Nitrogen doping of single and multi-walled carbon nanotubes is of great interest both fundamentally, to explore the effect of dopants on quasi-1D electrical conductors, and for applications such as field emission tips, lithium storage, composites and nanoelectronic devices. We present an extensive review of the current state of the art in nitrogen doping of carbon nanotubes, including synthesis techniques, and comparison with nitrogen doped carbon thin films and azofullerenes. Nitrogen doping significantly alters nanotube morphology, leading to compartmentalised 'bamboo' nanotube structures. We review spectroscopic studies of nitrogen dopants using techniques such as X-ray photoemission spectroscopy, electron energy loss spectroscopy and Raman studies, and associated theoretical models. We discuss the role of nanotube curvature and chirality (notably whether the nanotubes are metallic or semiconducting), and the effect of doping on nanotube surface chemistry. Finally we review the effect of nitrogen on the transport properties of carbon nanotubes, notably its ability to induce negative differential resistance in semiconducting tubes.

Cryptomelane-type manganese dioxide (K-MnO 2 ) nanofibers with typical diameters of 20-60 nm and lengths of 1-6 µm were prepared by reacting KMnO 4 with MnSO 4 under hydrothermal conditions. Rietveld refinement from synchrotron X-ray powder diffraction data showed that the K-MnO 2 nanofibers crystallize in a bodycentered tetragonal structure (space group I4/m) with unit cell parameters a ) 9.8241(5) Å and c ) 2.8523(1) Å and elongate along the <001> direction. The K-MnO 2 nanofibers had a mean chemical composition of K 0.11 (H 3 O) 0.05 MnO 2 . The optical band gap of the K-MnO 2 nanofibers was estimated to be 1.32 eV based on the UV-visible absorption. The K-MnO 2 nanofibers had four diagnostic infrared absorptions at 722, 593, 524, and 466 cm -l , which represents specific fingerprints of the vibrational features of MnO 2 materials containing (2 × 2) + (1 × 1) tunnel structures. The Raman scattering spectrum of the K-MnO 2 nanofibers had nine Raman bands with four main contributions at 183, 386, 574, and 634 cm -1 along with five weak ones at 286, 330, 470, 512, and 753 cm -1 , which are attributed to the Mn-O lattice vibrations within the MnO 6 octahedral frameworks. These intrinsic vibrational features can be conveniently used for online and/or in situ analyses of the K-MnO 2 nanofibers during electrochemical and/or ion-exchange reactions.

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