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. [Langmui r 1995, 11, 4371-4382], to electron-beam-lithography carried out at hi gh (>1000 eV) and low (<15 eV) energies. Lithography using high-energy electrons to make transformations of the short-alkyl-chain, amide-con taining monolayer used in this system required doses of electrons >30 mu C/cm(2), 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 mon olayers. Low-energy electron lithography of the same monolayer using a scanning tunneling microscope (STM) as the source proved more reliabl e and allowed the formation of 30-40 nm structures wherever the STM ti p passed over the surface with sufficient voltage and current. Our dat a highlight some of the difficulties encountered when using self-assem bled monolayer resists as components in ''positive'' electron-beam lit hography on gold and suggests constraints on using SAMs as ultimate re sists.