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Mathias Schubert - One of the best experts on this subject based on the ideXlab platform.
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Longitudinal Phonon plasmon mode coupling in β ga2o3
Applied Physics Letters, 2019Co-Authors: Mathias Schubert, Alyssa Mock, Rafal Korlacki, Sean Knight, Zbigniew Galazka, Gunther Wagner, Virginia D Wheeler, Marko J TadjerAbstract:In this letter, we investigate a set of n-type single crystals of monoclinic symmetry β-Ga2O3 with different free electron concentration values by generalized far infrared and infrared spectroscopic ellipsometry. In excellent agreement with our previous model prediction, we find here by experiment that Longitudinal-Phonon-plasmon coupled modes are polarized either within the monoclinic plane or perpendicular to the monoclinic plane. As predicted, all modes change the amplitude and frequency with the free electron concentration. The most important observation is that all Longitudinal-Phonon-plasmon coupled modes polarized within the monoclinic plane continuously change their direction as a function of free electron concentration.In this letter, we investigate a set of n-type single crystals of monoclinic symmetry β-Ga2O3 with different free electron concentration values by generalized far infrared and infrared spectroscopic ellipsometry. In excellent agreement with our previous model prediction, we find here by experiment that Longitudinal-Phonon-plasmon coupled modes are polarized either within the monoclinic plane or perpendicular to the monoclinic plane. As predicted, all modes change the amplitude and frequency with the free electron concentration. The most important observation is that all Longitudinal-Phonon-plasmon coupled modes polarized within the monoclinic plane continuously change their direction as a function of free electron concentration.
V. E. Zakhvataev - One of the best experts on this subject based on the ideXlab platform.
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Propagating Subterahertz Longitudinal Phonon-like Modes in a Lipid Bilayer in Aqueous Medium
Biochemistry (Moscow) Supplement Series A: Membrane and Cell Biology, 2018Co-Authors: V. E. ZakhvataevAbstract:It has been revealed recently that the subterahertz/terahertz vibrational motions in enzymes and DNA immersed in aqueous solutions can be underdamped. Importantly, these motions are associated with coherent delocalized modes that control functional processes. Analogous propagating Phonon-like modes have been found in free hydrated lipid bilayers. In the present work, subterahertz (frequencies of the order of tens and hundreds of gigahertz) Longitudinal acoustic oscillations in a bilayer lipid membrane immersed in aqueous medium are investigated theoretically. We consider driven oscillations excited by tangential mechanical tensions at the bilayer surfaces and thermally induced Phonon modes. The analysis is based on: (i) a generalized hydrodynamic model of two-dimensional lipid bilayer in aqueous medium; (ii) known estimates of frequencies and lifetimes of Longitudinal acoustic Phonons in free hydrated lipid bilayer and in water, which were obtained in the experiments on non-elastic X-ray scattering and the molecular dynamics simulations. We show that the membrane Phonon-like excitations are underdamped for the typical values of the system parameters, and the contribution of aqueous medium to the membrane mode damping is small compared to the contribution of the lipid bilayer. The obtained results suggest the possibility of realization of thermally induced Longitudinal membrane Phonons in physiological conditions, as well as the possibility of resonance amplification of the impact of subnanosecond electric impulses and impulses of subterahertz electromagnetic radiation on membrane dynamics.
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Subterahertz Longitudinal Phonon Modes Propagating in a Lipid Bilayer Immersed in an Aqueous Medium
Journal of Experimental and Theoretical Physics, 2018Co-Authors: V. E. ZakhvataevAbstract:The properties of subterahertz Longitudinal acoustic Phonon modes in the hydrophobic region of a lipid bilayer immersed in a compressible viscous aqueous medium are investigated theoretically. An approximate expression is obtained for the Mandelstam–Brillouin components of the dynamic structure factor of a bilayer. The analysis is based on a generalized hydrodynamic model of the “two-dimensional lipid bilayer + three-dimensional fluid medium” system, as well as on known sharp estimates for the frequencies and lifetimes of long-wavelength Longitudinal acoustic Phonons in a free hydrated lipid bilayer and in water, obtained from inelastic X-ray scattering experiments and molecular dynamics simulations. It is shown that, for characteristic values of the parameters of the membrane system, subterahertz Longitudinal Phonon-like excitations in the hydrophobic part of the bilayer are underdamped. In this case, the contribution of the viscous flow of the aqueous medium to the damping of a Longitudinal membrane mode is small compared with the contribution of the lipid bilayer. Quantitative estimates of the damping ratio agree well with the experimental results for the vibration mode of the enzyme lysozyme in aqueous solution [1]. It is also shown that a coupling between Longitudinal Phonon modes of the bilayer and relaxation processes in its fluid environment gives rise to an additional peak in the scattering spectrum, which corresponds to a non-propagating mode.
Shinichi Nakashima - One of the best experts on this subject based on the ideXlab platform.
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selective resonance effect of the folded Longitudinal Phonon modes in the raman spectra of sic
Physical Review B, 2000Co-Authors: Takuro Tomita, M Hundhausen, M Baba, Tohru Suemoto, Susumu Saito, Shinichi NakashimaAbstract:T. Tomita, S. Saito, M. Baba, M. Hundhausen, T. Suemoto, and S. Nakashima Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan Institut fur Technische Physik, University Erlangen-Nurnberg, Erwin-Rommel-Strasse 1, D-91058 Erlangen, Germany Department of Electrical and Electronic Engineering, Miyazaki University, 1-1 Gakuenkibanadai-nishi, Miyazaki 889-2192, Japan ~Received 21 September 1999!
