Quantifying the effective attenuation length in high-energy photoemission experiments

We have determined the effective attenuation length of photoelectrons over the range of kinetic energies from 4 to 6 keV in Co, Cu, Ge, and Gd2O3. The intensity of the substrate (Si) and overlayer core level peaks was measured as a function of the thickness of the wedge-shaped overlayers. Experimental values vary between 45-50 angstrom at 4 keV and 60-65 angstrom at 6 keV in Co, Cu, and Ge. Smaller values (30 angstrom to 50 angstrom, respectively) are found in Gd2O3. Our results confirm that, for different classes of materials, high energy photoemission spectroscopy has the necessary depth sensitivity to go beyond surface analysis, yielding important information on the electronic properties of the bulk and of buried layers and interfaces.