High-Resolution Atom Lithography High-Resolution Atom Lithography

Atom lithography schemes based on nanomanipulation of neutral atoms by laser fields have attracted a lot of attention as a promising way to overcome the resolution limits of the usual optical lithography. This technique uses potential wells of a standing light wave as a periodic array of focusing elements for an atomic beam in a setup for building nanostructures by controlled deposition of atoms on a surface. The method was first demonstrated with sodium at Harvard and Bell Labs, and subsequently with chromium (NIST) and aluminum atoms. The prospects of laser-focused nanofabrication with other technologically interesting materials (like iron and gallium) are currently under investigation.

In the case of a direct laser-guided atomic deposition, the diffraction resolution limit is determined by the de Broglie wavelength of atoms, and may reach several picometers for the typical atomic beams. In practice, however, this limit has never been relevant because of the surface diffusion process, the quality of the atomic beam, and severe aberrations of the sinusoidal potential of a standing light wave. As a result, all current atom lithography schemes suffer from a considerable background in the deposited structures. This complicates the process of forming electrically isolated nanostructures on the surface.

Recently, we applied our novel results in quantum control of rotational systems to the field of atom lithography. There is a deep mathematical analogy between the dynamics of kicked 2D rotors and dynamics of cold atoms in pulsed optical lattices. This connection has been used in numerous nonlinear dynamics studies, especially in atom optics modeling of classical and quantum chaotic phenomena.

High-Resolution Atom Lithography

Based on our theoretical work, we suggested a nanolithographic approach that uses spatially squeezed atomic (molecular) beams for nanofabrication at ultra-high resolution. The squeezing of the beam is achieved in the process of its traveling through a set of specially arranged standing light waves that provide focusing “kicks” to the beam before it hits the surface. Accumulative squeezing and optimized versions of this strategy are at the heart of this approach. The focusing is enhanced substantially, and at the same time spherical and chromatic aberrations are compensated.. Moreover, enhanced focusing by multiple standing laser fields may be applied to many interesting materials that cannot be strongly focused by a single standing wave due to the spectroscopic limitations.

Recently, our strategy was supported by experiments of M. Raizen’s group (Phys. Rev. Lett. 89, 283001 (2002)), that demonstrated accumulative squeezing of cold cesium atoms by a pulsed optical standing wave. This presents a first step towards the new lithographic technique, and we are currently exploring the prospects of related experiments in a beam configuration.