The recent increased use of surface-enhanced Raman spectroscopy (SERS) for chemical and biological sensing is intimately tied to the surging interest in developing plasmonic metallic nanostructures. Typically silver or gold, SERS substrates exploit the plasmon resonance and the associated localized surface fields to enhance Raman scattering from the molecule of interest. We will present an alternative plasmonic metal, gallium, for use as SERS substrates. Gallium's prevalence in optoelectronic device growth also suggests their potential for integrated SERS structures. Our previous work has demonstrated interesting properties of gallium that make it an attractive metal for SERS sensing schemes compared to Ag or Au; these include its thermal and oxidative stability. Also in contrast to the properties of Ag and Au, Ga plasmonic nanoparticles can be tuned for size resulting in a plasmon resonance that varies from the near IR through the visible and into the deep UV.

Gallium nanoparticles (NPs) deposited onto dielectric substrates (glass and sapphire) were grown by molecular beam epitaxy. Nanoparticles were tuned to different plasmon resonances (i.e. mean size) to discern the effect NP geometry (size, distribution, and interparticle spacing) has on the strength of the Raman enhancement. In this work, solutions of the standard Raman dye Cresyl Fast Violet were dropcast onto the NP substrate at varying concentrations to evaluate the linear correlation between SERS intensity and molecular concentration. Direct comparison between bare (unmetallized) surfaces and metallized surfaces were made to quantify the Raman enhancement resulting specifically from the presence of Ga NPs. The enhanced Raman signal in the presence of Ga NPs suggest that Ga NP are effective alternatives to Ag and Au for SERS applications.