Surface-plasmon-enhanced Spectroscopy Of Two-dimensional Materials

After decades of development,the field of plasmonic has extended to be one of the most important branches in nanophotonics,an interdisciplinary area that involves the fields of physics,chemistry,medical science,biology,energy,etc.Two-dimensional materials have received extensive scientific attention since they came into being.After more than ten years of development,they have great application prospects in micro-nano electronic devices,hypersensitive sensors,photo detectors,biological photonics and other aspects due to their excellent electron transport properties and photoelectric properties.The perfect match of surface plasmon and two-dimensional materials at the spatial nanometer scale makes surface plasmon of great academic value in the interaction between light and two-dimensional materials.So,this article focuses on the optics of two-dimensional materials and surface plasmon,introducing plasmonic and two-dimensional materials in details.We focus on the TMDS-metals heterojunction and the surface-enhanced spectra of the coupling system of silver nanocube-MoSe2-ultrasmooth gold film(NCOM-MoSe2).The main innovations and research achievements are as below:1.The Raman and fluorescence spectra of TMDS-metals heterojunction were investigated systematically.Two-dimensional materials exhibit peculiar optical and optoelectronic properties that can be tuned by electron/hole doping.Here,by transferring mechanically exfoliated few-layer MoS2 onto ultra-smooth Au films,we investigated high-quality molybdenum disulfide(MoS2)-Au heterojunctions by micro-Raman and photoluminescence.We found that The E~12g and A1g phonon modes of MoS2 show a redshift as the layer number reduces and even split into two peaks in monolayer MoS2,different from those on silicon oxide substrate.The obvious splitting and redshift of the main Raman peaks shows two functions of the gold film:first,the gold atom of the gold film may form a strong interaction with the sulfur atom of molybdenum disulfide;second,the mirror effect of the gold film provides the redshift and splitting of the Raman peaks.The photoluminescence peak from the direct-bandgap transition at 1.83 eV is quenched,while a much weaker peak at 1.75eV arises.This peak stems from trions due to the charge transfer with the gold film.These effects are gradually weaker as the increase of the number of layers of MoS2.Our research results have gained a new understanding of the electrical and optical properties of the MoS2-Au heterojunction,which is expected to be widely used in the field of nano-electronic devices and nano-optics based on two-dimensional materials-metal heterostructure.2.We develop silver nanocube-monolayer MoSe2-ultrasmooth gold film coupling system(NCOM-MoSe2),such plasmonic-nanocavity antennas system has realized simultaneous surface-enhanced Raman scattering(SERS)and surface-enhanced fluorescence(SEF)spectroscopy of monolayer MoSe2.We developed a method to successively deposit alumina films on metal nanoparticles to continuously tune the silver nanocube plasmon resonance peak to optimize the surface-enhanced Raman scattering and surface-enhanced fluorescence enhancement factors.After optimizing the spatial and the spectral overlaps between laser,excitonic and plasmonic resonances,the SERS and SEF enhancement factors can exceed 10~7 and 6000,respectively,at the same time on the same nanocube.3.With the further probing of surface-plasmon-enhanced spectroscopy of two-dimensional materials,we constructe a unified model to analyze microscopic mechanism of SEF and SERS.The comparison of the SERS and SEF enhancements allows the estimation of the ultrafast total decay lifetime of the bright exciton in monolayer MoSe2 in the plasmon nanocavity down to 22 femtoseconds,which is otherwise hard to realize using time-resolved techniques.Our work has scientific significance and provides a new mean for ultrafast optical spectroscopy and surface-enhanced spectra of nanocavity system.