An AES, LEED, and CO chemisorption study of copper overlayers on Rh(100)

A model bimetalhc system ~/~(~~) has been prepared by the thermal ~a~~at~o~ of copper onto a ~{~~) surface and studied by Auger ehztron spectroscopy, low-energy electron diffraction, and CO chemisorption. At 115 K, the copper overlayer growth follows a layer-by-layer mechanism at least to the third layer. The first monolayer grows pseudorno~~~~~ with respect to the ~1~) substrate whiIe the second monoIayer grows epitaxially with a Cn(1t.W) structure. Upon annealing the copper film, the first two Iayers are stable up to the copper deacon temperature while the copper deposits in excess of two layers nuchzate to form t~dim~sio~ copper ishmds on top of the copper bilayer, For CO ~be~so~ti#n, cupper blocks rhodium sites on a on~to-oue basis and induces a weakening of the R&-Co bond. CO on monoIa~er copper on Rh(1tB) exhibits an enhanced bonding strength with respect to bulk copper. The CO ~he~so~tive properties are discussed in the context of the electronic and geometric st~ctures of this model bimetallic system.