Homogeneous and heterogeneous nucleations in the surface phase transition: Si(111)4 × 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 × 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 × 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. (paper)