Electronic properties of Cs-intercalated single-walled carbon nanotubes derived from nuclear magnetic resonance

We report on the electronic properties of Cs-intercalated single-walled carbon nanotubes (SWNTs). A detailed analysis of the C-13 and Cs-133 nuclear magnetic resonance (NMR) spectra reveals an increased metallization of the pristine SWNTs under Cs intercalation. The 'metallization' of CsxC materials where x = 0-0.144 is evidenced from the increased local electronic density of states (DOS) n(E-F) at the Fermi level of the SWNTs as determined from spin-lattice relaxation measurements. In particular, there are two distinct electronic phases called alpha and beta and the transition between these occurs around x = 0.05. The electronic DOS at the Fermi level increases monotonically at low intercalation levels x < 0.05 (alpha-phase), whereas it reaches a plateau in the range 0.05 <= x <= 0.143 at high intercalation levels (beta-phase). The new beta-phase is accompanied by a hybridization of Cs(6s) orbitals with C(sp(2)) orbitals of the SWNTs. In both phases, two types of metallic nanotubes are found with a low and a high local n(E-F), corresponding to different local electronic band structures of the SWNTs.