Mechanical and Electrical Control of Excitons in Suspended Bilayer MoSe2
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二维过渡金属硫族化合物(Transition metal dichalcogenides,TMDs)如二硒化钼MoSe2等具有优异的电学、光学和机械性能,是研究纳米光机电耦合系统(Nano-opto-electro-mechanical coupling systems,NOEMS)的理想材料.由于二维激子的高效发光,基于通过NOEMS系统可对TMDs激子的吸收和发射特性进行动态调制.本文分别加工了悬浮结构的双层和单层MoSe2纳米光机电器件,通过低温下机械共振测量发现,双层MoSe2的机械共振线宽明显宽于单层MoSe2,进而机械品质因子更小,且随栅压增大共振线宽变宽,品质因子随之减小;光致发光(Pho-toluminescence,PL)光谱表明,尽管悬浮区域双层MoSe2层间激子的PL发射远低于单层MoSe2层内激子的PL发射,但双层MoSe2悬浮区域的层间激子PL强度高于硼氮衬底,并且观测到悬浮双层样品有衬底时淬灭的层内激子,且层内激子不受电压掺杂和应力的调控;此外,根据栅极电压调控的结果,我们发现在该悬浮系统中静电感应诱导的应变调控强于电压掺杂调控.
Two-dimensional transition metal chalcogenides(TMDs),such as molybdenum selenide(MoSe2),have excellent electri-cal,optical and mechanical properties,and are ideal materials for the study of nano-opto-electro-mechanical coupling systems(NO-EMS).The absorption and emission characteristics of TMDs excitons can be dynamically modulated based on the NOEMS system.In this paper,bilayer and monolayer MoSe2 nano-opto-electro-mechanical devices with suspended structure are fabricated respective-ly.By measuring mechanical resonance at a cryogenic temperature of 10 K,it is found that the mechanical resonance linewidth of bi-layer MoSe2 is significantly wider,hence lower mechanical quality factor,than that of monolayer MoSe2.PL photoluminescence of the inter-layer exciton in the suspended bilayer MoSe2 exhibits enhanced intensity than bilayers supported by a hexagonal boron ni-tride(h-BN)substrate,yet is far lower than the that of intra-layer exciton in the monolayer case.The intra-layer excitons,seen in the suspended bilayer MoSe2,however,are quenched in the h-BN-supported region.In addition,by applying a gate voltage,we find that the electrostatically-induced strain plays a more pronounced role than that of the electric doping in our suspended devices.
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