Spatially controlled surface chemistry by excimer laser ablation of thin films

Two-dimensional control over the surface chemistry of substrate materials is of interest to a wide range of applications from microelectronics to biomedical diagnostics. Here, we describe a general principle for creating spatially controlled surface chemistries by subsequent deposition of thin plasma polymer coatings followed by laser ablation. The creation of surfaces with spatially controlled wettability was used as an example. Plasma polymerization of n-heptylamine produced a hydrophilic surface on silicon wafer substrates while subsequent plasma polymerization of perfluoro-1,3- dimethylcyclohexane produced a hydrophobic surface. Excimer laser ablation at an energy density of 125 mJ/cm(2) was used to remove a defined thickness of the two-layer coating, completely removing the upper layer without exposing the substrate material. Excimer laser ablation resulted in two-dimensional control over the surface chemistry with a resolution of ca. 1 mum. Surface modifications were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Contact angle measurements were used to estimate the wettability of modified surfaces. The method was shown to be suitable for the precise control over the location of droplets containing aqueous solutions. In conclusion, the method described here represents an effective tool for the production of substrates with spatially controlled surface chemistry and wettability.