Plasmon-Mediated Drilling in Thin Metallic Nanostructures.

Thin and ultraflat conductive surfaces are of particular interest to use as substrates for tip-enhanced spectroscopy applications. Tip-enhanced spectroscopy exploits the excitation of a localized surface plasmon resonance mode at the apex of a metallized atomic force microscope tip, confining and enhancing the local electromagnetic field by several orders of magnitude. This allows for nanoscale mapping of the surface with high spatial resolution and surface sensitivity, as demonstrated when coupled to local Raman measurements. In gap-mode tip-enhanced spectroscopy, the specimen of interest is deposited onto a flat metallic surface and probed by a metallic tip, allowing for further electromagnetic confinement and subsequent enhancement. We investigate here a geometry where a gold tip is used in conjunction with a silver nanoplate, thus forming a heterometallic platform for local enhancement. When irradiated, a plasmon-mediated reaction is triggered at the tip-substrate junction due to the enhanced electric field and the transfer of hot electrons from the tip to the nanoplate. This resulting nanoscale reaction appears to be sufficient to ablate the thin silver plates even under weak laser intensity. Such an approach may be further exploited for patterning metallic nanostructures or photoinduced chemical reactions at metal surfaces.