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 io n scattering (ISS) and scanning tunneling microscopy (STM) measurements. Th e incorporated Ir atoms appear in STM as small depressions due to a chemica l contrast mechanism. Intermixing leads initially to step roughening and fi nally 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 am ount of deposited iridium. After Ir deposition at 620 K an ordered alloy la yer is formed which results in a (2 x 1) LEED superstructure. The iridium c ontent of the first layer is here reduced to less than 1% of a monolayer. I n the STM data the surface is marked by a chain-like structure due to imagi ng the electronic differences of the embedded Ir/Cu alloy layer which appea rs to be completely covered by a pure copper topmost layer.