Kinetics of Strain-Induced Domain Formation at Surfaces

Abstract

By applying an external and variable strain to a Si(100) sample, it is possible to alter the relative populations of the 2×1 and 1×2 domains in a controlled and reversible way. This means one alters the configuration of monatomic steps which are the domain boundaries. This is conveniently observed by bending a thin bar of Si and observing either the superlattice LEED reflections or STM images. This effect is driven by the relaxation of the energy associated with long-range strain fields in the bulk which are due to the anisotropy of the intrinsic surface stress tensor of the two reconstructed domains. It is similar to the reduction of magnetic field energy by the configuration of magnetic domains. Here, we first briefly review the experimental observations for both nominally flat and vicinal surfaces and show that they are consistent with the theory of Alerhand et al. While the kinetics to produce or remove the unequal domain populations depend on the temperature, the steady state depends only on the strain and the vicinality but not on the temperature. The kinetics closely follow a simple relaxation $\Delta \textup{I}(\textup{t})=\Delta \textup{I}(\infty )(1-e^{-t/\tau})$. 1/r is thermally activated with an activation energy of 2.2 ± 0.2 eV. One striking feature is that the time constants for establishing the asymmetric population upon applying the external strain are the same as those for removing the asymmetry after relieving the strain. Changing the populations requires moving steps and mass transport. It involves the same microscopic processes that are important in other phenomena like coarsening, step bunching, etc., and therefore understanding the kinetics in the present experiments may contribute to the understanding of a broader range of problems involving step motion.