Modelization of surface diffusion of a molecular dimer

A simple model for a dimer molecular diffusion on a crystalline surface, as a function of temperature, is presented. The dimer is formed by two particles coupled by a quadratic potential. The dimer diffusion is modeled by an overdamped Langevin equation in the presence of a two-dimensional periodic potential. Numerical simulation’s results exhibit some dynamical properties observed, for example, in ${\text{Si}}_2$ diffusion on a silicon $\left[100\right]$ surface. They can be used to predict the value of the effective friction parameter. Comparison between our model and experimental measurements is presented.

Figure 1

Plot of the two-dimensional potential and dimer most probable configurations in dimensionless units.

Figure 2

(Top) Typical evolution of dimer orientation corresponding to $ϵ=0.2$, $l_x\left(s\right)$ is the normalized dimer length as defined in the text. (Bottom) Histogram of the instantaneous dimer angle with respect to $x$ axis for $ϵ=0.2$.

Figure 3

Average resident dimensionless time in state $B$ (diamonds) and state $A$ (circles). $k_{B}T$ in $\text{eV}$.

Figure 4

Dimensionless diffusion coefficients in $x$ direction (black dots) and $y$ direction (white dots) for a ${\text{Si}}_2$ dimer. $k_{B}T$ in $\text{eV}$.