SYSTEMATIC CHANGE IN SURFACE-STRUCTURES ON SI(111) CLEAN SURFACES WITH TEMPERATURE

The temperature dependence of Si(111) surface structures has been studied. Reflection electron diffraction intensities have been measured for Si(111) clean surfaces as a function of temperature. Diffraction intensities change at 830, 1110 and 1410 K, corresponding to a low-temperature 7 x 7 phase <-> a high-temperature 7 x 7, 7 x 7 <-> 1 x 1 phase transition, and a surface order-disorder transition respectively. These temperatures are equivalent to 0.49(almost-equal-to 3/6)T(m), 0.66(almost-equal-to 4/6)T(m), and 0.84(almost-equal-to 5/6)T(m) respectively, where T(m) is the melting temperature of bulk Si on the absolute temperature scale. The significance of these temperatures is discussed in relation to the crystal surface sites, for example kinks, ledges and terraces.