| Heterostructures has become one of the focuses in the field of physics and materials because of its excellent performance and wide application in the fields of light-emitting diodes,high electron mobility transistors and tunneling field effect transistors.Normally,based on the alignment of their bands,heterostructures can be divided into three classes,i.e.,type I(symmetric),type II(staggered),and type III(broken).However,some special heterostructures do not belong to the above three types.In recent years,a new class of heterojunction has been discovered.A well-known example is the heterostructure of STO and LAO.Although both STO and LAO are insulators with wide-band gap,high-mobility electron gas will be generated at the interfaces when they are spliced into a heterostructure.The electron gas appeared in heterostructure has brought a lot of excellent properties such as superconductivity and magnetism,which makes it possess a broad application prospect.As a low-dimensional analogy,when such a heterojunction is extended to a two-dimensional(2D)heterojunction,there may also be the presence of electron gas at the resulting heterojunction.More importantly,since graphene was born,2D materials have become a new hot spot.At present,dozens of 2D materials have been successfully prepared,and people have successfully prepared 2D Heterostructure,such as Mo S2/WSe2longitudinal heterojunction,graphene/BN transverse heterojunction and so on.However,no electron gas has been reported.Therefore,the first part of this paper focuses on the mechanism of electron gas generation in two-dimensional system.Taking Mo2S3 and Mo S2 heterojunction as an example,we systematically explored the electronic properties of heterojunction.When we extended the Mo2S3/Mo S2heterojunction to the entire transition metal sulfide(TMDCs),we found that although Pd2S3 can also be obtained from Pd S2,Pd S2 has a different structure from other 2D TMDCs.Therefore,the structure of Pd S2 is preliminarily discussed in the second part.The research contents of this paper are as follows:(1)Firstly,we calculate the electronic properties of monolayer Mo2S3 and Mo S2respectively,which are both semiconductor structures.Then we constructed heterostructures of different widths and calculated the electronic properties respectively.Our results show that with the increase of the width m of the heterostructures,the electronic properties of these heterostructures will change from semiconductor to metal.By analyzing the layer-by-layer projected state density,we reveal that the physical mechanism of the transition behavior is the charge transfer caused by the interface polarity discontinuity.(2)We have calculated the electronic properties of the Pd S2 structure of the 1T phase,2H phase and the newly generated phase experimentally.By building different models,we successfully separated the splitting energy and hybridization energy of the crystal field.Our results show that the splitting energy of the crystal field has little effect on the energy between the different structures of Pd S2,and hybridization is the main factor affecting its stability. |
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