Controllable Preparation And Optoelectronic Properties Of Rhenium-based Transition Metal Sulfide Heterojunctions

Two-dimensional(2D)transition metal chalcogenide(TMDs)is a kind of layered material combined with weak interlayer interaction van der Waals force.Influenced by the quantum confinement effect,TMDs materials exhibit excellent optical and electrical properties,and thus have potential application in the field of optoelectronic and electronic devices.The heterojunction formed by stacking or matching of different TMDs materials not only enriches the two-dimensional TMDs family,but also shows many excellent properties different with any single semiconductor material However,most of the heterojunctions studied are based on hexagonal structure(2H)TMDs currently,have little research on the distorted octahedral(1 T')heterojunction with different interface structures and properties.Among them,the group VII-TMDs material,such as Re-based transition metal chalcogenide ReX2(X=S,Se),its great characteristic is the 1T' structure with lower lattice symmetry and weak interlayer coupling and unusual 2D in-plane anisotropic optical and electrical properties.Therefore,the interface structures and properties of the IT' heterojunction based on ReX2 will be different from that of 2H TMDs heterojunction.In addition,the strong in-plane anisotropy of ReX2 materials makes IT' heterojunction one more degree of freedom,and it is expected to construct some new optoelectronic devices which only existed in the concept.In this paper,we realized the controllable preparationon of the diverse interface structures and linear dichroism of IT' ReS2-ReSe2 lateral heterojunction synthesized by using two-step CVD growth method.For WO3 and ReO3 precursor with a large difference in the volatilization temperature,a large-area and high-lattice-quality 2H-1 T' WS2-ReS2 heterojunction has been synthesized by one-step CVD growth method under the action of switching H2.Finally,we designed and constructed the novel photoelectric device based on those heterojunction materials,and systematically explored their optical and electrical properities.The specific contents of this paper mainly divided into the following two parts:(1)Diverse atomically sharp interfaces and linear dichroism of IT' ReS2-ReSe2 lateral heterojunctionIn this work,the 1T' ReS2-ReSe2 heterojunction was synthesized on mica substrate by two-step CVD growth method.During the preparation of the heterojunction,we controlling the growth order of ReS2 and ReSe2,temperature,volatilization rate of the Re source and the time of H2 to solve the problems of sample crazing,alloying,and dendritic growth.The high-resolution scanning transmission electron microscope imaging results show that the ReS2-ReSe2 heterojunction has a high lattice quality and a sharp atomic interface structure.In particular,the b-axis of ReSe2 and ReS2 with 0°,1200 and 180°,which forms three interface structures and corresponding to three different epitaxial growth modes.The density functional theory calculation shows that the interface formation energy is the lowest when the b-axis of ReSe2 and ReS2 with 0°.Finally,we construct a photodiode device based on the ReS2-ReSe2 heterojunction with large rectifier ratio,and obtained polarization dependent photodiode characteristics in the two-dimensional in-plane heterojunctionfor the first time.(2)Controllable preparation and optoelectronic properties reserach of 2H-1T' WS2-ReS2 heterophase junctionBased on the different effect of H2 on the growth of WS2 and ReS2,we propose an innovative method to synthetise the heterojunction via one-step method by controlling the growth order by hydrogen.The STEM images show that the WS2 and ReS2 on both sides of the interface have high quality 2H and IT' structure,respectively,form the sharp and atomic level one-dimensional heterophase interface.The above results show that the switching effect of H2 in the growth of the WS2-ReS2 heterojunction.In addition,the external WS2 consisting of multiple crystal domains with the same orientation in the WS2-ReS2 heterojunction.The selective area electron diffraction patterns and the second harmonic generation images of the external WS2 show the same lattice orientation and nearly no grain boundary format in the WS2-ReS2 heterojunction.The SEM images of WS2-ReS2 heterojunction at different growth time show that the nucleation and growth of WS2 along the ReS2 b-axis.It means that the structure of ReS2 has a certain induction effect on the orientation and growth of WS2.Finally,we propose the model of WS2 epitaxial growth along the edge of ReS2.