Optical Properties Of Monolayer Films Controlled By Electrical Methods

Two-dimensional materials have been applied in many fields.Among them,the transition metal sulfide monolayer or multilayer film can be obtained by the micro-mechanical exfoliation due to the weak van der Waals force between the layers and the strong covalent bond in the layer.It is expected to be widely used in the field of optoelectronics due to its advantages,such as band dependenced on the number of layers,strong photoluminescence?PL?and spin-valley coupling.To use its excellent characteristics to achieve applications,it must involve the regulation of its photoelectric properties.One of the most important control methods is the application of electric fields.However,the direction of regulating electric field introduced in previous work is mostly perpendicular to the film plane,and there are few reports about the regulation of lateral electric field.The direction of the electric field has a great influence on the nanoscale monolayer film.In view of the above problems,PL properties of WS₂ monolayer molecular films controlled by the electrical methods are studied in this paper.The WS₂ monolayer prepared by micro-mechanical exfoliation is transferred to the microperiod electrode structure by the dry transfer method.The variations of its PL spectra under different voltages are studied.The obtained results are as following:1.Combining simulation with experimental data,it is proved that the original electric field distribution will adjust after the composition of the electrode?the dimension are 30?m or 10?m?and the WS₂ monolayer.The electric field effect of the WS₂ monolayer will depend on the relative spatial position of the two and the orientation of the positive and negative electrodes.In the end,the PL spectra of the monolayer shows the obvious luminous behavior modulated by the electric field due to horizontal and vertical electric fields component simultaneously.2.The PL spectra of the sample assembled with the electrode and WS₂monolayer are measured under room temperature and low temperature,respectively.It is found that the PL spectra of neutral excitons,trion and bound excitons could be controlled by the bias obviously.The adjustment of energy level and the migration of carrier lend to the peak shift and variation of PL intensity.In addition,the effect of high-frequency alternating voltage driven surface acoustic waves?SAW?on the PL properties of films is studied.The SAW generated by the alternating voltage combine with the periodic electrod induces the spatial separation of the carriers,and reduction in PL intensity of films is related to the amplitude of the SAW.In summary,this paper use the micro-period electrodes to generate a horizontal electric field to modulate the PL spectra of WS₂ monolayer,and a 9 times reduction of the PL intensity could be observed.This achievement could be applied to the field of photoelectric,such as field effect transistors,photodetectors,flexible electronic devices and heterojunction devices.