Synthesis And Characterization Of Two-dimensional ?-Ga₂O₃ Nanosheets And WS₂ Arrays,WS₂-MoS₂ Heterojunction Arrays

The discovery of graphene in 2004 has caused more and more attentions and researches on two-dimensional materials.Due to the ultrathin thickness and atomic-level flat surface,two-dimensional materials have special mechanical,electrical,optical,and thermal properties which are not absent in bulk materials.In recent years,a variety of new two-dimensional materials and their synthesis methods have continuously emerged,and their special properties gradually discovered.What's more,different types of heterojunctions can be formed between two-dimensional materials,not only their chemical composition but electronic structure are highly adjustable.These progresses have brought a foundation for the applications of two-dimensional materials in integrated circuits and flexible devices.Compared with other two-dimensional materials,ultrathin metal oxide(MO)has a larger dielectric constant and band gap.The diversity of chemical composition,crystal structure and easy-to-form oxygen defects make ultra-thin metal oxides have highly adjustable,it has a wide range of applications in electronics,optoelectronics and electrochemistry.Two-dimensional transition metal dichalcogenides(TMD)have a pivotal position in the two-dimensional material family because of their suitable and adjustable band gap and rich physical and chemical properties.The superior electrical properties make the TMD-TMD heterojunctions also play an important role in electronic devices,which are used in various types of diodes,photodetectors and field effect transistors.The arraying of large-scale TMD and its heterojunctions is a feasible way to realize the integration of TMD electronic devices,which will bring hope to the applications of TMD in the field of large-area integrated circuits.Based on the above considerations,the main researches content of this thesis are as follows:(1)By thermally evaporating metal gallium,Ga₂O₃ crystals are obtained firstly;and then ultrathin Ga₂O₃ nanosheets are obtained by mechanical peeling method.Optical microscope(OM)and atomic force microscope(AFM)studies have found that the nanosheets have rectangular or parallelogram geometric features,and the thinnest thickness is 8 nm.Raman spectroscopy,X-ray diffraction(XRD)and selected area electron diffraction(SAED)studies have found that Ga₂O₃ nanosheets are monoclinic crystals with high crystalline quality.X-ray energy spectrum analysis(EDS)showed that the Ga/O atomic ratio in the sample is 2:3,which is close to the stoichiometric ratio,and is uniformly distributed in the nanosheets.?-Ga₂O₃ field-effect transistors(FET)have good gate control performance.The forward turn-on characteristic shows that?-Ga₂O₃ is an n-type semiconductor with a switch ratio of up to 10⁸,a subthreshold swing of 150 m Vdec^-1,and an electric mobility of 10 cm²V^-1s^-1.(2)The patterned WS₂ array was fabricated by the combined mothed of laser-thermal etching technology.With the growth principle of WS₂,the shape of the WS₂arrays were adjusted and Mo S₂ epitaxially grew the periphery of the WS₂ arrays to prepare WS₂-Mo S₂ lateral heterojunction arrays.OM,AFM,PL and Raman spectra show that the boundaries of WS₂ arrays and WS₂-Mo S₂ heterojunction arrays are clearly distinguishable.Scanning transmission electron microscopy(STEM)observed that the heterojunction has an atomic-level sharp interface.The forward turn-on current of the heterojunction FET shows the n-type semiconductor behavior of the heterojunction,and the on-off ratio is as high as 10⁶.