| As a typical two-dimensional(2D)semiconductor material,monolayer molybdenum disulfide(Mo S2)shows versatile excellent properties,including good mechanical property and stability,great flexibility and transparency,and suitable direct bandgap,etc.Therefore,Mo S2 is not only appropriate for the research of basic science problems in low dimensional systems,but also shows wide application prospects in the fields of electronics and optoelectronics.However,low carrier mobility is the limiting factor for the practical applications of monolayer Mo S2.In recent years,researchers tried to improve the mobility of Mo S2 by various means,for example,improving the crystallinity,optimizing the contact quality,and enhancing the gating ability by improving the quality of dielectric layer,so the further improvement for electrical performances of Mo S2 devices is an important science problem.This dissertation takes monolayer Mo S2 as the core material,and control the properties of Mo S2 and its electronic devices by scratching lithography,substitutional doping,and twisted stacking to improving the quality of Mo S2.This dissertation is mainly constituted by the following three aspects:1.Scratching lithography technology for the patterning of 2D materials.Scratching lithography for samples is realized by mechanical scratch on the surface of2D materials by a metal tip through an electric displacement system.Taking wafer-scale monolayer Mo S2 as an example,various large-scale patterned films could be achieved by scratching lithography,and the patterned samples show clean surfaces and sharp edges.Lithography-free high-quality transistor devices are fabricated by the combination of scratching patterned Mo S2 channels and transferred electrodes,and the devices exhibit ultra-clean surfaces and interfaces.The devices also show excellent electrical performances with high room-temperature field-effect mobility and current on/off ratio of 50.7 cm2V-1s-1 and 1010,respectively.The precision of scratching lithography researches about 1?m,and this method shows the advantages in simple operation and low cost.Scratching lithography is suitable for various 2D materials on different substrates and provides new strategy for patterned processing and device fabrication.2.Substitutional oxygen doping of monolayer Mo S2 and its property control.In-situ substitutional oxygen doping of 2-inch wafer-scale monolayer Mo S2 is realized by chemical vapor deposition and uniform monolayer Mo S2-xOx films are obtained.Doping concentration in the Mo S2-xOx films are tunable by the oxygen flow rates in the chamber during the growth process and the doping concentrations increase with the increased oxygen flow rates.Ultrafast infrared spectroscopy measurements and first-principles calculations reveal a reduction of bandgaps of monolayer Mo S2-x Ox with increased doping levels accompanied by a direct-to-indirect band transition.Field-effect transistors and logic devices based on the Mo S2-x Ox films show excellent electronic performances,and the field-effect mobilities are improved particularly.Substitutional oxygen doping of monolayer Mo S2 provides material basis for the optimizing of electronic device performances.3.Twisted stacking of highly-oriented monolayer Mo S2.Wafer-scale highly-oriented monolayer Mo S2 with weak adhesive on the sapphire substrates are grown by chemical vapor deposition.Centimeter-scale stacked Mo S2 films are realized by the exfoliation of Mo S2 with weak adhesion and high alignment from the pristine substrates through water-assisted transfer and layer-by-layer stacking,and the twist angles between layers are precisely controlled.Spectroscopy and electrical properties of stacked Mo S2 films are modulated by the interlayer twist angles,and the Mo S2transistors show better electrical performances at a twisted angle of 30°because of the decoupling of interlayer interactions.This work paves the way to low dimensional twisted electronics and optoelectronics. |
PDF Full Text Request