microscopy and low energy electron diffraction techniques, we have investigated the structural rearrangement of Si(100)4×3-In surface induced by room temperature interaction with atomic hydrogen. The disintegration of the 4×3-In layer into three-dimensional In islands is substantiated by direct evidence. It has been found that In-denuded regions exhibit the stripes of 4a (a=3.84 A) periodicity, indicating that the Si substrate in the Si(100)4×3-In phase has a 4×1 reconstruction. The mode of atomic hydrogen interaction with Si(100)4×3-In surface phase has been determined. By comparing the present results with the known data of other submonolayer metal/silicon systems, the relationship between the adsorbate bonding and the mode of surface reaction with atomic hydrogen is established.

DIRECT OBSERVATION OF STRAINED LAYER FORMATION AT THE INITIAL STAGE OF IN THIN FILM GROWTH ON SI(100)

The growth of In thin films on Si(100)2×1 substrates at room temperature has been investigated mainly by scanning tunneling microscopy (STM). In this study, we found that In atoms form a mixed reconstruction phase of n×3 periodicity with 2×2 phase at coverage between 0.5 and 1.0 monolayer (ML), which has not been observed so far. In atoms begin to form flat two-dimensional (2D) islands above 1 ML. These islands have an apparent height of about 7 A and exhibit 2×1 periodicity associated with the lattice constant of Si bulk crystal, indicating the formation of a strained In layer. With increasing In coverage, the area of the islands increases. At coverage above 3 ML, however, this layer still does not dominate the entire surface and 2×2 and n×3 phases still remain. We suppose that this layer plays an important role as the intermediate structure from 2D growth to 3D growth.

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.

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.