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Scanning tunneling microscopy is used to study the arrangement of segregated carbon atoms with atomic resolution. Individual carbon atoms are visible only under special tip conditions, while they normally do not directly appear on STM topographs. Under all tip conditions, carbon atoms affect the corrugation of their metal neighbours, reducing the apparent height by 20 to 40 pm in the p(2 × 2) and 40 to 70 pm in the c(2 × 2) superstructure. Therefore the existence, structure and amount of carbon can be also derived from images without directly visible carbon atoms. A substrate lattice distortion in regions of the carbon c(2 × 2) superstructure was observed, exhibiting areas of the p4g structure known from earlier LEED studies of Ni(100).
Corresponding author: M. Schmid (schmid).