Spatially Resolved Site Selective Optical Spectroscopy on Nd Doped GaN Epitaxial Layers

2008 ◽  
Vol 1111 ◽  
Author(s):  
Nate Woodward ◽  
Naveen Jha ◽  
Eric Readinger ◽  
Grace Metcalfe ◽  
Michael Wraback ◽  
...  
Keyword(s):  
Energy Levels ◽  
Ion Concentration ◽  
Phonon Coupling ◽  
Laser Applications ◽  
Spatially Resolved ◽  
Electron Phonon Coupling ◽  
Wide Range ◽  
Localized Mode ◽  
Site Selective

AbstractDue to its favorable electronic and thermal properties GaN has been considered as a rare-earth host material for solid state amplifier and laser applications. To this end, we performed spatially resolved combined excitation emission spectroscopy (CEES) on Nd ions which were in-situ-doped into GaN epitaxial films grown by plasma assisted molecular beam epitaxy (PA-MBE) on c-plane sapphire substrate. For a wide range of concentration (up to 8at%) we find in the emission a dominant incorporation site, which can be identified with good certainty as a substitutional ‘Ga’ site. Energy levels and electron-phonon coupling to a localized mode can be identified. For the majority site, confocal spectral imaging under selective excitation show changes in emission intensity, excitation and emission wavelength on a submicron length scale suggesting spatial inhomogeneities in terms of Nd3+ ion concentration.

scholarly journals High-performance multiplexed fluorescence in situ hybridization in culture and tissue with matrix imprinting and clearing

2016 ◽  
Vol 113 (50) ◽  
pp. 14456-14461 ◽  
Author(s):  
Jeffrey R. Moffitt ◽  
Junjie Hao ◽  
Dhananjay Bambah-Mukku ◽  
Tian Lu ◽  
Catherine Dulac ◽  
...  
Keyword(s):  
In Situ Hybridization ◽  
Single Molecule ◽  
High Performance ◽  
Detection Efficiency ◽  
Tissue Samples ◽  
Spatially Resolved ◽  
Wide Range ◽  
Cellular Context ◽  
Target Binding

Highly multiplexed single-molecule FISH has emerged as a promising approach to spatially resolved single-cell transcriptomics because of its ability to directly image and profile numerous RNA species in their native cellular context. However, background—from off-target binding of FISH probes and cellular autofluorescence—can become limiting in a number of important applications, such as increasing the degree of multiplexing, imaging shorter RNAs, and imaging tissue samples. Here, we developed a sample clearing approach for FISH measurements. We identified off-target binding of FISH probes to cellular components other than RNA, such as proteins, as a major source of background. To remove this source of background, we embedded samples in polyacrylamide, anchored RNAs to this polyacrylamide matrix, and cleared cellular proteins and lipids, which are also sources of autofluorescence. To demonstrate the efficacy of this approach, we measured the copy number of 130 RNA species in cleared samples using multiplexed error-robust FISH (MERFISH). We observed a reduction both in the background because of off-target probe binding and in the cellular autofluorescence without detectable loss in RNA. This process led to an improved detection efficiency and detection limit of MERFISH, and an increased measurement throughput via extension of MERFISH into four color channels. We further demonstrated MERFISH measurements of complex tissue samples from the mouse brain using this matrix-imprinting and -clearing approach. We envision that this method will improve the performance of a wide range of in situ hybridization-based techniques in both cell culture and tissues.

Neutron Spectroscopy of Superconducting Fullerides

1992 ◽  
Vol 270 ◽  
Author(s):  
Kosmas Prassides ◽  
Christos Christides ◽  
John Tomkinson ◽  
Matthew J. Rosseinsky ◽  
D. W. Murphy ◽  
...  
Keyword(s):  
Low Temperatures ◽  
High Energy ◽  
Inelastic Neutron ◽  
Low Energy ◽  
Vibrational Modes ◽  
Phonon Coupling ◽  
Phonon Spectra ◽  
Electron Phonon Coupling ◽  
Wide Range ◽  
Mechanism Of Superconductivity

ABSTRACTThe phonon spectra of pristine fullerene, superconducting K3C60 and saturation-doped Rb6C60 measured by inelastic neutron scatteringin the energy range 2.5 - 200 meV at low temperatures reveal substantial broadening of five-fold degenerate Hg intramolecular vibrational modes both in the low-energy radial and the high-energy tangential part of the spectrum. This provides strong evidence for a traditional phonon-mediated mechanism of superconductivity in the fullerides but with an electron-phonon coupling strength distributed over a wide range of energies (33-195 meV) as a result of the finite curvature of the fullerene spherical cage.

scholarly journals Electron-momentum dependence of electron-phonon coupling underlies dramatic phonon renormalization in YNi2B2C

