Study On Surface-Enhanced Raman Scattering Of TCNQ Derivative/MoS₂ Nanocomposites

Surface-enhanced Raman scattering（SERS）is an ultra-sensitive non-destructive detection technology and has been widely used in food and drug detection,biological and medical sensing.In recent years,the study of non-metallic SERS substrates based on chemical enhanced mechanism（CM）has gradually become a hot field of SERS.And the discovery of the organic semiconductor SERS substrate which possessing the unique advantages of various structures,sample and highly controllable synthesis and preparation and regulable photoelectric properties has opened up a new field of SERS substrate research.However,owing to the underdeveloped candidate materials and relatively low SERS sensitivity,the practical applications of SERS detection based on organic materials is still a challenge.Herein,we explored to further enhance the SERS sensitivity ofπ-conjugated fluorinated7,7,8,8-tetracyanoquinodimethane derivatives（F_nTCNQ,n=2,4）by utilizing charge localization effect induced by two dimensional（2D）MoS₂ flakes and the influence of the charge localization on the SERS activity of the organic/2D-inorganic（O/2D-I）nanocomposite materials with various surface structures prepared by changing the deposition time.In addition,the CT mechanism between the probe molecules and the substrate and the mechanism of the influence of deposition time on SERS property of O/2D-I substrates were verified through theoretical simulation.And the specific research contents are as follows:1.F_nTCNQ nanostructures are grown on 2D MoS₂ film by using the Physical Vapor Deposition（PVD）method.And the Scanning Electron Microscope（SEM）microscopy showed that F₂TCNQ/MoS₂ nanocomposite has a dense distribution of 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane（F₂TCNQ）nanoparticles on its surface,while F₄TCNQ/MoS₂nanocomposite has the isolated 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodime-thane（F₄TCNQ）nanoislands on its surface.And we explore the SERS sensitivity of the two nanocomposite heterogeneous materials by using the Methylene Blue（MB）as the probe molecule.The difference in the number of C-F bonds between F₂TCNQ and F₄TCNQ molecules resulted in the different charge transfer（CT）directions of the nanocomposite substrates,and which contributed to high SERS sensitivity of F₄TCNQ/MoS₂nanocomposites with high enhancement factor（）of2.531×10⁶ and a low lowest detection limit concentration（）of 10^-10 mol/L.It proved that the F₄TCNQ/MoS₂ nanocomposite had a good stability,uniformity and repeatability,which made it have a wide application prospect in SERS field.2.F₄TCNQ/MoS₂ nanocomposites with different surface nanostructures were obtained by changing the growth time.And the SEM showed that the size of the nanoisland structure on the surface of nanocomposites increased with the increase of deposition time,and its distribution density first increased and then decreased.The Kelvin Probe Force Microscopy（KPFM）and SERS results from the substrate with different surface structures showed that the nanostructure of F₄TCNQ could affect the binding ability of electrons transferred from the surface of MoS₂ and the local work function distribution on the surface of F₄TCNQ/MoS₂ nanocomposites was changed to show different SERS sensitivity.The optimal growth time of F₄TCNQ/MoS₂ was 7 min.