Direct observation of the phase transition between the (7 × 7) and (1 × 1) structures of clean (111) silicon surfaces
ABSTRACT The phase transition process of clean (111) silicon surfaces between the (7 × 7) and (1 × 1) structures at about 830°C was directly observed by reflection electron microscopy, which had been briefly reported in a previous short communication (Osakabe et al., Japan. J. Appl. Phys, 19 (1980) L309). Smooth atomic steps, whose shapes change spontaneously and continually in a microscopic scale at high temperature of the (1 × 1) structure, transform into zig-zag steps at low temperature of the (7 × 7) structure, where the changes of the step shape stop. On cooling, domains of the (7 × 7) structure nucleate preferentially on upper terraces along the steps and expand on the terraces to the neighbouring steps. Out of phase boundaries with phase differences of 2πn/7 are seen to be formed. On heating the reversed process takes place. The out of phase boundaries are easy places to transform to the (1 × 1) structure. The observations clearly suggest the phase transition of the first order and the models of the (7 × 7) structure of ordered vacancies or adatoms rather than of static displacements of surface atoms.
- Surface Science Reports 09/1999; 34(6-8):171-294. · 24.56 Impact Factor
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ABSTRACT: Surface stress and energy are concepts which are often misunderstood. In this work, we will clarify the difference between the two. We describe the use of transmission electron microscopy to measure surface stress by quantitative analysis of strain contrast images. We find that images of surface-stress-induced strain fields can be used to measure quantitative differences in surface stress provided the imaging parameters are accurately determined. We have applied this method to measure the stress difference between the 7×7 and high temperature "1×1" phases of the Si(111) surface at the phase coexistence temperature and between metastable phase boundaries on the Si(111) and amorphous-Ge interface. We discuss the significance of these measurements and pitfalls to be avoided in image simulations.Surface Review and Letters 01/2012; 04(02). · 0.37 Impact Factor
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ABSTRACT: Growth of Au-adsorbed 5×2 domains on a vicinal Si(111) surface misoriented toward the [112¯] direction is studied by scanning tunneling microscopy (STM). We find that, at a coverage of 0.3 ML, the 5×2 domains are elongated in the [01¯1] or the [1¯01] direction, not parallel to the step edge. The boundary to the Si(111)-7×7 domain shows a characteristic structure depending on whether it faces faulted or unfaulted halves. Within the 5×2 domains, several rows of bright protrusions run parallel to the boundaries. We find that the domain width dAB in the [11¯0] direction is expressed as dAB=5Nrows+5, where the Nrows is the number of rows in the domain, and the length is represented in units of the lattice constant of the 1×1 surface. Moreover, we observe that phase boundaries of the 7×7 surface are often terminated by the 5×2 domains. Then, the component of the Burgers vector along the [11¯0] direction determines the domain width dAB and the number of rows Nrows, and is found to be the remainder of (dAB+5) divided by 7. These facts mean that the values of dAB are quantized; these are discrete at intervals of 5, and are increased by 35: the number 35 is the least common multiple of the periodicities of the 7×7 and the 5×2 structure in the [11¯0] direction. We propose a growth process of the 5×2 domain based on the STM observation.Physical Review B 01/1998; 57(4):2310-2314. · 3.66 Impact Factor