Thickness dependent morphology of Au and TiO₂ and optical study of TiO₂ thin films on patterns of self-assembled monolayers

We report morphology and optical study of thin films (of Au and TiO₂) grown on micron scale composite self-assembled monolayers (SAMs) patterns of polar (-COOH, -N) and non-polar (-CH₃) molecules. Extensive atomic force microscopy (AFM) study reveals the smooth growth of deposited films on polar SAMs, whereas the grown films initially formed clusters on non-polar SAM but smooth surface is achieved after few nanometer growth of the film. Photoluminescence (PL) spectra of TiO₂ on polar and non-polar SAMs clearly depend on the surface chemistry of SAM and thickness of the film. We have observed an ultraviolet shift as well as an additional PL peak as the thickness of the TiO₂ film was decreased and this variation was more prominent on non-polar SAM. Such variation in the PL spectra was not observed when TiO₂ films of the same thickness were grown on Au surface without the SAM in identical conditions. Variation in UV-IR reflectance data in terms of intensity and peak shift was also observed. These results with the flexibility of SAM patterning at micro-/nano-scale can be used to create versatile optical structures.