Auger electron spectroscopy investigation of SO2/Zr(0 0 0 1)

The adsorption of SO2 on Zr(0 0 0 1) at 150 K has been investigated under ultrahigh vacuum (UHV) conditions. Auger electron spectroscopy (AES) reveals saturation of both sulfur and oxygen signals at exposures of about 1 Langmuir (L). Changes in the overlapping Zr(MNV) + S(LMM) feature as well as in the Zr(MNN) feature are discussed. In particular, the Zr(MNN) feature changes with both exposure and annealing history, complicating the identification of sulfur using Auger peak-to-peak height ratios. We propose that SO2 dissociates on Zr(0 0 0 1) under these conditions, since no thermal desorption of sulfur dioxide is detected for exposures up to 5 L. However, the desorption of small quantities of 34 and 32 amu species near 250 K is observed by temperature programmed desorption (TPD) measurements. Integrated desorption peak areas of these species saturate near 1 L, consistent with the saturation behavior observed by AES. Electron bombardment (500 eV) reduces H2S desorption presumably by removing surface hydrogen via electron stimulated mechanisms, but has no effect on Auger spectra.