Physical Properties And Phase Engineering Of Two-Dimensional Ternary Atomic Layers

Two-dimensional(2D)layered materials got an enormous resurgence owing to the great success of graphene,an atomic carbon layer with hexagonal lattice structure.The availability of sizeable,thickness dependent tunable band gap,various crystal structures and abundance of elemental composition has given a tremendous importance to 2D materials.Among them,2D transition metal dichalcogenides(2D TMDs)are an incipient class that has been the center of attention especially over the period of last one decade.Until now,most of the work has been focused upon the binary TMDs.In fact,ternary TMDs formed via three elements can possess additional degrees of freedom and bring in more rich physical and chemical properties.However,difficulties involved in the synthesis of such 2D ternary materials has been the main hindrance for their further explorations.Thus,in this dissertation,an attempt has been made to highlight the prospects and potential of ternary TMDs through controllable synthesis of several ternary materials,along with the detail investigations of physical properties.In particular,this thesis presents the selective synthesis and phase engineering in ternary atomic layers of MPS3(M:Mn,Fe),MoSe2xTe(1-x)2,RexZrSe2,and TixZrSe2 through chemical vapor transport(CVT)method.Various characterization means have been performed,including X-ray diffraction(XRD),X-ray Photoelectron Spectroscopy(XPS),Raman spectroscopy,synchrotron based X-ray absorption fine structure spectroscopy(XAFS),scanning electron microscopy(SEM),scanning transmission electron microscopy(STEM)and Transmission electron microscopy(TEM).The electronics,optoelectronics and magnetic properties of ternary layers were investigated via physical property measurement system(PPMS),electron para magnetic resonance spectroscopy(EPR),angle resolved photoemission spectroscopy(ARPES),low temperature transport and Field effect transistors(FET).The first principle density functional theory(DFT)calculations further validated the claims and conclusions.The main results of this thesis are listed as following:1.Ternary layered MPS3(M:Mn,Fe)single crystals were synthesized via CVT method,and the magnetic properties as well as isotropy and anisotropy were investigated.The vibrating sample magnetometer results revealed that both MnPS3 and FePS3 were antiferromagnetic in nature.The EPR further confirmed that MnPS3 was isotropic,while FePS3 was highly anisotropic.2.Ternary Layered MoSe2xTe(1-x)2 single crystals were synthesized via CVT method and systematically characterized.The experimental ARPES and low temperature transport measurements clearly revealed the electrical characteristic transition from metallic MoTe2 to semiconducting MoSe0.08Te1.92,well in agreement with the DFT calculations.As a demonstration of potential applications,MoSe0.08Te1.92 FET device achieved excellent gate controllable characteristics with an ON-OFF ratio of-106,indicating its application in optoelectronics and magnetic applications.3.Re atoms were controllably intercalated inside ZrSe2 single crystals and formed ternary Re0.013ZrSe2 layers.The STEM and ARPES revealed that Re intercalation could cause semiconductor to metal transition in ZrSe2,further proved by low temperature transport measurements of electrical resistance as a function of temperature.4.Ti atoms were controllably intercalated inside ZrSe2 single crystals and formed ternary Ti0.08ZrSe2 layers.Combining with low temperature transport measurement,the comparison of ARPES revealed that Ti intercalation could result in a different band structure with noticeable changes in band dispersion for metallic Ti0.08ZrSe2 in contrast to semiconducting ZrSe2.