Well-oriented epitaxial gold nanotriangles and bowties on MoS2 for surface-enhanced Raman scattering

Abstract

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>_MoS². 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 × 10¹³ 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.