EFFECT OF A STM TIP ON THE SURFACE-DIFFUSION MEASUREMENT - A MONTE-CARLO STUDY

Monte Carlo simulations are performed to study the effect of an electr ic field on the surface diffusion of adatoms in a method that measures scanning tunneling microscopy tunneling-current fluctuations. The cor relation function of the tunneling-current fluctuations is proportiona l to the adatom density fluctuation. Diffusion coefficients are invers ely proportional to the time constant of the correlation function. Bot h the shape of the correlation and the measured time constant are calc ulated as a function of the ratio of the temperature to the characteri stic electrostatic energy (i.e., strength of the electric field) and a s a function of the initiating time of the measurement. The effect of the field is more pronounced when the measurement is carried out in th e early nonequilibrium time regime while the adatom density evolves to wards its equilibrium distribution under the spatially dependent elect rostatic potential due to the electric field.