Modified nanosphere lithography: application to the fabrication of ordered arrays of gold nanopyramids

In this work a modified approach to improve the capabilities of nanosphere lithography was performed to obtain ordered arrays of gold nanopyramids that can be used as Surface-Enhanced Raman Scattering (SERS) substrates. Specifically, shadow sphere lithography in combination with nanosphere lithography was used to fabricate metallic nanostructures of different sizes starting from the same mask of silica microspheres. An extensive study of the obtained samples with scanning electron microscopy, atomic force microscopy and Raman characterizations confirms that indeed this modification of the standard nanosphere lithography is an excellent candidate to produce ordered arrays of Au nanopyramids with good control on their geometric properties. Rhodamine 6G dye was used as a probe molecule to test our SERS substrates. These features can be used in turn to optimize the SERS substrates for several potential applications. Remarkably, it is shown that by this simple technique one can achieve enhancement factors and detection capabilities of dyes that are comparable with those obtained by using more sophisticated techniques as proposed recently in the literature.