STM STUDY OF STRUCTURAL DEFECTS ON IN-SITU PREPARED SI(111)1X1-H SURFACES

We have used scanning tunneling microscopy to study the structural def ects occurring on Si(111)1 x 1-H surfaces prepared by in situ hydrogen exposure of Si(111)7 x 7 surfaces at elevated temperatures. These def ects can be divided into four categories: point-like defects, holes in the first bulk bilayer, islands, and stacking-faulted regions. The tw o most frequently occurring point-like defects are identified as adato m trihydrides and top-layer atoms with a missing hydrogen atom. The is lands observed on the 1 x 1-H surfaces are single-layer linear islands and bilayer-high linear and triangular islands. We have identified th ree distinct types of island edges and proposed structural models for each type. These models, which involve different arrangements of tilte d monohydride edge species, are also applicable for the step edges on the created surfaces. The stacking-faulted regions, triangular in shap e, are found to have a double periodicity along the borders which is e xplained in terms of a dimerization of the surrounding second-layer at oms.