1X1 TO (7X7) PHASE-TRANSITION ON SI(111) UNDER HEATING CURRENT

We investigated the influence of heating current on the phase transiti on of the (7 x 7) reconstruction on a Si(lll) surface using ultra-high vacuum scanning electron microscopy. Just below the phase transition temperature, the (7 x 7) reconstruction nucleates at the upper edges o f the steps, and the (7 x 7) phase coexists with the '1 x 1' phase on the terrace. In this situation, the size of the (7 x 7) phase depends on the direction of the heating current, and the (7 x 7) phase is larg er under the step-up current than under the step-down current. This de pendence can be explained assuming that adatoms in the '1 x 1' phase a re forced to move in the same direction as the current.