Elad Harel - One of the best experts on this subject based on the ideXlab platform.
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Exciton−Phonon Spectroscopy of Quantum Dots Below the Single- Particle Homogeneous Line Width
Journal of Physical Chemistry Letters, 2018Co-Authors: Austin P Spencer, William O Hutson, Shawn Irgen-gioro, Elad HarelAbstract:We demonstrate that high-dimensionality coherent spectroscopy yields " super-resolved " spectra whereby peaks may be localized far below their homogeneous line width by resolving them across multiple, coherently coupled dimensions. We implement this technique using a fifth-order photon-echo spectroscopy called Gradient-Assisted Multidimensional Electronic−Raman Spectroscopy (GAMERS) that combines resonant and nonresonant excitation to disperse the optical response across three spectral dimensions: two involving excitonic transitions and one that encodes Phonon energies. In analogy to super-resolution localization microscopies, which separate spatially overlapping signals in time, GAMERS isolates signals spectrally using combined electronic and nuclear resolution. Optical Phonon lines in a colloidal solution of CdSe quantum dots at room temperature separated by less than 150 μeV are resolved despite the homogeneous line width of these transitions being nearly an order of magnitude broader. The frequency difference between these Phonon modes is attributed to softening of the Longitudinal Phonon mode upon excitation to the lowest exciton state. Further, such Phonon mode selectivity yields spectra with electronic line widths that approach the single particle limit. Through this enhanced spectral resolution, the GAMERS method yields insights into the nature of coupling between Longitudinal optical and acoustic Phonons and specific excitonic transitions that were previously hidden. M ultidimensional Fourier-transform electronic spectros-copy 1 is a class of powerful methods that disentangle the congested spectra of proteins 2−5 and nanostructured materi-als 6−8 by separating spectral features across multiple correlated dimensions. Among the many advantages of these techniques, their ability to resolve the homogeneous peak shapes of heterogeneous samples and to separate independent signal pathways that otherwise overlap in lower dimensionality spectra make them effective tools for studying the electronic and vibrational structure and dynamics of complex chemical systems. Analogous to how super-resolution localization microscopy 9 resolves overlapping features by separating their signals in time, we show that high-order coherent spectroscopy offers additional spectral dimensions along which overlapping homogeneous lines may be separated (Figure 1a). Specifically, in a colloidal solution of quantum dots (QDs), we demonstrate that Phonon peaks separated by 130 μeV may be distinguished even at room temperature where the homogeneous line width is ∼1 meV or greater, representing an improvement in functional resolution of nearly an order of magnitude. This dramatic resolution improvement enables identification of features in the electronic and Phonon structure of the ubiquitously studied cadmium selenide QD that are vitally relevant to charge carrier relaxation and exciton−Phonon coupling. Colloidal semiconductor nanocrystals, or quantum dots, exhibit confinement of the charge carrier wave function along one or more spatial dimensions of the particle. 10 A remarkable property of QDs is that their exceptionally narrow luminescent emission is tunable across a wide spectral range, 11,12 making them attractive targets for a wide range of applications from lasing 13 to biological imaging. 14 Yet, despite decades of steady progress in the synthesis of semiconductor QDs 15−18 as well as a myriad of optical studies, a comprehensive understanding of their photophysical properties has proven elusive. Not unlike many other complex chemical systems in solution, a fundamental limit to studying the electronic structure and carrier dynamics of QDs is their relatively broad absorption and emission line widths owing to interactions of carriers with the environment, particularly optical Phonons. 19−23 In addition to this source of homoge-neous line broadening, inhomogeneous broadening is also presenta result of static particle-to-particle variations (e.g., size, shape, ligand coverage, etc.). 24,25 These compounding layers of broadening lead to severe spectral congestion (Figure 1c), hindering investigations into the detailed electronic structure. There have been many important methods developed that separate homogeneous and inhomogeneous effects in order to characterize the underlying single-molecule states. Notably, photon-correlation Fourier spectroscopy (PCFS) has been utilized to study single-QD emission line shapes in solution at room temperature. 24 The line shapes of single-QDs in films
Marko J Tadjer - One of the best experts on this subject based on the ideXlab platform.
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Longitudinal Phonon plasmon mode coupling in β ga2o3
Applied Physics Letters, 2019Co-Authors: Mathias Schubert, Alyssa Mock, Rafal Korlacki, Sean Knight, Zbigniew Galazka, Gunther Wagner, Virginia D Wheeler, Marko J TadjerAbstract:In this letter, we investigate a set of n-type single crystals of monoclinic symmetry β-Ga2O3 with different free electron concentration values by generalized far infrared and infrared spectroscopic ellipsometry. In excellent agreement with our previous model prediction, we find here by experiment that Longitudinal-Phonon-plasmon coupled modes are polarized either within the monoclinic plane or perpendicular to the monoclinic plane. As predicted, all modes change the amplitude and frequency with the free electron concentration. The most important observation is that all Longitudinal-Phonon-plasmon coupled modes polarized within the monoclinic plane continuously change their direction as a function of free electron concentration.In this letter, we investigate a set of n-type single crystals of monoclinic symmetry β-Ga2O3 with different free electron concentration values by generalized far infrared and infrared spectroscopic ellipsometry. In excellent agreement with our previous model prediction, we find here by experiment that Longitudinal-Phonon-plasmon coupled modes are polarized either within the monoclinic plane or perpendicular to the monoclinic plane. As predicted, all modes change the amplitude and frequency with the free electron concentration. The most important observation is that all Longitudinal-Phonon-plasmon coupled modes polarized within the monoclinic plane continuously change their direction as a function of free electron concentration.
