Optical Phonon Lifetimes in Single-Walled Carbon Nanotubes by Time-Resolved Raman Scattering

Kang, Kyung‐Hwa; Ozel, Taner; Cahill, David G.; Shim, Moonsub

doi:10.1021/nl802447a

Cited by 48 publications

(75 citation statements)

References 36 publications

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“…The photoexcited electrons transfer most of their energy to the more strongly coupled optical phonons (SCOPs), 12 including the zone-center (G-mode) and K-point phonons with a characteristic time of a few hundred femtoseconds and effective temperature T oph ≈T e (with T oph the temperature of SCOPs). In turn, this non-equilibrium hot phonon population dissipates its energy into the secondary lower-energy phonons 22,23 (acoustic modes) through anharmonic interactions and a time constant of 1-2 ps at room temperature, as has been reported previously by Chatzakis et al 22 and others 22,[29][30][31] for SWNTs and graphite. The energy loss for the acoustic phonons to the substrate takes place in tens of picoseconds.…”

Section: In This Letter We Present the Temperature Dependence Of Thesupporting

confidence: 58%

Electron temperature dependence of the electron-phonon coupling strength in double-wall carbon nanotubes

Chatzakis¹

2013

Applied Physics Letters

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We applied Time-Resolved Two-Photon Photoemission spectroscopy to probe the electronphonon (e-ph) coupling strength in double-wall carbon nanotubes. The e-ph energy transfer rate G(T e ,T l ) from the electronic system to the lattice depends linearly on the electron (T e ) and lattice (T l ) temperatures for T e >Θ Debye . Moreover, we numerically solved the Two-Temperature Model.We found: (i) a T e decay with a 3.5 ps time constant and no significant change in T l ; (ii) an e-ph coupling factor of 2×10 16 W/m 3 ; (iii) a mass-enhancement parameter, λ, of (5.4±0.9)×10 -4 ; and (iv) a decay time of the electron energy density to the lattice of 1.34±0.85 ps. In carbon nanotubes 1 and graphene 2 , the electron-phonon (e-ph) interactions modify the dynamics of the charge carriers near the Fermi level by changing their mass and the relaxation rate. A dramatic manifestation of these interactions is found in superconductivity, in ballistic transport 3-9 phenomena in Raman spectra, 10 and in phonon dispersion. 11 A significant rise in the electron temperature, T e , with respect to the lattice temperature, T l , can be achieved by irradiating the material with ultra-short laser pulses. The e and ph systems equilibrate by exchanging energy (via scattering processes) with a rate defined by the coupling strength. The observed energy bottleneck suggests that only a limited set of the total phonon modes 12, 13 participate in the relaxation of the charge carrier energy. The e-ph coupling strength is highly important, and although it has been extensively investigated in single-wall carbon nanotubes (SWNTs) 4,9,14,15 and graphene, 16 very little is known for double-wall nanotubes (DWNTs).In this letter, we present the temperature dependence of the energy transfer rate G(T e ,T l ) from electrons to the lattice in DWNTs. Using time-resolved two-photon photoemission (TR-TPP) spectroscopy 17 , we record the non-thermal and the thermal evolution of the electron distributions and their subsequent equilibration with phonons. We analyze the dynamics of the excited electrons in the vicinity of the Fermi level and determine the e-ph interactions. We also solve numerically the Two-Temperature Model (TTM), which describes the hot electron and phonon energy evolution after the excitation. The e-ph coupling arises from the coupling in the inner tube, the coupling in the outer tube, and the coupling from electrons scattered from the inner to the outer tubes, though no significant increase in the total e-ph coupling in DWNTs compared to separate SWNTs was found 18 .In our experiment, IR ultra-short laser pulses were utilized to generate a non-equilibrium population of charge carriers in the conduction band by absorbing energy from the pulses. Further details of the experimental setup can be found elsewhere. 19 Our sample was 100 µm thick freestanding ''bucky'' paper with an outer diameter of the nanotubes of 4±1 nm provided by the Nanolab.The probe-photon energy exceeds the work function of the sample by ~0.25 eV, thus directly promoting elec...

