Surfactant Directed Growth of Gold Metal Nanoplates by Chemical Vapor Deposition

Surface supported, low dimensional gold nanostructures are of interest for plasmonic applications. Low dimensional nanostructures are readily accessible by solution-phase growth, where shape control through the addition of growth-directing surfactants is well established. Yet, shape control in chemical vapor deposition (CVD) has not been well explored, and metallic gold films are typically limited to nanoparticulate or thin film morphologies. This article describes the self-seeded growth of high aspect ratio gold plates and wires by CVD. A directed growth mechanism is proposed, where growth is directed by the coordinating N-heterocyclic carbene (NHC) and phosphine ligands originating from the thermal decomposition of the two gas-phase precursors, [Au­(HMDS) (NHC)] (HMDS = hexamethyldisilazide, NHC = 1,3-diisopropyl-imidazolidin-2-ylidene) and [Au­(HMDS) (PMe₃)]. These ligands acted as transient surfactants for plate growth between 370 and 460 °C and at high precursor flux. Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) evidence indicates that hydroxyl terminated substrate surfaces are passivated with trimethylsilyl (TMS) moieties originating from the HMDS ligand in both precursors, which promoted island type growth and directed precursor decomposition to occur on gold surfaces. Secondary nucleation is observed on all gold structures and is a crucial component to gas-phase surfactant-mediated CVD growth. This work identifies the potential to use precursor-bound coordinative ligands or gas-phase surfactants to direct growth of metal nanocrystals by CVD.