Iridium on Cu(100): Surface Segregation and Alloying

After deposition of submonolayer quantities of iridium on Cu(100) at 200 K strong intermixing of both species has been found by means of low energy ion scattering (ISS) and scanning tunneling microscopy (STM) measurements. The incorporated Ir atoms appear in STM as small depressions due to a chemical contrast mechanism. Intermixing leads initially to step roughening and finally also to surface etching. With ISS the amount of iridium remaining at 200 K in the first layer was determined to be less than 20% of the total amount of deposited iridium. After Ir deposition at 620 K an ordered alloy layer is formed which results in a (2 × 1) LEED superstructure. The iridium content of the first layer is here reduced to less than 1% of a monolayer. In the STM data the surface is marked by a chain-like structure due to imaging the electronic differences of the embedded Ir/Cu alloy layer which appears to be completely covered by a pure copper topmost layer.