Production and Characterisation of Nanoscale Structures using Atom Lithographic Techniques

Abstract

A metastable neon (Ne) beam generated by a liquid nitrogen cooled, DC discharge source was puried to an atomic beam consisting of a single metastable state. The atomic beam was cooled in the transverse direction by a two dimensional optical collimator, slowed in the longitudinal direction by a novel dual beam Zeeman slower, and then guided through a 30 arc by a hexapole magnetic guide. This resulted in a pure, UV free metastable atomic beam with a ux of (4.41.1)109 atoms s1. The metastable neon atomic beam was used to investigate the patterns formed in resist based atom lithography experiments utilising alkanethiol self-assembled monolayer resists. It was observed that very short chain alkanethiols, such as ethanethiol, do not form viable resist layers. They are likely desorbed from the surface during exposure to the metastable beam and replaced by background mechanical pump oil molecules. Above the critical dosage (71014 atoms cm2) these samples react in a manner similar to bare gold samples and form a carbonaceous resist layer. This dosage was found to be signifcantly aected by the vacuum infrastructure, highlighting the role contamination plays in the formation of negative contrast patterns in resist based atom lithography. Using ellipsometry the growth of a carbonaceous lm during exposure to a metastable atomic beam was characterised. The desorption cross-section of carbonaceous material from a silicon surface via Ne impact was determined to be many times larger than the polymerisation cross-section. The values determined, along with simple estimates for the mean residence time, volume, and cross-section of the contaminants involved provide insight for the application of the theory to other metastable atom experimental apparatus. Direct deposition lithography without laser cooling of the atomic beam was achieved and patterning observed for iron atoms with a local average transverse velocity of up to 4 ms1. A broadening of the experimentally deposited samples, from a full width half maximum of 35 nm predicted by simulations to >80 nm on SiOx substrates, was observed. The broadening is attributed to a substrate dependent diusion mechanism and the scattering and interference of the standing wave light mask near the substrate. An initial characterisation of the magnetic properties of co-deposited iron-nickel (Fe-Ni) structures has been conducted using the longitudinal magneto-optic Kerr eect. Variations in the Fe-Ni concentrations infuence the coercivity of the deposited structures. A reduction in the coercive field in regions with line structures was observed when applying a magnetic field parallel to the co-deposited lines. This has been attributed to the nucleation of magnetic domains in regions were the Fe-Ni alloy possesses a lower magnetic moment per atom. A magnetic anisotropy induced by the incident angle of the Ni atomic beam was also observed in regions without nanostructuring.