Nanopatterning of alkynes on hydrogen-terminated silicon surfaces by scanning probe-induced cathodic electrografting

The electrochemical cathodic electrografting reaction, previously demonstrated on bulk silicon surfaces, can be patterned on the nanoscale utilizing conducting probe atomic force microscopy (CPAFM). Alkyne electrografting is a particularly useful chemical technique since it leads to direct covalent attachment of conjugated alkynes to silicon. In addition, application of a forward bias during the reaction renders the surface less sensitive to oxidation and the resulting monolayers are very stable in air and basic aqueous solution. Alkyne monolayer lines can be drawn down to 40 nm resolution using a Pt-coated AFM tip, and the heights of the monolayers scale with the molecular length of the alkyne. The tip is biased (+) and the surface is biased (-) to drive the cathodic electrografting reaction under ambient conditions. The resistance of the monolayers to fluoride, as well as friction force microscopy, indicate that the alkynes are covalently bonded to the surface, not oxide-based, and hydrophobic. The reaction does not work with alkenes, and therefore hydrosilylation is not the primary mode of reaction. Wider lines (300 nm) can be produced using broadened Pt-coated AFM tips. This reaction could be important for the interfacing of conjugated molecules directly to silicon in a spatially controlled fashion.