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G Benedek - One of the best experts on this subject based on the ideXlab platform.
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evidence for a spin acoustic Surface plasmon from inelastic atom scattering
Scientific Reports, 2021Co-Authors: G Benedek, Davide Campi, M Bernasconi, V M Silkin, Igor V Silkin, I P ChernovAbstract:Closed-shell atoms scattered from a metal Surface exchange energy and momentum with Surface Phonons mostly via the interposed Surface valence electrons, i.e., via the creation of virtual electron-hole pairs. The latter can then decay into Surface Phonons via electron-Phonon interaction, as well as into acoustic Surface plasmons (ASPs). While the first channel is the basis of the current inelastic atom scattering (IAS) Surface-Phonon spectroscopy, no attempt to observe ASPs with IAS has been made so far. In this study we provide evidence of ASP in Ni(111) with both Ne atom scattering and He atom scattering. While the former measurements confirm and extend so far unexplained data, the latter illustrate the coupling of ASP with Phonons inside the Surface-projected Phonon continuum, leading to a substantial reduction of the ASP velocity and possibly to avoided crossing with the optical Surface Phonon branches. The analysis is substantiated by a self-consistent calculation of the Surface response function to atom collisions and of the first-principle Surface-Phonon dynamics of Ni(111). It is shown that in Ni(111) ASP originate from the majority-spin Shockley Surface state and are therefore collective oscillation of Surface electrons with the same spin, i.e. it represents a new kind of collective quasiparticle: a Spin Acoustic Surface Plasmon (SASP).
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Surface Phonons theoretical methods and results
2020Co-Authors: G Benedek, J P Toennies, Davide Campi, M Bernasconi, M J VerstraeteAbstract:The theoretical methods currently in use for the calculation of Surface Phonon dispersion curves and how they have evolved from the phenomenological force-constant models to the present day first principles theories are discussed. A selection of paradigmatic examples for the different classes of crystal Surfaces is presented with comparisons to the experimental data obtained from helium atom scattering or electron energy-loss spectroscopy.
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the physics of Surface Phonons
2018Co-Authors: G Benedek, J P ToenniesAbstract:The effect of the Surface termination on the Phonon dispersion curves is illustrated by comparison with the bulk dispersion curves. After a review of Rayleigh’s theory of Surface waves in elastic media the atomistic Born-von Karman theory for bulk Phonons is presented. How the Surface affects the Surface vibrations is illustrated by the Green’s function theory and slab calculations. The chapter closes with some illustrations of Surface Phonon dispersion curves and their classification.
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theory of atom scattering from Surface Phonon the role of electron Phonon interaction
2018Co-Authors: G Benedek, J P ToenniesAbstract:The forces that an He atom exerts on the atoms of a solid Surface causing inelastic scattering have much in common with the interatomic forces that govern the dynamics of the lattice. The scattering theory, described in Chap. 7 based on two-body collisions, provides the correct interpretation of data for closed-shell Surfaces, much as their lattice dynamics is well described by phenomenological interatomic potentials. The inelastic HAS experiments from metal Surfaces, however, cannot be successfully described in the same way. In this Chapter the approaches developed for the lattice dynamics of metals, where the interatomic forces are mediated by free electrons, such as the Multipole Expansion (ME) and the Density Functional Perturbation Theory (DFPT) are introduced for the analysis of inelastic HAS intensities from metal Surfaces. These theories have the important consequences that inelastic HAS intensities are directly proportional to the electron-Phonon coupling strength for individual Phonons and that HAS can detect deep sub-Surface Phonons. The propensity of HAS to excite certain Phonons of conducting Surfaces rather than others is found to depend on the electron-Phonon interaction and the Surface electron band structure.
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the effect of the Surface termination on force constants and dispersion curves
2018Co-Authors: G Benedek, Jan Peter ToenniesAbstract:The Born-von Karman model introduced in the previous Chapter, is used to illustrate how the invariance properties of the total energy, the equilibrium conditions and the emergence of the Surface stress affect the Surface force constants in the Surface region and the Surface Phonon dispersion curves. Then the effects of extended Surface and interplanar force constant perturbations, which in the case of metals may involve several layers, are discussed.
