The Study Of Interface-enhanced Raman Scattering Based On Two-dimensional Transition Metal Chalcogenides

As a powerful analysis technique of molecular detection,surface-enhanced Raman scattering（SERS）is applicable even at the single-molecule level.Because of its wide application in diverse areas such as biological sensing,optoelectronics,and catalysis chemistry,SERS has shown a promising prospect and attracted great attention.The selection and construction of substrates is the key to obtain high quality SERS signals.With the development of materials science,the emergence of two-dimensional layered materials with SERS activity opened a new page in the studies of SERS substrates over 30 years after SERS was first discovered.Recently,two-dimensional transition metal chalcogenides（2D TMCs）became a strong candidate for new SERS sensors due to their controllable synthesis technology and adjustable optical properties.However,the low sensitivity and poor universality of 2D TMCs is the dominant barrier toward their practical applications.It is generally recognized that the SERS effect of 2D TMCs mainly originates from the photo-induced charge transfer（PICT）processes between materials and adsorbed molecules,which would change the polarizability of the composite system to increase the Raman scattering cross section of molecules selectively.The PICT-driven Raman enhancement is closely related to the band structure and electronic properties of 2D materials.The properties of 2D TMCs were susceptible to various interface effects due to the low-dimensional characteristics.Exploring the relationship between the interface effects of 2D TMCs and their SERS activity would provide a deeper understanding and new possibility for the design of 2D TMCs sensors.Therefore,this paper focus on the study of various interface effects to improve SERS performance and extend applications of 2D TMCs.Our studies are outlined as followings:1.The influence of interlayer interface on SERS performance of 2D TMCs was explored by using 2D Pt Se₂ and Re S₂ with different numbers of layers as the research objects.Both experimental and DFT simulated results unveil that the layer-dependent SERS effects of 2D TMCs mainly depend on the interlayer coupling.For 2D TMCs with strong interlayer interactions,like Pt Se₂,on the one hand,the properties of the multilayer structure are significantly altered by the interlayer interaction when the layers are added,which includes the contraction of the electronic band gap and the decrease of the exciton energy,working together to impede the exciton resonance process.On the other hand,the interlayer interaction changes the charge distribution inside the TMCs,making the coupling between the surface and molecules become weak with the increase of layers.2.The influence of heterojunction engineering on SERS performance of 2D TMCs was explored.we designed and fabricated mixed-dimensional van der Waals heterojunction of Sn Se₂/Re S₂ nanowalls（SRNWs）to realize ultrasensitive molecular detection and signal screening for specific probe molecules.For one thing,the coupling of Sn Se₂ and Re S₂ NWs can improve the separation of electron–hole pairs,which can strengthen the transmission of charge to enhanced the PICT process between molecules and substrate.For another,the quasi optical cavities of Re S₂ nanowalls can enhance the intensity of near-field light.These synergistic effects could significantly improve the SERS performance.3.The influence of substrate-induced interfacial electron-phonon coupling（IEPC）on SERS performance of 2D TMCs was investigated.Taking monolayer Mo S₂ based on different insulating substrates as examples,we revealed the role of IEPC on SERS performance of 2D TMCs through the nonadiabatic molecular dynamics simulation and transient spectroscopy.The stronger IEPC accelerated the nonradiative recombination of photocarriers in 2D TMCs,inhibiting the PICT between 2D TMCs and molecules and leading to the decline in SERS performance.The stronger IEPC was more sensitive to temperature.The IEPC weakened with the decrease of temperature,and the SERS performance of 2D TMCs increased significantly.4.The influence of metal hybrid interface on SERS performance of 2D TMCs was explored.We fabricated VSe_2-xO_x@Pd sensors by assembling Pd clusters on oxygen-doped VSe₂nanosheets.The significantly improved SERS performance of the VSe_2-xO_x@Pd sensors was demonstrated by modulating the metal-support interactions（MSI）.The designed MSI offers efficient charge exchanges and enriched density of state near the Fermi level of VSe_2-xO_x@Pd to promote the PICT from Pd to the adsorbed molecules,and consequently enhance the SERS signals.The excellent SERS performance of VSe_2-xO_x@Pd enables real-time tracking of the intermediate products of Pd-catalyzed coupling reactions,offering an ideal platform to investigate the charge transfer resonance effects on heterogeneous catalytic reactions.