Controlled vapor growth of 2D magnetic Cr_(2)Se_(3)and its magnetic proximity effect in heterostructures

Two-dimensional(2D)magnetic materials have aroused tremendous interest due to the 2D confinement of magnetism and potential applications in spintronic and valleytronic devices.However,most of the currently 2D magnetic materials are achieved by the exfoliation from their bulks,of which the thickness and domain size are difficult to control,limiting the practical device applications.Here,we demonstrate the realization of thickness-tunable rhombohedral Cr_(2)Se_(3)nanosheets on different substrates via the chemical vapor deposition route.The magnetic transition temperature at about 75 K is observed.Furthermore,van der Waals heterostructures consisting of Cr_(2)Se_(3)nanosheets and monolayer WS2 are constructed.We observe the magnetic proximity effect in the heterostructures,which manifests the manipulation of the valley polarization in monolayer WS2.Our work contributes to the vapor growth and applications of 2D magnetic materials.

Vapor growth of WSe2/WS2 heterostructures with stacking dependent optical properties

Two-dimensional(2D)vertically stacked heterostructures based on layered transition-metal dichalcogenides(MDCs)have remarkablepote ntial in future applications due to their rich in terlayer related properties,such as in terlayer excitons,tun able interlayer band alignments.However,the controlled growth of TMDC bilayer heterostructures with preferred stacking structure remains challenging.Here,we report atwo-step van der Waals epitaxial vapor growth of WSe2/WS2 vertically stacked bilayer heterostructures with controllable commensurate crystallographic alignments(so called AA and AB stacki ng),by controlling the deposition temperature.Moire patter ns were obtai ned in bothAA and AB stacked WSe2/WS2 heterostructures.The stacking configuration of the vertical heterostructures was verified by the secondharmonic generation signals.Photoluminescenee and Raman spectroscopy studies further confirm that the heterostructures with differentstacking configuration have obviously different optical properties,which is ascribed to the distinct in terlayer coupling and resonance excitation between the distinguishing AA and AB stacked heterostructures.The controlled growth of AA and AB stacked heterostructures could provide an importa nee platform not only for fun dame ntal researches but also for functional electronic and optoelectronic deviceapplications.

Defect-induced distinct exciton-exciton interactions in WS2 monolayers

The optoelectronic properties of atomically thin transition metal dichalcogenides(TMDs)are largely influenced by defect populations(DPs).In this work,we fabricate WSmonolayers with different DPs by varying the fabrication methods and further reveal their distinct exciton-exciton interactions.Steady-state photoluminescence(PL)experiments show that the monolayer with the lowest DP shows optimal PL intensity at low excitation power;however,it is overtaken and significantly surpassed by monolayers with higher DPs at high excitation powers.Excitation-power-dependent experiments demonstrate that these monolayers exhibit distinct PL saturation behaviors with the threshold power differing by four orders of magnitude.Combined with in situ PL imaging and time-resolved PL experiments,we attribute such PL evolution discrepancies to the different DPs within these monolayers,which largely influence the exciton diffusion behavior and subsequently bring about distinct nonradiative exciton-exciton annihilations(EEAs).Valley polarization experiments are further employed to re-examine the DPs of these monolayers.This work reveals the distinct PL behaviors and underlying exciton dynamics in TMD monolayers with different DPs,which can largely facilitate the engineering of relevant high-performance devices for practical applications.

Van der Waals epitaxial growth and optoelectronics of a vertical MoS_(2)/WSe_(2)p-n junction

Two-dimensional(2D)transition metal dichalcogenides(TMDs)have attracted extensive attention due to their unique electronic and optical properties.In particular,TMDs can be fexibly combined to form diverse vertical van der Waals(vdWs)heterostructures without the limitation of lattice matching,which creates vast opportunities for fundamental investigation of novel optoelectronic applications.Here,we report an atomically thin vertical p-n junction WSe_(2)/MoS_(2)produced by a chemical vapor deposition method.Transmission electron microscopy and steady-state photoluminescence experiments reveal its high quality and excellent optical properties.Back gate feld efect transistor(FET)constructed using this p-n junction exhibits bipolar behaviors and a mobility of 9 cm^(2)/(V·s).In addition,the photodetector based on MoS_(2)/WSe_(2)heterostructures displays outstanding optoelectronic properties(R=8 A/W,D^(*)=2.93×10^(11)Jones,on/of ratio of 10^(4)),which benefted from the built-in electric feld across the interface.The direct growth of TMDs p-n vertical heterostructures may ofer a novel platform for future optoelectronic applications.