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.
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ABSTRACT: On a Si(111) vicinal face near the structural transition temperature (860°C), the 7×7 structure and 1×1 structure coexist on a terrace. The 7×7 structure is on the upper side of steps and the 1×1 structure is on the lower side of steps. The diffusion coefficient on the 1×1 structure is larger than that on the 7×7 structure. In this paper, taking account of the difference in the diffusion coefficient, we study the possibility of step instabilities, step wandering and step bunching, occuring during sublimation. © 2009 The Physical Society of Japan.Journal of the Physical Society of Japan 01/2009; · 2.09 Impact Factor
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ABSTRACT: Single-crystal thin foils of a-alumina were annealed i:i air and examined by transmission electron microscopy. Weak reflections, which are kinematically forbidden for the a-alumina unit cell, were obscrxed in selected-area diffraction patterns obtained from foils prepared parallel to (0001), (1012), and (1120) planes. These reflections are interpreted as giving evidence for surface periodicities which differ from those expected for the simple termination of the bulk crystal.Journal of the American Ceramic Society 03/2005; 69(9):C‐217 - C‐220. · 2.11 Impact Factor
Article: Thermal dynamics at surfaces[Show abstract] [Hide abstract]
ABSTRACT: The present paper describes what happens at the surface of a crystal as its temperature steadily increases from zero Kelvin close to the bulk melting temperature. We treat thermal motion, such as the diffusion of individual adatoms establishing mass transport, the formation of adatom or vacancy gases coexisting with islands or steps of the condensed phase, surface phonons and the anharmonicity of the surface potential being markedly different from the one in bulk, as well as thermally induced reconstructions, surface roughening, and finally surface melting, which usually well precedes bulk melting. The paper intends to give an overview with references to the original and review literature.Annalen der Physik 01/2009; · 1.51 Impact Factor