a Max-Planck-Institut für Eisenforschung, Postfach 140 444, D-40074 Düsseldorf, Germany
b Lehrstuhl für Festkörperphysik, Universität Erlangen–Nürnberg, Staudtstrasse 5, D-91058 Erlangen, Germany
Abstract:
Cosegregation is known to cause the formation of two-dimensional chemical compounds (surface compounds) which can be epitaxed to substrate surfaces of a suitable structure. In the present work the cosegregation-induced formation of the CrN surface compound on nitrided Fe–15%Cr–N(100) single crystal surfaces was studied by means of Auger electron spectroscopy and low-energy electron diffraction. Intensity versus energy spectra (I(E)) were measured and analysed fully dynamically to investigate the structural details of the CrN surface compound. It is found that nitrogen is segregated to the surface forming the sample's top layer and substantial amounts of chromium are cosegregated with nitrogen. Nitrogen atoms reside in four-fold symmetric hollow sites about 0.1 Å above the metallic substrate. There is a huge relative expansion of the distance between the first and second metal atom layers (Δd12/d0≈26%), while the distances between deeper layers are almost bulk-like. The small distance between the nitrogen and the top metal layer as well as the huge layer expansion Δd12/d0 are in agreement with results found for N/Cr(100).