Surface Science 188 (1987) 557-562 North-Holland, Amsterdam 557 THE ORIGIN OF CERTAIN FEATURES IN THE AUGER SPECTRUM OF Ru(0001): IMPURITIES, AUGER TRANSITIONS OR DIFFRACTION EFFECTS? Jas Pal S. BADYAL, Andrew J. GELLMAN * and Richard M. LAMBERT * * Department of Physical Chemistry, University of Cambridge, Cambridge, CB2 1EP, UK Received 25 March 1987; accepted for publication 11 June 1987 The origin of certain features in the 300-450 eV range of Ru(0001) Auger spectra has been clarified: the signals at 387 and 418 eV are of particular interest because they could be due to impurity Ti. Measurement of the temperature dependence and orientation dependence of these features, and observations on reference spectra from Ti-dosed Ru(0001) permit a resolution of the issue. It is shown that all but one of the peaks in the 300-450 eV range can be attributed essentially entirely to diffraction phenomena. In addition, the 418 eV signal contains a significant contribution from a Ru(MNN) Auger transition; Ti impurity does not appear to be a significant factor. 1. Introduction The Auger electron spectra obtained from extensively cleaned Ru(0001) surfaces are known to exhibit a number of weak features in the 300-450 eV energy range (see for example ref. [1] and fig. 1 of this article). These peaks have been attributed to various possible causes [1], including (i) the presence of Ti impurity (in the case o~ the signals at 387 and 418 eV) (ii) MNV or MVV Ru Auger transitions and (iii) diffraction effects resulting in the enhanced escape from the solid of secondary electrons with appropriate values of energy and momentum. Interference effects involving the primary electrons can give rise to enhanced emission at characteristic energies, and indeed such phenom- ena have been convincingly demonstrated in the case of Cu [2]. However, the associated EXAFS-like fine structure is not observed in the present case, so that secondary electron diffraction appears to be a more likely explanation. Diffraction effects in the secondary electron spectra of metals have been identified in a number of cases (e.g. ref. [3] and references therein); they have * Permanent address: School of Chemical Sciences, University of Illinois at Urbana-Champaign, 505 S. Mathews Avenue, Urbana, IL 61801, USA. * * To whom correspondence should be addressed. 0039-6028/87/$03.50 9 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)