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Philipp Kurzhals ◽  
Geoffroy Kremer ◽  
Thomas Jaouen ◽  
Christopher W. Nicholson ◽  
Rolf Heid ◽  
...  
Keyword(s):  
Fermi Surface ◽  
Inelastic Neutron Scattering ◽  
Density Wave ◽  
Momentum Dependence ◽  
Phonon Coupling ◽  
Electronic Band ◽  
Electron Momentum ◽  
Electron Phonon Coupling ◽  
Wide Range ◽  
Fermi Surface Nesting

AbstractElectron-phonon coupling, i.e., the scattering of lattice vibrations by electrons and vice versa, is ubiquitous in solids and can lead to emergent ground states such as superconductivity and charge-density wave order. A broad spectral phonon line shape is often interpreted as a marker of strong electron-phonon coupling associated with Fermi surface nesting, i.e., parallel sections of the Fermi surface connected by the phonon momentum. Alternatively broad phonons are known to arise from strong atomic lattice anharmonicity. Here, we show that strong phonon broadening can occur in the absence of both Fermi surface nesting and lattice anharmonicity, if electron-phonon coupling is strongly enhanced for specific values of electron-momentum, k. We use inelastic neutron scattering, soft x-ray angle-resolved photoemission spectroscopy measurements and ab-initio lattice dynamical and electronic band structure calculations to demonstrate this scenario in the highly anisotropic tetragonal electron-phonon superconductor YNi2B2C. This new scenario likely applies to a wide range of compounds.

scholarly journals Ultra-broadband photodetectors based on epitaxial graphene quantum dots

Nanophotonics ◽  
2018 ◽  
Vol 7 (4) ◽  
pp. 735-740 ◽  
Author(s):  
Abdel El Fatimy ◽  
Anindya Nath ◽  
Byoung Don Kong ◽  
Anthony K. Boyd ◽  
Rachael L. Myers-Ward ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Quantum Confinement ◽  
Strong Dependence ◽  
Graphene Quantum Dots ◽  
Hot Electron ◽  
Phonon Coupling ◽  
Electron Phonon Coupling ◽  
Wide Range ◽  
Absorbed Power ◽  
Weak Electron

AbstractGraphene is an ideal material for hot-electron bolometers due to its low heat capacity and weak electron-phonon coupling. Nanostructuring graphene with quantum-dot constrictions yields detectors of electromagnetic radiation with extraordinarily high intrinsic responsivity, higher than 1×109 V W−1 at 3 K. The sensing mechanism is bolometric in nature: the quantum confinement gap causes a strong dependence of the electrical resistance on the electron temperature. Here, we show that this quantum confinement gap does not impose a limitation on the photon energy for light detection and these quantum-dot bolometers work in a very broad spectral range, from terahertz through telecom to ultraviolet radiation, with responsivity independent of wavelength. We also measure the power dependence of the response. Although the responsivity decreases with increasing power, it stays higher than 1×108 V W−1 in a wide range of absorbed power, from 1 pW to 0.4 nW.

scholarly journals Dichotomy of superconductivity between monolayer FeS and FeSe

2019 ◽  
Vol 116 (49) ◽  
pp. 24470-24474
Author(s):  
Koshin Shigekawa ◽  
Kosuke Nakayama ◽  
Masato Kuno ◽  
Giao N. Phan ◽  
Kenta Owada ◽  
...  
Keyword(s):  
Molecular Beam ◽  
Photoemission Spectroscopy ◽  
Phonon Coupling ◽  
Superconducting Layer ◽  
Iron Based Superconductors ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Electron Phonon Coupling ◽  
Heavy Electron ◽  
Superconducting Pairing

The discovery of high-temperature (Tc) superconductivity in monolayer FeSe on SrTiO3 raised a fundamental question: Whether high Tc is commonly realized in monolayer iron-based superconductors. Tetragonal FeS is a key material to resolve this issue because bulk FeS is a superconductor with Tc comparable to that of isostructural FeSe. However, difficulty in synthesizing tetragonal monolayer FeS due to its metastable nature has hindered further investigations. Here we report elucidation of band structure of monolayer FeS on SrTiO3, enabled by a unique combination of in situ topotactic reaction and molecular-beam epitaxy. Our angle-resolved photoemission spectroscopy on FeS and FeSe revealed marked similarities in the electronic structure, such as heavy electron doping and interfacial electron–phonon coupling, both of which have been regarded as possible sources of high Tc in FeSe. However, surprisingly, high-Tc superconductivity is absent in monolayer FeS. This is linked to the weak superconducting pairing in electron-doped multilayer FeS in which the interfacial effects are absent. Our results strongly suggest that the cross-interface electron–phonon coupling enhances Tc only when it cooperates with the pairing interaction inherent to the superconducting layer. This finding provides a key insight to explore heterointerface high-Tc superconductors.

