Published in J. Vac. Sci. Technol. A 22, 1671 (2004).
Shu Nie (a), R. M. Feenstra (a), Ji Young Lee (b) and Myung-Ho Kang (b)
(a) Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA
(b) Dept. Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
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. .