The epitaxial growth of copper on the (110) surface of a tungsten single crystal studied by LEED, Auger electron, and work function techniques

The epitaxial growth of copper vapour deposited onto the (110) surface of a tungsten single crystal has been studied using low energy diffraction, Auger electron emission and electron energy loss spectra, while in a separate apparatus, work function changes have been measured. It is shown that the initial deposition of copper leads to the formation of a strained copper (111) monolayer, constrained in the tungsten [001] direction to match the substrate. In the [110] direction a sufficient degree of freedom exists to allow the formation of the observed close-packed structure. Further deposition results in the epitaxial growth of a film with periodicity characteristic of bulk copper (111) plane. Heating of the copper film to above 600 K results in the formation of large three-dimensional islands which evaporate at temperatures in excess of 1050 K leaving the tightly bound strained layer which finally desorbs above 1200 K. No evidence is found for the diffusion of copper into the tungsten substrate. The contact potential difference between a tungsten (110) surface and the copper (111) epitaxial film has been measured to be −0.33 ± 0.02 eV while for the strained layer it is −0.75 ± 0.03 eV (the tungsten having the highest work function).