Takashi Sueyoshi

Scanning tunneling microscopy observation of hydrogen‐terminated Si(111) surfaces at room temperature

Scanning tunneling microscopy has been applied to observe hydrogen‐terminated Si(111) surfaces at room temperature. A clear image was easily observed for a Si surface prepared by rinsing in pure water with very low dissolved oxygen after removal of native oxide by 1% HF solution dipping. A smooth surface in an atomic scale was exhibited in a 50×50 nm area. Completely triangular‐shaped holes were observed on the surface. The holes were surrounded by steps which were very likely directed toward 〈112〉. The treatment of the surface was remarkably stable even after a 3 h air exposure. Furthermore, nm size pits were found at the bottom part of the triangular‐shaped holes. The results imply that the nm size pits appeared to be due to microdefects and that the pits might be the origin of surface etching at the Si surface.

Dynamic observation of In adsorption on Si(111) surfaces by UHV high-temperature scanning tunneling microscopy

Indium adsorption and desorption processes on Si(l 11) surfaces were observed in situ by UHV high-temperature STM. By the deposition of In on the Si(111)7 X 7 surfaces at 380°C, the surface structure changed successively to √3 x √3, √31 X √31 and 4 X 1. The number densities of silicon atoms in the restructuring layers for the √3 X √3, √31 X √31, and 4 X I structures were evaluated to be about 0, 1 and 2 ML, respectively. High-resolution STM images were also taken after the deposition.

STM studies of Si(5 5 12) 2 × 1 surfaces

Abstract We carried out STM observations of Si(5 5 12) surfaces. STM images showed that the surface has a long period of about 5 nm along the 〈665〉 direction that coincides with a period of the bulk terminated structure, and a period of about 0.7 nm along the 〈110〉 direction that coincides with a 2-fold period of the bulk terminated structure; the 2 × 1 structure. The long period along the 〈665〉 direction is composed of 7 arrays of bright dots. These bright dots appear at the adatom positions of a surface structure model of the (5 5 12) surface proposed previously from RHEED pattern analysis. The phase shifts of the long period which are equivalent to steps are observed on the surface. A surface structural phase transition found in REM-RHEED studies at about 900°C was also observed.

Multilayer growth process of C60 on a Si(111) 7 × 7 surface

Abstract Scanning tunneling microscopy has been applied to study the multilayer growth process of C 60 molecules on a Si(111)7 × 7 surface. We have observed the local ordering of the first C 60 layer formed on the 7 × 7 structure at room temperature. This local ordering structure is made of distinct double domains in each of which the arrangement direction of C 60 molecules deviates +11° or −11° from the Si[211] direction. This structure coincides with the interfacial structure model proposed by Hang Xu et al. [Phys. Rev. Lett. 70 (1993) 1850]. The island growth of C 60 starts on this local ordering area when the coverage exceeds approximately 1 monolayer.

Observation of surface reconstruction and nano-fabrication on silicon under high temperature using a UHV-STM

Abstract In this paper we discuss three experiments on silicon (100) and (111) surface at high temperature obtained with an ultra-high-vacuum scanning tunneling microscope (UHV-STM). First, the initial stage of the crystalization process has directly been investigated on the Si(111) surface at a phase transition temperature of about 860°C. (7 × 7) domains nucleated from the step edges and expanded towards inner regions of the terraces, and the steps become straight [ 1 ¯ 1 ¯ 2 ] steps. Second, the high-temperature nano-fabrication method has been applied to Si surfaces. We succeeded in creating a hexagonal pyramid and a crater on the Si(111) surface, and a quadrangular pyramid on the Si(100) surface at 600°C. (5 × 5) domains can be observed on narrow terraces due to the relaxation of surface energy. Finally, we attempted to deposit gold (Au) atoms on silicon surfaces. Au atoms deposited on a high-temperature silicon surface migrated to the observation area while forming 5 × 1 structures. Then the Au atoms diffused into the bulk structure of silicon, and silicon (7 × 7) domains covered the surface again.

Study of the crystal growth of a (15,17,1) vicinal plane on a Si(110) surface using high‐temperature scanning tunneling microscopy

High‐temperature scanning tunneling microscopy was used to study the crystal growth of a (15,17,1) vicinal plane on a Si(110) surface, and the dynamic behavior of surface Si atoms at high temperature was directly observed. It was found that an impurity hillock, which may be SiC on the surface, pins step flows and bunches them together to form a vicinal plane such as (17,15,1), (17,15,1), (15,17,1), and (15,17,1) at 710 °C. The vicinal plane has a faceted structure and is formed by a periodic arrangement of monolayer steps and has a terrace of 2.5 nm in the 〈111〉 direction. The step‐edge direction is 〈112〉. At 695 °C, it was also found that the 16 structure was formed on a flat area. It was confirmed that the 16 structure and the vicinal plane (15,17,1) coexisted in a temperature range of about 700 °C to room temperature.

High-temperature scanning tunneling microscopy study of the phase transition of 16-structure appearing on a Si(110) surface

High-temperature scanning tunneling microscopy (HTSTM) has been developed which enables distortionless observation of the dynamic behavior of surface atoms at high temperatures up to 900°C on an atomic scale, and it was applied to analyze the mechanism of reversible phase transition between the 16-structure and the 1x1 structure appearing on a clean Si(110) surface. It has been found that, at first, the reconstruction and destruction of the 16-structure begin on the unit-cell level along the direction and then progress along the direction as a whole in order to complete the phase transition. The direct observation of the reconstruction at high temperatures is very important to investigate the mechanism of crystal growth.

Observation of solid phase epitaxy processes of Ar ion bombarded Si(001) surfaces by scanning tunneling microscopy

Scanning tunneling microscopy (STM) is used to investigate the surface morphology of Ar+‐ion bombarded Si(001) surfaces and to elucidate the very beginning stages of solid phase epitaxy (SPE) processes of the Ar+‐ion bombarded Si surfaces. The Ar+‐ion bombarded Si surface consists of hillocks of 1–2 nm in diameter and 0.35–0.75 nm in height. The onset of SPE initiates at around 590 °C, at which a temperature (2×2) structure surrounded by amorphous regions is partially observed on terraces of the surface. During annealing at 590–620 °C, the areas of the (2×2) and c(4×4) reconstruction surrounded by amorphous regions develop. New defect models for the (2×2) and c(4×4) structures are proposed where alternating arrangements of the buckled dimers together with missing dimer defects are considered.

Little Influence of Kinks on the Formation of c(4 × 2) Domains in a Si(001) Surface at Low Temperature

The structure of a Si(001) surface with monatomic steps is investigated by means of scanning tunneling microscopy at 95 K and Monte Carlo simulations (MCS) at various temperatures. In particular, we pay attention to the effect of kinks at the step edge on the formation of c (4×2) domains, and both studies reveal that the kinks do not govern the growth of the domains. MCS demonstrates that the nucleation of c (4×2) domains takes place at central regions of the terrace as a result of thermal fluctuation, and that the domains propagate to the step edge with decreasing temperature.

Comment on ‘Step structure of vicinal Ge(001) surfaces’ by B.A.G. Kersten, H.J.W. Zandvliet, D.H.A. Blank and A. van Silfhout

We have investigated detailed structures of monatomic steps on Ge(001) at room temperature by using high-resolution scanning tunneling microscopy. Our conclusions are different from those of Kersten et al. [Surf. Sci. 322 (1995) 1] for the same system. The most crucial difference is that we have not observed the nonbonded SB step. We have pointed out a possible reason for the different conclusions.