Raman Scattering and Superconductivity of Alkali-Fullerene Materials

1992 ◽  
Vol 270 ◽  
Author(s):  
J. S. Lannin ◽  
M. G. Mitch ◽  
W. Bacsa ◽  
S. J. Chase
Keyword(s):  
Thin Films ◽  
Raman Scattering ◽  
Raman Spectra ◽  
Solid Solutions ◽  
Thick Films ◽  
Ultrathin Film ◽  
Phonon Coupling ◽  
Electron Phonon Coupling ◽  
Scattering Measurements ◽  
Different Thickness

ABSTRACTRaman scattering measurements in alkali—fullerene alloys in ultrathin and thin films provide evidence for variations in electron—phonon coupling. For x — 3similar behavior of Rb3 C60 films of different thickness support substantial electron—phonon induced damping of specific Hg(i) modes derived from intramolecular modes of C60. In 400A thick films a reduction of induced scattering from Raman inactive C60 modes substantiates the importance ofHg(2), but not Hg(3) modes for phonon—mediated superconductivity. In contrast to RbxC60 and KxC60 ultrathin film solid solutions, similar Raman spectra for NaxC60 indicate substantially reduced coupling consistent with the absence of superconductivity in this system.

Anomalous low-temperature Raman scattering in a–Si1−xHx

1995 ◽  
Vol 10 (6) ◽  
pp. 1362-1370 ◽  
Author(s):  
D.M. Bhusari ◽  
Alka Kumbhar ◽  
S.T. Kshirsagar
Keyword(s):  
Thin Films ◽  
Low Temperature ◽  
Raman Scattering ◽  
Cross Section ◽  
Hydrogenated Amorphous Silicon ◽  
Phonon Coupling ◽  
Scattered Intensity ◽  
Electron Phonon Coupling ◽  
Scattering Measurements ◽  
Hydrogenated Amorphous

We have reported here on low-temperature Raman scattering measurements on thin films of hydrogenated amorphous silicon (α-Si:H) alloys having different H contents. The Stoke's intensity, 77KITO, scattered at 77 K by the TO-phonon is found to be several times greater than its corresponding magnitude (300KITO) at 300 K. The ratio (77KITO/300KITO) is observed to vary exponentially with an increase in H concentration of the film. After eliminating various possible contributions to the scattering cross section, and therefore to the scattered intensity, this anomalous light scattering at 77 K is attributed to the possibility of polarizability modulation, which is believed to be caused due to a possible reduction in light-induced migration of H in α-Si:H and to the charge-carrier-induced enhancement of electron phonon coupling at 77 K.

scholarly journals Resonance and antiresonance in Raman scattering in GaSe and InSe crystals

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. Osiekowicz ◽  
D. Staszczuk ◽  
K. Olkowska-Pucko ◽  
Ł. Kipczak ◽  
M. Grzeszczyk ◽  
...  
Keyword(s):  
Raman Scattering ◽  
Temperature Effect ◽  
Band Gap ◽  
Raman Spectra ◽  
Quantum Interference ◽  
Optical Band Gap ◽  
Phonon Coupling ◽  
Phonon Modes ◽  
Electron Phonon Coupling ◽  
Resonant Raman

AbstractThe temperature effect on the Raman scattering efficiency is investigated in $$\varepsilon$$ ε -GaSe and $$\gamma$$ γ -InSe crystals. We found that varying the temperature over a broad range from 5 to 350 K permits to achieve both the resonant conditions and the antiresonance behaviour in Raman scattering of the studied materials. The resonant conditions of Raman scattering are observed at about 270 K under the 1.96 eV excitation for GaSe due to the energy proximity of the optical band gap. In the case of InSe, the resonant Raman spectra are apparent at about 50 and 270 K under correspondingly the 2.41 eV and 2.54 eV excitations as a result of the energy proximity of the so-called B transition. Interestingly, the observed resonances for both materials are followed by an antiresonance behaviour noticeable at higher temperatures than the detected resonances. The significant variations of phonon-modes intensities can be explained in terms of electron-phonon coupling and quantum interference of contributions from different points of the Brillouin zone.

scholarly journals New Insights into the Role of Weak Electron–Phonon Coupling in Nanostructured ZnO Thin Films

