Thickness-dependent excitonic properties of atomically thin 2H-MoTe2

Two-dimensional(2D)2H-MoTe2 is a promising semiconductor because of its small bandgap,strong absorption,and low thermal conductivity.In this paper,we systematically study the optical and excitonic properties of atomically thin 2H-MoTe2(1–5 layers).Due to the fact that the optical contrast and Raman spectra of 2H-MoTe2 with different thicknesses exhibit distinctly different behaviors,we establish a quantitative method by using optical images and Raman spectra to directly identify the layers of 2H-MoTe2 thin films.Besides,excitonic states and binding energy in monolayer/bilayer 2H-MoTe2 are measured by temperature-dependent photoluminescence(PL)spectroscopy.At temperature T=3.3 K,we can observe an exciton emission at^1.19 eV and trion emission at^1.16 eV for monolayer 2H-MoTe2.While at room temperature,the exciton emission and trion emission both disappear for their small binding energy.We determine the exciton binding energy to be 185 meV(179 meV),trion binding energy to be 20 meV(18 me V)for the monolayer(bilayer)2H-MoTe2.The thoroughly studies of the excitonic states in atomically thin 2H-MoTe2 will provide guidance for future practical applications.

Interfacial amplification for graphene-based position-sensitive-detectors

Position-sensitive-detectors(PSDs)based on lateral photoeffect have been widely used in diverse applications1–9,including optical engineering,aerospace and military fields.With increasing demand in long distance,low energy consumption,and weak signal sensing systems,the poor responsivity of conventional PSDs has become a bottleneck limiting their applications,for example,silicon p–n or p–i–n junctions2–5,or other materials and architectures6–10.Herein,we present a high-performance graphene-based PSDs with revolutionary interfacial amplification mechanism.Signal amplification in the order of~10^(4) has been demonstrated by utilizing the ultrahigh mobility of graphene and long lifetime of photo-induced carriers at the interface of SiO_(2)/Si.This would improve the detection limit of Si-based PSDs fromμW to nW level,without sacrificing the spatial resolution and response speed.Such interfacial amplification mechanism is compatible with current Si technology and can be easily extended to other sensing systems11,12.