B Bart Smeets

Atom lithography of Fe

Direct write atom lithography is a technique in which nearly resonant light is used to pattern an atom beam. Nanostructures are formed when the patterned beam falls onto a substrate. We have applied this lithography scheme to a ferromagnetic element, using a 372nm laser light standing wave to pattern a beam of iron atoms. In this proof-of-principle experiment, we have deposited a grid of 50-nm-wide lines 186nm apart. These ultraregular, large-scale, ferromagnetic wire arrays may generate exciting new developments in the fields of spintronics and nanomagnetics.

Progress towards atom lithography on iron

We aim to apply atom optical techniques to iron to produce periodic magnetic nanostructures. Laser cooling has been observed experimentally, and calculations predict that a bright beam can be obtained with 200 µrad divergence. We expect to be able to laser focus this beam to feature sizes around 10 nm by the use of nanoseale mechanical beam masking and velocity selection via a supersonic source. In separate calculations, we have modelled surface diffusion of the atoms during deposition using a kinetic Monte Carlo approach taking into account the Ehrlich-Schwoebel barrier. These calculations successfully explain anomalous broadening of structures observed in similar experiments on chromium [Anderson et al., Phys. Rev. A 59 (1999) 2476].

Barrier-limited surface diffusion in atom lithography

Thermally activated surface diffusion 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 adatom...