Nonlinear optical study of the Si(111)7×7 to 1×1 phase transition: Superheating and the nature of the 1×1 phase

The reversible 7×71×1 phase transition of Si(111) is investigated by means of optical second-harmonic (SH) generation. The SH response increases sharply at Tc1130 K. The symmetry and magnitude of the SH signal are compatible with an adatom gas model for the 1×1 phase in which the number of dangling bonds is increased by roughly 25% with respect to the 7×7 structure. The behavior observed under conditions of laser heating provides clear evidence of superheating of the Si(111)7×7 phase by more than 50 K above Tc on the nanosecond time scale. © 1995 The American Physical Society.