Experimental and Theoretical Exploration of the Anisotropy of Styrene Diffusion on Hydrogen Terminated Si(100)-2 x 1

The anisotropy associated with the diffusion of styrene on the hydrogen-terminated silicon(100)-2 x 1 surface arises largely because of the surface reconstruction. This anisotropy was determined by using a novel scanning tunneling microscopy (STM) technique and by a combination of dispersion-corrected density functional theory (DFT) with Monte Carlo (MC) simulations. The SIM tip was used to create a box of clean silicon surrounded by H-Si. Styrene molecules diffuse from the H-Si surface to the clean surface, where they stick with unit probability. The reduction of the box dimensions following the room-temperature diffusion of styrene are measured using STM and reflect the diffusion anisotropy without influence from the STM tip. DFT calculations were used to compute the dispersion binding of styrene on H-Si as well as the barrier heights associated with diffusion. These data were used to provide input for the MC diffusion simulations. Experiment and theory predict results that are in excellent agreement, viz., slight diffusion anisotropies of 1.1 +/- 0.1 and 1.06 +/- 0.04, respectively.