Temperature-dependent surface morphology of Au/Cu(001)

The electronic structure of low-coverage (1 monolayer or less) Au/Cu(001) has been probed over a wide temperature range with angle-resolved photoelectron spectroscopy by use of synchrotron radiation and resonance lamp emission. Concurrent with the change in the low-energy electron diffraction pattern at ½ monolayer coverage from a $p(1\mathrm{}\times 1)$ at $T\approx -100\mathrm{}°$C to a $c(2\mathrm{}\times 2)$ at room temperature, striking changes in the valence-band structure and a 0.33±0.03-eV shift in the Au $4f_{\frac{5}{2}}$ peak were observed. Similar changes were observed at coverages near 1 monolayer. Evidence is presented which suggests that this is the in situ observation of the formation of a surface alloy from a metal overlayer.