Controlled Synthesis And Optical And Photoelectric Properties Of Metal Chalcogenides’ Ultrathin Nanostructures

Some graphene-like materials,including hexagonal boron nitride（h-BN）,transitional metal chalcogenides（TMCs）,transitional metal oxides,black phosphorus etc.,have drawn great attention since the discovery of graphene in 2004.The particular characteristics of the structures of these materials grant them scale effects,quantum effects and much other specificity,resulting in their unique physical and chemical characteristics attracting researchers to discover.One of them is photoelectric property.This paper covers the well-controlled synthesis,optical and electrical properties of tin sulfide（SnS₂）,tin diselenide（SnSe₂）,zirconium trisulfide（ZrS₃）and zirconium triselenide（ZrSe₃）.First,two-dimensional structures of tin dichalcogenides（SnX₂,X= S,Se）were obtained by liquid synthesis while one-dimensional ZrS₃ and ZrSe₃ nanowires/nanobelts were fabricated through solid synthesis.Then the photodetectors based on SnS₂ were assembled in the assistance of microfabrication technique and their photoelectric performance was measured.In addition,the nonlinear optical properties of the four materials were measured and analyzed by means of Z-scan techniques.The contents are as follows:1.Ultrathin SnS₂ nanosheets were synthesized by a time-controlled simple ultrasonic method,and had their morphology,chemical constituent,structure and thickness gauged.Then they were fabricated onto a SiO₂/Si substrate to form a nanosheet-based phototransistor which exhibits a broad range photoresponse from 254 to 980 nm,dependence of photocurrent on optical power and wavelength with a best response at 532nm,fast-response,and long-term stability.Under illumination of 532-nm light with an optical power of 19.3mW/cm²,the photoswitch current ratio（PCR）is about 8.7,while the photoresponsivity and response time are 0.65mA/W and 0.36s,respectively.We also investigated its photoelectrical capacities in different working atmosphere,discovering its better performance in vacuum.2.SnS₂ nanosheets and SnSe₂ hexgonal nanosheets were prepared by a facile ethanol thermal and hydrothermal method,respectively.The size,morphology,structure and optical features of the as-prepared samples were characterized by scanning electron microscope,X-ray diffraction,high resolution transmission electron microscopy and ultraviolet visible absorption spectroscopy,respectively.The nonlinear absorption performance of SnS₂ and SnSe₂ dispersions were investigated by open aperature Z-scan technique with nanosecond pulse and picosecond pulse at 532nm for the first time.Besides,we also studied the influence of the input energy on nonlinear optical properties of SnS₂ and SnSe₂ nanosheets dispersions,which indicates that SnS₂ and SnSe₂ dispersions exhibit saturable absorption behavior under low input energy and the changeover from SA to RSA by adjusting input energy.And Z-scan measurement reveals that SnS₂ nanosheets dispersions exhibit RSA response under picosecond laser pulse,which is in contrast to the SA observed in the SnSe₂ nanosheets dispersions resulted from different band gap-The RSA.performance coupled to the smaller optical limiting threshold（0.23J/cm²）makes SnS₂ nanosheet a promising 2D material for protecting sensitive optical component or eyes from laser-induces damage.And the SA response indicates SnSe₂ nanosheets are more suitable to be applied in passive mode lockers and optical switches.3.ZrS₃ and ZrSe₃ nanobelts were directly synthesized via chemical vapor transport method.The third-order optical nonlinearities of ZrS₃ and ZrSe₃ dispersions are studied by using Z-scan technique with nanosecond pulses at 532nm,and we studied the nonlinear absorption properties of ZrS₃/graphene composite,and the effects solvents on the nonlinear optical performance of ZrSe₃ dispersion are also investigated,and the optical limiting property of ZrSe₃ dispersion were measured by using picosecond laser pulse at 532nm.Experimental results show that the two compounds have a strong reverse saturable absorption property in the nanosecond regime.The composites exhibit an enhanced nonlinear absorption response at the same input energy.In addition,nonlinear optical performance of ZrSe₃ depends on organic solvent dispersions,which can be ascribed to the different linear absorbance and the value of the local field correction factor.Meanwhile,the optical limiting threshold of ZrSe₃ is 2.2J/cm² under picosecond laser pulse.