5 research outputs found
Density functional theory calculations of the carbon ELNES of small diameter armchair and zigzag nanotubes: core-hole, curvature and momentum transfer orientation effects
We perform density functional theory calculations on a series of armchair and
zigzag nanotubes of diameters less than 1nm using the all-electron
Full-Potential(-Linearised)-Augmented-Plane-Wave (FPLAPW) method. Emphasis is
laid on the effects of curvature, the electron beam orientation and the
inclusion of the core-hole on the carbon electron energy loss K-edge. The
electron energy loss near-edge spectra of all the studied tubes show strong
curvature effects compared to that of flat graphene. The curvature induced
hybridisation is shown to have a more drastic effect on the
electronic properties of zigzag tubes than on those of armchair tubes. We show
that the core-hole effect must be accounted for in order to correctly reproduce
electron energy loss measurements. We also find that, the energy loss near edge
spectra of these carbon systems are dominantly dipole selected and that they
can be expressed simply as a proportionality with the local momentum projected
density of states, thus portraying the weak energy dependence of the transition
matrix elements. Compared to graphite, the ELNES of carbon nanotubes show a
reduced anisotropy.Comment: 25 pages, 15 figures, revtex4 submitted for publication to Phys. Rev.
Phase analysis of nanocomposite magnetic materials by electron energy loss spectrometry
EELS (electron energy loss spectrometry) in the transmission electron
microscope (TEM) was used to determine the
composition of a nanocrystalline magnetic specimen. The relative amounts
of the hard magnetic phase Nd2Fe14B and the soft magnetic phase Fe3B at
the point of measurement was measured by standard EELS quantification. In
order to determine the structure of Fe3B present, the fine
structure of the boron K-ionisation edge was analysed. Comparison of the
experimental spectra with simulations of the fine structures based on the
TELNES extension of the WIEN97 program package, a full potential
linearised augmented plane wave approach to the calculation of
electronic structure in crystals, shows that the tetragonal form of
Fe3B is predominant