Spaced Hybrid TiO2/Au Nanotube Arrays with Tailored Optical Properties for Surface-Enhanced Raman Scattering

Controlling the overall geometry of plasmonic materials allows for tailoring their optical response and the effects that can be exploited to enhance the performance of a wide range of devices. This study demonstrates a simple method to control the size and distribution of gold (Au) nanoparticles grown on the surface of spaced titanium dioxide (TiO2) nanotubes by varying the deposition time of magnetron sputtering. While shorter depositions led to small and well-separated Au nanoparticles, longer depositions promoted the formation of quasi-continuous layers with small interparticle gaps. The optical spectra of Au/TiO2 nanotubes showed a region of strong absorption (200-550 nm) for all samples and a region of decreasing absorption with an increase of effective Au thickness (550-1100 nm). This behavior led to distinct trends in the Raman signal enhancement of the underlying TiO2 nanotubes depending on the excitation laser wavelength. Furthermore, the quasi-continuous layers formed at higher effective Au thicknesses promoted an amplification of the signal and an improvement in the detection limit of target molecules in surface-enhanced Raman scattering (SERS) experiments. These findings suggest a simple method for designing efficient devices with tailored light absorption and potential applications in detectors and other optical devices.