Depth profiling of noble gas atoms implanted in Al matrix: A photoelectron energy loss spectroscopy study

A non-destructive spectroscopic method based on core level photoelectron energy loss spectra (PEELS) measured at variable emission angle is proposed for depth profiling of implanted atoms in a solid matrix. Extrinsic plasmon excitation during the photoelectron path to the solid surface being the dominant loss mechanism and neglecting elastic scattering, analytic relations are obtained for several depth profiles (Gaussian, triangular, square) between calculated relative intensities of first-order and second-order plasmon excitation peaks and the distribution characteristics (average depth and width). This method is illustrated by PEELS analysis of a model system, namely shallow implantation of argon ions (EION = 2.0 keV, 35° incidence, 3 ML) into Al(001) matrix. The average depth (dPEELS = 2.0 ± 0.1 nm) of subsurface Ar bubbles obtained from energy loss spectra of Ar 2p photoelectrons (inelastic mean free path IMFP = 2.15 nm at EKIN = 1011 eV) is significantly smaller than the average depth of the distribution calculated from SRIM code (dSRIM = 3.8 nm). This discrepancy, found for all model depth profiles, is attributed to significant sputtered thickness (≈1.7 nm) of Al, as well as some possible diffusion of argon-vacancy complexes towards the surface during Ar ion implantation.