Controllable Preparation And Growth Mechanism Of Germanium Diselenide And Germanium Selenide Nanostructures

The successful exfoliation of graphene stimulates a large number of research in two-dimensional（2D）atomic crystal materials.Many 2D materials,such as transition metal-sulfur compounds,topological insulators,and black phosphorus（BP）,have been extensively investigated.As a new member of 2D materials,BP has attracted significant attention due to its in-plane anisotropic structure.Compared with conventional in-plane isotropic 2D materials such as graphene and Mo S₂,the emergence of these unique anisotropic 2D materials greatly enriches the properties of 2D materials and provides a new degree of freedom to design and modulate electronic and optoelectronic devices.However,the weak stability of BP in the atmospheric environment has created great difficulties for the subsequent research and application of the relevant properties.As important Group IV-VI semiconductor materials,germanium diselenide（GeSe₂）and germanium selenide（GeSe）not only possess properties such as anisotropic electricity and optics induced by low-symmetry crystal structures but are also extremely stable in atmospheric environments.Therefore,it is extremely important and meaningful to study the controlled preparation of P-type semiconductors GeSe₂ and GeSe.The main research contents of this thesis are as follows:（1）Controlled preparation of GeSe₂ nanosheets and large-area nanofilms was achieved by chemical vapor deposition,and the morphologies and micro/nanostructure of the system were characterized.With the aid of computational fluid dynamics simulation,the influence of precursor concentration on the morphology evolution of nanostructures was studied under different vertical positions of substrates.The nonlinear optical properties of GeSe₂ nanofilm were studied by z-scan measuring.The saturation absorption and reverse saturation absorption properties of GeSe₂ nanofilm were demonstrated under different excitation wavelengths,which is expected to be further applied in the field of nonlinear optical devices.（2）Controllable preparation of GeSe thin film was realized by vapor deposition.Combined with systematic characterization methods,the important regulation of space-confined method in the growth process of GeSe flakes was studied,and the thickness of GeSe flakes was greatly reduced.The differences of GeSe growth modes induced by different types of substrates were studied.On the substrate surface with weak reactivity,the layered edge atoms of GeSe did not bond with the substrate and tended to grow laterally on the substrate surface.The in-plane anisotropy of GeSe thin films is studied by polarized Raman spectroscopy,which lays a foundation for its application in the fields of anisotropic optoelectronic devices.（3）On the basis of using the same precursor（high purity GeSe powder）,the planar structure of non-layered material Ge was realized.The growth mechanism of selective synthesis of GeSe₂,GeSe,and Ge low dimensional materials was investigated by systematic characterization and experimental results.In the absence of hydrogen,the precursor partially decomposes in the heating center,and the resulting Se molecule reacts with the undecomposed GeSe vapor molecule to form GeSe₂,which nucleates and grows on the downstream substrate.In contrast,hydrogen would preferentially react with Se molecules and inhibit the growth of GeSe₂ nanostructures,while the remaining GeSe and Ge molecules nucleated and grew on substrates at different temperature regions.