Fabrication And Investigation Towards Two-dimensional Transition Metal Materials

Since the discovery of two-dimensional materials such as graphene,boron nitride and black phosphorus with appealing properties,predication and fabrication of novel two-dimensional materials have become an intense subject in both the researcch and industry fields.In order to compensate the intrinsic bottleneck of graphene in the application in semiconductors,two-dimensional transition metal materials have therefore become an emphasis due to their rich and tunable band gap characteristics.In the entire process of two-dimensional materials researches,there are mainly four research contents.Firstly,it is the successful predictions of the new materials'structures and properties by means of theoretical calculation.Secondly,by laboratory means,such as MBE,the new materials can be successfully prepared and their basic properties are in accordance with the prediction.Thirdly,with the help of large-scale preparation methods,such as PVD/CVD,it's committed to finding preparation methods capable of being put into industrial application.Finally,the mature materials can be successfully applied in practical applications,such as functional devices or catalytic energy storage.In this paper,we work on the three main contents of two-dimensional materials research:1.Preparation of new two-dimensional materials;2.Macroscopic preparation of two-dimensional materials and its'applications in practical;3.Study on the interfacial interaction between two-dimensional materials and substrates.In our study,with the help of molecular beam epitaxy growth method and physical/chemical vapor deposition growth method,two-dimensional materials were successfully prepared,and then various experiment were carried out to characterize the morphology structure and properties of materials,such as the synchrotron based GIXRD,photoelectron spectroscopy method,atomic force microscope and so on.DFT theoretical calculation was also combined to verify the rationality of the experimental conclusion,and the new materials application in practical fields such as photoelectric devices and energy conversion were also discussed.The main work is as follows:1)In the aid of molecular beam epitaxy growth,we report the preparation of NiSe₂,which has been predicted to be a promising candidate in the field of two-dimensional materials,by directly selenylation of the nickel substrate after epitaxial growth of selenium on a nickel foil.With the combination of photoelectron spectroscopy?PES?,X-ray diffraction?XRD?,scanning electron microscopy?SEM?and density function theory?DFT?calculations,it is possible to identify the phases transition among the previously reported stable Ni-Se phases and the ultimate formation of 1T NiSe₂.This work is conducive to regulating the fabrication of compounds between the interface of Se and Ni by annealing,and provides research strategies for the preparation of two-dimensional NiSe₂ materials.2)By utilizing the convenient physical vapor deposition,a simple and low-cost synthesis route is developed to fabricate high-quality orthorhombic MoO₃ crystals with single crystallinity and significant size.A combined characterization techniques of atomic force microscopy,X-ray photoelectron spectroscopy, synchrotron-based X-ray diffraction and Raman spectroscopy confirm the high quality of?-MoO₃ crystal from the point view of both electronic and physical structures.Compared to previous reports in literature,we demonstrate herein a rather simplified one-step approach with only the MoO₃ powder needed.In the end,corresponding electrochromic performance has also been tested which reveals high transmittance and remarkable optical properties which may broadens the potential applications of MoO₃ single crystal in nanosensors,photoelectric devices and so on.3)Based on the interaction mechanism research between two-dimensional materials and metal substrates,we investigate the growth of cobalt phthalocyanine?CoPc? on a Bi?111?surface and emphasize on the interface electronic structures utilizing photoelectron spectroscopy.Combined with density functional theory?DFT? calculations,we found that charge transfer from bismuth substrate to the molecule results in the emergence of an interface component in the Co 3p core level at lower binding energy,core-levels associated to the molecular ligand?C 1s and N1s?are less influenced by the adsorption.Charge transfer is shown to be mainly from the underlying bismuth substrate to the empty states located at the central Co atom in the CoPc molecules.This report may provide a fundamental basis to the on-surface engineering of interfaces for molecular devices and spintronics.