Ultrathin Wetting Layer-Free Plasmonic Gold Films

Ultrathin gold films are enticing for plasmonic and metamaterial devices, thanks to their useful optical and optoelectronic properties. Yet, deposition of ultrathin continuous Au films of a few nanometer thickness is challenging and generally requires wetting layers, resulting in increased optical losses and incompatibility with optoelectronic device requirements. We demonstrate wetting layer-free plasmonic gold films with thicknesses down to 3 nm obtained by deposition on substrates cooled to cryogenic temperatures. We systematically study the effect of substrate temperature on the properties of the deposited Au films and show that substrate cooling suppresses the Volmer-Weber growth mode of Au, promoting early stage formation of continuous Au films with improved surface morphology and enhanced optoelectronic properties. Our results pave the way for straightforward implementation of ultrathin Au-based optoelectronic and plasmonic devices, as well as metamaterials and metasurfaces.