Yasuyuki Ohba

Atomic‐hydrogen‐induced Ag cluster formation on Si(111)‐√3×√3–Ag surface observed by scanning tunneling microscopy

The scanning tunneling microscope has been used to study structural transformation of the Si(111)‐√3×√3(R30°)–Ag surface caused by atomic hydrogen adsorption. Atomically resolved scanning tunneling microscope images reveal a structure model for exchange adsorption of hydrogen and silver atoms. It has been shown that the proposed model can well explain various experimental results reported so far on this system.

Reconstruction and growth of Ag on hydrogen-terminated Si(111) surfaces

Abstract Initial stage of Ag film formation on hydrogen-terminated Si(111) surfaces at room temperature (RT) and high temperatures has been investigated by scanning tunneling microscopy. Ag atoms formed clusters on the hydrogen-terminated Si(111) at all temperatures, though the size and number were different in each case. When Ag was deposited at RT, relatively large and uniform Ag clusters were formed on the surface, compared with Ag deposition on a clean Si(111)-7×7 surface. On increasing the deposition temperature to 200 and 300°C, the size of Ag clusters became larger and the number of Ag clusters became less. When the surface where Ag was deposited on the hydrogen-terminated Si(111) at RT was annealed at 350°C, shallow and deep areas of 3 − Ag structure appeared, due to hydrogen desorption. We demonstrate the usefulness of hydrogen termination for Ag deposition on the Si surface to fabricate flat and uniform thin films.

Growth processes of Si(111)-√3×√3-Ag studied by scanning tunneling microscope

Domain growth processes of Si(111)√3×√3-R30 o -Ag surfaces and their dependence upon deposition conditions have been investigated by means of scanning tunneling microscope. When Ag is deposited at room temperature, small islands are formed on the terraces. After annealing at 350 o C, these small islands change into √3-Ag domains on the terraces without diffusion of Ag atoms to the step edges. On the other hand, when Ag is deposited on a hot substrate of about 350 o C, the √3-Ag domains nucleate at the step edges and few √3-Ag domains are observed on the terraces. Moreover, two kinds of √3-Ag domains are found in either case: one domain is geometrically higher than the other domain

Scanning tunneling microscopy observation of hydrogen-induced Ag cluster formation on the Si(111) surfaces

Using a scanning tunneling microscopy (STM) we have studied the nucleation and growth process of Ag clusters induced by the atomic hydrogen adsorption on the Si(111) √3×√3(R30°)‐Ag (simply √3‐Ag) surface. Size distributions of the clusters have been investigated as a function of the exposure of atomic hydrogen, and it is strongly suggested that the surface migration of Ag atoms over the hydrogen‐reacted regions is largely suppressed compared with that on the √3‐Ag surface. The size of Ag clusters is less than 150 A and their average height is estimated to be 3.1 atomic layers, consistent with previous ion scattering results. We have proposed the model of nucleation and growth process of hydrogen‐induced Ag clustering in which the broadened H/√3‐Ag regions suppress the migration of expelled Ag atoms and lead to the formation of many small clusters.

Scanning Tunneling Microscope Observation of Si(111)–3×1–Ag Structure

A scanning tunneling microscope has been used to study the Si(111)-3×1-Ag surface. The 3×1-Ag surface has been observed to consist of a bright row and small protrusions; the bright row points in the direction and the protrusions point in the and directions. The width of 3×1-Ag domains, nucleated on the Si-7×7 terraces, has been found to be (21n-2)a, where n is an integer (n=1, 2,) and a is the lattice constant of Si (a=3.84 A). Detailed investigation on domain boundaries reveals that both sides of the 3×1-Ag domain face the unfaulted halves of the 7×7 structure. Moreover, two types of domain boundaries have been observed: one which runs across the corner holes, and another is that runs apart from the corner holes, leaving a narrow 7×7 terrace of one adatom width. Possible structural models for the 3×1-Ag surface are proposed based on the present STM results.

Scanning tunneling microscope observations of Si(111)3 × 1-Ag and 6 × 1-Ag structures

Abstract Using scanning tunneling microscopy, we have studied the Si(111)3 × 1-Ag and 6 × 1-Ag structures. The 3 × 1-Ag structure has been observed to consist of a bright row and two small protrusions. The bright row points in the 1 10> directions, and the protrusions incline about 10° from the 2 > directions, resulting to point in the diagonal directions of the 3 × 1 unit meshes. We found that the 6 × 1-Ag structure consists of alternative arrangements of two kinds of 3 × 1-Ag structures of which the protrusions incline about +10° and −10° from the 2 > directions, respectively. Possible structural models for the 3 × 1-Ag and 6 × 1-Ag are proposed, based on the present STM results.

Hydrogen-Induced Ag Cluster Formation on the Si(111) √ 3×√ 3(R30°)-Ag Surface Observed by Scanning Tunneling Microscopy

The scanning tunneling microscope (STM) has been used to study structural transformation of the Si(111) √ 3×√ 3(R30°)–Ag surface caused by atomic hydrogen adsorption. When atomic hydrogen adsorbs on the √ 3-Ag surface, the Ag atoms are expelled to form clusters. The size of the Ag clusters has been confirmed to be less than 150 A in agreement with previous ion scattering results. Spatial distributions of the clusters, observed as functions of the exposure to atomic hydrogen, reveal that surface diffusion of Ag atoms over the hydrogen-covered regions is largely suppressed compared with that on the √ 3-Ag surface. The clusters are hexagonal and their orientations suggest the formation of Ag(111) clusters.

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.