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High-temperature scanning tunneling microscopy (HTSTM) has been applied to analyze the mechanism of a reversible phase transition between the ‘16×2’ structure and the 1×1 structure appearing on a clean Si(110) surface. The ‘16×2’ structure is the dominant structure on the clean Si(110) surface at room temperature. It has also been shown that the (17,15,1)2×1 steps, whose length is 5 nm in the 〈111〉 direction, exist in the domain of the ‘16×2’ structure. The transition ‘16×2’+(17,15,1)2×1 step⇔(17,15,1)2×1⇔1×1 is observed upon heating, where the first process starts at 968 K and the second finishes at 1043 K. The temperature width between the phase transition is about 80 K. From taking account of the two processes of the transitions, we can say that the system undergoes at first the Ising transition and, at a higher temperature, a roughening transition. Namely, Tc (=968 K) is the temperature for the Ising transition and TR (=1043 K) is that for the roughening transition.

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.

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.

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.