The anisotropic component of the non-linear susceptibility of (111)-(7 x 7) around the 3.3eV 2-photon energy, which originated in the strained surface layer, was observed to increase with temperature. This was accompanied by a jump in response to a phase transition to so-called (1 x 1). The temperature dependence of the second-harmonic response, which was attributed to the (111)-(7 x 7) and (1 x 1) structural symmetry, was related to modifications which were induced by the thermal excitation of surface phonon modes.

Thermally Enhanced Second-Harmonic Generation from Si(111)-7 x 7 and "1 x 1" T.Suzuki, S.Kogo, M.Tsukakoshi, M.Aono: Physical Review B, 1999, 59[19], 12305-8