Abstract

Recently we have shown that the Si(111)-7 × 7 ↔ "1 × 1" phase transition around 860°C can be observed by means of surface second-harmonic generation (SHG) of laser pulses as an abrupt change of the SH intensity, which originates from an interface in the "1 × 1" phase formed between the disordered surface layer and the underlying ordered layer having a 3 m surface symmetry.¹ This system involves a basic problem of the two-dimensional phase transition requiring large scale rearrangement of atoms,² and a number of studies have been devoted to this problem using various techniques such as low energy electron diffraction, reflection electron microscopy, reflection high energy electron diffraction, low energy electron microscopy, and recently by STM. Nevertheless, many kinetic features of this phase transition have remained to be studied experimentally, including how fast the 7×7 structure changes into the "1 × 1" structure and how fast the 7 × 7 structure nucleates in the disordered "1 × 1" structure in response to the temperature variation. Thus we have carried out SHG measurements of the kinetics of the 7 × 7 ↔ "1 × 1" phase transition by two ways: one through SHG of delayed probe laser pulses during a laser-induced rapid temperature jump,³ and the other by SH response to temperature variations on a longer time scale induced by switching the heating currents.

© 1995 IEEE