Entropy explains metal-insulator transition of the Si(111)-In nanowire array.

Density functional theory calculations are performed to determine the mechanism and origin of the intensively debated (4 x 1)-(8 x 2) phase transition of the Si(111)-In nanowire array. The calculations (i) show the existence of soft phonon modes that transform the nanowire structure between the metallic In zigzag chains of the room-temperature phase and the insulating In hexagons formed at low temperature and (ii) demonstrate that the subtle balance between the energy lowering due to the hexagon formation and the larger vibrational entropy of the zigzag chains causes the phase transition.