An Ex Situ Reflection Mode XANES Study of Underpotentially Deposited Copper Monolayers

Abstract

Reflection mode XANES was performed ex situ on a copper monolayer underpotentially deposited onto a polycrystalline gold electrode. According to calculations based on reference substances, the thickness of the adsorbate layer was 0.21 nm and its oxidation state was close to +I. The ex situ spectra were found to be very similar to the previously published in situ data indicating that the adsorbate layer on the electrode surface does not significantly change after the removal from the electrolyte. The results showed that the reflection mode XAS is well suited for the study of adsorbate systems.

Surface-sensitive reflection-mode EXAFS from layered sample systems: the influence of surface and interface roughness

“…To our best knowledge, no systematic investigations have been performed so far, and the existing publications show contradictory results. For example, a systematic decrease of the Fourier-transform amplitudes with increasing roughness was found in a study by Borthen & Strehblow (1997), while the opposite was the conclusion of a more recent publication (Keil et al, 2005b). Most of the publications up to now have just neglected all roughness effects in the data analysis (e.g.…”

“…Owing to the calculation procedure, these simulated reflectivity spectra R(E, Â) contain the near-range order structural information of the chosen model compounds, either by a direct input of structural parameters and an ab initio calculation of the refractive index (Lü tzenkirchen- Hecht & Frahm, 2006;Benzi et al, 2008) or by using spectra of suited reference compounds (Borthen & Strehblow, 1997;Lü tzenkirchen-Hecht et al, 2003). Here we have used high-quality transmission-mode XAS data which were obtained from polycrystalline reference materials (metal foils, oxide powders) at beamlines RÖ MO 2 and BW1 at HASYLAB (DESY, Hamburg, Germany) operating with 100-150 mA of 4.45 GeV positrons.…”

“…However, such an extraction is in general not possible for thin film sample systems with layer thicknesses smaller than the X-ray penetration depth, or in the case of an inhomogeneous distribution of the X-ray absorbing atom within the sample. In those situations the experimental reflection-mode XAS data have to be compared with (ab initio) model calculations assuming the presence of certain structures and thicknesses of the involved surface layers (see, for example, Borthen & Strehblow, 1997;Lü tzenkirchen-Hecht & Frahm, 2006;Benzi et al, 2008). Nevertheless, a variation of the grazing angle allows a depth profiling of the materials under investigation similar to X-ray photoelectron spectroscopy (XPS).…”

“…However, it has to be mentioned that for liquids and interfaces with logarithmic height-height correlation functions more complex models and further parameters have to be used (see, for example, Palasantzas, 1993). While intense calculations and many successful experiments have been performed for specular and non-specular X-ray scattering at fixed photon energies, and thus the influence of the different lateral and vertical roughness features in multilayered samples are well understood, only few studies have been conducted with regard to the influence of roughness on grazing-incidence X-ray absorption spectroscopy, and more specifically on reflectionmode XAS (Borthen & Strehblow, 1997). To our best knowledge, no systematic investigations have been performed so far, and the existing publications show contradictory results.…”

Time-resolved in situ investigations of reactive sputtering processes by grazing incidence X-ray absorption spectroscopy

“…(1)) which were extracted from experimental data of reference compounds (e.g. [26]), implying that spectra of amorphous thin film samples cannot be modelled properly by such simple calculations. Thus, we calculated n(E) data on a pure ab-initio basis as follows below.…”