Showing papers by "Zheyu Fang published in 2020"
TL;DR: An ultrathin circular polarimeter consisting of chiral plasmonic metasurface and monolayer semiconductor is proposed to detect light with different circular polarization within a compact device and demonstrates the remarkable performance of the proposed device in detecting and distinguishing circularly polarized light.
Abstract: Two-dimensional materials are ideal platforms for intriguing physics and optoelectronic applications because of their ultrathin thicknesses and excellent properties in optics and electronics. Further studies on enhancing the interaction between light and two-dimensional materials by combining metallic nanostructures have generated broad interests in recent years, such as enhanced photoluminescence, strong coupling and functional optoelectronics. In this work, an ultrathin circular polarimeter consisting of chiral plasmonic metasurface and monolayer semiconductor is proposed to detect light with different circular polarization within a compact device. A designed chiral plasmonic metasurface with sub-wavelength thickness is integrated with monolayer MoSe2, and the circular-polarization-dependent photocurrent responses of right and left circularly polarized light for both left- and right-handed metasurfaces are experimentally demonstrated. The photoresponse circular dichroism is also obtained, which further indicates the remarkable performance of the proposed device in detecting and distinguishing circularly polarized light. This design offers a great potential to realize multifunctional measurements in an ultrathin and ultracompact two-dimensional device for future integrated optics and optoelectronic applications with circularly polarized light.
28 citations
Abstract: With the recent development of the metasurface, generating an optical vortex in optical far or near fields is realized in various ways. However, to generate vortices in both the near and far fields simultaneously is still a challenge, although it has great potential in the future compact and versatile photonic system. Here, a bi-channel optical vortex generator in both the near and far fields is proposed and demonstrated within a single metasurface, where the surface plasmon vortex and the far-field optical vortex can be simultaneously generated under circularly polarized light. The ability of generating vortices with arbitrary topological charges is experimentally demonstrated, which agrees well with simulations. This approach provides great freedom to integrate different vortex generators in a single device and offers new opportunities for integrated optical communications, trapping, and other related fields.
22 citations
TL;DR: A theoretical model of two coupled oscillators is proposed, where the expanded general solutions of such a model result in a series of eigenvalues that correspond to the renormalization of energy levels in modulated MoS2, and provides an alternative method to describe energy transfer between metallic structures and 2D semiconductors.
Abstract: The energy transfer from plasmonic nanostructures to semiconductors has been extensively studied to enhance light-harvesting and tailor light-matter interactions. In this study, the efficient energy transfer from an Au metasurface to monolayered MoS2 within a near-field coupling regime is reported. The metasurface is designed and fabricated to demonstrate strong photoluminescence (PL) and cathodoluminescence (CL) emission spectra. In the coupled heterostructure of MoS2 with a metasurface, both the Raman shift and absorption spectral intensities of monolayered MoS2 are affected. The spectral profile and PL peak position can be tailored owing to the energy transfer between plasmonic nanostructures and semiconductors. This is confirmed by ultrafast lifetime measurement. A theoretical model of two coupled oscillators is proposed, where the expanded general solutions (EGS) of such a model result in a series of eigenvalues that correspond to the renormalization of energy levels in modulated MoS2. The model can predict the peak shift up to tens of nanometers in hybrid structures and hence provides an alternative method to describe energy transfer between metallic structures and two-dimensional (2D) semiconductors. A viable approach for studying light-matter interactions in 2D semiconductors via near-field energy transfer is presented, which may stimulate the applications of functional nanophotonic devices.
18 citations
TL;DR: This work finds that the MoS2 with smaller interlayer distances achieves a SERS enhancement factor as high as 5.31 × 105, which is one of the highest enhancement facotr to date among the two dimensional nanomaterials SERS sensor.
Abstract: Two-dimensional nanomaterials, such as graphene and molybdenum disulfide (MoS2), have recently attracted widespread attention as surface-enhanced Raman scattering (SERS) substrates. However, their SERS enhancement is of a smaller magnitude than that of noble metal nanomaterials, and therefore, the detection sensitivity still needs to be substantially improved for practical applications. Here, we present the first detailed studies on the effect of the (MoS2) interlayer distances on the SERS intensity enhancement. We find that MoS2 with smaller interlayer distances achieves an SERS enhancement factor as high as 5.31 × 105, which is one of the highest enhancement factors to date among the two-dimensional nanomaterial SERS sensors. This remarkable SERS sensitivity is attributed to the highly efficient charge transfer from MoS2 to probe molecules. The charge-transfer ability directly determines the variable quantity dz2 orbitals of Mo elements in the MoS2-molecule system and then tunes the Raman intensity of probe molecules. Our work contributes to reveal the influence of MoS2 interlayer spacing on SERS detection and to open a new way for designing a highly sensitive nonmetal SERS technology.
18 citations
TL;DR: The ultrafast transition between exciton and trion is demonstrated, which provides an insight into the intrinsic modulation on populations of excitonic states and provides important implications for developing durable and stableexcitonic devices in future.
