Browsing by Author "Magill, Brenden A."

Now showing 1 - 8 of 8
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    Dynamics of photoexcited carriers and spins in InAsP ternary alloys
    Meeker, M. A.; Magill, Brenden A.; Merritt, T. R.; Bhowmick, M.; McCutcheon, K.; Khodaparast, Giti A.; Tischler, J. G.; McGill, S.; Choi, S. G.; Palmstrom, C. J. (AIP Publishing, 2013-06)
    The recent rapid progress in the field of spintronics involves extensive measurements of carrier and spin relaxation dynamics in III-V semiconductors. In addition, as the switching rates in devices are pushed to higher frequencies, it is important to understand carrier dynamic phenomena in semiconductors on femtosecond time-scales. In this work, we employed time and spin resolved differential transmission measurements; to probe carrier and spin relaxation times in several InAsP ternary alloys. Our results demonstrate the sensitivity of the spin and carrier dynamics in this material system to the excitation wavelengths, the As concentrations, and temperature. (C) 2013 AIP Publishing LLC.
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    Multi-photon patterning of photoactive o-nitrobenzyl ligands bound to gold surfaces
    Magill, Brenden A.; Guo, Xi; Peck, Cheryl L.; Reyes, Roberto L.; See, Erich M.; Santos, Webster L.; Robinson, Hans D. (Royal Society of Chemistry, 2019-01-01)
    We quantitatively investigate lithographic patterning of a thiol-anchored self-assembled monolayer (SAM) of photocleavable o-nitrobenzyl ligands on gold through a multi-photon absorption process at 1.7 eV (730 nm wavelength). The photocleaving rate increases faster than the square of the incident light intensity, indicating a process more complex than simple two-photon absorption. We tentatively ascribe this observation to two-photon absorption that triggers the formation of a long-lived intermediate aci-nitro species whose decomposition yield is partially determined either by absorption of additional photons or by a local temperature that is elevated by the incident light. At the highest light intensities, thermal processes compete with photoactivation and lead to damage of the SAM. The threshold is high enough that this destructive process can largely be avoided, even while power densities are kept sufficiently large that complete photoactivation takes place on time scales of tens of seconds to a few minutes. This means that this type of ligand can be activated at visible and near infrared wavelengths where plasmonic resonances can easily be engineered in metal nanostructures, even though their single-photon reactivity at these wavelengths is negligible. This will allow selective functionalization of plasmon hotspots, which in addition to high resolution lithographic applications would be of benefit to applications such as Surface Enhanced Raman Spectroscopy and plasmonic photocatalysis as well as directed bottom-up nanoassembly.
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    Optical properties of Pb0.52Zr0.48TiO3 nanorod arrays: second harmonic generation and multiphoton carrier dynamics
    Mudiyanselage, Rathsara R. H. H.; Burton, John; Magill, Brenden A.; McMillan, Kiara; Gagliano, Gabriella; Morral, Ada J.; Kang, Min Gyu; Kang, Han Byul; Priya, Shashank; Stanton, Christopher J.; Khodaparast, Giti A. (2021-07)
    Nonlinear optical properties of poled and unpoled, lead zirconate-titanate (Pb0.52Zr0.48TiO3) nanorod arrays, grown on Pt-coated Si with similar to 200 nm diameter and similar to 600 nm height, were investigated. Clear signatures of second harmonic generations (SHG), from 490-525 nm (2.38-2.53 eV) at room temperature, were observed. Furthermore, time resolved differential reflectivity measurements were performed to study dynamical properties of photoexcited carriers in the range of 690-1000 nm where multiphoton processes were responsible for the photo-excitations. We compared this excitation scheme, which is sensitive mainly to the surface states, to when the photoexcited energy (similar to 3.1 eV) was close to the band gap of the nanorods. Our results offer promises for employing these nanostructures in nonlinear photonic applications.
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    Photoluminescence lineshape and dynamics of localized excitonic transitions in InAsP epitaxial layers
    Merritt, T. R.; Meeker, M. A.; Magill, Brenden A.; Khodaparast, Giti A.; McGill, S.; Tischler, J. G.; Choi, S. G.; Palmstrom, C. J. (American Institute of Physics, 2014-05-21)
    The excitonic radiative transitions of InAsxP1-x (x = 0.13 and x = 0.40) alloy epitaxial layers were studied through magnetic field and temperature dependent photoluminescence and time-resolved photoluminescence spectroscopy. While the linewidth and lineshape of the exciton transition for x = 0.40 indicate the presence of alloy broadening due to random anion distribution and the existence of localized exciton states, those of x = 0.13 suggest that this type of compositional disorder is absent in x = 0.13. This localization is further supported by the behavior of the exciton transitions at low temperature and high magnetic fields. InAs0.4P0.6 exhibits anomalous "S-shaped" temperature dependence of the excition emission peak below 100K as well as linewidth broadening at high magnetic fields due to the compression of the excitonic volume amid compositional fluctuations. Finally, photoluminescence decay patterns suggest that the excitons radiatively relax through two channels, a fast and a slow decay. While the lifetime of the fast decay is comparable for both compositions (similar to 30 ps), that of the slow decay increases from 206 ps to 427 ps as x increases from 0.13 to 0.40, attributable to carrier migration between the localization states of InAs0.4P0.6. (C) 2014 AIP Publishing LLC.
