SEGREGATION OF IMPURITIES ON CR(100) STUDIED BY AES AND STM

With increasing annealing temperature, Auger electron spectroscopy (AE S) of a Cr(100) single crystal shows segregation of C, N and O as the dominating segregating species, indicating competitive segregation of these elements. An STM study of N structures shows a c(2 x 2) superstr ucture at N coverages up to 1/2. The local N coverage can be increased by insertion of N-rich domain boundaries up to 2/3, where a c(3 root 2 x root 2)R+/-45 degrees structure forms, followed by a first-order p hase transformation to a p(1 x 1) structure. The existence of patches of the N-rich p(1 x 1) structure at coverages below 2/3 is probably du e to additional carbon impurities stabilizing this structure. The poss ibility of inverse corrugation on the pure Cr(100) surface is discusse d.