Structure determination of adsorbates on single crystal electrodes with X‐ray standing waves

Abstract

Adsorption / Electrochemistry / Interfaces / Metals 1 Spectroscopy, X-ray TI submonolayers were deposited from an aqueous electrolyte on a Cu(l11) surface. The electrodes were studied inside and outsidc the electrolyte with standing X-ray wave fields. These measurements allow to determine the fraction and the position of TI atoms which occupy adsorption sites coherently relative to the bulk diffraction planes. The results show that the method can be applied to ex-situ as well as in-situ structure studies of the soridpiquid interface. The influence of oxygen on immersed and emersed Cu electrodes is discussed in detail.

In situx-ray standing-wave analysis of electrodeposited Cu monolayers on GaAs(001)

“…Submonolayers of Cu deposited from an acidic solution of CuSO 4 at cathodic potentials adsorb predominantly in substitutional positions on the GaAs͑001͒ electrode. Part of the Cu, about 0.5 ML for n-type GaAs but only Ϸ0.05 ML for p-type GaAs, diffuse a few nm into the bulk.…”

“…3,4 Later, surface x-ray diffraction 5 was successfully employed, 6 yielding detailed information about the interface structure, the structure of adsorbates, and potential-dependent structural processes of clean metal electrode surfaces. 7 Comparably little work has been done using semiconductor electrodes.…”

Surface Second Harmonic Generation Studies of Single Crystal Metal Surfaces

“…Previous studies have suggested that oxygen containing species might be present on the surface of copper throughout the double layer charging region, including at the PZC, even though there is not evidence of its presence in the voltammetry. 69 Support for this conclusion came from dosing the clean Cu(lll) surface in UHV with increasing exposures to oxygen. The resulting oxygen containing surface gives an SH response which is more similar to that obtained in the electrochemical cell.…”

“…It is interesting in retrospect to note that under their experimental conditions which included much care to reduce the presence of oxygen in solution, the thallium free surface displayed a rotational anisotropy similar to what Bradley et al 23 later obtained for oxygen dosed Cu(lll) in UHV. X-ray grazing incidence data by Materlin et al 69 also suggests that thallium grows on the surface of Cu(lll) in a disordered manner, largely due to the difficulty in producing an oxygen free substrate during electrodeposition in their grazing incidence cell. Later studies from this laboratory 23 ' 71 in which the electrolytes used and the surface preparation lead to an SH rotational anisotropy closer to that of clean Cu(lll) in UHV resulted in an SH anisotropy indicative of a relatively ordered overlayer growth on the surface.…”

X-Ray Standing Waves on Surfaces

“…Conventional XSW are generated using dynamical Bragg reflection [ 1-31 from perfect single crystals [4][5][6][7][8][9][10]. In this case the periodicity of the standing wave field is equivalent to the d-spacing of the (hkl) diffracting planes and, thus, this technique is a precise tool (± 1% of the d-spacing)[51 for measuring bond-lengths between adsorbate atoms and surface/bulk lattice positions over the range of 1 to 4A (i.e.…”