Phase transition of the Si(111)-4x1-In surface reconstruction   investigated by electron transport measurements
  We measure the electron conductivity of the surface states and the subsurface space charge layer originating from the Si(111)-4x1-In reconstruction as a function of temperature. The conductivity of the surface states drops sharply around 130 K with decreasing temperature, revealing a metal-insulator phase transition of the surface reconstruction. In contrast, the influence of the phase transition on the conductivity of the space charge layer is limited to temperatures above 60 K. This means that the surface Fermi level remains strongly pinned despite the phase transition, indicating the presence of free carriers in the surface states down to rather low temperatures. 
Takashi Uchihashi and Urs Ramsperger