STUDY ON PHASE TRANSITION OF Si (111) 7x7 STRUCTURE BY MONTE-CARLO SIMULATION

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<1> Modeling of 7x7 structureThe surface structure is described in terms of two states of each unit which is defined as a triangular half of the 7x7 unit cell. The two states ; one a stacking-faulted structure and the other '1x1' structure, is expressed by a number operator in the lattice gas model. The Hamiltonian of the system is given by a functional of the number operators. We derive relations between the in interactions and formation energies of components of 7x7 structure and find existence of a type of three-body interaction. Considering the '1x1' structure a set of disordered states, we introduce the degeneracy.<2> Numerical calculationWe performed numerical calculations for the above model by Monte-Calro simulation. It results that(1) the structure undergoes the first order transition as the experiments (2) the characteristic features of growing patterns from F-step, U-step, terrace on the quenched surface are well reproduced (3) the temperature dependence of the critical size for nucleation on the quenched surface is qualitatively in agreement with the experimental result.<3> Publication of resultsThe above results have been got by various trials. The result in each stage was published in reported in Research Bulletin of Fukuoka Institute of Technology and reported in several meetings of Physical Society of Japan. Now, we are going to submit a paper which include the new results to some scientific journal.