The Investigation Of The Perparation Of Sm Doped Monolayers Of Molybdenum Disulfide With Rare Earth Elements And Their Electrical Properties

Rare earth(RE)element-doped two-dimensional(2D)transition-metal dichalcogenides(TMDCs)with applications in luminescence and magnetics have received considerable attention in recent years.To date,the effect on the electrical properties of single molecular layer TMDCs doped with rare earth elements needs further investigation due to the difficulty in achieving effective single molecular layer doping in 2D-TMDCs and the introduction of rare earth elements with different valence states and atomic configurations.Herein,we report a unique growth strategy to introduce the rare-earth element Sm into monolayer MoS₂ to achieve stable doping growth of rare-earth elements in monolayer materials.The results were confirmed by physical characterization methods.In this thesis,it is found that Sm doping enhances the electrical properties of monolayer MoS₂.In particular,the device switching current ratio was increased by a factor of 5,while the mobility was increased by 40%.The details are shown below:(1)The original atmospheric pressure chemical vapor deposition(CVD)method has been improved by using an atmospheric pressure chemical vapor deposition method with the substrate face down on top of the Mo source.Stable monolayers of large-sized Sm-doped MoS₂ films were obtained using a narrow growth space.The experimental parameters during the growth of 2D materials were also optimised to obtain the best parameters suitable for the doping growth of monolayer films.(2)Physical characterization was used to confirm that the rare earth elements Sm were incorporated into the monolayer MoS₂ by substitution doping.Sm-doped monolayers of MoS₂ were characterized by Raman spectra and AFM,and the characteristic peaks of the photoluminescence spectra were weakened and blue-shifted.The valence states of Sm,O and Mo were analyzed by X-ray photoelectron spectroscopy and the shift of the core energy level to lower energy levels confirms the introduction of Sm as a p-type impurity state into the monolayer MoS₂.Sm doping content was calculated to be 1.1 at%.The diffraction pattern of the doped monolayer of MoS₂ shows that the doping does not change the crystal structure of the monolayer of MoS₂.(3)Sm doped monolayer MoS₂ and monolayer MoS₂ back-gate field effect transistors have been successfully prepared by micro and nano-processing methods such as wet transfer,UV exposure,electron beam exposure and electron beam evaporation coating.Electrical measurements showed that Sm element doping led to considerable changes in the electronic band structure of the host MoS₂.The 4f orbital of element Sm and the 4d orbital of element Mo hybridize at the valence band edge of monolayer MoS₂,bringing the Fermi energy level closer to the valence band to form p-type doping,resulting in a shift of the threshold voltage towards the positive gate voltage after doping.The lattice distortion caused by the doped atoms leads to a non-uniform charge distribution of the monolayer MoS₂,suppressing its n-type properties.The results of this study have a positive contribution to the application of rare earth element-doped monolayer 2D layered materials in optoelectronic devices.