Two-dimensional Semiconductor Interface Regulation For Flexible Optical And Electrical Applications

As the core and foundation of modern information industry,microelectronic devices have made great progress in the past half century following Moore’s Law.However,as the size of the transistor is further reduced,the control of the gate electric field on the channel is gradually reduced,and the short channel effect is difficult to overcome.In the post-Moore era,two-dimensional（2D）semiconductors with layered structures have aroused wide interest among scientific researchers.Compared with traditional semiconductor with bulk structure,two-dimensional semiconductors have the following unique advantages:1.The atomically thin body thickness and the dangling-bond free surface;2.Excellent mechanical properties（strain limit over 10%）;3.Adjustable contact interface:By adjusting the contact interface between two-dimensional materials and substrate or metal,the mechanical exfoliation yield,strain engineering efficiency and electrical transport characteristics of the materials can be optimized.Here,this paper takes the 2D-substrate and 2D-metal interface as the entry point respectively,put forward the Au-mesh mechanical exfoliation method.It not only optimized the 2D-tape interface to promote large-scale dry exfoliation,but also improved the interface force of 2D-substrate to improve the yield of solution-free dry transfer,and finally realized the high quality and large-scale exfolaition of 2D monolayer and heterojunction arrays.In order to mitigate the challenge of low efficiency regulation of 2D flexible optical band gap,a PVA polymer encapsulation method was proposed,which not only greatly improved the interface forces but also realized high efficiency regulation of the optical band gap of monolayer 2D materials.In order to mitigate the challenge of low strain tolerance of flexible 2D electronics,a sliding contact structure in metal-2D interface is proposed to release mechanical strain,so as to greatly increase the strain limit of flexible 2D electronics.The main research results and contents are summarized as follows:1.Firstly,from the perspective of 2D-tape contact interface,the interface forces between the 2D material and the Au mesh is locally controllable;At the same time,from the perspective of 2D-substrate interface,the interface force was enhanced by the functionalization of the substrate,and then the 2D arrays on Au-mesh tape was released to the target substrate surface by dry transfer.Together,this paper demonstrates a scalable method to dry exfoliate various 2D monolayer arrays onto different substrates without involving any solutions and contaminations,representing the optimization between material yield,scalability and quality.2.this paper reports a simple strain engineering method by encapsulating the monolayer 2D material in the flexible PVA substrate through spin-coating approach.The strong interaction force between spin-coated PVA and 2D material ensures the mechanical strain can be effectively transferred with negligible slippage or decoupling.By applying uniaxial strain to monolayer MoS₂,this paper observe a higher bandgap modulation up to～300 meV and a highest modulation rate of～136 meV/%,which is approximate two times improvement compared to best results achieved.Moreover,this simple strategy could be well extended to other 2D materials such as WS2 or WSe2,leading to optimal bandgap modulation.3.this paper reports a sliding contact device structure for efficient strain releasing.By fabricating weakly coupled metal-2D junction with a van der Waals gap in between,the applied strain could be effectively released through their interface sliding,hence minimized strain is transferred to 2D lattice.Therefore,this paper observed stable device behavior with electrodes stretching over 110%,much higher than 2D devices using evaporated metal contacts.Furthermore,through multi-cycle straining-releasing measurements,this paper found the electrodes still form intimate contact with nearly constant contact resistance during sliding,confirming the optimization of device flexibility and electrical properties at the same time.Finally,this paper demonstrate this vd W sliding contact is a general device geometry and could be well-extended to various 2D or 3D bulk materials,leading to devices with much higher strain tolerance.