1,721,022 research outputs found
Electron-phonon Coupling In Low-dimensional Organic Superconductors
No full textThe relative importance of the coupling of electrons with intra- and inter-molecular phonons in setting up the organic superconductivity is addressed. We base our considerations on a firmly established set of electron molecular vibration coupling constants for the TMTTF molecule. By the use of three different models of the BCS, strong coupling and non adiabatic type we find that, in order to attain critical temperatures (T(c)) in the typical range of 1 to 10 K, large values for the electron inter-molecular phonon coupling constants are needed. We also report a theoretical analysis of the effects of isotopic substitution of the carbon atoms in a TTF based molecule. Through a simple model of two coupled oscillators and by the use of the experimental data available for TMTTF, we estimate isotopic T(c) shifts which may be useful for qualitative comparison with experimental data
OPTICAL STUDIES OF THE INTERPLAY BETWEEN ELECTRON LATTICE AND ELECTRON ELECTRON INTERACTIONS IN ORGANIC MOLECULAR CONDUCTORS
No full textElectronic interactions in the organic conductors (TMTSF)2X (X=ClO4 and PF6) and TMTTF2X (X=Br and PF6) from their infrared spectra
No full textAccurate measurements of the polarized reflectance spectra of the series of isostructural organic conductors (TMTSF)2ClO4, (TMTSF)2PF6, (TMTTF)2Br, and (TMTSF)2PF6 (where TMTSF denotes tetramethyltetraselenafulvalane and TMTTF denotes tetramethyltetrathiafulvalene) at room temperature are reported. A dimerized molecular chain model is used to analyze these spectra as well as those previously reported [C. C. Homes and J. E. Eldridge, Phys. Rev. B 42, 9522 (1990); J. E. Eldridge and C. C. Homes, ibid. 43, 13 971 (1991)] for (TMTSF)2BF4 and (TMTSF)2ReO4 and the corresponding conductivity spectra obtained by Kramers-Kronig transformation. The complex structures observed in the spectra are successfully accounted for by assuming that the double occupancy of the band states is effectively excluded so that the Fermi level lies inside a narrow gap induced in these materials by a small dimerization of the molecular stacks. The spectral changes observed among different members of the series are reproduced by varying a limited number of model parameters in a way that follows closely the known changes of the crystal structural properties. Fitting of the experimental data enables us to estimate the parameters of the band structure, namely the transfer integral and the dimerization gap amplitude. Use of self-consistent relations inherent in the adopted model allows us to conclude that a static potential rather than a Peierls-type phonon-induced mechanism plays the dominant role in driving the formation of charge-density waves and the opening of the gap. The same model analysis accounts for the presence of vibronic structures induced by the coupling of the conduction electrons with intramolecular vibrational modes of TMTSF or TMTTF. It has been thereby possible to evaluate the coupling constants for the individual vibrational modes with a greater degree of reliability than in previous attempts. The general physical picture of the studied materials at room temperature as narrow-gap correlated semiconductors is briefly discussed
Reversible chirality inversion of photochromic methacrylic polymers upon irradiation with one-handed circularly polarized light
No full textElectron-electron Interactions and 4kf Localization In the Bechgaard Salts and Their Sulfur Analogs - A Spectroscopic Outlook
No full textWe present the main results of a comparative study of the room temperature infrared reflectance and conductivity spectra of four representative slightly dimerized quarter-filled molecular conductors: (TMTSF)2ClO4, (TMTSF)2PF6, (TMTTF)2Br, and (TMTTF)2PF6. Our analysis based on a 1D dimerized molecular chain model assuming strong on-site correlation (U) has been successful in explaining the relation between the variation of the spectral features and of the amplitude of the stack dimerization in the above series. The results indicate that a narrow 4k(F) dimerization gap opens at the Fermi level in all the studied materials
Immiscibility between carbonic fluids and granitic melts during crustal anatexis: A fluid and melt inclusion study in the enclaves of the Neogene Volcanic Province of SE Spain
No full textIn the restitic crustal enclaves in the Neogene volcanics of El Hoyazo and Mazarron (SE Spain), associations of fluid and silicate melt inclusions indicative of immiscibility are frequently observed in the Bt-poor, Crd-rich graphitic metapelites. These occurrences, extremely rare for anatectic crustal rocks, have been studied by microthermometry, micro-Raman spectroscopy and EMP analysis. Both at El Hoyazo and Mazarron the immiscible FI and MI are hosted in plagioclase and cordierite, with microstructures that suggest primary trapping. The FI hosted in cordierite are monophase, whereas they may contain crystals of calcite when hosted in plagioclase, indicating fluid-host reaction during cooling. Decrepitation microstructures have not been observed. The MI contain fresh glass of peraluminous, felsic rhyolitic composition, typical of anatectic S-type melts. In all samples the fluids are CO(2)-dominated (> 85 mol%), with minor amounts of N(2) and CH(4), and traces of CO and H(2). The nucleation of graphite, induced by the laser beam in some inclusions, demonstrates that the fluids are graphite-saturated. Large scatter in microthermometric behaviour of FI indicates significant density variations. Only in one sample from El Hoyazo are fluid densities compatible with the estimated P-T conditions of trapping (5-7 kbar, 850 +/- 50 degrees C), whereas in the remaining samples the extremely low densities, suggesting trapping pressures < 1 kbar, are in contrast with the microstructural indications of primary entrapment and little evidence of decrepitation. In addition, although some measured compositions are compatible with C-O-H-N fluid speciation at the estimated P-T conditions of anatexis, the lack of H(2)O in all FI is inconsistent with the slightly hydrated character of coexisting glasses. The possible mechanisms accounting for departure of densities and compositions of FI from expected values are discussed, and leakage of H(2)O suggested as the most plausible. (c) 2006 Elsevier B.V. All rights reserved
MOLECULAR CLUSTER-MODELS FOR THE ANALYSIS OF THE OPTICAL-SPECTRA OF ORGANIC CHARGE-TRANSFER CRYSTALS - PROPERTIES AND APPLICATIONS
No full textRaman Investigation on Silicon Nitride Chips after Soldering onto Copper Substrates
Full text linkThe unique electrical properties of silicon nitride have increased the applications in microelectronics, especially in the manufacture of integrated circuits. Silicon nitride is mainly used as a passivation barrier against water and sodium ion diffusion and as an electrical insulator between polysilicon layers in capacitors. The interface with different materials, like semiconductors and metals, through soldering may induce residual strains in the final assembly. Therefore, the dentification and quantification of strain becomes strategically important in optimizing processes to enhance the performance, duration, and reliability of devices. This work analyzes the thermomechanical local strain of semiconductor materials used to realize optoelectronic components. The strain induced in the β-Si3N4 chips by the soldering process performed with AuSn pre-formed on copper substrates is investigated by Raman spectroscopy in a temperature range of −50 to 180 °C. The variation in the position of the E1g Raman peak allows the calculation of the local stress present in the active layer, from which the strain induced during the assembly process can be determined. The main reason for the strain is attributed to the differences in thermal expansion coefficients among the various materials involved, particularly between the chip, the interconnection material, and the substrate. Micro-Raman spectroscopy allows for the assessment of how different materials and assembly processes impact the strain, enabling more informed decisions to optimize the overall device structure
Raman and 2D electronic spectroscopies: A fruitful alliance for the investigation of ground and excited state vibrations in chlorophyll a
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