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LEED, AES and Thermal Desorption Studies of Chemisorbed Hydrogen and Hydrocarbons (C3H2, C2H4, C6H6, C6H12) on the (111) and Stepped (6(111)x(100)) Iridium Crystal Surfaces. Comparison with Platinum.
CALIFORNIA UNIV BERKELEY
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The adsorption of hydrogen, ethylene, acetylene, cyclohexane and benzene was studied on both the 111 and stepped 6111x100 crystal surfaces of iridium. The techniques used were low-energy electron diffraction, Auger electron spectroscopy and thermal desorption mass spectrometry. No indication for ordering of the carbonaceous residue was found on the stepped iridium surface in these experiments. The hydrocarbon molecules form only poorly ordered surface structures on both iridium surfaces when the adsorption is carried out at 30C. The hydrogen desorption spectra from the iridium surfaces exposed to C2H4, C2H2 or C6H6 exhibit two hydrogen desorption peaks, one around 200C and the second around 350C. The relative intensities of these two peaks depend strongly on the surface used. Arguments are presented that decomposition of the hydrocarbon molecules C-H bond breaking and possibly also C-C bond breaking occurs easier on the stepped iridium surface than on the 111 surface. The results are compared with those obtained previously on similar crystal surfaces of platinum. It appears that C-H bond breaking occurs more easily on iridium than on platinum.
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