Joshua D. Caldwell - One of the best experts on this subject based on the ideXlab platform.
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strong confinement of optical fields using localized Surface Phonon polaritons in cubic boron nitride
Optics Letters, 2018Co-Authors: Ioannis Chatzakis, Athith Krishna, J C Culbertson, Nicholas Sharac, Alexander J Giles, M G Spencer, Joshua D. CaldwellAbstract:Phonon polaritons (PhPs) are long-lived electromagnetic modes that originate from the coupling of infrared (IR) photons with the bound ionic lattice of a polar crystal. Cubic-boron nitride (cBN) is such a polar, semiconductor material which, due to the light atomic masses, can support high-frequency optical Phonons. Here we report on random arrays of cBN nanostructures fabricated via an unpatterned reactive ion etching process. Fourier-transform infrared reflection spectra suggest the presence of localized Surface PhPs within the reststrahlen band, with quality factors in excess of 38 observed. These can provide the basis of next-generation IR optical components such as antennas for communication, improved chemical spectroscopies, and enhanced emitters, sources, and detectors.
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strong coupling effects between ir inactive zone folded lo Phonon and localized Surface Phonon polariton modes in sic nanopillars
Advanced Study Institute on NATO ASI on Quantum Nano-Photonics, 2017Co-Authors: Michael A Meeker, Alexander J Giles, Dmitry N Chigrin, Chase T Ellis, Francisco J Bezares, Joseph G Tischler, Orest J Glemboki, Richard Kasica, Loretta Shirey, Joshua D. CaldwellAbstract:While plasmonics have a broad range of technological applications including infrared photovoltaics and photodetectors, plasmonic metals are subject to high optical losses in the long-wave infrared spectral regime. In order to reduce optical losses in the infrared, alternatives to plasmonic metals are being explored. One promising alternative employs polar dielectric materials, which exhibit a highly-reflective, optically-metallic spectral band (Reststrahlen band), bounded by the LO and TO optical Phonons, and are capable of supporting plasmonic-like resonance in the infrared. In polar dielectrics, plasmonic-like resonances, known as Surface Phonon polariton (SPhP) resonances, arise from a coupling between incident light and collective oscillations of bound lattice charges, which are mediated by the optical Phonons. In this study, we have examined the SPhP resonances of SiC nanopillars with constant height of 950 nm and width in the range of 200–400 nm, as a function of their aspect ratio (AR=Length/Width=0.5–16). As the nanopillar width is decreased, we have found that localized SPhP resonances redshift towards the zone folded LO (ZFLO) Phonon that is normally not infrared active. However, as localized SPhP resonances are spectrally tuned through the ZFLO mode, we have found that the latter mode becomes infrared active. Furthermore, reflectance measurements have revealed strong coupling between the ZFLO and both the monopolar and dipolar localized SPhP resonances.
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Low-loss, infrared and terahertz nanophotonics using Surface Phonon polaritons
Nanophotonics, 2015Co-Authors: Joshua D. Caldwell, L. Lindsay, Vincenzo Giannini, Igor Vurgaftman, Thomas L. Reinecke, Stefan A Maier, Orest J. GlembockiAbstract:The excitation of Surface-Phonon-polariton (SPhP) modes in polar dielectric crystals and the associated new developments in the field of SPhPs are reviewed. The emphasis of this work is on providing an understanding of the general phenomenon, including the origin of the Reststrahlen band, the role that optical Phonons in polar dielectric lattices play in supporting sub-diffraction-limited modes and how the relatively long optical Phonon lifetimes can lead to the low optical losses observed within these materials. Based on this overview, the achievements attained to date and the potential technological advantages of these materials are discussed for localized modes in nanostructures, propagating modes on Surfaces and in waveguides and novel metamaterial designs, with the goal of realizing low-loss nanophotonics and metamaterials in the mid-infrared to terahertz spectral ranges.
