Browsing by Author "Heyne, Belinda Josiane M."

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    Engineered impurity-doped materials for Quantum Information Processing applications - nano-structures and disordered materials
    (2017) Lutz, Thomas; Tittel, Wolfgang; Barclay, Paul E.; Moazzen-Ahmadi, Nasser; Simon, Christoph; Heyne, Belinda Josiane M.; Loncar, Marko; Pierce, Greg David
    In this thesis we explore various ways to extend population lifetimes and coherence times of solid-state emitters. We focus on rare-earth-ion doped host materials and silicon vacancy centers in diamond, both of which are used for applications in quantum information processing and quantum communications. Enhanced lifetimes and coherence times would improve the performance of these applications. One approach investigates the possibility to suppress lattice vibrations that cause decoherence and population relaxation by engineering the phonon density of states through nano-structuring of the emitter's host material. Towards this end we study different materials and methods to obtain the desired nano-materials. Using various optical spectroscopic methods, we show that population dynamics can indeed be influenced by modifying the structure of the surrounding host material. However, we also find that the employed fabrication and synthesis methods often induce crystal damage that, in turn, degrades spectroscopic properties. As a second approach, we study rare-earth-ions in disordered host materials. Detailed spectroscopic characterizations are presented and we show with the example of an erbium doped fiber that such materials can indeed feature better properties, specifically longer population lifetimes, than the commonly used bulk crystals. We found optimal operation parameters for the erbium doped fiber which made it possible to use this medium for successful proof of principle experiments demonstrating a multimode quantum memory that operates within the convenient telecom band (around 1550 nm wavelength). Besides increasing the fundamental knowledge, the results of the studies presented in this thesis are highly relevant for the fields of quantum communications and quantum information processing since nano-structured materials are beginning to be investigated for on-chip implementations of various applications such as quantum memories and quantum gates. In addition, we found that population dynamics driven by detrimental lattice vibrations can indeed be modified in small powder materials and thus, with improved fabrication techniques, the complete suppression of lattice vibrations should be possible, benefiting a plethora of applications.
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    Mid Infrared Investigation of Two Isomers of the CO-N2O van der Waals Complex
    (2017) Barclay, Aaron; Moazzen-Ahmadi, Nasser; Heyne, Belinda Josiane M.; Thompson, Robert Ian; Jackel, Brian
    Infrared spectra in the carbon monoxide CO stretch region (~2150 cm−1) and in the nu3 asymmetric stretch region of N2O (~2223 cm−1) are assigned to the previously unobserved O-bonded form of the CO-N2O dimer (“isomer 2”). This van der Waals complex has a planar skewed T-shaped structure like that of the previously observed C-bonded form (“isomer 1”), but with the CO rotated by 180°. In addition to the fundamental band, combination bands for both isomers are observed and intermolecular frequencies for the out of plane torsion and the in-plane CO-rock, or disrotatory bend are reported. Vibrational assignment of these bands is achieved by comparison with data recently published (A. Barclay et al., Chem. Phys. Letters, 651 (2016) 62), concerning OC-CO2. We show that the most recent ab initio potential energy surface is inadequate in predicting the intermolecular frequencies for both isomers (CO-N2O and OC-N2O).
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    Proton Conduction and Lithium Extraction in Chromium (III) Phosphonate Metal-Organic Frameworks
    (2024-01-24) Zhang, Jinfeng; Shimizu, George Kisa Hayashi; Heyne, Belinda Josiane M.; Thangadurai, Venkataraman; Ling, Chang-Chun; Demadis, Konstantinos
    Phosphonate metal-organic frameworks (MOFs) present potential candidates for functional materials due to their inherent structural stability and the capacity for synthetic manipulation. However, a trade-off often arises in the form of compromised crystallinity and structural predictability, which poses a significant hurdle in fabricating porous materials. This thesis focuses on an in-depth investigation into the synthetic approach and the performance of ordered chromium phosphonate MOFs concerning proton conduction and lithium extraction. An approach utilizing a hydrogen-bonded metal-organic framework (HMOF) intermediate was adopted to balance crystallinity and stability and evaluated thoroughly in Chapter 3. Salts made of hexaaquochromium(III) cations and phosphonate anions were dehydrated to form stable MOFs. Intriguingly, this method maintains partial structural crystallinity and engenders a varied pore size distribution during the thermal dehydration conversion step. This variability, in turn, affects the proton conductivity by providing different proton mobility efficiency, with as broad as two orders of magnitude in proton conduction among different MOFs. Chapter 4 explores the use of the HMOF to MOF strategy, focusing on the impact of reagent stoichiometry, ligand geometry, and binary solvent systems on proton conduction. It reveals that fine-tuning reactant stoichiometry is a viable method for enhancing proton mobility channels. The chapter also investigates how ligand geometry influences proton conductor performance, finding that more flexible structures maintain conductivity regardless of structural changes caused by water percolation. Additionally, it highlights the role of binary solvent systems in HMOF synthesis, noting that higher solvent content in HMOFs leads to lower crystallinity and reduced proton conduction after thermal dehydration, though the dehydration process itself minimally affects proton conductivity. Chapter 5 pivoted focus to explore the potential of chromium phosphonates as direct lithium extraction (DLE) adsorbents. To achieve optimal Li+ uptake capacity and selectivity, DLE adsorbents were designed to incorporate a Li+ favorable ’pocket’, templated during synthesis, along with a specific pore aperture for Li+ sieving. The study investigates the influence of pH, contact time, and concentration on adsorption, indicating a pseudo-second order kinetic model and monolayer chemisorption. Durability tests reveal these adsorbents maintain consistent uptake capacity and high stability.