Browsing by Author "Mohite, Aditya"

Now showing 1 - 5 of 5
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    Design Oxygen Evolution Reaction Support Materials to Enable Efficient (Photo)electrochemical Water Splitting
    (2023-10-20) Ko, Hyujin; Mohite, Aditya
    Photoelectrochemical(PEC) water splitting is considered one of the most promising technologies for clean hydrogen generation from solar energy. IrOx electrocatalysts have been widely used for water electrolysis due to the strong acidic conditions and slow kinetics in Oxygen Evolution Reaction (OER) at the anode. Given the high cost and lack of Ir on the earth, reducing Iridium content for OER is a crucial aspect towards the commercialization of PEC water splitting. In this research, we have synthesized and investigated low-loading precious metal catalysts using iridium and transition metals with different ratios. Additionally, we modified the surface of the electrode using conductive epoxy and sanded graphite sheets to improve limited stability via corrosion in the strong acidic electrolyte and detachment of the catalyst. The OER activity of low-loading precious metal catalysts increased as the thickness of the graphite decreased and defected. The Ir-based bimetallic nanoparticles showed enhanced OER activity compared to Ir-only. This research provides valuable insights into the effective utilization of precious metals and making efficient structure for OER, which will be crucial in improving hydrogen production through water splitting and making the process more economical.
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    Enhancement strategy for perovskite solution process: A study of spray coating for 2D perovskites and quantum dots
    (2024-07-19) Zhou, Francis; Mohite, Aditya
    Perovskite solar cells are emerging as formidable competitors to traditional silicon-based cells. The biggest challenges faced by researchers are the reproducibility and commercialization of perovskite photovoltaics (PV). Due to the enhanced stability and lowered recombination rate, 2D perovskites are favored over 3D. This study evaluates the efficacy of spray coating versus spin coating, testing variables such as temperature dependence and additives to optimize deposition conditions. The use of surface energy reduction methods improves inherent drawbacks of spray coating, like non-uniform film formation. Furthermore, this research extends to perovskite quantum dots (QDs), investigated for their promising applications as single-photon sources due to their tunable bandgap and excellent band alignment with QDs. Dependencies of quantum dot formation on thermal shock are analyzed, setting the stage for future advancements in quantum dot technology and enhancing our understanding of 2D perovskite and quantum dot integration.
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    Nano-imaging to Determine the Interstitial Nature of Mn(II) Doping in 2D Halide Perovskites
    (2022-06-14) Torma, Andrew J; Mohite, Aditya
    Andrew Jonathon Torma By performing correlated nanoscale X-ray microscopy, temporally resolved photoluminescence measurements, and magnetic force microscopy on the inorganic 2D perovskite Cs2PbI2Cl2, we show that doping Mn2+ into the structure results in a lattice expansion. The observed lattice expansion contrasts with the predicted contraction expected to arise from the B-site metal substitution, thus implying that Mn2+ does not replace the Pb2+ sites. Photoluminescence and electron paramagnetic resonance measurements confirm the presence of Mn2+ in the lattice, while correlated nano-XRD and X-ray fluorescence track the local strain and chemical composition. Density functional theory calculations predict that Mn2+ atoms reside at the interstitial sites between two octahedra in the triangle formed by one Cl- and two I- atoms, which results in a locally expanded structure. These measurements shed light on the fate of transition metal dopants, local structure, and optical emission when they are doped at dilute concentrations into a wide band-gap semiconductor.