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low loss extreme subdiffraction photon confinement via silicon carbide localized Surface Phonon polariton resonators
Nano Letters, 2013Co-Authors: Joshua D. Caldwell, Orest J. Glembocki, Vincenzo Giannini, Igor Vurgaftman, Nicholas Sharac, Yan Francescato, Francisco J Bezares, J P Long, Jeffrey C Owrutsky, Joseph G TischlerAbstract:Plasmonics provides great promise for nanophotonic applications. However, the high optical losses inherent in metal-based plasmonic systems have limited progress. Thus, it is critical to identify alternative low-loss materials. One alternative is polar dielectrics that support Surface Phonon polariton (SPhP) modes, where the confinement of infrared light is aided by optical Phonons. Using fabricated 6H-silicon carbide nanopillar antenna arrays, we report on the observation of subdiffraction, localized SPhP resonances. They exhibit a dipolar resonance transverse to the nanopillar axis and a monopolar resonance associated with the longitudinal axis dependent upon the SiC substrate. Both exhibit exceptionally narrow linewidths (7–24 cm–1), with quality factors of 40–135, which exceed the theoretical limit of plasmonic systems, with extreme subwavelength confinement of (λres3/Veff)1/3 = 50–200. Under certain conditions, the modes are Raman-active, enabling their study in the visible spectral range. These obse...
Gang Chen - One of the best experts on this subject based on the ideXlab platform.
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Surface Phonon polaritons mediated energy transfer between nanoscale gaps
Nano Letters, 2009Co-Authors: Sheng Shen, Arvind Narayanaswamy, Gang ChenAbstract:Surface Phonon polaritons are electromagnetic waves that propagate along the interfaces of polar dielectrics and exhibit a large local-field enhancement near the interfaces at infrared frequencies. Theoretical calculations show that such Surface waves can lead to breakdown of the Planck’s blackbody radiation law in the near field. Here, we experimentally demonstrate that Surface Phonon polaritons dramatically enhance energy transfer between two Surfaces at small gaps by measuring radiation heat transfer between a microsphere and a flat Surface down to 30 nm separation. The corresponding heat transfer coefficients at nanoscale gaps are 3 orders of magnitude larger than that of the blackbody radiation limit. The high energy flux can be exploited to develop new radiative cooling and thermophotovoltaic technologies.
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measurement of silicon dioxide Surface Phonon polariton propagation length by attenuated total reflection
Applied Physics Letters, 2007Co-Authors: Dyezone A Chen, Gang ChenAbstract:The authors present an experimental measurement of the propagation length of Surface Phonon-polaritons on amorphous silicon dioxide using the method of attenuated total reflection. The measurements yield a propagation length of 10.8±1.3μm for the silicon dioxide Surface Phonon-polariton resonance at 9μm, which is in good agreement with the calculated value.
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Surface Phonon polariton mediated thermal conductivity enhancement of amorphous thin films
Physical Review B, 2005Co-Authors: Dyezone A Chen, Arvind Narayanaswamy, Gang ChenAbstract:We predict theoretically that the effective in-plane thermal conductivity of polar, amorphous thin films can be increased by Surface Phonon-polaritons significantly beyond their intrinsic bulk values. We show that the thermal conductivity due to Surface Phonon-polaritons increases with decreasing film thickness. In particular, for a 40-nm-thick film of amorphous silicon dioxide, we calculate a total thermal conductivity of $4\phantom{\rule{0.3em}{0ex}}\mathrm{W}\phantom{\rule{0.2em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 500 K, which is an increase of $\ensuremath{\sim}100%$ over the intrinsic Phonon thermal conductivity.
Gilbert C Walker - One of the best experts on this subject based on the ideXlab platform.
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near field infrared pump probe imaging of Surface Phonon coupling in boron nitride nanotubes
Science & Engineering Faculty, 2016Co-Authors: Leonid Gilburd, Yoshio Bando, Dmitri Golberg, Gilbert C WalkerAbstract:Surface Phonon modes are lattice vibrational modes of a solid Surface. Two common Surface modes, called longitudinal and transverse optical modes, exhibit lattice vibration along or perpendicular to the direction of the wave. We report a two-color, infrared pump-infrared probe technique based on scattering type near-field optical microscopy (s-SNOM) to spatially resolve coupling between Surface Phonon modes. Spatially varying couplings between the longitudinal optical and Surface Phonon polariton modes of boron nitride nanotubes are observed, and a simple model is proposed.
