Spectroscopic Study Of Two-dimensional WSe₂ Heterostructure

With the continuous progress of the times,people’s demands for device size miniaturization and function integration are constantly increasing.This trend is bound to pose a number of scientific challenges,among which finding new materials that can meet or solve these questions have always been the direction of scientific research workers.In 2004,the successful separation of graphene breaking a new world in the field of two-dimensional atomic crystal materials.Prior to this,most physicists believed that thermodynamic fluctuations did not allow any two-dimensional crystals to exist at a finite temperature.Therefore,the discovery of graphene immediately shocked the condensed matter physics community,so that this two-dimensional material with atomic layer thickness quickly appeared in the research topics of many scientists.In the past ten years,a large number of two-dimensional materials have been excavated and their respective physical and chemical properties have also been fully excavated and confirmed forcefully,from the initial graphene to the later hexagonal boron nitride and transition metal sulfides,and then the two-dimensional magnetic and ferroelectric materials that have emerged in the past few years,the family of two-dimensional material systems are constantly being expanded,and have a wide range of applications in many fields.In recent years,researchers have focused their attention on how to control these two-dimensional materials,among which the construction of heterogeneous or homogeneous structures is one of the most important methods.In this heterostructure at the atomic level,the coupling effect on the interface and the behavior of carriers have a great influence on the modification of materials and the discovery of new phenomena,which determine the new properties and potential applications of the materials in the new structure.At present,it is not clear whether there will be interactions between layers in this structure and what factors will affect these interactions.In short,we do not have a thorough understanding of the coupling mechanism on this interface.Therefore,this article combines static photoluminescence spectroscopy and other spectroscopy techniques to conduct an in-depth and systematic discussion on the influencing factors or coupling mechanisms of the interaction between the heterostructure layers.The detailed discussion results of the paper are as follows:1.The effect of annealing on the photoluminescence properties of two-dimensional WSe₂/BN heterostructures.The thin-layer sample preparation method of traditional mechanical peeling was used to obtain a few-layer boron nitride sample and a single-layer WSe₂sample on the Si O₂and PDMS flexible substrates,and then the single-layer WSe₂sample on the PDMS was stacked on the two-dimensional microscopy platform.On the surface of the boron nitride sample,the heterostructure sample has a single layer and a heterostructure region to achieve a comparison between a single layer and a heterojunction.The photoluminescence spectra of the samples were collected at different temperatures,and it was found that excitons dominated the luminescence performance of the samples at room temperature,but the heterojunction region would be dominated by defects at low temperatures.After annealing the samples,it was found that the luminescence phenomenon of the heterojunction gradually recovered to be consistent with the luminescence phenomenon of the single-layer sample at different annealing temperatures.When the annealing temperature reaches 300°C,the luminescence of the heterostructure region is basically the same as that of the single layer.Conclusions are obtained:1)The construction of heterostructures will cause huge changes in the photoluminescence peak intensity.2)Annealing can eliminate the influence of extrinsic factors between layers caused by the construction of heterostructures.2.Study on photoluminescence spectra based on WSe₂/Fe₃GeTe₂heterostructureBy constructing the WSe₂/Fe₃GeTe₂heterostructure and using photoluminescence spectroscopy and microscopic spectroscopy,a systematic and in-depth study of the changes in optical properties brought about by the interaction between the layers of the heterostructure has been carried out.We use conventional mechanical peeling to obtain Fe₃GeTe₂samples with different thicknesses,and build a series of samples with different thicknesses in the same stacking method as single-layer WSe₂.The thickness order is calibrated by measuring the different transmittances of Fe₃GeTe₂by a micro spectrometer.Finally,the photoluminescence spectra of different regions of the series of samples were collected.It was found that the heterostructures composed of Fe₃GeTe₂with different thicknesses showed blue shift and red shift respectively compared with the emission peak of monolayer WSe₂in the thicker and thinner case.When we further collected variable temperature data on heterogeneous structure samples,we found that the above mentioned red shift and blue shift phenomenon changed significantly around 220 K,which was manifested in the increase in peak shift.Due to the repeated occurrence of the above phenomenon,we preliminarily believe that there is an interlayer coupling in the WSe₂/Fe₃GeTe₂ heterostructure.