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Section: In This Letter We Present the Temperature Dependence Of Thesupporting

confidence: 58%

Electron temperature dependence of the electron-phonon coupling strength in double-wall carbon nanotubes

Chatzakis¹

2013

Applied Physics Letters

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“…TRR as well as trARPES has been previously applied to graphene, graphite, and carbon nanotubes123202521262728, but they have never been applied to one compound simultaneously as we have done in this paper. G-phonons in graphite and related materials are believed to play the role of “hot” phonons in the 2T description due to strong coupling to electrons.…”

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confidence: 99%

Novel Electron-Phonon Relaxation Pathway in Graphite Revealed by Time-Resolved Raman Scattering and Angle-Resolved Photoemission Spectroscopy

Yang

Parham

Dessau

et al. 2017

Sci Rep

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Time dynamics of photoexcited electron-hole pairs is important for a number of technologies, in particular solar cells. We combined ultrafast pump-probe Raman scattering and photoemission to directly follow electron-hole excitations as well as the G-phonon in graphite after an excitation by an intense laser pulse. This phonon is known to couple relatively strongly to electrons. Cross-correlating effective electronic and phonon temperatures places new constraints on model-based fits. The accepted two-temperature model predicts that G-phonon population should start to increase as soon as excited electron-hole pairs are created and that the rate of increase should not depend strongly on the pump fluence. Instead we found that the increase of the G-phonon population occurs with a delay of ~65 fs. This time-delay is also evidenced by the absence of the so-called self-pumping for G phonons. It decreases with increased pump fluence. We show that these observations imply a new relaxation pathway: Instead of hot carriers transferring energy to G-phonons directly, the energy is first transferred to optical phonons near the zone boundary K-points, which then decay into G-phonons via phonon-phonon scattering. Our work demonstrates that phonon-phonon interactions must be included in any calculations of hot carrier relaxation in optical absorbers even when only short timescales are considered.

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“…Additional ultrafast techniques have been employed to investigate electron-phonon coupling, and in particular, time-resolved anti-stokes Raman scattering measurements have been used to determine the population lifetimes of the G-band phonons in SWNTs. 19,20 However, the information obtained from such time-resolved measurements is limited to population lifetimes of phonons and do not provide the additional phase information and dephasing times that are accessible with CP spectroscopy. Recent CP studies on SWNTs have produced direct observation of CP oscillations of both the radial breathing mode (RBM) and G-band phonons, in addition to their phase information and dephasing times.…”

Section: -16mentioning

confidence: 99%

Polarization dependence of coherent phonon generation and detection in highly-aligned single-walled carbon nanotubes

et al. 2011

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We have investigated the polarization dependence of the generation and detection of radial breathing mode (RBM) coherent phonons (CP) in highly-aligned single-walled carbon nanotubes. Using polarization-dependent pump-probe differential-transmission spectroscopy, we measured RBM CPs as a function of angle for two different geometries. In Type I geometry, the pump and probe polarizations were fixed, and the sample orientation was rotated, whereas, in Type II geometry, the probe polarization and sample orientation were fixed, and the pump polarization was rotated. In both geometries, we observed an almost complete quenching of the RBM CPs when the pump polarization was perpendicular to the nanotubes. For both Type I and II geometries, we have developed a microscopic theoretical model to simulate CP generation and detection as a function of polarization angle and found that the CP signal decreases as the angle goes from 0• (parallel to the tube) to 90• (perpendicular to the tube). We compare theory with experiment in detail for RBM CPs created by pumping at the E44 optical transition in an ensemble of single-walled carbon nanotubes with a diameter distribution centered around 3 nm, taking into account realistic band structure and imperfect nanotube alignment in the sample. We theoretically determined a cos 8 (θ) dependence for Type I CP spectroscopy experiments and a cos 4 (φ) polarization dependence for Type II CP spectroscopy experiments, and after including misalignment effects to our fitting, we determined the nematic order parameter of our sample to be 0.81.

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Optical Phonon Lifetimes in Single-Walled Carbon Nanotubes by Time-Resolved Raman Scattering

Cited by 48 publications

References 36 publications

Electron temperature dependence of the electron-phonon coupling strength in double-wall carbon nanotubes

Electron temperature dependence of the electron-phonon coupling strength in double-wall carbon nanotubes

Novel Electron-Phonon Relaxation Pathway in Graphite Revealed by Time-Resolved Raman Scattering and Angle-Resolved Photoemission Spectroscopy

Polarization dependence of coherent phonon generation and detection in highly-aligned single-walled carbon nanotubes

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