XPS Characterization of Copper and Silver Nanostructures

X-ray Photoelectron Spectroscopy (XPS) is uniquely suited for the direct characterization of nanomaterials in terms of elemental composition, chemical and electronic states of the elements and thin layer thicknesses. Here we present examples where XPS analysis provides critical information for understanding the growth and oxidation mechanisms of metal nanostructures.

Studies of solid-state oxidation of copper nanoparticles (NP) by in-situ plasmon spectroscopy complemented by electron microscopies showed formation of oxide/(metal+void) core-shell structure.¹ XPS analysis allows us to unambiguously identify the presence of both CuO and Cu₂O phases in the oxide shell, and to calculate the relative thicknesses of each layer. These data, in combination with electrochemistry, provide proof for a quantitative model of Cu NPs oxidation.

In a recent study, we investigated the mechanism of the electroless formation of nanostructured silver nanoplatelet (NPL) films in the presence of a Fe(III)-tartrate complex.² Electron microscopy and XRD showed that NPLs are formed by secondary nucleation on the edges, while nucleation on the flat (111)-oriented faces is suppressed. XPS analysis of NPLs confirmed strong Fe(III)-tartrate adsorption to the Ag NPS surface. XPS studies of the Fe chemical environment reveal the possible formation of polymeric complexes in the adsorbed layer, which may explain the almost complete inhibition of secondary nucleation on the flat (111) surfaces of Ag NPLs.

References:

1. D. Susman, Y. Feldman, T. A. Bendikov, A.Vaskevich, I. Rubinstein,
   Nanoscale, 2017, 9, 12573-12589.
2. Muench, A. Vaskevich, R. Popovitz-Biro, T. Bendikov, Y. Feldman, I. Rubinstein,
   Nanoscale, 2017, under revision.

^* Prof. Israel Rubinstein deceased on October 21, 2017.