Buckling of Si and Ge (111)2×1 Surfaces

Voltage-dependent scanning tunneling microscopy is used to determine the buckling of pi-bonded chains on Si and Ge(111)2x1 surfaces. Images are acquired over a wide range of voltages, and are compared with theoretical constant-density contours generated from first-principles electronic-structure calculations. The theoretical predictions for (2 -1 -1) corrugation shifts are quite different for positive and negative buckling; experimental results for Si are found to agree with the former and those for Ge agree with the latter. In addition to an expected shift in ( 2 -1 -1) corrugation between small-magnitude positive and negative voltages, a further shift is also seen in both experiment and theory between small and large positive voltages. .