GaN-based platforms with Au-Ag alloyed metal layer for surface enhanced Raman scattering

The fabrication procedure of efficient surface enhanced Raman scattering (SERS) platforms is demonstrated based on reproducibly photo-etched GaN epitaxial layers covered by a thin Au-Ag layer and subjected to partial de-alloying. Using a gold-rich Au57Ag43 alloy (70/30 wt. %), it is possible to preserve about 19 at. % of silver in the layer, even after etching in nitric acid for up to 24 h. A large enhancement of the Raman signal from the test 4-mercaptobenzoic acid molecules attached to such porous Au-Ag metal layer is obtained due to the presence of a high percentage of Ag. For the optimal etching time, in the range of 6-24 h, an enhancement factor (EF) greater than 10(7) was obtained. The contribution of different features of our SERS platforms such as the size of pores, nano-roughness, and the chemical composition of the metal layer for the EF parameter are critically discussed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769106]