Direct writing of self-assembled monolayers on gold coated substrates using a CW argon laser

The ability to engineer surface properties such as hydrophobicity, charge, and adhesion at the micrometer scale is the key to developments in emerging technologies (e.g. bio-sensors, and barrier-free microfluidic systems). Development of a methodology to manipulate surface properties of a self-assembled monolayer of alkanethiol on a gold film was the objective of this paper. This system is broadly studied and widely believed to serve as the platform of choice to develop a variety of biological technologies. The proposed approach is unique in that it eliminates the need for photolithography, is non-contact, and can be extended to other systems such as SAMs on silicon wafers or polymeric substrates. For this study, an initial hydrophobic monolayer of l-hexadecanethiol on a 300 Å gold sputtered film is used. Localized regions are then desorbed in a nitrogen atmosphere by scanning the focal spot of a 488 nm CW Argon ion laser beam. The beam with a Gaussian spatial profile was scanned at a rate slower than the heat diffusion rate along the surface. After completing the scans, the sample is dipped into a dilute solution of 16-mercaptohexadecanoic acid and a hydrophilic monolayer self-assembles along the previously irradiated regions. The resultant lines are viewed by wetting with tridecane.