Abstract
Angle-resolved photoemission of Cr2p 3 2 N 1s and C 1s core level photoelectrons was used to determine the structure of segregated surface phases on an Fe-15%Cr(100) single crystal containing dissolved N and C. The surface phases of CrN and CrC were generated at elevated temperature by a controlled annealing procedure. Polar angle intensity distributions of photoelectrons (X-ray photoelectron diffraction) were recorded in the [001] and [011] azimuths, respectively. LEED showed a sharp 1 × 1 pattern for both surface phases. For CrN the angular intensity distributions exhibited forward scattering peaks for Cr2p 3 2 but not for N 1s. For CrC, on the other hand, Cr2p 3 2 and C 1s showed both strong forward scattering features in all distributions. It follows that the segregated surface phases are about two to four layers thick and epitaxed to the substrate (100) surface. The CrN phase consists of two Cr layers with an adsorbed N layer, while the CrC phase consists of at least three complete planes and has a NaCl structure, with CrC(100)∥FeCr(100) and CrC[010]∥FeCr[011]. The positions of forward scattering peaks for CrN indicate a lattice expansion between the first and second layer of about 16%.
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