Surface thermal expansion of Ge(111)

The thermal expansion of the Ge(111) surface has been measured by reflectio n high-energy electron diffraction (RHEED) based on a simple kinematic mode l. Measurements of the RHEED streak shift towards the shadow edge gives a t hermal expansion perpendicular to the Ge(111) surface, about 11 times that of the bulk over the temperature range from 300 K to 600 K. The Debye-Walle r extinction of the RHEED streak intensity with temperature gives an effect ive surface Debye temperature of 96 +/- 11 K for Ge(111). The enhanced ther mal expansion perpendicular to the Ge(111) surface is expected to result fr om the weakening of the harmonic restore force constant of the interlayer p otential. (C) 1999 Elsevier Science B.V. All rights reserved.