“…With increasing Li concentration, the Drude plasma edge shifts into the visible from the infrared. [19][20][21][22] Stage 3 is green, stage 2 is red, and stage 1 is golden; these assignments are confirmed by in-situ Raman spectroscopy (supporting information) and agree well with previous reports 23 . The entire intercalation sequence is reversible if voltage is reduced to zero.…”
Section: Observation and Simulationsupporting
confidence: 79%
“…This process created disk shaped graphite crystals of 50m diameter. Their thickness was larger than 100nm, the optical skin depth in graphite, 19 as confirmed by the absence of Si modes in measured Raman spectra. Ti contacts was defined by a second round of e-beam lithography and deposited by e-beam evaporation.…”
Section: Sample Preparation and Device Fabricationmentioning
“…With increasing Li concentration, the Drude plasma edge shifts into the visible from the infrared. [19][20][21][22] Stage 3 is green, stage 2 is red, and stage 1 is golden; these assignments are confirmed by in-situ Raman spectroscopy (supporting information) and agree well with previous reports 23 . The entire intercalation sequence is reversible if voltage is reduced to zero.…”
Section: Observation and Simulationsupporting
confidence: 79%
“…This process created disk shaped graphite crystals of 50m diameter. Their thickness was larger than 100nm, the optical skin depth in graphite, 19 as confirmed by the absence of Si modes in measured Raman spectra. Ti contacts was defined by a second round of e-beam lithography and deposited by e-beam evaporation.…”
Section: Sample Preparation and Device Fabricationmentioning
“…This feature can be classified as a conventional π plasmon also presented in pristine graphite at ω πp ≈ 7 eV 19,20,39,56 and in the GICs at lower energies. [19][20][21][22][23][24][25] The redshift of the πp plasma frequency in CaC 6 in comparison with the plasmon frequency in pure graphite can be explained by the presence of a broad peak centered at 4.6 eV at small Q's in the imaginary part of seen in Figs. 2(c) and 3(c).…”
Section: Calculation Results and Discussionmentioning
confidence: 95%
“…[15][16][17][18] The collective electronic excitations, to the best of our knowledge, were neither investigated in YbC 6 nor in CaC 6 . At the same time, there exist a rich literature [19][20][21][22][23][24][25][26] on this topic for other GICs. Thus in a variety of these compounds, modifications of the low-energy π plasmon mode existing in pure graphite at the 7-12 eV energy range were observed [27][28][29] resulting in a plasmon frequency shift to lower energies.…”
The low-energy dielectric properties of CaC 6 -a representative graphite intercalated compound (GIC)-were investigated by ab initio time-dependent density functional theory calculations with full inclusion of local field effects. The calculations predict the existence of several kinds of plasmons in CaC 6 with energy below 10 eV. The mode with the largest energy is a conventional "πp" mode strongly dispersing in the hexagonal basal plane and almost nondispersing in the perpendicular direction. In the 2.3-3 eV energy range, we find a long-lived intraband plasmon with negative (positive) dispersion with momentum transfer in (perpendicular to) the basal plane. In the 0-1.5 eV energy range, a mode with linear soundlike dispersion along all three high-symmetry directions is observed. All the three modes present strong anisotropy originated from the band structure. The physical origin of these excitation modes is discussed in terms of intra-and interband transitions. The crucial role of local field effects in the propagation of the two lowest-energy modes at large momentum transfers and in the determination of its dispersion over extended momentum-transfer region is analyzed.
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