Stimulated CO Dissociation and Surface Graphitization by Microfocused X-ray and Electron Beams
Articolo
Data di Pubblicazione:
2018
Citazione:
Stimulated CO Dissociation and Surface Graphitization by Microfocused X-ray and Electron Beams / F. Genuzio, P. Genoni, T.O. Menteş, B. Santos, A. Sala, C. Lenardi, A. Locatelli. - In: JOURNAL OF PHYSICAL CHEMISTRY. C. - ISSN 1932-7447. - American Chemical Society(2018). [Epub ahead of print] [10.1021/acs.jpcc.8b09043]
Abstract:
The irradiation with photons or electrons can dramatically influence the chemical stability of a molecule, either free or adsorbed on a surface, inducing its fragmentation or desorption. We revisit here the exostimulated dissociation of CO, a prototypical case, choosing hcp thin cobalt films as model support. Intense, microfocused soft X-rays or electron beams are used to locally stimulate CO dissociation. Fast-XPS gives direct access to the adsorbates' chemical state and coverage during irradiation, enabling the kinetics of the process to be monitored in real time. The energy-dependent cross sections for photon and electron stimulated molecular dissociation and desorption are estimated for a fixed initial CO coverage of 1/3 ML. In the soft X-ray regime, the desorption channel always prevails over dissociation and is significantly enhanced above the O K edge. The relative dissociation probability increases steadily with increasing photon energy, reaching 30% at 780 eV. Furthermore, we show that low energy electrons in the range 50 to 200 eV dissociate CO more efficiently than X-rays. The prolonged irradiation of the Co surface in CO ambient is found to produce a continuous increase of the carbon coverage, initially promoting the formation of carbides and subsequently accumulating sp2 carbon on the surface. Far from being a detrimental effect, the CO stimulated dissociation can be exploited to lithographically graft carbon-rich microscopic patterns on Co, with resolution well into the nanometer scale. A brief thermal treatment following irradiation results in the formation of a graphitic carbon overlayer, which effectively protects Co from oxidation upon exposure to ambient conditions, preserving its out-of-plane magnetic anisotropy and domain configuration.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
Electronic, Optical and Magnetic Materials; Energy (all); Physical and Theoretical Chemistry; Surfaces, Coatings and Films
Elenco autori:
F. Genuzio, P. Genoni, T.O. Menteş, B. Santos, A. Sala, C. Lenardi, A. Locatelli
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