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Multi-mode heterodyned 5th-order infrared spectroscopy
摘要： Fifth-order multidimensional infrared spectroscopy with heterodyned detection was carried out in the three-beam dual-frequency configuration. Numerous 5th-order cross peaks were detected for the 4-azidobutyrate-N-hydroxysuccinimide ester compound in solution involving several vibrational modes ranging in frequency from 1045 to 2100 cm?1. Cross peaks involving overtones (2X/Z) and combination bands (XY/Z) among the tags, modes X and Y excited by the first two mid-IR laser pulses, and the reporter, modes Z excited by the third laser pulse, were acquired and the factors affecting the amplitude of 5th-order cross peaks are discussed. The 5th-order cross peaks were detected among modes that are spatially close (a few bonds apart) as well as for modes spatially separated by ca. 12 ? (eight bonds apart). In both cases, the waiting time dependences for the 3rd and 5th order cross peaks were found to be different. In particular, the waiting time at which the cross-peak maximum is reached, the decay time, and the value of a plateau at large waiting times were all differing strongly. The differences are explained by reduced sensitivity of the 5th-order signals to modes coupled weakly to the reporter mode and different relaxation dynamics involving overtone state of the tag. The ability of the 5th-order peaks to single out the modes coupled strongly to the reporter can help identifying specific energy relaxation and transport pathways, which will be useful for understanding energy transport dynamics in molecules. The absorptive 5th-order cross peaks were constructed which report on three-point correlation functions. It is shown that in addition to the triple-frequency correlation functions, a correlation of the frequencies with the mode coupling (anharmonicity) can be naturally measured by the 5th-order spectroscopy. The current limit for detecting 5th-order signals was estimated at the level of 1 × 10?3 in reduced anharmonicity, which is determined by the corresponding two-state anharmonicity divided by the reporter mode spectral width. Given the simplicity of recording the 5th-order cross peaks in the three-beam configuration, the approach carries a potential for a broad use.
关键词： vibrational modes,anharmonicity,heterodyned detection,fifth-order,multidimensional infrared spectroscopy,energy transport
更新于2025-09-23 15:22:29
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Temperature Dependence of Raman and Photoluminescence Spectra of Ternary Alloyed CdSe0.3Te0.7 Quantum Dots
摘要： The Raman and photoluminescence spectra of ternary alloyed CdSe0.3Te0.7 quantum dots (QDs) have been studied at temperatures between 84 K and 293 K. The average diameter of QDs is about 5.1 nm. The temperature dependence of the longitudinal optical (LO) phonon frequencies and the phonon band width was analyzed and the anharmonic constants relating to various high-order phonon processes was determined. While the three-phonon processes plays a dominant role in the temperature-dependent shift of the LO-phonon frequencies, the four-phonon processes contribute to the increase of the phonon linewidth with increasing temperature. The photoluminescence (PL) spectra were used to study the temperature dependence of the bandgap, the linewidth and the integrated PL intensity. At low temperatures below about 120 K, the PL linewidth decreases and the PL intensity increases as temperature increases. This temperature behavior can be ascribed to the exciton ?ne structure.
关键词： light-emitting diodes,anharmonicity,exciton ?ne structure,photoluminescence,Raman scattering,phonon
更新于2025-09-16 10:30:52
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Anharmonicity of Bi <sub/>2</sub> Se <sub/>3</sub> revealed by fs transient optical spectroscopy
摘要： We investigate the anharmonic effects in Bi2Se3 crystals using femtosecond transient optical spectroscopy at 5–280 K. The re?ectivity time series consist of exponential decay due to hot carriers and decaying oscillations due to the A1 1g phonon vibration. Vibration frequency and dephasing time of this optical phonon mode are obtained as a function of temperature, decreasing with increasing temperature; both the red shift in frequency and the increased dephasing rate induced by heating can be well described using the anharmonicity model including lattice thermal expansion and phonon-phonon coupling.
关键词： Bi2Se3,femtosecond transient optical spectroscopy,phonon dynamics,anharmonicity,thermal expansion,phonon-phonon coupling
更新于2025-09-11 14:15:04
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Phonon thermodynamics and elastic behavior of GaN at high temperatures and pressures
摘要： The effects of temperature and pressure on the phonons of GaN were calculated for both the wurtzite and zinc-blende structures. The quasiharmonic approximation (QHA) gave reasonable results for the temperature dependence of the phonon DOS at zero pressure but unreliably predicted the combined effects of temperature and pressure. Pressure was found to change the explicit anharmonicity, altering the thermal shifts of phonons and more notably qualitatively changing the evolution of phonon lifetimes with increasing temperature. These effects were largest for the optical modes, and phonon frequencies below approximately 5 THz were adequately predicted with the QHA. The elastic anisotropies of GaN in both wurtzite and zinc-blende structures were calculated from the elastic constants as a function of pressure at 0 K. The elastic anisotropy increased with pressure until reaching elastic instabilities at 40 GPa (zinc blende) and 65 GPa (wurtzite). The calculated instabilities are consistent with proposed transformation pathways to rocksalt GaN and place upper bounds on the pressures at which wurtzite and zinc-blende GaN can be metastable.
关键词： phonon thermodynamics,high pressures,elastic anisotropy,anharmonicity,high temperatures,GaN,elastic behavior,quasiharmonic approximation
更新于2025-09-09 09:28:46
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Unusual polarization and temperature-dependent Raman response in Weyl semimetal NbIrTe4
摘要： We carry out a systematic study of polarized- and temperature-dependent Raman scattering of layered Weyl semimetal NbIrTe4 on the (002) crystal surface, under parallel and perpendicular polarization Raman spectroscopy geometry in back scattering way, the angle-dependent Raman peaks intensity is recorded by rotating the single crystal from 0° to 360°, in combination with group theory analysis, all the prominent Raman peaks are assigned to A1 and B1 vibrational modes, moreover, we show that the angular dependence of Raman peak intensity of A1 mode is rather unusual and can be explained by complex values for Raman tensor elements, which is traced back to electron-phonon interaction in this material. Meanwhile, lattice anharmonic vibrational behavior is studied by investigating the temperature-dependent Raman scattering spectra, it is observed that all the Raman peaks show linear sti?ening behavior as the temperature decreased from 293 K to 83 K, the temperature coe?cients of four prominent Raman peaks suggest the anharmonicity of the lattice in layered NbIrTe4 crystal.
关键词： Lattice anharmonicity,Electron-phonon coupling,Vibrational modes,Polarized Raman scattering
更新于2025-09-04 15:30:14