Surface alloy formation of Fe on Cr(100) studied by scanning tunneling microscopy

Surface alloy formation of Fe on a Cr(100) surface was studied using a UHV scanning tunneling microscope. As we deposited Fe of less than 1 ML at room temperature and subsequently annealed the substrate at temperatures between 200 ^∘{}C and 300 ^∘{}C, we observed that Fe atoms incorporate into the Cr(100) surface, forming a well-ordered surface alloy of Fe0.5Cr0.5. These two elements were differentiated by imaging at the bias voltages near their surface states. The surface alloying was also confirmed by imaging at the bias voltages of their Shockley image states. By annealing the Fe layer of {~}1 ML at 250 ^∘{}C, we found that the solubility of Fe into the Cr(100) surface is {~}25% at that temperature. Fe overlayer shows kinetically roughened mound structure at room temperature while it shows equilibrium two-dimensional islands at 300 ^∘{}C.