EELS and AES investigation of Rh thin film growth on polycrystalline Al substrate

Abstract A Rh/Al model catalyst was prepared by depositing rhodium atoms onto polycrystalline aluminium substrates. The plasmon loss associated with the Al (LMM) Auger peak was measured and the plasmon gain was successfully resolved. The loss channel at 16–17 eV which occurs in electron energy loss spectroscopy (EELS) as well as in Auger electron spectroscopy (AES) was established to be a Rh 4 d→p transition. The spectral shape of the Rh N 2,3 (4 p ) states generated by inner-shell transitions, is identical in both samples (polycrystalline Rh foil and Rh deposited onto Al foil), suggesting similar local electronic environment for Rh atoms although the macroscopic electronic structure of these samples are essentially different. The dramatic changes found during the sample heating and CO adsorption/desorption experiments by AES and TDS can be correlated to EELS results showing a gradual suppression of plasmon losses characteristic of Rh and an increase of the concentration of nearly free electrons at the surface. A Rh–Al alloy is probably formed on the surface after annealing to 673 K.