Intercalation processes of single-walled carbon nanotube ropes

The intercalation processes of alkali metal vapor into single-walled carbon nanotube (SWNT) crystalline ropes were investigated by Raman and X-ray photoemission spectroscopy. Two stable states, KCsimilar to27 and KCx (x<9), were identified by the evolution of Raman shift of the E-2g mode upon dosing with K. This E-2g mode first shows an upshift, then disappears, and finally reappears at downshifted wave numbers, in a similar manner to that of graphite intercalation compounds. The upshift of the Raman peak for the KC27 state indicates that K is intercalated between two tubes rather than between three tubes. The absence of Raman peaks between the two stable phases indicates that phases with intermediate K/C atomic ratios are unstable compared to the KCsimilar to27 and KCx (x<9) phases.