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    Surface Modification of Polycrystalline Diamond
    (2024-04-12) Li, Chenxi; Ajayan, Pulickel; Vajtai, Robert; Mohite, Aditya
    The dissertation investigates surface modification techniques on polycrystalline diamond surfaces, exploring their impacts on properties relevant to electronic, surface- cleaning, and nanofabricating applications. Firstly, a comparative study elucidates the oxidation of microcrystalline diamond powder (DP) and polycrystalline diamond film (PCD) via wet chemical treatments and dry processes. The investigation reveals that sulfuric/nitric acids (H2SO4/HNO3) treatment at 360°C demonstrates superior oxidation performance, while oxygen (O2) plasma treatment enhances oxygen content on PCD surfaces. This study provides insights into oxidation mechanisms and guides the optimization of diamond surface cleaning conditions. Secondly, a novel strategy for aminating boron-doped diamond (BDD) via UV irradiation in ammonia (NH3) is presented. By employing hydrobromic acid (HBr) treatment, primary amine dominance is achieved, enhancing amination efficiency. The study also demonstrates the influence of preoxidation states on amine group coverage, offering insights into surface cleaning effects and mechanisms through theoretical simulations. Thirdly, the dissertation explores the functionalization of hydrogen (H)-terminated diamond surfaces with nitrogen (N) and I sulfur (S) heteroatoms, revealing improved electrical conductivity compared to H- terminated diamonds. Pre-functionalization with S promotes sequential amination efficiency on diamond surface, facilitating reduced UV-exposure times. Density functional theory (DFT) simulations indicate downshifts in bandgap upon functionalization, suggesting enhanced surface conductivity for various electronic applications. Finally, a top-down approach for fabricating diamond nanostructures using metal masks and reactive-ion etching (RIE) process is presented. Silver (Ag) mask exhibits distinct etching profiles, where diamond nanorods (DNRs) cluster is preferably formed after etching and preserves single crystallinities with features resembling diamond nanotubes. Preliminary electrical measurements show Schottky-like conductivity features, indicating potential applications in nanodiamond-based electronics. Collectively, these investigations contribute to a deeper understanding of surface modification techniques on polycrystalline diamond surfaces, offering insights into their utilities across diverse technological domains.
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    Unraveling exciton photo-physics in low-dimensional perovskites towards classical and quantum light emissions
    (2024-04-11) Zhang, Hao; Mohite, Aditya
    Organic-inorganic (hybrid) halide perovskite, an arising class of low-cost semiconductor materials, has gained great research interest due to the intriguing photo-physical properties as well as great potentials in photovoltaics and light emitting applications. Such chemically-altered semiconductor platforms enable physical tunability of charge carriers in different dimensionalities, ranging from 3D bulk materials to 0D quantum dots, resulting in novel physical behaviors and light emission properties. Despite great research attention and wide applications in opto-electronics, the fundamental physical properties of the electron-hole pair quasiparticles termed excitons, such as exciton-phonon interactions in 2D perovskites, and the fine structures in perovskite nanocrystals, are still underexplored. In this thesis, we will focus on the exciton properties in two specific type of perovskites systems: two-dimensional perovskites and zero-dimensional perovskite quantum dots. Using a series of spectroscopic and structural characterizations, we will investigate how excitons in 2D perovskites interact with the lattice vibrations and structural dynamics, and the intrinsic exciton behaviors in buried quantum dots, such as fine structure splitting and quantum light emissions at the single-dot level. In the first part, we study the exciton-phonon coupling and carrier dynamics using the ultrafast spectroscopy and stead-state cryogenic spectroscopies, which provides a correlated prospective of the light-induced structural dynamics and origin of exciton-phono couplings in multi-layered 2D perovskites. We suggest that the creation of a dense electron–hole plasma triggers the relaxation of lattice distortion at shorter timescales by modulating the crystal cohesive energy. We also demonstrate close to 3D like exciton-LO phonon coupling, as well as unique light-matter interactions such as exciton-polaritons and lasing properties in 2D perovskites. In the second part, we will demonstrate a novel material platform of perovskite-based quantum emitters, by embedding FAPbI3 based perovskite quantum dots (QDs) into the wide-bandgap 3D perovskite FAPbBr3 using one-step solution processed technique. Spectroscopic characterizations reveal the quantum nature of light emission from the buried QDs, as well as rich exciton fine structures such as triplets and singlets with assistance of magneto-spectroscopy. Such buried QDs exhibit a clear photon-antibunching signature, with second-order correlation function g2(0) to be ~0.15 at T = 6K. Photoluminescence suggests ultra narrow emissions lines with 130 μeV FWHM. High-resolution transmission electron microscope (HR-TEM) confirms the presence of nanometer-sized domains, which indicates the formation of quantum dots during the rapid crystallization of the precursor solvent. The embedded emitters exhibit a mono-exponential radiative decay (τ = 300 ps), with additional multi-exciton states from bi-excitons and trions, as well as temperature-dependent linewidth broadening and phonon sidebands, expected for colloidal FA-based nanocrystals. In addition, direct spectroscopic signatures of the exciton fine states - such as triplets splitting and singlet states brightening - are clearly resolved under magnetic field, revealing the spectral origin and rich photo-physics from the embedded QDs. Furthermore, we have firstly demonstrated the capability of electrical-driven single-photon emission in perovskite by sandwiching the system between electron-transport and hole-transport layers. Our results may pave the pathway of on-chip integration of low-cost single-photon sources for quantum optical systems.