Raman scattering from in-plane lattice modes in low-stage graphite-alkali-metal compounds

Eklund, P. C.; Dresselhaus, G.; Dresselhaus, M. S.; Fischer, J. E.

doi:10.1103/physrevb.16.3330

Cited by 94 publications

(78 citation statements)

References 6 publications

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“…The charge transfer dependence proposed here also explains the series of GICs CsC 8 , RbC 8 to KC 8 , 35 which show a similar trend. The gradient of these effects is similar, but the overall values are different, since in XC 8 GICs (where X = intercalant) the charge transfer is less.…”

Section: Analysis and Discussion Of Resultssupporting

confidence: 73%

Nonadiabatic phonons within the doped graphene layers ofXC6compounds

et al. 2010

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We report Raman scattering measurements of BaC6, SrC6, YbC6, and CaC6, which permit a systematic study of the phonons and the electron-phonon interaction within the doped graphene layers of these compounds. The out-of-plane carbon phonon softens as the spacing of the graphene layers is reduced in the series BaC6, SrC6, YbC6, and CaC6. This is due to increasing charge in the π * electronic band. Electron-phonon interaction effects between the in-plane carbon modes at ≈ 1500 cm −1 and the π * electrons cause a strong non-adiabatic renormalization. As charge is transferred into the π * band these non-adiabatic effects are found to increase concurrent with a reduction in the phonon lifetime.

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Section: Analysis and Discussion Of Resultssupporting

confidence: 73%

Nonadiabatic phonons within the doped graphene layers ofXC6compounds

et al. 2010

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“…The same effect was observed at low doping levels by Iwasa et al for vapor-doped K-SWNT [15]. We interpret the continuous and linear downshift for K/C > 0.015 as evidence for valence electron transfer from K atoms to the C anti-bonding band, which lengthens the C-C bond and softens the tangential vibrational modes, similar to the behavior observed in graphite intercalation compounds [16,17]. A straight line can be fit to the data for 0.015 < K/C < 0.04 from which we obtain / Q ~ 370 cm -1 /electron per C, close to the value ~ 340 cm -1 /electron per C observed in alkali doped C 60 [18] but larger than the value ~ 280 cm -1 /electron per C observed in KC 8 graphite [16,17].…”

Section: Resultssupporting

confidence: 66%

“…We interpret the continuous and linear downshift for K/C > 0.015 as evidence for valence electron transfer from K atoms to the C anti-bonding band, which lengthens the C-C bond and softens the tangential vibrational modes, similar to the behavior observed in graphite intercalation compounds [16,17]. A straight line can be fit to the data for 0.015 < K/C < 0.04 from which we obtain / Q ~ 370 cm -1 /electron per C, close to the value ~ 340 cm -1 /electron per C observed in alkali doped C 60 [18] but larger than the value ~ 280 cm -1 /electron per C observed in KC 8 graphite [16,17]. Applying our value to the shift measured on K vapor-doped SWNT [2] implies a composition of KC 8.3 for that sample, consistent with the saturation weight uptake using the same synthesis conditions [1].…”

Section: Resultsmentioning

confidence: 77%

In situ Raman scattering studies of alkali-doped single wall carbon nanotubes

Claye

Rahman

Fischer

et al. 2001

Chemical Physics Letters

150

148

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Electrochemical doping and in-situ Raman scattering were used to study charge transfer in K-and Li-doped single wall carbon nanotubes (SWNT) as a function of alkali concentration. An 8 cm -1 downshift was observed for the tangential phonon mode of SWNT doped to stoichiometries of KC 24 and Li 1.25 C 6 . The shift in both systems is reversible upon de-doping despite an irreversible loss of crystallinity. These results indicate that the tangential mode shifts result from electron transfer from alkali dopants to the SWNT, and that these modes are only weakly affected by long-range order within the ropes. Comments ABSTRACTElectrochemical doping and in-situ Raman scattering were used to study charge transfer in K-and Li-doped single wall carbon nanotubes (SWNT) as a function of alkali concentration. An 8 cm -1 downshift was observed for the tangential phonon mode of SWNT doped to stoichiometries of KC 24 and Li 1.25 C 6 . The shift in both systems is reversible upon de-doping despite an irreversible loss of crystallinity. These results indicate that the tangential mode shifts result from electron transfer from alkali dopants to the SWNT, and that these modes are only weakly affected by long-range order within the ropes. IntroductionSingle wall carbon nanotubes (SWNT) constitute the newest carbon system in which chemical doping strongly modifies the physical properties [1,2]. The weak Van der Waals bonding between individual nanotubes in a semicrystalline bundle, or "rope", presumably allows for the insertion of dopants in the host lattice, as in graphite intercalation compounds and doped phases of C 60 .Alkali doping decreases the resistivity of bulk samples by a factor of 30-100 at 300K [1,3]. A similar result was observed for an individual SWNT rope [4], proving that the enhanced electron transport in bulk samples is an intrinsic property of the ropes. This phenomenon can be explained by valence electron transfer from the alkali atoms into the C anti-bonding band, which moves the Fermi energy into a region of higher density of states and enhances the conductivity. This mechanism has long been known in graphite intercalation compounds, doped polyacetylene and fullerides. Charge transfer from the alkalis to the nanotubes was proven using Raman scattering, which showed a softening of the tangential vibrational modes for the C-C bond upon doping with K or Rb [2]. A stiffening of the tangential modes and a decrease in resistivity were observed upon doping with electron acceptors, confirming the amphoteric nature of SWNT [1,2]. At this point, however, little is known about the reversibility of these phenomena and their dependence on dopant concentration. One of the limiting factors in this regard is the difficulty of controlling the composition using the vapor phase doping technique. An alternative method is electrochemical doping, which offers precise control of guest stoichiometry and allows for in-situ measurements on the guest-host systems. In-situ Raman scattering and

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“…Much clarification of our findings came with a mass determination of the emitted clusters resulting from the laser ablation of a graphite surface (see Fig. 3) by the Exxon The Raman spectra of stages 1, 2 and 3 rubidium intercalated graphite, in which a single layer of rubidium is intercalated between 1, 2 and 3 layers of graphene, respectively, taken from a 1977 paper with Eklund et al [8].…”

mentioning

confidence: 96%

“…But the special optical, transport, thermal, vibrational, spectroscopic properties of graphite intercalation compounds were interesting in their own right (see Fig. 2(b)), as is shown for example in the Raman spectra for stages 1, 2 and 3 donor intercalation compounds with single layers of Rb sandwiched between one, two and three layers of graphene [8].…”

mentioning

confidence: 98%