Homogeneous and heterogeneous nucleations in the surface phase transition: Si(111)4 x 1-In

Homogeneous and heterogeneous nucleations in a reduced-dimensional system undergoing a first-order structural phase transition were examined by using low electron energy diffraction and scanning tunneling microscopy. The high-temperature 4 x 1 phase of a Si(111)-In surface was supercooled at temperatures below the transition temperature (T-c) and evolved slowly into a low-temperature 8 x 2 phase with time. The transition rate decreased significantly as the temperature approached T-c. The kinetics of the observed homogeneous nucleation was analyzed by classical nucleation theory. The introduction of oxygen atoms reduced the hysteresis and accelerated nucleation significantly, showing that the T-c-raising oxygen impurity plays the role of a nucleation seed for heterogeneous nucleation.