Oxidation of Metallic Nanoparticles - COMSOL.com

FIG. 5: Oxidation in dependence of the oxide workfunction of a nanoparticle with R = 5nm and an initialoxide layer of 1 nm. All other parameters are given inTab. 1.rising temperature, the initial fast oxidationincreases rapidly. The slow increase is alsoaffected by a change of slope. The change of theoxidation rate is due to the increase of the ioniccurrent, which is exponentially affected by thetemperature.In Fig. 5 the oxidation in dependence of theoxygen work function is shown. Forthe initial fast oxidation is visible. Forthe growth shows a linearbehavior. This can be attributed to growthkinetics limited by the electron current. In Fig. 6the effect of different growth regions, which ispossible with the Level set method, is shown.Deformations of the metal-oxide interface arevisible where the growth rate is enhanced.5. Summary and OutlookIn this work a Level set based method isintroduced to model the oxidation dynamics ofmetallic nanoparticles. A comparison betweenexperimental data from the oxidation of Conanoparticles shows good agreement with thesimulations. It has also been shown, that it ispossible with the proposed approach to modeldifferent regions of growth within thenanoparticle. For the future, further studies onthe influence of the latter are planned.FIG. 6: Regions with different growths rates ofnanoparticle as well as an oxide-metal interface (greenlayer) are shown. A distortion of the interface isvisible at the areas with increased oxide growth rate.6. AppendixSymbol Definition ValueMetal oxide work function 2(eV)work function (eV) 2.5Mott potential (eV) -0.5T Temperature (K) 3002a Ionic jump distance 4.25Ionic defect concentration atmetal oxide interface (Ionic defect concentration atoxide oxygen interface (Oxide volume increase pertransported ionic defectTable 1: Parameters used for simulationsReferences19.191 J. Blackman, Metallic Nanoparticles, Elsevier (2009)2 S. P. Gubin, Magnetic Nanoparticles, Wiley-VCH(2009)3 G. A. Niklasson, R. Karmhag, Surface Science 532–535, 324–327 (2003)4 N. Cabrera et al., Rept. Progr.Phys. 12, 163 (1949)5 A. T. Fromhold, E.A. Cook, Phys. Rev. 158, 600–612 (1967)6 S. Osher, R. Fedkiw, Level Set Methods and DynamicImplicit Surfaces, Springer (2002)