Ion-Beam-Driven Amortization of Ca2La8 (SiO4)6O2 Single Crystals

1993 ◽  
Vol 321 ◽  
Author(s):  
W. J. Weber ◽  
N. J. Hess ◽  
L. M. Wang
Keyword(s):  
Single Crystals ◽  
Structural Changes ◽  
Ion Beam ◽  
National Laboratory ◽  
Energy Levels ◽  
Argonne National Laboratory ◽  
Line Broadening ◽  
Spatially Resolved ◽  
Two Stages

ABSTRACTSingle crystals of Ca2La8(SiO4)6O2, with 1% Nd substituted for La, were irradiated with 0.8 MeV Ne+ and 1.5 MeV Kr+ ions over the temperature range from 15 K to 773 K. The irradiations were carried out using the HVEM-Tandem Facility at Argonne National Laboratory. The structural changes and the ion fluence for complete amorphization were determined by in situ transmission electron Microscopy. The ion fluence for complete amorphization increased with temperature in two stages associated with defect annealing processes. The critical temperature for amorphization increased from -360 K for 0.8 MeV Ne+ to -710 K for 1.5 MeV Kr+. During in situ annealing studies, irradiation-enhanced recrystallization was observed at 923 K. Spatially-resolved fluorescence spectra of the Nd ion excited with 488.0 nm laser excitation showed marked line-broadening toward the center of the amorphous regions. Initial Measurements indicate the subtle shifts of the 9I9/2 groundstate energy levels can be measured by pumping directly into the excited state 4F3/2 Manifold suggesting that the line broadening observed originates from a distribution of geometrically distorted Nd sites.

RAMAN SCATTERING AND SUPERCONDUCTIVITY OF AxC60

1992 ◽  
Vol 06 (23n24) ◽  
pp. 4013-4018 ◽  
Author(s):  
M.G. Mitch ◽  
S.J. Chase ◽  
J.S. Lannin
Keyword(s):  
Raman Scattering ◽  
Line Width ◽  
Ultrathin Films ◽  
Low Frequency ◽  
Phonon Coupling ◽  
Line Broadening ◽  
Vibrational Coupling ◽  
Electron Phonon Coupling ◽  
Scattering Measurements

Raman scattering measurements of line width variations in A x C 60 ultrathin films provide detailed information on vibrational coupling of H g or A g modes relevant to superconductivity. In situ, UHV studies of 400A thick Rb 3 C 60 and K 3 C 60 films indicate somewhat similar behavior, suggesting the predominance of low frequency H g (2) radial modes for electron-phonon coupling. Measurements of nonsuperconducting Na x C 60 in ultrathin films, in contrast, yield reduced line broadening effects for H g (8) and H g (2) modes relative to Rb and K materials.

scholarly journals Sensitivity of pelagic CaCO<sub>3</sub> dissolution to ocean acidification in an ocean biogeochemical model

2013 ◽  
Vol 10 (7) ◽  
pp. 11343-11373
Author(s):  
A. Regenberg ◽  
B. Schneider ◽  
R. Gangst&amp;oslash;
Keyword(s):  
Ocean Acidification ◽  
Ion Concentration ◽  
Biogeochemical Model ◽  
Saturation State ◽  
Saturation Concentration ◽  
Carbonate Ion ◽  
Biogeochemical Models ◽  
Wide Range ◽  
The Impact

Abstract. In ocean biogeochemical models pelagic CaCO3 dissolution is usually calculated as R = k * Sn, where k is the dissolution rate constant transforming S, the degree of (under-) saturation of seawater with respect to CaCO3, into a time dependent rate R, and n is the reaction rate order. Generally, there are two ways to define the saturation state of seawater with respect to CaCO3: (1) Δ[CO32−], which reflects the difference between the in-situ carbonate ion concentration and the saturation concentration, and (2) Ω, which is approximated by the ratio of in-situ carbonate ion concentration over the saturation concentration. Although describing the same phenomenon, the deviation from equilibrium, both expressions are not equally applicable for the calculation of CaCO3 dissolution in the ocean across pressure gradients, as they differ in their sensitivity to ocean acidification (change of [CO32−]) over depth. In the present study we use a marine biogeochemical model to test the sensitivity of pelagic CaCO3 dissolution to ocean acidification (1–4 × CO2 + stabilization), exploring the possible parameter space for CaCO3 dissolution kinetics as given in the literature. We find that at the millennial time scale there is a wide range of CaCO3 particle flux attenuation into the ocean interior (e.g. a reduction of −55 to −85% at 1000 m depth), which means that there are significant differences in the impact on particle ballasting, depending on the kinetic expression applied.

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