Structural Properties of Cleaved Silicon and Germanium Surfaces

Structures of silicon and germanium (111) surfaces produced at room temperature by the Gobeli—Allen cleavage technique have been studied by low-energy electron diffraction. Both have a rectangular unit mesh which measures √3×1 with respect to the parallel threefold symmetrical substrate mesh. Thus three domain orientations can occur and various combinations of them have been observed. Step disorder, generally peripheral, with a high degree of variability was also observed. Transitions at higher temperatures to the structures, probably more stable, reported previously by Lander and Morrison took place. This confirms the conclusion that the latter structures are properties of the clean surfaces. Implications of these results for surface physics and chemistry are discussed. The inherent difficulty of predicting theoretically the surface structures of these and many other systems is emphasized. These results demonstrate the complexity of surface-structure phenomena, the power of the display type of low-energy electron diffraction equipment, and uses of proper cleavage techniques.