Spectromicroscopy of pulses transporting alkali metal in a surface reaction

The NO + H2 reaction on a potassium promoted Rh(110) surface is shown to sustain the formation of spatio-temporal periodic patterns leading to mass transport phenomena. The excitation of pulses and the mass transport mechanism are studied in the 10-7 and 10-6 mbar pressure range, with the potassium coverage varying between K = 0.05 and K = 0.12 ML. Using spectroscopic photoemission and spectroscopic low energy electron microscopy (SPELEEM) as well as related microprobe diffraction techniques, we show that the excitation mechanism comprises a cyclic structural transformation: K + O-coadsorbate → (2 × 1)-N → c(2 × 4)-2O,N → K + O coadsorbate. Laterally resolved spectroscopy demonstrates that potassium is accumulated in front of the nitrogen pulses, suggesting that adsorbed nitrogen acts as a diffusion barrier for potassium. © 2013 The Owner Societies

Coherent x-ray scattering in an XPEEM setup

International audienceX-ray photoemission electron microscopy has been one of the most productive x-ray microscopy tools with chemical and magnetic sensitivity. We demonstrate that an existing XPEEM setup can be readily adapted to simultaneously perform coherent x-ray scattering measurements in reflectivity mode. Photon-in photon-out x-ray scattering measurement provides the sensitivity to buried interfaces as well as the possibility to work under external fields not accessible in an electron-based measurement. XPEEM, in turn, greatly alleviates the difficulties associated with the reconstruction methods used in coherent diffraction imaging. The combination of the two methods is demonstrated for a spin-ice lattice showing both chemical and magnetic contrast