Surface Science 202 (1988) L621-L626 North-Nolland, Amsterdam L621 SURFACE SCIENCE LETTERS zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO SURFACE EXTENDED ENERGY LOSS FINE STRU~E AND LOCAL SPIN DENSITY INVESTIGATION OF CARBIDIC CARBON ON THE Ni(100) SURFACE G. CHIARELLO * Dipartimento di Fisica, Universita della Catabria, 87030 Arcavacata di Rende (CS). Italy J. A~~ZEL~ * *, R. FOU~NIER, N. RUSSO * * * and D.R. SALAHUB DCpartement de Chimie, UniversitP de MontrPal. CP 6128, Succursale A, MontrPai, Quebec, Canada H3C 3J7 Received 23 March 1988; accepted for publication 17 May 1988 The structural properties of a carbidic carbon layer on the Ni(100) surface have been investigated both experimentally by surface extended energy loss fine structure (SEELFS) and theoretically by the linear-combination-of-Gaussian-type-orbitals model-potential local-spin-den- sity (LCGTO-MP-LSD) method. Both experimental and theoretical results indicate that the most stable site for carbon chemisorption is the fourfold hollow site. The Ni-C distance derived from SEELFS analysis was found to be 1.75+0.05 A, in good agreement with that obtained by theoretica calculation (1.79 A). The calculated vibrational frequency of the adsorbed carbon atom is found to be 407 cm-’ in excellent agreement with the experimental value of 410 cm-‘. The dissociation of molecules containing carbon atoms such as CO, C,H,, C,H,, on transition metal surfaces gives rise to two different carbon phases classified from their Auger line shape as “carbidic carbon” and “graphitic carbon” [1,2]. The carbidic phase is active in methanation reactions whereas graphitic carbon is a poison for the surfaces [1,2]. On Ni(ll1) and Ni(ll0) surfaces under vacuum conditions the carbidic phase changes into graphitic carbon, upon increasing the surface temperature from about 400 to 700 K. In the same conditions no conversion of carbidic to graphitic phase has been observed on the Ni(lOO) surface [2,3]. In addition, the chemisorption of carbon on this surface induces a distortion of the first layer * Permanent address: CISE-Tecnologie Innovative, P.O. Box 12081, 20134, Milano, Italy. ** Permanent address: CRAY Research Inc., 1333 Northland Drive, Mendota Heights, MN 55120, USA. *** Permanent address: Dipartimento di Chimica, Universita della Calabria, 87030 Arcavacata di Rende (CS), Italy. 0039~6028/88/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)