Fano resonance and spectrally modified photoluminescence enhancement in monolayer MoS2 integrated with plasmonic nanoantenna array (1503.03440v1)

Abstract: The manipulation of light-matter interactions in two-dimensional atomically thin crystals is critical for obtaining new optoelectronic functionalities in these strongly confined materials. Here, by integrating chemically grown monolayers of MoS2 with a silver-bowtie nanoantenna array supporting narrow surface-lattice plasmonic resonances, a unique two-dimensional optical system has been achieved. The enhanced exciton-plasmon coupling enables profound changes in the emission and excitation processes leading to spectrally tunable, large photoluminescence enhancement as well as surface-enhanced Raman scattering at room temperature. Furthermore, at low temperatures, due to the decreased damping of MoS2 excitons interacting with the plasmonic resonances of the bowtie array, stronger exciton-plasmon coupling is achieved resulting in a Fano lineshape in the reflection spectrum. The Fano lineshape, which is due to the interference between the pathways involving the excitation of the exciton and plasmon, can be tuned by altering the coupling strengths between the two systems via changing the design of the bowties lattice. The ability to manipulate the optical properties of two-dimensional systems with tunable plasmonic resonators offers a new platform for the design of novel optical devices with precisely tailored responses.

• The paper reveals that tuning the nanoantenna design induces Fano resonance and significantly enhances light emission in monolayer MoS₂.
• It employs silver bowtie arrays to achieve strong exciton-plasmon coupling and a pronounced Purcell effect at room and low temperatures.
• The findings offer a path toward ultra-thin photonic devices with precise spectral control and efficient optical switching applications.

Enhanced Light-Matter Interactions in Monolayer MoS₂ via Plasmonic Nanoantenna Arrays

This paper presents a detailed investigation into the enhancement of photoluminescence (PL) and Raman scattering in monolayer molybdenum disulfide (MoS₂) through its integration with a silver bowtie nanoantenna array. The paper primarily explores the mechanisms underpinning the observed increases in light-matter interaction strength and the tunability of these effects, notably Fano resonance phenomena in the optical response of the system.

The paper leverages the atomically thin structure of MoS₂, a transition metal dichalcogenide (TMD) known for its distinct direct-gap semiconductor properties and other promising optoelectronic attributes, to explore the manipulation of its optical emission properties. This manipulation is achieved by coupling MoS₂ with plasmonic resonances supported by the bowtie nanoantenna array. The design of the array, featuring localized surface plasmon resonances (LSPs), introduces strong, coherent coupling to the excitons in the monolayer MoS₂, significantly enhancing PL and Raman signals at room temperature.

Key Findings and Methodologies

• Fano Resonance: At reduced temperatures, the paper reports the emergence of Fano resonance lineshapes in the reflection spectra. These resonances are attributed to the interplay between narrow excitonic resonances from MoS₂ and the broad plasmonic resonances of the bowtie array. This interference, modifiable by altering the nanoantenna design, represents a tunable optical feature of the coupled system.
• Spectral and Emission Tuning: By varying the geometrical parameters of the silver bowtie nanoantenna array, the authors manage to tune the spectral positions and linewidths of the lattice-coupled LSP modes. This flexibility allows the researchers to demonstrate significant PL enhancements—up to 40 times more than in unmodified MoS₂—linked closely to these tunings.
• Strong Exciton-Plasmon Coupling: At low temperatures, the paper reveals that the exciton-plasmon coupling strength increases due to lower exciton damping, resulting in a more pronounced Fano resonance in the reflection spectrum and suggesting a hybrid light-matter state.
• Purcell Enhancement: The enhancement in the spontaneous emission rate, or Purcell effect, observed in the system is explained through the increased local electromagnetic field sourced from the plasmonic array. This effect varies depending on the spatial overlap and spectral proximity between the excitons and the lattice-LSP modes.

Practical and Theoretical Implications

This work demonstrates a versatile platform, emphasizing the possibilities for engineering optoelectronic devices that require high-intensity light emission and precise spectral control. The findings suggest potential applications in novel ultra-thin photonic devices, including light-emitting diodes, sensors, and transistors. Moreover, the tunability of the observed Fano resonances accentuates potential uses in optical switches and sensors, exploiting their sensitivity to environmental perturbations.

Future Directions

The research paves the way for further exploration into hybrid exciton-plasmon systems, potentially advancing the understanding of strong coupling regimes and expanding the functional capability of 2D material-integrated plasmonic devices. Future studies could explore other TMD materials, alternative plasmonic structures, or even different lattice designs to broaden the range of applicable optoelectronic solutions. The interface between strong coupling phenomena and active feedback mechanisms in such systems could also stimulate significant advances in dynamic optical control.

In summary, this paper outlines a significant stride in understanding and manipulating the light-matter interaction in two-dimensional systems through plasmonic enhancements. The integration of atomically thin semiconductors like MoS₂ with tailored plasmonic structures offers promising avenues for both fundamental physics exploration and the development of next-gen photonic technologies.