Abstract: Devices operating with excitons have promising prospects for overcoming the dilemma of response time and integration in current generation of electron- or/and photon-based elements and devices. Although the intrinsic properties including edges, grain boundaries, and defects of atomically thin semiconductors have been demonstrated as a powerful tool to adjust the bandgap and exciton energy, investigating the intrinsic modulation of spatiotemporal dynamics still remains challenging on account of the short exciton diffusion length. Here, we achieve the attractive remote lightening phenomenon, in which the emission region could be far away (up to 14.6 μm) from the excitation center, by utilizing a femtosecond laser with ultrahigh peak power as excitation source and the edge region with high photoluminescence efficiency as a bright emitter. Furthermore, the ultrafast transition between exciton and trion is demonstrated, which provides insight into the intrinsic modulation on populations of exciton and trion states. The complete cascaded physical scenario of exciton spatiotemporal dynamics is eventually established. This work can refresh our perspective on the spatial nonuniformities of CVD-grown atomically thin semiconductors and provide important implications for developing durable and stable excitonic devices in the future.
17 citations
02 Jun 2020
TL;DR: This study study study the exciton dynamics from the standpoint of the acceptor in MoS2/CdSe quantum rod (QR) heterostructures and realizes efficiently enhanced photoluminescence (PL) by suppressing exciton-exciton annihilation (EEA).
Abstract: Energy transfer in heterostructures is an essential interface interaction for extraordinary energy conversion properties, which promote promising applications in light-emitting and photovoltaic devices. However, when atomic-layered transition metal dichalcogenides (TMDCs) act as the energy acceptor because of strong Coulomb interactions, the transferred energy can be consumed by nonradiative exciton annihilations, which hampers the development of light-emitting devices. Hence, revealing the mechanism of energy transfer and the related relaxation processes from the aspect of the acceptor in the heterostructure is key to reducing nonradiative loss and optimizing luminescence. Here, we study the exciton dynamics from the standpoint of the acceptor in MoS2/CdSe quantum rod (QR) heterostructures and realize efficiently enhanced photoluminescence (PL). Through femtosecond pump–probe measurements, it is directly observed that energy transfer from CdSe QRs largely raises the exciton population of the acceptor, MoS2, providing a larger emission “source”. In addition, the dielectric environment introduced by CdSe QRs efficiently enhances the PL by suppressing exciton–exciton annihilation (EEA). This study provides new insights for on-chip applications such as light-emitting diodes and optical conversion devices based on low dimensional semiconductor heterostructures.
10 citations
9 citations
TL;DR: These observations demonstrate a viable approach for the control of pseudo-Landau levels, which tailors the electronic structure of graphene, and further ignites applications in graphene valley electronics.
Abstract: Graphene has attracted great interests in various areas including optoelectronics, spintronics, and nanomechanics due to its unique electronic structure, a linear dispersion with a zero bandgap around the Dirac point. Shifts of Dirac cones in graphene creates pseudo-magnetic field, which generates an energy gap and brings a zero-magnetic-field analogue of the quantum Hall effect. Recent studies have demonstrated that graphene pseudo-magnetic effects can be generated by vacancy defects, atom adsorption, zigzag or armchair edges, and external strain. Here, a larger than 100 T pseudo-magnetic field is reported that generated on the step area of graphene; and with the ultrahigh vacuum scanning tunneling microscopy, the observed Landau levels can be effectively tailored by graphene phonons. The zero pseudo-Landau level is suppressed due to the phonon-mediated inelastic tunneling, and this is observed by the scanning tunneling spectroscopy spectrum and confirmed by the Vienna ab initio simulation package calculation, where graphene phonons modulate the flow of tunneling electrons and further mediate pseudo-Landau levels. These observations demonstrate a viable approach for the control of pseudo-Landau levels, which tailors the electronic structure of graphene, and further ignites applications in graphene valley electronics.
6 citations
3 citations
TL;DR: In this paper, the authors used cathodoluminescence to probe photonic responses of nanostructures at high spatial and energy resolution, providing a powerful tool to investigate the radiative properties under electron excitation.
Abstract: Cathodoluminescence can probe photonic responses of nanostructures at high spatial and energy resolution, providing a powerful tool to investigate the radiative properties under electron excitation...
3 citations
TL;DR: In this article, an active controllable way of realizing the inversion symmetry breaking of single layer graphene, which is induced by the contrasted AB sub-lattice charge polarization, was proposed.
01 May 2020
TL;DR: In this article, the exciton dynamics from the aspect of acceptor is revealed by the time-resolved differential reflection measurement and the enhanced photoluminescence of heterostructure is achieved by energy transfer and the suppression of exciton-exciton annihilation.
Abstract: The exciton dynamics from the aspect of acceptor is revealed by the time-resolved differential reflection measurement and the enhanced photoluminescence of heterostructure is achieved by energy transfer and the suppression of exciton-exciton annihilation.