Nanomaterials ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 632 ◽  
Author(s):  
Ashish Gandhi ◽  
Wei-Shan Yeoh ◽  
Ming-An Wu ◽  
Ching-Hao Liao ◽  
Dai-Yao Chiu ◽  
...  
Keyword(s):  
Thin Films ◽  
Raman Scattering ◽  
High Performance ◽  
Zno Thin Films ◽  
Phonon Coupling ◽  
X Ray Diffraction ◽  
Electron Phonon Coupling ◽  
Weak Electron ◽  
Confined System

High-quality crystalline nanostructured ZnO thin films were grown on sapphire substrates by reactive sputtering. As-grown and post-annealed films (in air) with various grain sizes (2 to 29 nm) were investigated by scanning electron microscopy, X-ray diffraction, and Raman scattering. The electron–phonon coupling (EPC) strength, deduced from the ratio of the second- to the first-order Raman scattering intensity, diminished by reducing the ZnO grain size, which mainly relates to the Fröhlich interactions. Our finding suggests that in the spatially quantum-confined system the low polar nature leads to weak EPC. The outcome of this study is important for the development of nanoscale high-performance optoelectronic devices.

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.

Degradation of Polystyrene on Silver Substrates during Surface-Enhanced Raman Scattering

1988 ◽  
Vol 42 (7) ◽  
pp. 1207-1213 ◽  
Author(s):  
R. S. Venkatachalam ◽  
F. J. Boerio ◽  
M. R. Carnevale ◽  
P. G. Roth
Keyword(s):  
Thin Films ◽  
Raman Scattering ◽  
Raman Spectra ◽  
Thick Films ◽  
Surface Enhanced Raman Scattering ◽  
Solid Polymer ◽  
Silver Surface ◽  
Surface Enhanced ◽  
Surface Enhanced Raman ◽  
Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) by films of polystyrene adsorbed onto silver island films was investigated. Films that were only a few tens of angstroms in thickness degraded rapidly during laser irradiation to form graphite-like species at the silver surface. However, no degradation was observed while Raman spectra of the solid polymer were obtained, indicating that the graphitization was probably induced by laser heating of the substrate and catalyzed by silver. For thin films of polystyrene, the rate of graphitization was high and was proportional to laser power. However, the degradation reaction was inhibited for thick films or for thin films overcoated with thick films of a second polymer. The Raman spectra were similar for all films thicker than approximately a hundred angstroms, even those overcoated with a thick film of a second polymer having a large Raman scattering cross section, indicating that most of the observed scattering originated from polymer molecules within a few tens of angstroms of the silver surface. It was concluded that SERS can be used to probe the molecular structure of polymer/metal interfaces without interference by scattering from the bulk of the polymer.

scholarly journals Raman study of electron-phonon coupling in thin films of the spinel oxide superconductor LiTi2O4

2017 ◽  
Vol 96 (9) ◽  
Author(s):  
D. Chen ◽  
Y.-L. Jia ◽  
T.-T. Zhang ◽  
Z. Fang ◽  
K. Jin ◽  
...  
Keyword(s):  
Thin Films ◽  
Oxide Superconductor ◽  
Phonon Coupling ◽  
Spinel Oxide ◽  
Electron Phonon Coupling ◽  
Raman Study

scholarly journals Creating better superconductors by periodic nanopatterning

2017 ◽  
Vol 3 (2) ◽  
Author(s):  
Milan Allan ◽  
Mark H Fischer ◽  
Oliver Ostojic ◽  
Arjo Andringa
Keyword(s):  
Thin Films ◽  
Transition Temperature ◽  
Numerical Methods ◽  
Model Calculation ◽  
Lattice Mismatch ◽  
Specific Pattern ◽  
Design Parameters ◽  
Phonon Coupling ◽  
Electron Phonon Coupling ◽  
Correct Design

The quest to create superconductors with higher transition temperatures is as old as superconductivity itself. One strategy, popular after the realization that (conventional) superconductivity is mediated by phonons, is to chemically combine different elements within the crystalline unit cell to maximize the electron-phonon coupling. This led to the discovery of NbTi and Nb_33Sn, to name just the most technologically relevant examples. Here, we propose a radically different approach to transform a ‘pristine’ material into a better (meta-) superconductor by making use of modern fabrication techniques: designing and engineering the electronic properties of thin films via periodic patterning on the nanoscale. We present a model calculation to explore the key effects of different supercells that could be fabricated using nanofabrication or deliberate lattice mismatch, and demonstrate that specific pattern will enhance the coupling and the transition temperature. We also discuss how numerical methods could predict the correct design parameters to improve superconductivity in materials including Al, NbTi, and MgB_22.

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