Interaction between single walled carbon nanotube and 1D crystal in CuX@SWCNT (X = Cl, Br, I) nanostructures

CuX@SWCNT (X = Cl, Br, I) nanostructures were prepared by capillary filling of 1.4-1.6 nm single-walled carbon nanotubes (SWCNT) with copper halides. The structure of CuX@SWCNT (X = Cl, Br, I) represents a distorted two-layer hcp of halogen atoms arranged along the SWCNT. The EXAFS and the high angle angular dark field (HAADF) HRTEM data indicate that Cu is partially coordinated by C. According to the optical absorption, valence band photoemission spectroscopy and work function measurements, a Fermi level (FL) downshift as compared with the initial value for the nanotubes and a corresponding charge transfer from the nanotubes to the 1D crystals is observed for CuX@SWCNT nanostructures. The FL shift increases in the sequence CuI < CuBr < CuCl due to an increase of the electron affinity for the halogen atoms. The XPS data confirm the acceptor effect of copper halides and indicate that metallic and semiconducting nanotubes behave differently. Raman spectroscopy performed under electrochemical charging allowed estimation of the value of charge transfer between the nanotube walls and the intercalated 1D crystal. The X-ray absorption and emission spectra for carbon and copper thresholds revealed a new energy level composed of the carbon 2p(z) and copper 3d-orbitals. This indicates the Cu-C bonding, which in line with the structural HAADF HRTEM and EXAFS data. (C) 2012 Elsevier Ltd. All rights reserved.