Synthesis And Electronic Structure Of Two-Dimensional Aluminum Antimonide And Bismuth(110) Thin Films

Since the discovery of graphene,two-dimensional(2D)van der Waals(vd W)layered materials have been a hot spot in various research fields.2D vd W layered materials contain rich physical properties and have excellent application prospects,thus it is necessary to explore and synthesize new 2D families to promote highly performant properties and device research.In this thesis,we fabricate two types of Al Sb and Bi(110)films(a verified 2D topological insulator)with different layer thicknesses and flat surfaces by using molecular beam epitaxy(MBE)growth method.We utilize scanning tunneling microscopy/spectroscopy(STM/STS)to characterize their atomic structures and electronic properties.The main results are followings:(1)Recently,a large member of Ga As-like traditional semiconductors are predicted to be energetically more stable as 2D vd W materials in energy,rather than their truncated 3D bulk counterpart.Here,we examine such proposals by growing Al Sb and In Sb ultrathin films on graphene covered Si C(0001)substrates with MBE.We characterize their structural morphology and electronic structure with STM and find that the atomic arrangement of Al Sb film at ultrathin limit is consistent with the proposed double layer honeycomb(DLHC)structure.Al Sb films exhibit an insulating gap of 0.93 e V,which is close to the theoretical gap of 1.06 e V in the proposed DLHC form,but contrasts with their gap value of 1.6 e V in 3D bulk form.However,In Sb,another theoretically proposed vd W crystal at 2D limit,robustly grows into islands of bulk structure and a 2×2 reconstruction of the(111)surface,irrespective of the thickness of the islands.Our study proves 2D vd W crystals,despite not fully agree with the theoretical predictions,can indeed form out of traditional 3D semiconductors at ultrathin limit,paving the way for in-depth study of their physical properties and nanoelectronics applications.(2)In recent years,the novel topological properties of 2D Bi(110),Bi(111),and omniplanar bismuthene have attracted extensive attention.Here,we use MBE to synthesize Bi(110)thin films by low temperature MBE growth.We observe the topological edge states of 3 ML Bi(110)with STS characteristics.By postannealing,the Bi(110)films tend to form elongated and higher nanoribbons,while the electronic structure gradually changes from semiconductor to metallic states.Further depositing Pb on the Bi(110)thin film at low temperature,we find that most Pb atoms tend to accumulate near the boundaries of the Bi(110)in the form of metal clusters,while just a small amount can randomly distribute on the surface of the Bi(110)thin film.Our results show that the Pb clusters have little effect on the bulk electronic structure of Bi(110)films.