Study On The Preparation Of Large-Scale Monolayer Mos₂ And The Characteristics Of Er-Doped Single Layer Mos₂

Transition metal dichalcogenides（TMDs）have broad application potential in the fields of flexible electronics and transparent electronics,photoelectronics,future spintronics and valley electronics because of their unique physical and chemical characteristics with adjustable bandgap at low dimension scale,which make it possible for atomic scale devices.However,the rapid developments of these new fields urgently require large-scale monolayer MoS₂ materials with high-quality and wider spectral response range.This paper focuses on the development of novel controllable preparation methods for large-scale monolayer MoS₂（m-MoS₂）thin films with high-quality and the effect of Er dopant on the characteristics of m-MoS₂.The source concentration controlled by variable vaporization temperature and CVD method with limited velocity were proposed to prepare single layer and large-scale monolayer MoS₂ thin films,respectively.On these basis,the preparation and characterization of Er-doped MoS₂ were investigated.The main works and achievements are as follows:1.Monolayer MoS₂ films were prepared by the CVD method using variable vaporization temperature to control source concentration.The effects of growth location and the temperature gradient as well as distance from MoO₃ to substrate on controlable growth of monolayer MoS₂were investigated by controlling the vaporization rate of MoO₃ using gradually temperature.It was found that the temperature gradient could control and adjust the reactant concentration along the space from MoO₃ to substrate.And thus,the single-layer MoS₂ film was realized under the negative and the positive temperature gradient.Subsequently,it was revealed that the growth of MoS₂ film was limited by reaction kinetics under high reactant concentration,while the growth mode was dominated by thermodynamic mode and self-limiting growth of Mo under low reactant concentration.2.The rate-limited CVD technique was used to fabricate large-scale monolayer MoS₂ films.The incorporation of quasi-closed crucible resulted in the reduction of the growth rate and the transformation from a reaction kinetic process to a thermodynamic process.In addition,the method improved the immunity of monolayer to the wide process window.3.The rare earth element Er-doped monolayer MoS₂ film was proposed and realized experimentally using ErCl₃?6H₂O as the dopant.The results indicated Er impurity in MoS₂ exists in the form of Er³⁺and formed four dopant levels,⁴F_9/2,⁴I_9/2,⁴I_11/21/2 and ⁴I_13/2.And thus,both UC with five emissions from 710 nm to 813 nm and DC emission located at 1531 nm in Er-doped monolayer MoS₂ were observed under the 980 nm laser.4.The effects of Er atom concentration on single-layer MoS₂ were theoretically investigated.The results indicated the introduction Er³⁺formed a strong covalent bond between S and Er,thus leading to the enhancement of the absorption and anisotropy of monolayer MoS₂ from infrared,near infrared to visible.5.The magnetic and its origin of Er-doped monolayer MoS₂ were investigated.The experiment results indicated the incorporation of Er enhanced the room temperature magnetic.It was found that the magnetic derived from the magnetic moment and the local magnetic moment in the Er-doped monolayer system.The system magnetic moment mainly originated from the orbital localization and high spin polarization of Er-f,the spin polarization of the Mo-4d orbital,as well as the double exchange between the 5p orbital of Er and 3p orbital of S.In addtion,the formation of local magnetic moment is mainly caused by lattice distortion around Er atom,polyvalent properties of Er and Mo cations and the localization of Er-f orbital.