Poster
Production and Spectroscopic Characterisation of Multiwall Boron Nitride Nanotubes
E. Borowiak-Palen1, T. Pichler2, G. Behr3, G.G. Fuentes4, M. H. Rümmeli5 M. Knupfer6, J. Fink7 Leibniz Institute for Solid State and Materials Research Dresden, P.O. Box 270016 D01171 Dresden, Germany. Tel: +49 (351) 4659501 1) T.Pichler@IFW-Dresden.de 2) E.Borowiak@IFW-Dresden.de 4) M.Ruemmeli@IFW-Dresden.de 5)M.Knupfer@IFW-Dresden.de 6) J.Fink@IFW-Dresden.de Centro de Ingenieria Avanzada de Superficies AIN, 31191 Cordovilla, Pamplona, Spain. Tel. +34 948 421101 3) gfuentes@ain.es Objectives: The existence of the nanotubular allotropic form of hexagonal boron nitride (h-BN) was recently proposed using tight binding calculations by Rubio et al.1 The band structure for this new class of metastable structures is predicted to have a large band gap leading to promising potential uses in blue and violet photoluminescence devices2. In recent years BN nanotubes have been fabricated using different methods. Results and Conclusions: We report on infrared (IR) and electron energy-loss spectroscopy (EELS) studies of high purity multiwall BN nanotubes synthesised by substitution reactions. The IR pattern of the BN tubes shows the presence of both tangential (∼800 cm-1) and longitudinal (∼1400 cm-1) modes characteristic of h-BN. We show that the different energy positions and the LO-TO splitting observed for the BN-tubes can be explained by simple geometrical considerations. The dielectric function, ε, of the BN-tubes obtained from the electron energy loss-function reveals an intense π-π* interband transition at 5.4 eV, which is shifted to lower energies by 0.6 eV when compared to hexagonal BN. In addition, the absorption onset of the optically allowed transitions is less abrupt and begins at lower energies than that of h-BN. We ascribe this effect to the presence of tubes with small inner diameters (below 3 nm) in good agreement with recent theoretical band structure calculations. In addition, we have studied the high purity multiwall BN nanotubes by TEM microscopy (Fig.1) and EELS core level excitations. These show similarities between the lattice structure and chemical environment (B1s and N1s) of the BN tubes and h-BN. Preferential orientation of the nanotubes can also give rise to apparent changes in the shape core level excitation spectra.
1st NANOFORUM Workshop
Sinaia (Romania)
October 5-7, 2003
Poster
Fig1. TEM images of MWBNNT (left image) and starting SWCNT (right image).
References: 1) A. Rubio, J. L. Corkill, M. Cohen, Phys. Rev. B. 49, 5081 (1994) 2) X. D. Bai, E. G. Wang, J. Yu, Appl. Phys. Lett., 77, 67 (2000)
1st NANOFORUM Workshop
Sinaia (Romania)
October 5-7, 2003