Journal of Electron Spectroscopy and Related Phenomena, 48 (1989) 143- 153 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands 143 zyxwvutsrqp AN INTERPRETATION OF THE ELECTRON ENERGY LOSS SPECTRA OF CLEAN AND OXYGEN EXPOSED HAFNIUM J.M. SANZ, M.A. BARON, E. ELIZALDE and F. YUBERO Departamento de Fisica Aplicada C-XZZ, Universidad Autdnoma de Madrid, Cantoblanco, E- 28049 M adrid (Spain) (Received 1 June 1988) ABSTRACT Electron energy loss spectra (EELS) have been taken on clean and oxygen exposed hafnium surfaces by means of a cylindrical mirror analyzer (CMA) in the energy range 4 to 60 eV. Results are compared with the dielectric function deduced from a Kramers-Kronig analysis of previous ELS investigations. Bulk and surface collective excitations, as well as interband transitions, are identified and discussed in light of previous studies. An exciton at 15 eV has been tentatively identified in the oxidized surface. INTRODUCTION zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Electron energy loss spectroscopy (EELS) has become a very useful tech- nique for surface analysis, giving important information concerning the elec- tron structure and collective electron excitations. However, although a large amount of experimental and theoretical work has been realized in the last dec- ade [ 1,2], the analysis and interpretation of the characteristic energy losses in noble and transition metals remain difficult and in some cases contradictory. Very few EELS data are available for either clean or oxygen-exposed hafnium. Lynch and Swan [ 31 have published EELS spectra in the reflection mode of most of the 4d and 5d transition metals including hafnium, but with a very scarce interpretation of the data. Lynch et al. [4] have studied the optical properties of hafnium using synchrotron radiation. These authors calculated the energy-loss function Im ( - l/z) and discussed it in terms of double volume and surface plasmons and interband transitions. However, from their sample preparation method one would expect that the results are very affected by the contamination of the surface. In fact the loss function obtained by Frandon et al. [5] by transmission EELS is indeed quite different. These authors have also published transmission EELS spectra of hafnium oxide with a very brief discussion of the data. It appears that no discussion or interpretation of the characteristic electron zyxwvutsr 0368-2048/89/$03.50 0 1989 Elsevier Science Publishers B.V.