Wafer-scale Synthesis And Application Investigation Of Single-crystal Molybdenum Disulfide

Two-dimensional(2D)transition metal dichalcogenides(TMDCs)have emerged as very promising candidates to extend Moore's law,due to their atomic thickness,unique optical/electronic properties,and excellent thermal stability.To realize the industry-compatible integration of 2D electronics,the batch production of wafer-scale TMDCs monolayers or thin films has become significantly essential.Chemical vapor deposition(CVD)route has demonstrated great potential in the batch production of high-quality 2D materials.However,the derived TMDCs films still suffered from relatively limited size,unsatisfactory domain size and uncontrollable thickness.Moreover,the high-density grain boundaries usually serve as charge carrier scattering centers and thus degrade the device electronic mobility and the related performance.To tackle this,wafer-scale monolayer TMDCs films with large-scale uniform crystal quality,possesing few or even without domain boundaries,are highly desired.Based on the above backgroud,this dissertation,taking MoS₂ as an example,aims to develop a novel CVD strategy to achieve the controllable synthesis of wafer-scale uniform monolayer MoS₂ films,thickness-tunable single-crystal flakes,and wafer-scale single-crystal monolayers.The practical applications of the derived MoS₂ materials in high-performance field effect transistors and new structured photodetectors will also be discussed.The main dissertation contains the following three parts:1.Batch production of 6-inch uniform monolayer MoS₂ on novel soda-lime glassThe direct syntheses of 6-inch uniform monolayer MoS₂ films have been realized on the solid soda-lime glass,through a designed“face-to-face”metal precursor supply route in a facile CVD process.The highly uniform monolayer film can be achieved within a quite short time of 8 min,with the composite domains possessing an edge length larger than 400?m.This highly efficient growth phenomenon was proven to be facilitated by the sodium catalysts that are homogenously distributed in glass,according to the experimental facts and density functional theory calculations.With the incorporation of sodium,the highest energy barrier for MoS₂ growth(that of the step from Mo₂S₂ to Mo₂S₄)greatly reduced from 0.53 to 0.29 e V,corresponding to an enhanced growth rate by 16 times.By exploiting the hydrophilicity feature of glass,an etching-free transfer method has also been developed to transfer the large-area MoS₂ films onto targeted substrates.This work should pave ways for the cost-effective wafer-scale production,environment-friendly transfer,as well as versatile applications of highly uniform TMDCs films in both fundamental research and industrial aspects.2.Thickness tunable growth of few-layer MoS₂ flakes and optoelectronic device related applicationsThe controllable growth of thickness tunable wedding-cake-like MoS₂ flakes has been demonstrated on 6-inch soda-lime glass,by using NaCl-coated Mo foils as metal precursors.The thicknesses of the few-layer MoS₂ triangular flakes can be tuned from monolayer to twenty layers by controlling the concentrations of Na Cl promoters.By virtue of its thickness dependent bandgap variation characteristics,monolayer-multilayer MoS₂ lateral junctions have been utilized to construct high performance optoelectronic devices,presenting a relatively high rectification ratio(¹0³)and extra high photoresponsitivity(¹0⁴A/W).Thanks to the scalable sizes,uniform distributions of the flakes and homogeneous optical properties,the applications of the few-layer MoS₂ flakes with wafer-scale sample sizes have also been developed in ultraviolet(UV)irradiation filtering eyewears.This research should hereby propel the scalable production of layer-controlled 2D semiconductors,as well as their optical and optoelectric related applications.3.Epitaxial growth of wafer-scale single-crystal MoS₂ monolayer on a single-crystal Au(111)templateThe epitaxial growth route has been introducd to accomplish the synthesis of wafer-scale single-crystal MoS₂ monolayers on vicinal Au(111)thin films.The Au(111)template is obtained by melting and resolidifying commercial Au foil on W foil substrate.By utilizing onsite scanning tunneling microscope(STM)characterizations combined with first-principles calculations,the nucleation of MoS₂ monolayer is definitely defined to be dominantly guided by the Au<110>steps on Au(111).The binding energy for MoS₂(per MoS₂ unit)docking to B-step is 0.16 e V higher than that to A-step,leading to the unidirectional growth of MoS₂along the B-step edges.This work develops a new method/system for preparing wafer-scale single-crystal 2D materials and sheds light on their practical applications in high-performance nanoelectronics.