In this study, we experimentally demonstrate the enhancement of valley contrast through exciton-to-trion conversion at room temperature. Cetyltrimethylammonium bromide (CTAB), a well-known organic molecule commonly used in the intercalation of 2D materials, is shown to facilitate electron transfer to a tungsten disulfide (WS2) monolayer through chemical doping. Specifically, a 1 mM CTAB solution is drop-casted onto the WS2 monolayer, inducing the conversion from exciton to trion emission within the material. The introduction of a trion-abundant environment in WS2 results in a notable increase in valley contrast without the application of external bias. To the best of our knowledge, this study represents the first demonstration of valley contrast enhancement through the chemical doping of CTAB. Consequently, this research provides a detailed exploration of liquid-controlled electron doping from the perspective of valleytronics.
We inversely design plasmonic nanotweezers by topology optimization. Strikingly, the resulting structure resembles a double nanohole, but with additional surrounding features, surpassing the electric field enhancements of our previous algorithmically designed systems by ~45%.
Hexagonal boron nitride (hBN)—a 2D crystalline sheet consisting of alternating boron and nitrogen atoms—is emerging as a promising candidate for integrated photonics due to its exceptional properties. It is one of the widest bandgap materials (6 eV) with a transparency window including ultraviolet and visible regime. Importantly, hBN hosts ultra-bright single photon emitters (SPEs) operating at room temperature, which have attracted intense research attention since their discovery in 2016. hBN hosts a broad range of SPEs in energies showing exceptional brightness with several million counts at the detector. In addition, these emitters benefit from weak electron-phonon coupling indicated by the high intensity of zero phonon lines and weak intensity in the phonon sideband. This, together with the high degree of inherent chemical inertness, makes hBN an attractive candidate for next-generation photonic quantum integrated circuits.
Integration of fluorescent nanoparticles into photonic resonators is crucial for on-chip integration and applications in nanophotonics and quantum technologies. In this work we demonstrate a cavity design with a pocket at its center to host fluorescent nanoparticles. Simulations show that filling the pocket with a particle drastically reduces the mode volume to ~ 0.015 (λ/n)3 and strongly increases the field overlap of the fluorescent material with the cavity mode thus achieving more efficient coupling. We then demonstrate a method to fabricate dielectric cavities that naturally form a nano-pocket during the processing steps. Finally, the functionality of devices with and without particle in the pocket are directly compared. We show a PL enhancement by a factor of 20 and 2.5-fold lifetime reduction at room temperature versus 3.5 PL enhancement and 1.7 lifetime reduction for cavities with particle in a pocket and particle outside a pocket, respectively.
We report second harmonic generation (SHG) from thick hexagonal boron nitride (hBN) flakes with approximately 109 layers. Surprisingly, the resulting signal is stronger when compared to previously reported few-layer experiments that showed the SHG efficiency gradually decreasing with the increasing thickness. This confirms that thick hBN flakes can serve as a platform for nonlinear optics, which is useful because thick flakes are easy to exfoliate while retaining a large flake size. We also show spatial second harmonic maps revealing that SHG remains a useful tool for the characterization of the layer structure even in the case of a large number of layers.
Engineering solid state quantum systems is amongst grand challenges in realizing integrated quantum photonic circuitry. While several 3D systems (such as diamond, silicon carbide, zinc oxide) have been thoroughly studied, solid state emitters in two dimensional (2D) materials are still in their infancy.
In this talk I will introduce hexagonal boron nitride (hBN) as a promising layered material that hosts ultra bright quantum emitters. I will present several avenues to engineer these emitters in large exfoliated sheets, multilayers and 2D monolayers using top down and bottom up approaches. I will also discuss potential atomistic structures of the defects supported by density functional theory.
I will then highlight promising avenues to integrate the emitters with plasmonic and photonic cavities to achieve improved collection efficiency and Purcell enhancement. These are fundamental experiments to realize integrated quantum photonics with 2D materials. I will summarize by outlning challenges and promising directions in the field of quantum emitters and nanophotonics with 2D materials and other wide band gap materials.
The fundamental study and realisation of practical devices for quantum nanophotonic systems stems from the development of hybridised devices, consisting of a single photon source and various other constituents, which aid in controlling light-matter interactions. Emitters hosted within hexagonal boron nitride (hBN) are such a source favoured for this role, owing to its high quantum efficiency, brightness, and robustness. In our work, we explore and demonstrate the integration of hBN emitters with plasmonics, in two distinct arrangements – gold nanospheres, and a gold plasmonic nanocavity array. The former involves the utilisation of an atomic force microscope (AFM) tip to precisely position gold nanospheres to within close proximity to the quantum emitters and observe the resulting emission enhancement and fluorescence lifetime reduction. A fluorescence enhancement of over 300% and a saturated count rate in excess of 5M counts/sec is achieved, emphasising the potential of this material for hybridisation. The latter arrangement involves the direct transfer of a gold plasmonic lattice on top of an emitter hosted within hBN, similarly, to achieve emission enhancement as well as a reduction in fluorescence lifetime and provides an approach for achieving scalable, integrated hybrid systems based on low-loss plasmonic nanoparticle arrays. Both these systems give promising solutions for future employment of quantum emitters in hBN for integrated nanophotonic devices and provide us insight into the complex photodynamics, which envelop the emitters hosted within the material.
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