title: Transformation dynamics of Ni clusters into NiO rings under electron beam irradiation.
abstract: We report the transformation of nickel clusters into NiO rings by an electron beam induced nanoscale Kirkendall effect. High-purity nickel clusters consisting of a few thousand atoms have been used as precursors and were synthesized with the superfluid helium droplet technique. Aberration-corrected, analytical scanning transmission electron microscopy was applied to oxidise and simultaneously analyse the nanostructures. The transient dynamics of the oxidation could be documented by time lapse series using high-angle annular dark-field imaging and electron energy-loss spectroscopy. A two-step Cabrera-Mott oxidation mechanism was identified. It was found that water adsorbed adjacent to the clusters acts as oxygen source for the electron beam induced oxidation. The size-dependent oxidation rate was estimated by quantitative EELS measurements combined with molecular dynamics simulations. Our findings could serve to better control sample changes during examination in an electron microscope, and might provide a methodology to generate other metal oxide nanostructures.
authors.affiliation: Institute of Electron Microscopy and Nanoanalysis, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria; Graz Centre for Electron Microscopy, Steyrergasse 17, 8010 Graz, Austria. Electronic address: daniel.knez@felmi-zfe.at.
authors.forename: Daniel
authors.initials: D
authors.lastname: Knez
authors.affiliation: Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria.
authors.forename: Philipp
authors.initials: P
authors.lastname: Thaler
authors.affiliation: Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria.
authors.forename: Alexander
authors.initials: A
authors.lastname: Volk
authors.affiliation: Institute of Electron Microscopy and Nanoanalysis, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria; Graz Centre for Electron Microscopy, Steyrergasse 17, 8010 Graz, Austria.
authors.forename: Gerald
authors.initials: G
authors.lastname: Kothleitner
authors.affiliation: Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria.
authors.forename: Wolfgang E
authors.initials: WE
authors.lastname: Ernst
authors.affiliation: Institute of Electron Microscopy and Nanoanalysis, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria; Graz Centre for Electron Microscopy, Steyrergasse 17, 8010 Graz, Austria.
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Hofer
keywords: Cabrera-Mott oxidation; Electron beam induced oxidation; Kirkendall effect; Ni clusters; NiO rings; Sample damage