A NOVEL THICK-LAYER ELECTROCHEMICAL-CELL FOR IN-SITU X-RAY-DIFFRACTION

In this article we describe an electrochemical cell allowing x-ray dif fraction from the working electrode in situ. The key feature of our no vel design is a hemispherical fused silica dome serving as the x-ray w indow. The electrode is covered with a thick layer of electrolyte duri ng the x-ray measurement, avoiding mass transport limitations inherent to common setups, where the thickness of the electrolyte layer is str ongly reduced for the diffraction experiment. This allows in particula r the monitoring of electrode processes which are associated with the consumption of species from solution and/or generation of a significan t amount of reaction products. All solid angles in the hemisphere abov e the sample surface are accessible for the incoming and outgoing x-ra y beam at a constant path length in the electrolyte. Thus, our cell is perfectly suitable for in situ surface x-ray diffraction, truncation rod scattering, and specular reflectivity measurements. We demonstrate the performance of the new cell by monitoring the electrochemical str ipping of a 50 nm thick amorphous As layer on GaAs(001) in 0.5 M H2SO4 in situ with x rays. (C) 1998 American Institute of Physics.