The Study Of Ultraviolet-ozone Modification And Optical Properties Of Two-dimensional Materials

Two-dimensional layered materials have attracted great attention because of their unique properties and promising applications,e.g.transition metal dichalcogenides?TMDs?and black phosphorus.However,it is found that the properties of two-dimensional layered materials are strongly dependent on their thicknesses and the defects inside.With the increase of layer numbers,molybdenum disulfide will change from direct band gap to indirect band gap,and with the decrease of luminescence efficiency.The introduction of defects in the preparation process will also affect the properties of the material.It is found that the surface modification of samples by plasma,laser irradiation and ultraviolet-ozone treatments can improve the performance of the samples.However,the surface of the sample treated by laser irradiation is not uniform,and plasma treatment would damage the sample.Ultraviolet-ozone modification has gradually attracted the interests as a moderate and controllable technique.This paper mainly focuses on the optical properties of two-dimensional layered materials under ultraviolet-ozone treatment,and the main research contents and achievements are summarized as follows:1?The optical properties of ultraviolet-ozone treated MoS₂ is studied at first.The results of optical contrast,Raman spectra,PL spectra and surface morphology of samples with different processing time prove that a self-limiting layer has been produced on MoS₂ through ultraviolet-ozone treatment.The thickness of this self-limiting layer is 2.4 nm,and it can prevent the further oxidation of MoS₂.2?The SERS of MoS₂ after ultraviolet-ozone modification is studied.R6G molecule of10^-55 M is chosen as probe molecule.It is found that the Raman signal of R6G molecule on MoS₂ increases first and then decreases with the increase of ozone treatment time.On the treated monolayer,bilayer and four layers MoS₂,the Raman signal intensity of R6G molecule can be enhanced up to 4 times,6 times and 57 times as compared to that on intrinsic sample,respectively.However,after the formation of the self-limiting layer,the Raman signal of the R6G molecule decreased obviously.This is mainly due to the fact that the ultraviolet-ozone treatment first induces the P-type doping of MoS₂ and improves the charge transfer between R6G molecule and MoS₂,so that the Raman signal of R6G molecule is enhanced.However,the self-limiting layer can't enhance the Raman signal of R6G molecule,which causes the weakening of SERS effect.Therefore,ultraviolet-ozone modification can be used as an effective means to regulate the SERS effect of MoS₂.3?The thickness of black phosphorous is modified by ultraviolet-ozone modification.By controlling the oxidation time of ultraviolet-ozone,the thickness of black phosphorus can be accurately controlled from bulk to few layers.It is found that in the process of thinning,a new fluorescence peak appears in the visible light range?620 nm?,and its intensity increases with the increase of treatment time.This peak is related to the presence of P_x O_y.At the same time,the oxidation layer obtained by ultraviolet-ozone can improve the stability of black phosphorus in air.