Simulation of electron energy loss near-edge structure at the Al and N K edges and Al L(23) edge in cubic aluminium nitride.

Calculations of electron energy near edge structures (ELNES) are compared with experimental data obtained in a high-resolution transmission electron microscope. This study concerns small precipitates of aluminium nitride in low carbon steel. The ELNES technique allows to clearly establish that these precipitates crystallize in a cubic rather than in a hexagonal crystallographic cell. The influence on simulated spectra of different parameters are investigated: the size of the atomic shell and its relation with the electron inelastic mean free path. We also examine the influence of the core hole and the sensitivity to cell parameters. We particularly examine the Al L(23) near edge structure and features relating to the different transition channels (A(1g), E(g) and T(2g)). Results of a multiple scattering and band structure calculations using ICXANES and WIEN97 codes, respectively, are compared in the region from 0 to 30 eV above the edge onsets. Both calculations are in a rather good agreement.

Electron spectroscopy imaging to study ELNES at a nanoscale.

Series of energy-filtered TEM images have been acquired with very narrow energy slit using a post-column energy filter. This allowed us to reconstruct spectra with an energy resolution estimated to 2 eV, and a spatial resolution in the order of 0.5 nm. In that way, fine structures of the N-K edge in AlN/GaN heterostructures have been investigated and compared to EELS spectra. The fine structure in the two nitrides is very sensitive to the local environment. Very good agreement between ESI and EELS spectra was found. Moreover, this technique allowed analysis of the AlN/GaN interface at a nanoscale. The second example is an application of the technique to construct bonding maps. In this case, maps differentiating AlN nanoprecipitates with either the cubic or the hexagonal phase were created.