Physics - Conference Items
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Item Establishing composition dependent k · p parameters for (Al,Ga)N alloys(Institute of Electrical and Electronics Engineers (IEEE), 2024-10-23) Singh, Amit Kumar; Gomez-Iglesias, Alvaro; Schulz, Stefan; Horizon 2020; Science Foundation IrelandDeep UV (Al,Ga)N-based light emitters exhibit very low quantum efficiencies when compared to UV emitters at longer wavelengths. To improve the efficiencies of e.g. (Al,Ga)N-based light emitting diodes, theory and simulation can help to guide the device design. The theoretical framework underlying device simulations is often based on drift-diffusion models coupled with a self-consistent Schrodinger-Poisson equation solver. To achieve accurate and predictive models, understanding the composition dependence of material input parameters is of central importance. We target the composition dependence of k⋅p parameters in AlxGa(1−x)N alloys by using density functional theory (DFT) to obtain effective band structures from alloy disordered supercells. Building on these effective band structures, a numerically efficient fitting scheme based on the Sobol-sequence method is employed to extract effective electron masses, me(x) , Luttinger-like parameters Ai(x) , with i=1…6 , and crystal field splitting energy, ΔCF , as a function of Al content, x , in the system. Our calculations reveal that for me(x) a linear interpolation of the GaN and AlN values provides a good description of the DFT data. However, for Ai(x) and ΔCF(x) this simple approximation breaks down and we find that composition dependent bowing parameters are required to describe effective DFT band structures accurately.Item Dual wavelengths inverse spatially offset Raman spectroscopy for bone characterization(Society of Photo-Optical Instrumentation Engineers (SPIE), 2023-03-06) Ma, Hui; Gautam, Rekha; Konugolu Venkata Sekar, Sanathana; O'Flynn, Carrie; Henn, Patrick; Andersson-Engels, Stefan; Boudoux, Caroline; Tunnell, James W.Osteoporosis is a disease that weakens bones increasing the possibility of bone fracture. The gold standard to diagnose osteoporosis is measuring bone mineral density (BMD). Since BMD only partly determines the strength of the bone, more information on chemical composition and microstructure is needed. Here, we implemented a novel dual-wavelength inverse Spatially Offset Raman Spectroscopy (SORS) to characterize tissue chemical composition covering both the fingerprint and high-wavenumber regions. This system provides a greater probing depth keeping the spectrometer setting constant. The results from hydroxyapatite (HA) and water phantom demonstrate the potential of the Raman system to assess bone mineral and matrix quality in-vivo.Item Time resolved SPAD micro-camera probe for wide-field FLIm in microendoscopy(Society of Photo‑Optical Instrumentation Engineers (SPIE), 2023-03-06) Angelone, Dario; Konugolu Venkata Sekar, Sanathana; Messina, Walter; Matheson, Andrew B.; Erdogan, Ahmet T.; Henderson, Robert K.; Burke, Ray; Andersson-Engels, Stefan; James W. Tunnell; Horizon 2020; Science Foundation Ireland; EPSRC Interdisciplinary Research CollaborationWe propose a handheld single photon avalanche diode (SPAD) micro-camera probe for wide-field in-vivo fluorescence lifetime imaging (FLIm) applications. The presented probe includes a novel 3D stacked 1.4 mm × 1.4 mm SPAD array, an integrated excitation light source, and imaging optics. The spatial and temporal performance of the integrated system was characterised using a USAF test target and range of fluorescence lifetime beads.Item Colorectal cancer detection based on the extraction of scattering properties and biochemical concentrations from fluorescence spectroscopy measurements(Optica Publishing Group, 2022-04) Nogueira, Marcelo S.; Matthews, Robert; Killeen, Shane; Oâ Riordain, Micheal; Andersson-Engels, Stefan; Science Foundation IrelandWe report the first study estimating fluorophore and chromophore concentrations with scattering properties for colorectal cancer detection, as well as one of the first studies performing such estimation based on fluorescence spectra alone.Item Investigation of lung volume measurements in neonates using gas in scattering media absorption spectroscopy(Optica Publishing Group, 2022-04) Pacheco, Andrea; Jayet, Bapiste; Grygoryev, Konstantin; Messina, Walter; Dehghani, Hamid; Krite Svanberh, Emilie; Dempsey, Eugene M.; Andersson-Engels, Stefan; Science Foundation IrelandWe perform phantom and numerical studies of the changes in molecular oxygen and water vapor spectroscopic signals, showing the potential of measuring pulmonary volume changes with GASMAS technique in neonates.