The Study Of Controlled Growth And Broadband Tunable Photoluminescence Properties Of WSe₂

Graphene has attracted enormous attention due to its excellent electrical properties,optical properties and ultra-high electron mobility.However,intrinsic graphene has a zero bandgap structure,which limits the application of graphene in optoelectronic devices.Although a smaller bandgap can be obtained by doping or other complex methods,its electron mobility will be greatly reduced.WSe2 is a graphene-like material.Monolayer WSe2 is a semiconductor material with direct bandgap of ~1.2eV,which compensates the drawback of graphene's zero bandgap,and greatly fascinates its potential application in optoelectronic devices.In this paper,we employed the vapor transport(VT)or chemical vapor deposition(CVD)method with optimal growth conditions to deposit high-quality,large-scale monolayer WSe2.The resulting products were characterized by optical microscope,Raman spectroscopy,atomic force microscopy and auger spectrometer.Firstly,in order to prepare WSe2 flakes with highest density of edges,graphene quantum dot were spin-coated on cleaned Si O2(300 nm)/Si substrates during the growth of monolayer WSe2 by vapor transport to prepare porous few-layer WSe2 flakes.Those WSe2 flakes have a large number of triangular or circular holes.The size of holes varies from several hundreds of nanometers to several microns.The presence of holes has greatly enhanced the density of edges of WSe2 flakes.Highest density of edges emerges on 4-layer WSe2 flake,which is greatly enhanced by 580% compared to those well-defined triangular 4-layer flakes.Secondly,in order to tune the luminescence of WSe2,WSe2 flakes with different W/Se nonstoichiometry prepared by using vapor transport and chemical vapor deposition.The excitonic energy of monolayer WSe2 can be unprecedented widely shifted from 1.53 eV to 1.79 eV.Finally a DFT calculation was preformed and shows that nonstoichiometry of WSe2 modifies the bandgap and induces such large shift of PL broadband which is much better than that of other reported Monolayer WSe2(1.6eV-1.7eV).