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    Photoluminescence Study of Carrier Localization and Recombination in Nearly Strain-Balanced Nonpolar InGaN/AlGaN Quantum Wells
    Cao, Yang; Dzuba, Brandon; Magill, Brenden A.; Senichev, Alexander; Trang Nguyen; Diaz, Rosa E.; Manfra, Michael J.; McGill, Stephen; Garcia, Carlos; Khodaparast, Giti A.; Malis, Oana (Wiley-V C H, 2022-02-16)
    Temperature-dependent continuous-excitation and time-resolved photoluminescence are studied to probe carrier localization and recombination in nearly strain-balanced m-plane In0.09Ga0.91N/Al0.19Ga0.81N multi-quantum wells grown by plasma-assisted molecular-beam epitaxy. An average localization depth of 21 meV is estimated for the undoped sample. This depth is much smaller than the reported values in polar structures and m-plane InGaN quantum wells. As part of this study, temperature and magnetic field dependence of time-resolved photoluminescence is performed. At 2 K, an initial fast decay time of approximate to 0.3 ns is measured for both undoped and doped structures. The undoped sample also exhibits a slow decay component with a time scale of 2.2 ns. The existence of two relaxation paths in the undoped structure can be attributed to different localization centers. The fast relaxation decays are relatively insensitive to external magnetic fields, while the slower relaxation time constant decreases significantly with increasing magnetic fields. The fast decay time scale in the undoped sample is likely due to indium fluctuations in the quantum well. The slow decay time may be related to carrier localization in the barriers. The addition of doping leads to a single fast decay time likely due to stronger exciton localization in the InGaN quantum wells.
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    Probe of the excitonic transitions and lifetimes in quasi-2D organic-inorganic halide perovskites
    Magill, Brenden A.; Wang, Kai; McGill, Stephen; Stanton, Christopher J.; Priya, Shashank; Khodaparast, Giti A. (AIP Publishing, 2022-01-01)
    Traditional organic-inorganic halide perovskites (OIHPs), in which perovskites layers are separated by an organic spacer material, have been mainly explored for photovoltaics devices, but they also offer promises for nonlinear optics and quantum light applications. These attributes include (a) high quantum efficiency, (b) large binding energy of excitons in low-dimensional structures, (c) polarons of long coherence times at room temperature, and (d) a large spin-orbit coupling. OIHP systems can be engineered to have photoluminescence (PL) emissions from UV to IR regions, in addition to power conversion efficiencies, in excess of 24%. This class of materials offers broad tunability of its properties, through controlling the number of atomic layers in the quantum well, tuning the organic spacer thickness, or even engineering the composition with exotic dopants. In this work, we present PL and time-resolved PL measurements of quasi-2D BA(2)PbI(4) and provide new insights on the temperature dependence of their excitonic dynamics and fine structures of their PL emissions. We observed long lifetimes, which can result from the formation of large polarons, screening the Coulomb interactions of the charge carriers and reducing the scattering of the carriers with charge defects.
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    Room temperature ferromagnetic resonance in hetero-epitaxial BTO-BFO/LSMO magnetoelectric composite
    Madon, Benjamin; Kang, Han Byul; Kang, Min-Gyu; Maurya, Deepam; Magill, Brenden A.; Alves, Marcos J.P.; Wegrowe, Jean-Eric; Drouhin, Henri-Jean; Priya, Shashank; Khodaparast, Giti A. (American Institute of Physics, 2018-10-30)
    We synthesized epitaxial BTO-BFO heterostructure with decreased leakage and simultaneously improved the multiferroic properties. This study provides new direction for ferromagnetic resonance studies, in high quality BTO-BFO films grown on LSMO. We observed small Gilbert damping (=0.004) and the absence of large inhomogeneous broadening, in a film with 80 nm thickness of BTO-BFO on LSMO (110). This fact offers opportunities for employing this material system for spin transfer in multifunctional materials where controlling magnetization by a flow of spin angular momentum, or spin current, is crucial toward developing nanoscale spin-based memory and devices. Magnetic insulators, such as BTO-BFO on LSMO, are potentially excellent candidates for pure spin current without the existence of charge current.
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    Upconverting nanocomposites dispersed in urea-containing acrylics
    Inglefield, David Lott, Jr.; Merritt, Travis R.; Magill, Brenden A.; Long, Timothy E.; Khodaparast, Giti A. (The Royal Society of Chemistry, 2015-05-08)
    Lanthanide-doped upconverting nanoparticles (UCNPs) have the ability to convert low energy photons into high energy photons, making this material appealing for a variety of scientific pursuits, from solar energy conversion to bioimaging. A combination of polymers and nanocomposites increases the utility of these upconverting nanoparticles allowing nanoparticles to be added to any device compatible with polymer coatings. Here, trifluoroacetate salt decomposition enables Er/Yb doped NaYF4 upconverting nanoparticle synthesis. The subsequent deposition of a silica nanoshell yields polar silica-coated upconverting nanoparticles, enabling composite formation with polar urea-containing methacrylic polymers. Hydrogen bonding between urea groups in the polymer and the silica-coated nanoparticles allowed for dispersion of the upconverting nanoparticles to form upconverting composite films. These films exhibit desirable upconversion comparable to the nanoparticles dispersed in methanol. Urea-containing polymers are promising candidates for matrices in nanocomposites formed with polar silica nanoparticles due to favorable polymer-nanoparticle interactions. This architecture is superior to urea-methacrylate homopolymers, since the central low glass transition temperature block will provide critical ductility to the film, thus rendering the film to be durable for optical applications.