Synthesis Of Transition-metal Dichalcogenide Nanostructures With Tunable Dimensionality

Two-dimensional layered transition metal dichalcogenide materials possess the fascinating characteristics of adjustable band gap,large specific surface area and different phases,which endows great potential in the fields of optoelectronics,magnetism,valley electronics,catalysis.Therefore,it has become the focus among scientific researchers all over the world.Transition metal chalcogenide materials have a variety of morphologies and structures,and different inner structures determine their distinct physical and chemical properties,while controlling the dimensionality of transition metal dichalcogenide materials is an important approach to explore their novel physical and chemical properties.Previous reports have already demonstrated that 1D transition metal dichalcogenide nanoribbons can be built by bottom-up chemical measurements and tailored to show a host of distinguish properties related to optoelectronics,spintronics,catalysis,and photovoltaic energy conversion,which have attracted widespread attention.However,at present,there is a lack of controllable methods to prepare one-dimensional nanoribbons,which hinders the study of their properties.Therefore,it is necessary to develop an efficient and convenient method to prepare one-dimensional nanoribbon structures of transition metal dichalcogenides.In view of this,we adopted a self-designed space-confined chemical vapor deposition method to achieve the controllable growth of a variety of transition metal dichalcogenides one-dimensional nanoribbons on diverse substrates,and used a series of characterization methods to systematically study the micro-nano structure,surface potential,chemical composition and other aspects of materials.The corresponding growth mechanism has also been proposed.The main research results of the paper are summarized as follows:（1）We have prepared WS₂ samples with three different morphologies,which are WS₂ nanosheets,dendritic structure and one-dimensional nanoribbons by using the space-confined chemical vapor deposition method.By adjusting the growth parameters,the controllable growth of WS₂ nanoribbons on four different substrates was achieved.These results provide the experimental support to explore the interaction between the substrate and the one-dimensional nanoribbons of transition metal dichalcogenide in the future.（2）We have successfully prepared WSe₂ one-dimensional nanoribbons and other different morphologies of WS₂ on four different substrates:Si O₂ /Si,highly oriented pyrolytic graphite,flexible mica,and sapphire substrates by using space-confined chemical vapor deposition method.After analyzing the characterization results of WSe₂ nanoribbons on different substrates,we reasoned that substrate engineering has a regulatory effect on the growth of one-dimensional nanoribbons.（3）Through the further application of the space-confined chemical vapor deposition method,we have grown samples of WS_2（1-x）Se_2xalloy nanoribbons,Mo S₂ nanoribbons,and Mo Se₂ nanoribbons,which indicates that the method has universal applicability.Combined with computational fluid dynamics,we proposed the corresponding growth mechanism of transition metal dichalcogenide one-dimensional nanoribbons.（4）The Kelvin probe force microscope and the conductive atomic force microscope were used to systematically study the surface potential distribution and electrical properties of the WSe₂ nanoribbons grown on highly oriented pyrolytic graphite substrate,and we established the evolution laws between its surface potential and the number of layers.At the same time,we found the formation of Schottky-barrier at the nanoscale junction between the metal tip and WSe₂ nanoribbons.Subsequently,we also studied the surface potential distribution of WS₂ nanoribbons,and the results showed that the surface potential of WS₂ one-dimensional nanoribbons was lower than that of single-layer WS₂ two-dimensional nanosheets.