Measurement and modeling of temperature-dependent step bunching on Si(111)

Direct Current (DC) induced step bunching on Si(111) is a long-standing puzzle, with the required DC direction for bunching (relative to the ``step-down'' vicinal surface direction) reversing multiple times with increasing temperature. It was recently proposed [1,2] that this could be explained if step attachment is \textit{faster (slower)} than terrace diffusion in Temperature Regime II (Regimes I and III). We have numerically simulated a similar model and directly compared with measurements of how the step bunching depends on the initial terrace width $l_{0}$ in all three regimes [3]. Using realistic parameter values for terrace diffusion and step attachment, this model can account for the bunching behavior in all three temperature regimes, provided there indeed exist modest (0.2 -- 0.4 eV) temperature-dependent variations in the relative activation barriers for attachment and diffusion, and/or modest changes in the respective activation attempt rates. Work supported by NSF. [1] N. Suga \textit{et al.}, \textit{Jpn. J. Appl. Phys.} \textbf{39}, 4412 (2000). [2] T. Zhao \textit{et al.}, \textit{Phy. Rev. B} \textbf{71}, 155326 (2005). [3] B.J. Gibbons \textit{et al.}, submitted to Surf. Sci; Surf. Sci. Lett. \textbf{575}, L51-56 (2005).