Growth,Transport And Electric Field Tuning Of Two-Dimensional Transition Metal Tellurides

Two-dimensional(2D)transition metal tellurides have rich physical properties and application potentials in spintronics,low-power energy devices and information storage.Because of their interlayer van der Waals forces,thin layer nanodevices can be prepared by mechanincal exfoliation,which is beneficial to external tunable methods(defects,field effect transistor,strains,stacking,etc.)to adjust the energy band structure and electronic properties of materials.In this dissertation,we first obtained ZrTe2 nanosheet samples with two thicknesses by mechanical exfoliation method.The longitudinal negative magnetic resistance is observed when the magnetic field is parallel to the current direction,and the whole process of negative magnetic resistance caused by the conductivity fluctuations was studied.Subsequently,we developed and improved a set of controllable chemical vapor transport methods,and successfully synthesized ZrTe3-x superconducting nanosheets.The 2D superconductivity of the nano-sheets was studied by rotating out-of-plane angle.In addition,we grew CrSiTe3 magnetic single crystal by self-melting method.The steep magnetic resistance transport phenomenon caused by the competition between orbital and spin magnetic moment was found,and the sign reversal of anomalous Hall slope was found near the Curie temperature.Finally,we utilized solid-state proton field effect transistor to study the process of H ion intercalation in Fe3GaTe2(FGaT)nanosheet.The sign tunable exchange bias effects were achieved under various protonic gate voltages,and a linear dependence of coercive field on gate voltage was also observed.This paper is divided into the following five chapters:First chapter is mainly divided into four parts to elaborate the research background of the paper.In the first part,the types and research progress of 2D transition metal tellurides are briefly described.In the second part,three preparation methods of 2D transition metal telluride are reviewed.In the third part,the physical properties including topological properties,charge density waves,superconductivity,magnetism and quantum effects of the 2D transition metal telluride are summarized in detail.Finally,the fourth part also describes the liquid,ion gel and solid-state field effect transistors and their applications.The second chapter explores the reason of negative magnetoresistance(NMR)in non-magnetic ZrTe2 nanosheet.When the magnetic field is parallel to the current direction,the NMR behavior of ZrTe2 nanosheets prepared by mechanical exfoliation is observed,and the negative magnetoresistance disappears above 15 K.Fitting the nonlinear Hall by the two-band model,we found that the mobility basically remains unchanged below 15 K,but it decreases with the increase of the temperatures,consistent with the temperature where the NMR disappears.Those results reveal the existence of conductance fluctuation(the spatial fluctuation of carrier mobility distorts the current path)in ZrTe2 nanosheeets.In addition,according to the systematic analysis of the measured planar Hall effects,temperature-sensitive NMR,anisotropic magnetic transport,and high carrier concentration,we further ruled out the possibility of NMR caused by other reasons.In Chapter 3,a novel two-dimensional superconducting nano-sheet ZrTe3-x grown by an improved chemical vapor transport(CVT)method is introduced,including crystal structure,chemical composition,defects,Raman spectra,atomic structure and electrical properties.The superconducting phase transition appears near Tc=3.4 K due to the suppression of charge density waves by the introduction of defects.In addition,during the anisotropy measurement of superconductivity,we found the properties of two-dimensional superconductivity and the mutual verification of Berezinsky-Kosterlitz-Thouless(BKT)phase transition.In Chapter 4,we investigated low-temperature transport properties in layered magnetic materials CrSiTe3 and gate tuning of FGaT by solid-state proton field transistor.First,the physical properties of two dimensional magnetic semiconductor CrSiTe3 are studied.The competing behavior of orbital and spin magnetic moments results in a steep magnetic resistance and a sign reversal of Hall near the curie temperature.We successfully tuned the low-temperature transport properties of FGaT thin layer samples by using solid-state proton conductor field effect transistor.By driving the proton into or out of the samples via a gate voltage,the sign of exchange bias effects can be tuned to be both positive and negative under field cooling(FC)and zero field cooling(ZFC).When the gate voltage is less than-7 V and-6.5 V,the FC and ZFC exchange bias disappear respectively.In addition,the amplitude of anomalous Hall does not change significantly under protonic voltages,while the coercive field decreases with the decrease of gate voltages.In the fifth chapter,we give a brief summary of present work work and an outlook for the future research direction.