Shape-Controlled, Single-Crystal Gold Surface Nanostructures

Size, shape and crystallinity play a critical role in the wavelength-dependent optical responses and plasmonic local near-field distributions of metallic nanostructures. While their enhanced local fields can drive new and useful chemical and physical processes, the ability to fabricate shape-controlled single-crystal metal nanostructures and position them precisely on substrates for device applications represents a significant barrier to harnessing their greater potential. Here, we describe a novel electroless deposition process in the presence of anionic additives that yields additive-specific, shape-controlled, single-crystal plasmonic Au nanostructures on Ag(100) and Au(100) substrates. Deposition of Au in the presence of SO₄^2- ions results in the formation of smooth Au(111)-faceted square pyramids that show large surface enhanced Raman responses. The use of halide additives such as Cl^- and Br^- that interact strongly with (100) facets produces highly textured hillock-type structures characterized by edge and screw-type dislocations (Cl^-), or flat platelet-like features characterized by large area Au(100) terraces with (110) step edges (Br^-). Use of additive combinations provides structures that comprise characteristics derived from each additive including new square pyramidal structures with dominant Au(110) facets (SO₄^2-and Br^-). Finally we demonstrate that this bottom-up electroless deposition process, when combined with top-down lithographic patterning methods, can be used to position shape-controlled, single-crystal Au nanostructures with precise location and orientation on surfaces. We anticipate that this approach will be employed as a powerful new tool to tune the plasmonic characteristics of nanostructures and facilitate their broader integration into device applications.