Electronic pathways in nanostructure fabrication

A potentially interesting technique to fabricate nanostructures of sub-10 nm size is electron beam induced deposition (EBID), in which electrons dissociate precursor molecules adsorbed to a substrate surface. The solid deposits that can be made with EBID can be as small as 1 nm. There is little information available on the dissociation processes of the complex precursor molecules adsorbed at surfaces. This paper is meant to raise the interest of surface scientists to investigate the complex surface phenomena observed in EBID. We demonstrate the necessity of having good data on the dissociation cross-sections, by calculating the EBID spatial resolution for three different cross-sections which are usually taken as an approximation of the real cross-section. The electron scattering in the substrate is simulated using Monte Carlo techniques. The spatial resolution due to secondary electron dissociation turns out to be higher for cross-section distributions with a steep fall-off towards high energies, although the dissociation rate is lower. The spatial resolution due to the primary electrons can be very high when using finely focused beams and having a cross-section which does not fall off too fast towards high energies. In the cases presented, the total number of molecules dissociated by the primaries is about equal to the number of molecules dissociated by the secondaries. Furthermore, experimental results of structures made with EBID are presented which demonstrate the complex nature of the process, i.e. the dependence of the deposited mass and/or the location of the deposits on substrate material, surface condition, substrate temperature and precursor gas pressure.