Making gold nanostructures using self-assembled monolayers and a scanning tunneling microscope

We explored the applicability of a system of self-assembled monolayer (SAM) resists on gold, recently developed by Tam-Chang et al. [Langmuir 1995, 11, 4371-4382], to electron-beam lithography carried out at high (>1000 eV) and low (<15 eV) energies. Lithography using high-energy electrons to make transformations of the short-alkyl-chain, amide-containing monolayer used in this system required doses of electrons >30 μC/cm2, whereas contamination from the chamber in moderate vacuum (10-6 Torr) interfered with the process and provided equally useful resist layers against a cyanide etch of the gold in the absence of monolayers. Low-energy electron lithography of the same monolayer using a scanning tunneling microscope (STM) as the source proved more reliable and allowed the formation of 30-40 nm structures wherever the STM tip passed over the surface with sufficient voltage and current. Our data highlight some of the difficulties encountered when using self-assembled monolayer resists as components in "positive" electron-beam lithography on gold and suggests constraints on using SAMs as ultimate resists.