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one dimensional Surface Phonon polaritons in boron nitride nanotubes
Nature Communications, 2014Co-Authors: Behnood G Ghamsari, Leonid Gilburd, Yoshio Bando, Dmitri Golberg, Jianhua Jiang, Gregory O Andreev, Chunyi Zhi, Pierre Berini, Gilbert C WalkerAbstract:Surface plasmon and Phonon polaritons are useful for sub-diffraction limit waveguiding of light, but Phonon polaritons are advantageous in the mid-infrared. Xu et al. show that one-dimensional boron nitride nanotubes can support propagating Phonon polaritons, making them a suitable platform for further study.
Rodolphe Vaillon - One of the best experts on this subject based on the ideXlab platform.
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coexistence of multiple regimes for near field thermal radiation between two layers supporting Surface Phonon polaritons in the infrared
Physical Review B, 2011Co-Authors: Mathieu Francoeur, Pinar M Menguc, Rodolphe VaillonAbstract:We demonstrate the coexistence of different near-field thermal radiation regimes between two layers supporting Surface Phonon polaritons (SPhPs) in the infrared. These regimes exist when the distance of separation between the media $d$ is much smaller than the dominant emission wavelength. This coexistence is noticed after computations of the near-field radiative heat transfer coefficient ${h}_{r}$ for silicon carbide films using fluctuational electrodynamics and following an asymptotic analysis of ${h}_{r}$. We show that the emergence of these regimes is a function of a dimensionless variable $D$ defined as the ratio of the layer thickness $t$ to $d$. When $D$ $\ensuremath{\gg}$ 1 for both films, SPhPs dominating near-field radiant energy exchange do not couple within the layers, such that ${h}_{r}$ follows a ${d}^{\ensuremath{-}2}$ power law as for the case of two planar half-spaces. When $D$ $\ensuremath{\ll}$ 1 for both layers, the dominant SPhPs couple within the films, thus resulting in a splitting of the spectral distribution of flux into two distinct modes. Despite this splitting, the asymptotic expansion reveals that ${h}_{r}$ varies as ${d}^{\ensuremath{-}2}$ due to the fact that the spectral bands of high emission and absorption are essentially the same for both films. However, when both layers have a thickness of the order of a nanometer or less, a purely theoretical regime emerges where ${h}_{r}$ follows a ${d}^{\ensuremath{-}4}$ asymptote. Also, when one layer has $D$ $\ensuremath{\ll}$ 1 while the other one is characterized by $D$ $\ensuremath{\gg}$ 1, there is an important mismatch between the spectral bands of high emission and absorption of the films, thus resulting in a ${h}_{r}$ varying as ${d}^{\ensuremath{-}3}$. These various near-field thermal radiation regimes are finally summarized in a comprehensive regime map. This map provides a clear understanding of near-field thermal radiation regimes between two layers, which are particularly important for designing highly efficient nanoscale-gap thermophotovoltaic power generation devices.
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near field radiative heat transfer enhancement via Surface Phonon polaritons coupling in thin films
Applied Physics Letters, 2008Co-Authors: Mathieu Francoeur, Pinar M Menguc, Rodolphe VaillonAbstract:We investigate near-field thermal radiation between a nanometric film and a bulk SiC using fluctuational electrodynamics. Results show a narrow spectral band enhancement of the radiative flux for nanometric emitters due to coupling of Surface Phonon polaritons inside the film. For a 10nm thick SiC emitter, the total radiative flux is 2.2 times larger than for a bulk emitter. The total radiative flux is increased by a factor of 3.3 if a dielectric is coated with a 10nm SiC film due to a splitting of the resonant frequency into two distinct ones, which has practical interests for near-field thermophotovoltaic devices.