A thermal desorption and x-ray photoelectron spectroscopy study of the surface chemistry of iron pentacarbonyl

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Abstract
We have studied the surface chemistry of iron pentacarbonyl by using thermal programmed desorption and x-ray photoelectron spectroscopy (XPS). Thermal desorption is mostly molecular and takes place in two stages. At low coverages a peak at 195 K was detected. For exposures above 4 L a second peak due to multilayer growth is seen with maximum below 180 K. A small fraction of the chemisorbed carbonyl decomposes as seen by XPS. The iron pentacarbonyl fragmentation takes place between 170 and 240 K and results in the deposition of metallic iron and chemisorbed carbon monoxide. Metal film growth is inhibited by coadsorbed CO. The samples need to be flashed to above 600 K in order to desorb this CO and allow further iron deposition. However, we found that films can be grown in a steady-state condition by exposing the sample to Fe(CO)5 at 300 K. Displacement of CO by either the incoming molecules of by new CO product of the decomposition may explain the lack of poisoning at these low temperatures.

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