ELECTRON YIELD DETECTORS FOR NEAR SURFACE EXAFS AT ATMOSPHERIC PRESSURE

Abstract
Simple He-filled electron detectors have been developed by Kordesch and Hoffman as a method for near-surface EXAFS investigation using a reflection geometry. we report Our experience on beam line X11 at NSLS in Brookhaven National Laboratory for the gold L and nickel K edges. Thin foils were mounted such that the transmission and electron yield data could be obtained simultaneously. The X11 monochromator was operated in the two-crystal mode and a series of scans was taken primarily as a function of helium flow rate, and to a lesser extent, the positive voltage applied to the electron collecting gold wires. Minor changes were made in the geometry of the electron detector. The electron detector output was connected directly to a Keithley Mode1 427 current amplifier. Preliminary data analysis in the form of background subtraction and transformation to k (the wave vector) was done on-line. Typical data in the form of background subtracted relative yield vs. k for both transmission and electron detection indicate agreement within the linewidth of the plots. We anticipate that the interatomic spacing and coordination number determined from both the techniques will agree well. Electron-yield EXAFS data were successfully obtained from a Ni surface covered with a thin layer of H₂O. This illustrates the potential of these detectors to study in-sith wet electrochemistry. A sharp white line was observed in both transmission and electron-yield EXAFS for Ni(OH)₂ and in eiectron yield EXAFS for NiO.