Barrier-limited surface diffusion in atom lithography

Thermally activated surfacediffusion has a strong influence on structure widths in atom lithography. We investigate the effects of two barriers to thermally activated atomic diffusion on atom lithography: a thermally activated Ehrlich–Schwoebel (ES) barrier, and pollution from the residual gas in the vacuum system. We performed kinetic Monte Carlo simulations using a one-dimensional surface grid. We find that the ES barrier fails to explain the lack of temperature dependence observed experimentally [W. R. Anderson et al., Phys. Rev. A 59, 2476 (1999)]. The dependencies of the structure width on temperature, vacuum conditions, and beam characteristics can be explained using the pollutant adatom hypothesis. Only the variation of structure width with deposition duration was not entirely reproduced by this model. We attribute this to the one-dimensional nature of our simulations. These results demonstrate that barrier-limited diffusion can play an important role in atom lithography, and that pollutant adatoms are a likely candidate barrier.