title: Electronic structure analyses of BN network materials using high energy-resolution spectroscopy methods based on transmission electron microscopy.
abstract: Electronic structures of boron-nitride (BN) nanotubes and a BN cone-structure material were studied by using a high energy-resolution electron energy-loss spectroscopy (EELS) microscope. A trial of the whole electronic structure study of hexagonal BN (h-BN), which consists of flat BN honeycomb layers, was conducted by a combination of EELS and X-ray emission spectroscopy (XES) based on transmission electron microscopy (TEM) (TEM-EELS/XES). The pi and pi+sigma plasmon energies of BN nanotubes (BNT) were smaller than those of h-BN. The pi+sigma energy was explained by the surface plasmon excitation. The spectrum of a two-wall BNT of 2.7 nm in diameter showed a new spectral onset at 4 eV. The valence electron excitation spectra obtained from the tip region of the BN cone with an apex angle of 20 degrees showed similar intensity distribution with those of BNTs. The B K-shell electron excitation spectra obtained from the bottom edge region of the BN cone showed additional peak intensity when compared with those of h-BN and BNT. The B K-shell electron excitation spectra and B K-emission spectra of h-BN were compared with a result of a LDA band calculation. It showed that high symmetry points in the band diagram appear as peak and/or shoulder structures in the EELS and XES spectra. Interband transitions appeared in the imaginary part of the dielectric function of h-BN experimentally obtained were assigned in the band diagram. The analysis also presented that the LDA calculation estimated the bandgap energy smaller than the real material by an amount of 2 eV. Those results of TEM-EELS/XES analysis presented that high energy-resolution spectroscopy methods combined with TEM is a promising method to analyze whole electronic structures of nanometer scale materials.
authors.affiliation: Institute for Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan. terauchi@tagen.tohoku.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Terauchi
mesh_terms: D001895:Boron / Q000737:chemistry*; D046032:Microscopy, Energy-Filtering Transmission Electron; D043942:Nanotubes / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission
chemical_list: D009584:Nitrogen; D001895:Boron