Highly Polarized Light Emission of Monolayer WSe₂ Coupled with Gap‐Plasmon Nanocavity

Abstract

complex device functions, it is desirable to develop polarization-sensitive 2D materials or hybrid structures which will boost the development of smart optoelectronic devices, e.g., polarized photodetectors [7,8] or light emitting diodes. [9] Group-VI transition metal dichalcogenide (TMDC) monolayers, with the form of MX 2 (M = Mo, W and X = S, Se, etc.), possess two energy-degenerate but inequivalent valleys (K and -K) in the six corners of the Brillouin zone, which respond differently to the left-and rightcircularly polarized light. [10] However, the valley polarization (defined as circular dichroism) is typically quite low, especially at room temperature, owing to the effects such as electron-hole exchange interaction and phonon-assisted intervalley scattering. [11,12] To gain an obvious valley polarization, resonant excitation condition and cryogenic temperature are required, which largely limits the potential for practical applications. Similar requests also apply to a decent valley coherence for TMDC materials, in which linearly polarized light emission can be obtained as a result of coherent superposition of circularly polarized photon emission from K and -K valleys. [13] Different from 2H phase Group-VI TMDC, there are also 2D materials with an anisotropic crystal structure which naturally leads to polarization-sensitive absorption or emission properties. [14,15] For example, orthorhombic black phosphorus (BP) shows higher absorption and photoluminescence (PL) along the armchair direction than along the zigzag direction. [16,17] Meanwhile, germanium selenide (GeSe) also has the orthorhombic crystal structure which enables anisotropic absorption with a maximum anisotropic absorption ratio of 3.02 at 808 nm. [18] Currently, the limitations of these anisotropic 2D semiconductors mainly lie in two points: 1) Some of the materials, e.g., BP, suffers from low chemical stability so that the preparation and fabrication procedures have to be conducted in an inert atmosphere; 2) The anisotropic ratio for both absorption and PL emission is usually low and needs further enhancement towards practical applications.2D materials are famous for their flexibility and convenience for integration with other materials or nanostructures. By coupling monolayer semiconductors to plasmonic or dielectric As contemporary star materials, 2D monolayer semiconductors have drawn huge research interests owing to their striking electrical and optical properties, rendering them ideal candidates as building blocks for novel optoelectronic devices. Towards light emitting devices with extended functions, it is necessary to manipulate the polarization of light emission from monolayer semiconductors. However, most of these monolayer semiconductors exhibit no or very limited polarization sensitivity inherited from their structural anisotropy, making it challenging to develop highly polarized light sources. Herein, by embedding monolayer tungsten diselenide (WSe 2 ) in a nanowireon-film nanocavity, highly polarized light emission is demonstrated...

Ultrahigh Polarization-Sensitive Raman Scattering and Photon Emission in a Plasmonic Au/Biphenyl-4-thiol/Ag Nanowire Nanocavity

“…The photon emission intensity variation with the polarization angle agrees with the electric field enhancement in the nanocavity. It can be confirmed by simulations and literature study that the obtained polarization-sensitive Raman scattering and PL emission results are due to the designed anisotropic nanocavity. When the electric field of pumped light is perpendicular to the Ag nanowire, the local electric field enhancement is much stronger than those parallel aligned to the nanowire, leading to a stronger light–matter interaction.…”

“…Since the laser light spot size is much larger than the NW diameter, the actual dichroic ratio is much higher. Carefully etching WSe 2 to only maintain the part below the Ag NW can enhance the dichroic ratio enormously . The designed nanocavity shows promising applications for the generation of highly polarized light sources.…”

“…Carefully etching WSe 2 to only maintain the part below the Ag NW can enhance the dichroic ratio enormously. 25 The designed nanocavity shows promising applications for the generation of highly polarized light sources. It is worth mentioning that the fabricated nanocavity is not at the optimized geometry but designed based on the available experiments.…”

“…Polarization-sensitive infrared photodetectors have garnered significant attention in recent years. − To enhance the dichroic ratio of emitted light or Raman scattering, combining a metallic nanowire (NW) with a metal film to form an anisotropic nanocavity seems a new pathway. In 2021, Zhu et al achieved a PL dichroic ratio of WSe 2 up to 110 using an anisotropic nanocavity. However, PL quenching that occurs due to direct contact between 2D materials and metals has not been considered.…”

Excitation and emission distinguished photoluminescence enhancement in a plasmon–exciton intermediate coupling system

“…All these three parameters can be modified by coupling with surface plasmons. In addition to enhancing the emission intensity and accelerating the decay rate, plasmonic nanostructures can also tune the emission polarization, 5–8 providing various possibilities to manipulate the PL properties of quantum emitters and improve the performances of light-emitting devices. When the coupling strength is larger than the mean dissipation rate of the plasmons and excitons, the plasmon–exciton interaction enters into the strong coupling regime.…”