Investigation On Nonlinearity And Ultrafast Spectroscopy Of Novel Two-dimensional Materials

In two-dimensional materials,the behavior of electrons is bound within two-dimensional plane,so the wave function describing its behavior will change.When the thickness of the material is reduced to close as the exciton Bohr radius,the quantum confinement effect will modify its continuous electron energy band to discrete energy level,and the lower dielectric screening effect will cause the excitons to be more firmly bound by the Coulomb effect.These effects will cause the photophysical phenomenon in two-dimensional material significantly differing from that of bulk morphology,such as "phonon bottleneck" effect,carrier multiplication effect.Due to the atomic thickness,the strong light-matter interaction triggers unique nonlinear optical properties.The dynamic process of the carrier can be controlled by its size effect,temperature,external electromagnetic field,bias voltage and charge transfer at the heterojunctions interface,etc.The unique carrier behavior of the two-dimensional material and the controllable methods make it show great application potential in optoelectronic devices,especially micro-nano devices.Thanks to graphene's broadband nonlinear absorption and ultrafast carrier dynamics,broadband saturable absorbers and ultra-fast optical modulators are constructed.Due to the tunable direct band gap structure,in-plane anisotropy and ultra-high carrier mobility,high-performance black phosphorus photodetectors are realized.Due to reduced dielectric screening,strong Coulomb interaction makes the excitons tightly bound,triggering complex many-body luminescence in transition metal sulfides(TMDs).The ultralong carrier lifetime,diffusion length,and low non-radiative recombination in 3D and 2D perovskites have gained tremendous attention in solar cells and light-emitting devices(light emitting diodes(LEDs),nanolasers).Therefore,it is of great significance to study the basic behavior and controllable characteristics of intrinsic photoinduced species in two-dimensional materials.In this article,we will introduce the unique photoproduct dynamics and nonlinear optical properties in two novel two-dimensional materials.(1)First,the basic process of optical nonlinearity and carrier dynamics caused by photo-excited carriers and their applications in various optoelectronic devices are reviewed.Introduce the Z-scan and P-scan methods for characterizing nonlinear properties,and time-resolved spectroscopy techniques to study carrier behavior,especially femtosecond-resolved transient absorption spectroscopy technique.(2)Using Z-scan and transient absorption spectroscopy techniques to study the third-order nonlinear characteristics and intrinsic carrier behavior of black phosphorous-analogue binary two-dimensional Tin sulfide(SnS).Experimental results show that SnS has broadband saturation absorption characteristics and ultrafast carrier dynamics,indicating that it can be used in passive mode-locking and ultrafast optical modulators.(3)The effect of size on the nonlinearity and carrier dynamics of SnS nanosheets was studied.When the thickness of SnS nanoplates is reduced,the third-order nonlinearity is significantly enhanced due to the size-dependent quantum confinement effect,and the slower carrier cooling process for the phonon bottleneck effect.(4)Based on the principle of nonlinear absorption is an effective means to realize optical non-commutative transmission and photonic diodes.The theoretical simulation and experimental methods are combined to study the saturation absorption characteristics based on SnS and copper antimonene sulfide(CAS).The optical asymmetric transmission achieved by the reversely saturable absorption characteristics of quantum dots has a maximum forward and reverse non-commutative transmission coefficient of 2.0,which lays the foundation for the development of optical diodes based on nonlinear effect.(5)The kinetic process of MXene's broadband photoinduced has been systematically studied.Specifically,the dynamics of non-equilibrium carriers between bands in the ultravioletvisible band,and the dynamics of surface plasmon(SP)of transversal and longitudinal modes Among them,the lifetime of transversal SP is less than 100 fs,while the transition between intrabands and the lifetime of longitudinal SP reach the order of ns.Our work provides the necessary reference for the development of wide-band optoelectronic devices based on MXene.