Ultraviolet-Visible Plasmonic Properties of Gallium Nanoparticles Investigated by Variable-Angle Spectroscopic and Mueller Matrix Ellipsometry
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2014-07-16
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© 2014 American Chemical Society.Self-assembled, irregular ensembles of hemispherical Ga nanoparticles (NPs) were deposited on sapphire by molecular beam epitaxy. These samples, whose constituent unimodal or bimodal distribution of NP sizes was controlled by deposition time, exhibited localized surface plasmon resonances tunable from the ultraviolet to the visible (UV/vis) spectral range. The optical response of each sample was characterized using a variable-angle spectroscopic ellipsometer, and the dielectric response of the ensemble of NPs on each sample was parametrized using Lorentz oscillators. From this, a relationship was found between NP size and the deduced Lorentzian parameters (resonant frequency, damping, oscillator strength) for most unimodal and bimodal samples at most frequencies and angles of incidence. However, for samples with a bimodal size distribution, Mueller matrix ellipsometry revealed nonspecular scattering at particular frequencies and angles, suggesting a resonant interparticle coupling effect consistent with recently observed strong local field enhancements in the ultraviolet. (Graph presented).
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Yang, Y, N Akozbek, TH Kim, JM Sanz, F Moreno, M Losurdo, AS Brown, HO Everitt, et al. (2014). Ultraviolet-Visible Plasmonic Properties of Gallium Nanoparticles Investigated by Variable-Angle Spectroscopic and Mueller Matrix Ellipsometry. ACS Photonics, 1(7). pp. 582–589. 10.1021/ph500042v Retrieved from https://hdl.handle.net/10161/13863.
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April S. Brown
Dr. April Brown received her B.S.E.E. from North Carolina State University in 1981, her M.S.E.E. and Ph.D. from Cornell University in 1984 and 1985, respectively. She worked at the Hughes Research Laboratories (now HRL LLC) in Malibu, Ca. from 1986-1993, and spent one year at the Army Research Office in the Physics Division (1988). She joined the Georgia Institute of Technology in 1994 as an Associate Professor and was promoted to Professor in 1999. She was Associate Dean in the College of Engineering from 1999-2001 and Executive Assistant to the President from 2001-2002. In addition, she was named Pettit Professor in Microelectronics in 2001. She joined Duke University as Professor and Chair in July 2002.
Henry Everitt
Dr. Everitt is the Army's senior technologist (ST) for optical sciences, a senior executive currently working for the Army Research Laboratory in Houston, TX. Through his adjunct appointment in the Duke Physics Department, he leads an active experimental research group in molecular physics, novel terahertz imaging, nanophotonics, and ultrafast spectroscopy of wide bandage semiconductors with colleagues on campus and through an international network of collaborators. Four principal research areas are being pursued: 1) Molecular Physics. The longest research effort involves the use of molecular rotational spectroscopy and time-resolved techniques to investigate molecular collision dynamics. These studies will help us develop more efficient terahertz sources, detect and identify clouds of trace gases, and understand nonequilibrium atmospheres and interstellar media. In collaboration with Prof. Frank De Lucia, formerly of Duke Physics, Dr. Everitt was the first to map out the complete rotational and vibrational energy transfer map of methyl fluoride, leading to the demonstration of a compact, tunable terahertz laser for use in ground-based spectroscopy and astronomical observation. Their double resonance technique has now been adapted as a new means for remotely identifying the constituents of a trace gas cloud at distances up to 1 km. 2) Terahertz Imaging. This newest activity uses powerful, cw, tunable millimeter- and submillimeter-wave sources to adapt various coherent imaging techniques to the terahertz spectral region. Interferometry, digital holography, tomography, synthetic aperture RADAR, ISAR, ellipsometry, and polarimetry are all explored to develop practical tools for non-destructive measurements of visually opaque materials. The lab contains a unique combination of tunable sources, Schottky diode detectors, heterodyne receivers, and bolometers, plus a one-of-a-kind THz beam characterization and imaging instrument. The lab also explores ways of optimizing and accelerating these slow imaging methodologies, including methods for mapping strain in opaque composite materials with on-campus collaborators Profs. Nan Jokerst, Willie Padilla, and David Smith. 3) Ultraviolet Nanoplasmonics. Using metal nanoparticles to concentrate electromagnetic fields locally is an area of active research, most of which concentrates on using metal nanoparticles active in the visible and ultraviolet spectral regions. There are significant advantages of extending plasmonics into the ultraviolet, including enhanced Raman cross sections, accelerated photo-degradation of toxins, and accelerated excitonic recombination. In partnership with Profs. Jie Liu (Duke Chemistry), April Brown (Duke ECE), Naomi Halas (Rice Univ.), Fernando Moreno (Univ. Cantabria), and others, we have been identifying and exploring new nanostructured metals including rhodium, gallium, and aluminum for ultraviolet plasmonics. We have recently demonstrated ultraviolet surface enhanced Raman spectra and tailored photocatalytic behavior of important chemical reactions. 4) Ultrafast Spectroscopy. This effort concentrates on the ultrafast spectroscopic characterization of wide bandgap semiconductor heterostructures and nanostructures. We use independently tunable pump and probe wavelengths that span the ultraviolet-visible-infrared regions from 200 nm to 12 microns with pulses shorter than 150 fs. The objective is to manipulate and control carrier, exciton, and phonon transport and relaxation pathways in metal oxide and III-N semiconductors, sometimes doped with rare-earth atoms, using quantum efficiency, cw and time-resolved photoluminescence and differential transmission measurements. Areas of recent interest include characterization of efficient phosphorescence in sulfur-doped ZnO with Prof. Jie Liu, carrier dynamics in III-N epilayers and multiple quantum wells with Prof. April Brown, and characterization of radiative and nonradiative recombination of rare earth dopants in wide bandgap semiconductor hosts.
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