Fabrication of pure gold nanostructures by electron beam induced deposition with Au(CO)Cl precursor: deposition characteristics and primary beam scattering effects

In the search for a direct write, high-purity electron beam induced deposition (EBID) process, a new gold precursor that is commonly available is investigated. This precursor, Au(CO)Cl, can indeed be used to produce a high-purity golden nanostructure (> 95 at% Au), at a wide variety of electron beam parameters. The use of a mass spectrometer to determine the components of the actual precursor vapour showed that the Au(CO) Cl density in the vapour is very low (estimated at < 0.1%), while the main component is CO. This indicates that the electron decomposition cross-section of the actual precursor is roughly two orders of magnitude higher than for common EBID precursors. A remarkable observation is a skirt deposition at positions between 5 and 200 mu m away from the beam impact point. This skirt cannot be attributed to secondary electrons of type II (SE2), but results from local scattering of the primary beam on its way through the precursor gas. The skirt deposition is quantified experimentally and by modelling and must be present in all EBID processes with any precursor, delivered through a local supply system with fluxes in the range 10(16)-10(19) molecules cm(-2) s(-1). It is shown that the skirt effect can be minimized by increasing the applied beam energy and by reducing the gas path length.