Well-oriented Epitaxial Gold Nanotriangles and Bowties on MoS2 for Surface-enhanced Raman Scattering

We report on epitaxial growth of Au nanotriangles (AuNTs) and bowties consisting of opposing tip-to-tip AuNTs with a few-nanometer gap on n-layer MoS2. These AuNTs exhibit well-defined crystallographic orientations with the average size determined by the MoS2 thickness. Monolayer (1L) MoS2 shows the weakest coalescence, corroborating the layer-dependent interactions among Au and n-layer MoS2. High-resolution transmission electron microscopy characterization confirms the lattice directing of thin MoS2 sheets on the AuNT formation with [111]Au||[001]MoS2 and <211>Au||<210>MoS(2). By introducing misfit dislocation arrays, the system with an 8.8% lattice misfit is stress-free. In particular, subwavelength-sized gold bowtie nanoantennas can be easily found on the MoS2 surface with a spacing gap down to 3 nm and a density up to 1.6 × 10(13) m(-2). This technique is low cost, time-saving and free of impurities compared to the conventional lithography technologies. Meanwhile, the equilateral AuNTs can enhance Raman signals of thin MoS2 sheets far stronger than that by ordinary gold films, indicating the potential use of AuNTs as SERS substrates for SERS applications.