Preparation and Photoelectric Performance of ReS2 Nanomaterials

Author:Xu Xiang

Supervisor:bai jin tao


Degree Year:2019





In recent years,as the deepening research of graphene which is a representative of two-dimensional layered nanomaterials,many graphene-like two-dimensional layered materials have attracted extensive attention.ReS2,the transition metal dichalcogenides(TMDs),is one of the graphene-like two-dimensional layered materials.Due to the fact that ReS2 possesses a lot of unique physical and chemical properties which are different from the tranditional TMDs(such MoS2 and WS2),firstly,ReS2 always displays a direct band gap from bulk to monolayer;secondly,ReS2 has strong in-plane anisotropy;thirdly,the optical and electrical properties of ReS2 almost don’t change with the increasing of its layers.However,most previous studies on ReS2 only focused on its mechanical properties and linear optical properties,while there are still some uncertain nonlinear optical properties and photoelectrochemistry properties of ReS2 waiting to be reveal.Based on this,this paper focuses on the performance and application of ReS2 in nonlinear optical property and photoelectrochemical,and carries out the following works:(1)Fabrication and transfer of ReS2 films and nanosheets.We discussed various of preparation and transfer methods of ReS2 films.First of all,high-quality layered ReS2 were fabricated by the most convenient mechanical exfoliation method.Secondly,in orde to meet the requirement of ReS2 area in subsequent experiments,liquid phase exfoliation method combined with vacuum filtration transfer method were used to fabricate ReS2 films in N-methylpyrrolidone(NMP)solution.Finally,we did some improve by summarizing the deficiencies in the exfoliation experiment:based on the mixed enthalpy theory,the optimal ethanol concentration for exfoliating ReS2 was found,ReS2 was greenly and efficiently exfoliated.We obtained ReS2 films with controllable thickness and area by electrophoretic deposition method.Raman spectra,TEM,AFM,XRD,XPS,and visible absorption spectra were used to study the quality of those ReS2 films.These works pave the way of subsequent research and application of ReS2 in nonlinear optics and photoelectrochemistry,and also provide a guide for other nanomaterials in green and efficient preparation.(2)Nonlinear optical properties of ReS2 films.According to the theoretical basis and laboratory conditions,a set of femtosecond Z-scan measure system was built and then used to characterize the nonlinear optical properties of ReS2 films with different thickness.The results show that ReS2 shows obvious thickness dependent saturable absorption property which increases with the increasing of the material thickness.Important nonlinear optical parameters of ReS2 such as saturable absorption coefficient?NL,imaginary part of the third order optical susceptibilityIm?(3)and the figure of merit(FOM)were obtained by fitting the experimental data.It provides a theoretical basis for the subsequent application of ReS2 in the nonlinear optical applications.This part was published together with the fourth part in:Journal of Lightwave Technology(IF:3.652)(3)Research of ReS2 passively Q-switched fiber laser.Based on the saturable absorption property of ReS2,ReS2 nanosheets were transferred onto the fiber connector tip to form a saturable absorber,which was used as a Q-switched device to obtain stable output pulses with 1532 nm central wavelength,64 kHz maximum repetition frequency and 38 nJ maximum single-pulse energy in a Q-switched fiber laser at communication band of 1.5μm.This part of work,as the application of ReS2 in nonlinear optics,provides the experimental basis for the subsequent construction of mode-locked fiber laser.This part was published in an international journal:Optical and Quantum Electronics(IF:1.168).(4)Research of mode-locked fiber laser based on ReS2 saturable absorber.Firstly,the ReS2 saturable absorber was improved by summarizing the Q-switched experiment.Two ReS2 films were laid up and down a microfiber respectively to form a unique“sandwich”structure in order to increase the interaction of light and matter.Secondly,the saturable absorption property of the ReS2 saturable absorber were characterized by a home-made typical twin-detector measurement system.Finally,the device was placed in a mode-locked fiber laser at communication band of 1.5μm and obtained stable ultrashort pulses with 1563.3 nm central wavelength and 3.8 ps pulse duration.This part of work provides a new idea for the preparation of other nanomaterials based saturable absorbers.This part was published together with the second part in:Journal of Lightwave Technology(IF:3.652).(5)Photoelectrochemical properties of ReS2 films.ReS2 films were used as photoelectrodes and a 3-electrode photo-electrochemical cell was used as a reactor.Photoelectrochemical properties of ReS2 films with different thickness were studied and stable and fast photocurrent with sub-second reponse time was obtained.The calculations of electronic band structure,effective mass and the densities of stated of monolayer,2-layer and bulk ReS2 by first-principle give a theoretical explanation for the photoelectric response.This part of work not only provides experimental basis for the research of ReS2 photoelectrochemical properties but also lays the foundation for the manufacturing,research and application of photoelectric detectors and other solar energy conversion equipment based on ReS2.This part was published in:Materials and Design(IF:4.525).