Mechanical And Electrical Control Of Excitons In Suspended Few-layer MoSe₂

Molybdenum diselenide（MoSe₂）has attracted much attention for its excellent electrical,optical and mechanical properties.Compared with monolayer MoSe₂ with direct band gap,bilayer MoSe₂ with indirect band gap exhibits excellent physical properties for its interlayer excitons while greatly weakened PL ability.In this paper,we prepared suspended monolayer and bilayer MoSe₂ NOEMS nanodevices by suspending monolayer and bilayer MoSe₂ above metal mirrors based on van der Waals heterostructures.The mechanical modulation mechanism and dynamic modulation of the absorption and emission properties of the intra/interlayer excitons in these systems have been investigated in detail,which provides an experimental foundations for the study of the interlayer excitons in the suspended few-layer TMDs.The main studies are as follows:1.The mechanical resonance characteristics of the suspended monolayer and bilayer MoSe₂ NOEMS nanodevices were measured and characterized by optical interferometry.It was found that the quality factor Q of the devices had reciprocal relationship with temperature and decreased with increasing gate voltage V_g.Moreover,at low temperature10 K,the Q of monolayer MoSe₂ is much larger than that of bilayer MoSe₂ under the same experimental conditions,which means that monolayer MoSe₂ have longer storage time of mechanical resonance energy.In addition,the line width of bilayer MoSe₂ is wider at a fixed grid voltage,which means that the vibration performance of monolayer MoSe₂ is better than bilayer.2.We performed photoluminescence（PL）spectroscopic measurements and characterized the electrical modulation properties of the suspended monolayer and bilayer MoSe₂ NOEMS nanodevices.The results show that at T=10 K,the PL emission intensity of interlayer excitons in the suspended region of bilayer MoSe₂ is much lower than that of intralayer excitons in monolayer MoSe₂.However,the PL intensity of interlayer（or intralayer）excitons in the suspended region of bilayer（or monolayer）MoSe₂ is higher than that of h-BN substrate,which indicating that the h-BN substrate attenuates the electron-hole complex luminescence.Secondly,the PL intensity of the interlayer exciton is stronger than that in the suspended region in the h-BN substrate under positive gate voltage,while almost unaffected with the gate voltage but quenched at h-BN substrate.It is noticed that the PL intensity of the interlayer exciton is always stronger than that in the h-BN substrate under negative gate pressure.In addition,the interlayer excitons exhibit enhanced nonradiative jumping with the increasing gate voltage V_g,and the strain regulation induced by electrostatic induction is found to be stronger than the voltage-doping regulation in this suspended systems.