Disorder-Engineered Hybrid Plasmonic Cavities for Emission Control of Defects in hBN

Defect-based quantum emitters in hexagonal boron nitride (hBN) are promising building blocks for scalable quantum photonics due to their stable single-photon emission at room temperature. However, enhancing their emission intensity and controlling the decay dynamics remain significant challenges. This study demonstrates a low-cost, scalable fabrication approach to integrate plasmonic nanocavities with defect-based quantum emitters in hBN nanoflakes. Using the thermal dewetting process, we realize two distinct configurations: stochastic Ag nanoparticles (AgNPs) on hBN flakes and hybrid plasmonic nanocavities formed by AgNPs on top of hBN flakes supported on gold/silicon dioxide (Au/SiO2) substrates. While AgNPs on bare hBN yield up to a two-fold photoluminescence (PL) enhancement with reduced emitter lifetimes, the hybrid nanocavity architecture provides a dramatic, up to 100-fold PL enhancement and improved uniformity across multiple. emitters, all without requiring deterministic positioning. Finite-difference time-domain (FDTD) simulations and time-resolved PL measurements confirm size-dependent control over decay dynamics and cavity-emitter interactions. Our versatile solution overcomes key quantum photonic device development challenges, including material integration, emission intensity optimization, and spectral multiplexity. Future work will explore potential applications in integrated photonic circuits hosting on-chip quantum systems and hBN-based label-free single-molecule detection through such quantum nanoantennas.

💡 Research Summary

The paper presents a low‑cost, scalable method to integrate plasmonic nanocavities with defect‑based quantum emitters in hexagonal boron nitride (hBN) flakes, aiming to boost photoluminescence (PL) intensity and tailor decay dynamics. Using thermal dewetting of thin silver (Ag) films, the authors generate stochastic Ag nanoparticles (AgNPs) without lithography. Two configurations are explored: (i) AgNPs directly deposited on hBN flakes placed on a SiO₂/Si substrate, and (ii) a hybrid architecture where hBN flakes rest on a gold (Au)/SiO₂ bilayer and AgNPs are formed on top.

Two distinct nanoparticle size regimes are investigated: ~35 nm particles (small) and ~110 nm particles (large). Small AgNPs primarily act as quenchers, reducing PL by up to a factor of two while slightly shortening the emitter lifetime. In contrast, large AgNPs support a surface‑plasmon resonance that overlaps the zero‑phonon line (ZPL) of hBN defects (~684 nm). When coupled to these larger particles, the near‑field enhancement leads to dramatic PL amplification—up to 100‑fold on average—and a pronounced reduction in radiative lifetime (from ~2 ns down to ~0.2 ns).

Finite‑difference time‑domain (FDTD) simulations reveal that particles larger than 100 nm concentrate the electric field by 10²–10³ times and confine the mode volume to the order of (λ)³, yielding Purcell factors of 50–100. The Au layer in the hybrid design acts as a reflective mirror, creating a metal‑dielectric hybrid mode that further boosts field confinement and directs emission. Simulated hBN thicknesses (10–50 nm) show modest influence on coupling strength, indicating robustness against flake‑to‑flake variations.

Time‑resolved PL measurements confirm the accelerated decay, while saturation power curves demonstrate a five‑fold reduction in the excitation power required to reach saturation in the hybrid structures. Second‑order correlation (g²(τ)) measurements under both continuous‑wave and pulsed excitation maintain sub‑Poissonian statistics (g²(0) ≈ 0.3–0.1), confirming that single‑photon purity is preserved despite the strong plasmonic interaction.

The fabrication approach relies solely on thermal dewetting, eliminating the need for electron‑beam or photolithography and enabling large‑area (inch‑scale) production at minimal cost. However, the stochastic nature of nanoparticle placement means that deterministic control over individual emitter‑cavity coupling is limited; performance is evaluated statistically across many emitters. The authors suggest that integrating deterministic transfer techniques or employing guided self‑assembly could further improve uniformity and enable deterministic positioning.

Overall, the work demonstrates that disorder‑engineered hybrid plasmonic cavities can provide up to two orders of magnitude enhancement in hBN defect emission while simultaneously shortening lifetimes and preserving quantum‑optical properties. This platform offers a practical pathway toward on‑chip quantum photonic circuits, high‑sensitivity label‑free single‑molecule sensing, and scalable quantum nano‑antenna arrays, addressing key challenges of material integration, emission intensity optimization, and spectral multiplexing in solid‑state quantum photonics.