Automated sub-100 nm local anodic oxidation (LAO)-directed nanopatterning of organic monolayer-modified silicon surfaces

Abstract

The fabrication of silicon oxide nanopatterns using the local anodic oxidation (LAO) by a conducting AFM tip of different organic monolayer (decyl, dodecyl, hexadecyl and undecanoic acid)-modified Si(111) surfaces is reported. It is demonstrated that the threshold bias voltage of oxide formation increases with the monolayer thickness and decreases when acid end groups are used instead of methyl. The automatization of the LAO process has allowed the perfect replication of vectorized complex drawings (e.g. compass card and longship) on silicon using the undecanoic acid monolayer as the model molecular resist. Under optimized experimental conditions (namely, bias voltage of 8 V applied to the surface and writing rate of 1 μm s⁻¹), highly reproducible and uniform 2–3 nm thick oxide patterns have been electrogenerated with a minimum lateral resolution of 80 nm. Interestingly, the silicon oxide nanopatterns have been selectively dissolved in diluted hydrogen fluoride solution to generate potentially reactive hydrogenated areas. These hydrogenated sites have then been used for the electroless deposition of gold nanoparticles by galvanic displacement. This approach was found to be convenient and fast to metallize the patterns initially produced by LAO. The average diameter of deposited gold particles decreased from 20 to 2 nm with decreasing the gold salt concentration from 100 to 1 μM.