Edge effect in the ELNES of Co oxide absorption edges

EELS probes the unoccupied density of states above the Fermi level. The analysis of the energy-loss near edge structure provides an insight into the local electronic and geometrical structure of the excited atom. Surface composition can be different from that of the bulk, especially for the transition metal oxides due to either thermodynamic or kinetic factors during the preparation. This also depends on the reducing /oxidizing nature of their environment. The surface structure is most important for applications in catalysis and thin film growth. For example, the (001) SrTiO3 crystal surface terminates with two TiO2 layers, and with substantial reorganization in the outermost layer when annealed at high-purity oxygen [1-2]. It can be expected that such surface layer effects are pronounced and easily detectable by EELS as the thickness gradually reduces to the thin edge regions where two free surfaces meet (A typical edge and surface layer is schematically shown in Fig.1). In this work, electron energy loss (EEL) spectra (low and core loss spectra, respectively) obtained from CoO and Co3O4 particles have been collected from specimen areas of different thickness, i.e. from the bulk regions towards thin edge regions. The energy loss near edge structur