Preparation And Device Characteristics Of Low-dimensional Te Nanowires And Wse₂ Films

Low-dimensional nanomaterials,such as nanowires,nanotubes,nanorods,nanosheets and etc.,have attracted much attention in the past two decades due to their low-dimensionalization,which leads to unique physical and chemical properties that are different from bulk.Controllable synthesis and regulation of the device characteristics of low dimensional nanomaterials remains a challenge in the research of materials.Therefore,it is of scientific importance to investigate controllable synthesis and regulation of low-dimensional nanomaterials.In this thesis,single crystal tellurium nanowires and tungsten diselenide nanosheets based thin films were studied.One-dimensional tellurium nanowires were synthesized in a three-temperature zone tube furnace by physical vapor deposition.WSe₂ nanosheets were prepared by supercritical and liquid phase exfoliation process,following the preparation of WSe₂ films by space-confined self-assembly method.The morphology,structure and composition of the prepared materials were characterized by atomic force microscope(AFM),scanning electron microscope(SEM),transmission electron microscope(TEM),scanning transmission electron microscope(STEM)and Raman spectra,respectively.Finally,electronic devices of as prepared materials were fabricated by micro-nanofabrication techniques including electron beam lithography.The electrical transport properties of tellurium nanowires were explored using a micro-operated low temperature probe station and a physical property measurement system.The field effect transistor and photoelectric response were investigated by a micro-operated low temperature probe station for WSe₂ nanosheets-based thin films.The synthesis of tellurium crystal was first grown by physical vapor deposition method in a three-temperature zone tube furnace with different substrates,which including silicon wafer,highly directional pyrolytic graphite,copper foil and fluorite mica sheets.With the optimization of synthesis conditions,one-dimensional crystalline tellurium nanowires were successfully synthesized on fluorite mica sheets.Then the nanowires were transferred by polydimethylsiloxane for the morphology,structure and composition characterization by AFM,SEM,TEM,STEM and Raman.These results show that 1D tellurium nanowires with uniform size and high crystalline quality have been synthetized.The synthesized tellurium nanowires transferred onto SiO₂/Si wafers and patterned into field effect transistors devices with different metal electrodes such as Cr/Au?Ni/Au?Pd/Au.The interfacial properties with different metal-semiconductor contacts were systematically inspected.The results show that the FETs with Pd/Au electrodes shows good performance that the room temperature FET has a mobility of 220 cm²V^-1S^-1 and switching ratio of 4000.Furthermore,the electrical transport properties of one-dimensional tellurium nanowires were tested by PPMS under the condition of high magnetic field at low temperature.The magnetoresistance effect and quantum oscillation were observed.Secondly,the WSe₂nanosheets were obtained by supercritical pretreatment and liquid phase exfoliation,and then assembled into thin films.The morphology,structure and composition of WSe₂nanosheets and as prepared thin films were characterized,which indicates large WSe₂ thin films have been synthetized with intrinsic crystal structure and physical properties.The electronic devices of the WSe₂ thin film was fabricated with fork-finger electrode by micro-nano electronic devices fabrication techniques.The field effect transistor and photoelectric responses of the WSe₂ thin film were analyzed,showing good ohmic contact and excellent light response(6.4?A/W)and photodetection(3.2×10⁴ Jone).