Atom lithography using a Bose Einstein Condensate and an Atom Laser beam

Abstract

Atom lithography is a technique where the gradient forces applied by laser fields on a beam of atoms are used to direct the atoms into nanostructures deposited on a plane surface. It has been the topic of considerable study in the scope of atom optics over the last two decades as it can provide a scheme of writing nanometer structures directly onto a substrate in parallel process. The main application in the development of nano-lithography could be the race for an increased density of three-dimensional transistors in the computer chips. One of the certain objectives in this technology is to minimize the size of fabricated structures, which is limited by the oven sources of atoms. This thesis studies the possibility of exploiting a Bose Einstein Condensate of rubidium-85 (85Rb) and rubidium-87 (87Rb) as a source of ultra-cold atoms instead of traditional oven sources of neutral atoms in atom lithography and nano fabrication, which is a new emerging area and is deemed to break the mentioned limitation providing one with superior structure linewidths. For this purpose, two major regimes are considered. Firstly, by dropping a condensed atom cloud into an optical focusing potential, we seek the optimal ways of achieving the smallest structures possible. Secondly, we investigate the focusing dynamics of an atom laser beam as a highly bright, coherent and a monochromatic matter-wave. The focusing potential utilized in both cases can be produced in any arbitrary geometries such that, optical lattices as well as harmonic potentials are chosen as our preferred focusing fields. In both stated configurations, the inter-atomic interactions within the BEC and atom laser play a key role in estimating the resultant focal spot sizes and peak densities. While this significant factor is taken into account via our proposed theoretical models, we extract and implement the optical properties of potential fields in the process of focusing to obtain reasonably the highest achievable structure resolutions. Furthermore, by tuning the atomic interaction strength within the condensate and atom laser beam over a large flexible range via a Feshbach resonance, we explore the interaction impact on a focused profile. The tunability of interactions between atoms can be advantageous and deleterious for the structure flux, which is discussed by examples. More specifically, the influence of the three-body recombination losses on focused structures are studied through our numerical and analytical approaches. This especially becomes remarkable in high density regimes. Overall, it is shown that nanofabrication using a Bose Einstein Condensate and an atom laser offers a dramatic improvement in resolution of the write beam up to 8 nm as it considerably reduces several detrimental aberrations such as the longitudinal and transverse velocity distributions and consequently the beam divergence, which even results in a self-focusing (converging) beam. Show more