Engineering Low-dimensional Materials for Quantum Photonic and Plasmonic Applications
Creators: name: Xu, Xiaohui
Publisher: name: Purdue University Graduate School
Year: 2022
Subjects: Functional materials
Optical properties of materials
Quantum optics and quantum optomechanics
Photonics, optoelectronics and optical communications

description: Low-dimensional materials (LDMs) are substances that have at least one dimension with thicknesses in the nanometer (nm) scale. They have attracted tremendous research interests in many fields due to their unique properties that are absent in bulk materials. For instance, in quantum optics/photonics, LDMs offer unique advantages for effective light extraction and coupling with photonic/plasmonic structures; in chemistry, the large surface-to-volume ratio of LDMs enables more efficient chemical processes that are useful for numerous applications. In this thesis, several types of LDMs are studied and engineered with the goal to improve their impact in plasmonic and quantum photonic applications. Two-dimensional hexagonal boron nitride (hBN) is receiving increasing attention in quantum optics/photonics as it hosts various types of quantum emitters that are promising for quantum computing, quantum sensing, etc. In the first study, we explore and demonstrate a radiation- and lithography-free route to deterministically create single-photon emitters (SPEs) in hBN by nanoindentation with an atomic force microscopy. The method applies to hBN on flat, chip-compatible silicon-based substrates, and an SPE yield of up to 36% is achieved. This marks an important step toward the deterministic creation and integration of hBN SPEs with photonic and plasmonic devices. In the second study, the recently discovered negatively charged boron vacancy (V<sub>B</sub><sup>-</sup>) spin defect in hBN is investigated. V<sub>B</sub><sup>-</sup> defects are optically active with spin properties suitable for sensing at extreme scales. To resolve the low brightness issue of V<sub>B</sub><sup>-</sup> defects, we couple them with an optimized nano-patch antenna structure and observe emission intensity enhancement that is nearly an order of magnitude higher than previous reports. Our achievements pave the way for the practical integration of V<sub>B</sub><sup>-</sup> defects for quantum sensing. Zero-dimensional nanodiamond is another important host material for solid-state SPEs. Specifically, the negatively charged silicon vacancy (SiV) center in nanodiamonds exhibits optical properties that are suitable for quantum information technologies. In the third study, we, for the first time, demonstrate the creation of single SiV centers in nanodiamonds with an average size of ~20 nm using ion implantation. Stable single-photon emission is confirmed at room temperature, with zero-phonon line (ZPL) wavelengths in the range of 730 – 803 nm. This confirms the feasibility of single-photon emitter creation in nanodiamonds with ion implantation, and offers new opportunities to integrate diamond color centers for hybrid quantum photonic systems. Finally, we have also explored using metal-semiconductor hybrid nanoparticles for plasmon-enhanced photocatalysis. A core-shell nanoparticle structure is synthesized, with titanium nitride (TiN) and titanium dioxide (TiO<sub>2</sub>) being the core and shell material respectively. It is observed that such core-shell nanoparticles effectively catalyze the generation of single oxygen molecules under 700-nm laser excitation. The main mechanism behind is the hot electron injection from the TiN core to the TiO<sub>2</sub> shell. Considering the chemical inertness and low cost of TiN, TiN@TiO<sub>2</sub> NPs hold great potential as plasmonic photosensitizers for photodynamic therapy and other photocatalytic applications at red-to-near-infrared (NIR) wavelengths.