Extended X-ray absorption fine structure spectroscopy of surfaces and thin films

This work presents temperature- and angular-dependent extended X-ray absorption fine structure spectroscopy (EXAFS) measurements on surfaces and thin 3d transition metal films. The analysis was enhanced to extract electronic information from the interstitial regions between atoms, alongside local structure and dynamics. The study focused on the reconstruction of copper and nickel single crystal surfaces upon chemisorption of carbon, nitrogen, and oxygen atoms, utilizing surface EXAFS (SEXAFS) measurements at the K-edges of light adsorbates. A notable anisotropy in thermal adsorbate-substrate vibrations, both in- and out-of-plane, was characteristic of the reconstructed surfaces, with the reconstruction "strength" assessed through this anisotropy. The temperature dependence of the SEXAFS data was described using anharmonic effective pair potentials, revealing a correlation between greater anharmonicity and reconstruction strength. Neglecting the anisotropy and anharmonicity led to inaccuracies in SEXAFS analysis. Low-frequency oscillations in the SEXAFS spectra confirmed backscattering at interstitial charge densities, first identified unambiguously here. The study of low-Z atom chemisorption clarified these oscillations as backscattering rather than multi-electron excitations. Additionally, magnetic EXAFS (MEXAFS) measurements for Fe and Co films were conducted, revealing that thermal vibrations and local spin fluctuations inf