Effective attenuation length dependence on photoelectron kinetic energy for gold from 1 keV to 10 keV: Role of island growth in overlayer experiments

We analyzed the experiments of Rubio-Zuazo and Castro [J. Electron Spectrosc. Relat. Phenom. 184 (2011) 384] who reported measurements of effective attenuation lengths (EALs) of gold for electron energies between 1 keV and 15 keV. They deposited thin films of gold on a copper substrate and measured the intensities of various Cu and Au photoelectron lines excited by synchrotron X-rays. Their derived EALs were based on the assumption that their films were of uniform thickness (i.e., layer-by-layer film growth). We considered two other forms of film growth: island formation (Volmer-Weber film growth) and island growth on a continuous monatomic wetting layer (Stranski-Krastanov film growth). We utilized the National Institute of Standards and Technology Database for the Simulation of Electron Spectra for Surface Analysis (SESSA) to determine the fractional Au island areas for each Au film thickness that would give the same intensity changes of Cu and Au photoelectron lines that were observed in the experiments. These results showed that growth of the Au film as islands provided a better description of the experimental results than uniform film growth. We could also distinguish Stranski-Krastanov film growth from Volmer-Weber growth and believe that the former is more likely.