The Growth Of CrTe₃ Thin Film And The Construction Of CrTe₂/Bi₂Te₃ Heterojunction

Since the advent of graphene,two-dimensional van der Waals layered materials have been researched in recent years due to their excellent properties and broad prospects.Magnetism in two dimensions has long been at the heart of numerous theoretical,experimental and technological advances,such as the study of topology,the manipulation and detection of spin.Two-dimensional magnetism also has a wide range of applications in future memory devices.Therefore,it is particularly important to find and synthesize new two-dimensional materials.In this thesis,we have prepared Cr Te₃ thin films and Cr Te₂/Bi₂Te₃ heterojunctions by molecular beam epitaxy,and characterized them using a low-temperature scanning tunneling microscope.The main conclusions are as follows:(1)Cr Te₃ single crystal exhibits antiferromagnetic properties,with a transition temperature of 55 K.Theoretical calculations show that the single-layer Cr Te₃ film still exhibits antiferromagnetic order.In order to explore its single-layer magnetic properties experimentally,We use highly oriented pyrolytic graphite(HOPG)as the substrate,and use molecular beam epitaxy to grow single-layer and double-layer Cr Te₃ films.Through STM characterization,we found that the morphology of Cr Te₃ presents zigzag pattern.The electronic states are periodically arranged in space,and the period is the same as that of the zigzag pattern on the surface.The electronic state has an energy gap near the Fermi surface,and the size of the energy gap will gradually decrease with the increase of the layer thickness,and it will also be affected by the boundary and surrounding Cr Te₂ regions.Cr Te₃will have domain boundaries at different domains and boundaries,and the energy gap at the domain boundaries will be greatly reduced,which is related to the length of the domain boundaries.Through the K doping experiment,it is shown that doping K will reduce the energy gap of Cr Te₃.Through spin-polarized scanning tunneling microscope measurement,there is no single-layer Cr Te₃ ferromagnetic or antiferromagnetic signal.(2)It is found that there is a topological Hall effect on the Cr₂Te₃/Bi₂Te₃ heterojunction.They believe that this is a signal of magnetic skyrmions.But so far,no magnetic skyrmions have been characterized in real space.In order to find and characterize skyrmions in real space,We use graphene as a substrate and use molecular beam epitaxy to grow a Bi₂Te₃film.Then we grow a Cr Te₂ film on the Bi₂Te₃ film to construct a Cr Te₂/Bi₂Te₃heterojunction.Through STM characterization,it is found that the Cr Te₂ film is embedded in the inside of the Bi₂Te₃ film,and there are three areas on the surface,the Bi₂Te₃ film,the multilayer Cr Te₂ area,and the moirépattern area.After measurement,the moirépattern area is also Cr Te₂,and whether the moirépattern can be formed depends on the growth of Cr Te₂on different Bi atomic layers of the Bi₂Te₃ film.By characterizing its electronic state,we found that the electronic state of the Cr Te₂ sample grown on the Bi₂Te₃ film is the same as that on the graphene.Through spin-polarized scanning tunneling microscope measurement,no trace of skyrmions was found.