Research About Surface Plasmon-Enhanced Optoelectronic Properties Of Monolayer MoS₂

Molybdenum Disulphide?MoS₂?is a two-dimensional nanomaterial with excellent physical and chemical properties.By adjusting the number of layers,a band gap width of1.3¹.8 eV can be obtained.The MoS₂ field-effect transistor?FET?owns reasonable electron mobility and superior on/off ratio?>10⁷?which is able to be the alternative materials of silicon-based semiconductor.As for MoS₂ photodetector,an ultra-high gain arsing from the separation of photo-generated carriers can also be observed.By adjusting the number of MoS₂ layers,different monochromatic light can be detected in the visible range.However,the absorption rate of single-layer MoS₂ is less than 8%in the visible range,which limits the key efficiency of the detector.To address this problem,plasmonic materials had been employed to address the poor light absorbance.By integrating plasmonic materials with monolayer MoS₂,the key efficiency of the detector can be greatly enhanced.In this regard,the field-effect transistor is used as a research model to study its photoelectric performance.On this basis,the Au@SiO₂ particles were spin-coated into the channel of the device and photocurrent of corresponding device was greatly enhanced.Furthermore,plasmon hot electron doping effect inside monolayer MoS₂ excitonic and associated trionic emission behavior under the influence of back-gate voltages were explored and revealed with the introduction of Au nanoparticles and periodic Au nanodisk arrays.Monolayer MoS₂ films were exfoliated by using the scotch-tape based cage technique and directly transferred onto silicon substrate with 300-nm-thick layer of SiO₂.The electrodes were fabricated using EBL approach followed by Ti/Au?5 nm/45 nm?electrodes deposition.The electronic properties of MoS₂ field-effect transistor were tested by a semi-automatic probe station after 2 h annealing step at 200?in an Ar atmosphere.The output characteristic curves were linear and can be modulated by back-gate voltages effectively,indicating an ohmic-like contact.The transfer characteristic curves demonstrated that MoS₂ field-effect transistor is N-type one.Au@SiO₂ core-shell nanoparticles were prepared by citric acid-reduced gold salt solution method,following by spin-coating into the channel of monolayer MoS₂photodector.Attributing to the localized surface plamon resonance generated by Au@SiO₂ core-shell nanoparticles,photocurrent of corresponding monolayer MoS₂photodector can be significanty enhanced.Owing to the simulation in the distribution of spatial electromagnetic field around a single Au@SiO₂ core-shell nanoparticle,hot spot effect was illustrated.Moreover,photoluminescence spectra at ultra-low temperature were employed to research the electrical regulation of excitonic and associated tronic emission in monolayer MoS₂.By experiment,clear blue shifts of the characteristic spectral peaks of quasi-particles in monolayer MoS₂ were obtained by combining Au nanoparticles or periodic Au nanodisk arrays with monolayer MoS₂.We also achieve electrical control of the bingding energies of quasiparticles in monolayer MoS₂ when coupling with localized surface plasmon resonance.Finite difference time domain simulation reveals the spatial electromagnetic filed distribution around Au nanodisk and monolayer MoS₂,with enhanced-absorbance in visible range,respectively.It can be referred that the coupled oscillators and hot electrons induced doping effect can co-ordinarily cause the blue shifts of excitonic and associated trionic spectral peaks.The ability to control the optical properties of such a coupled trion-plasmon system by electrostatic doping dynamically opens a platform for designing next generation optoelectronic and valleytronic applications.