Photoemission investigation of the temperature effect on Si--Au interfaces

We report extensive photoemission measurements carried out with synchrotron radiation and with conventional light sources on Si(111)--Au interfaces. The coverage dependence has been studied in detail at room temperature (RT) with synchrotron radiation. We have found considerable intermixing at all coverages, and the photoemission spectrum characteristic for pure gold was not even observed at coverages of about 150 monolayers. A deeper insight into the intermixing mechanism is obtained from the te,perature dependence of the spectra, which was studied for surfaces covered with 10 monolayers. Considerable intermixing is observed for interfaces prepared and measured at liquid nitrogen temperatures (LNT). Several hours of annealing at RT are required for an interface prepared at LNT to obtain the equilibrium situation reached immediately after preparation at RT. These results indicate that the thermal energy of the sample is not the only energy responsible for intermixing during interface preparation. We propose that an important contribution comes from the condensation energy of gold. The photoemission spectra show that the intermixing increases with the temperature up to approx. =3500C