Chemical and morphological characterizations of CoNi alloy nanoparticles formed by co-evaporation onto highly oriented pyrolytic graphite

CoNi alloy nanoparticles, formed by co-evaporation onto freshly cleaved highly oriented pyrolytic graphite (HOPG) surfaces, have been studied using time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and scanning electron (SEM) and atomic force (AFM) microscopies. ToF-SIMS detected CoxNiy fragments, indicating alloy formation. Even under ultra-high vacuum, the nanoparticles reacted with residual C- and O-containing gases to form surface contaminants (carbides, oxides, etc.) as revealed by both XPS and ToF-SIMS. On prolonged exposure to air, both the zerovalent metal and carbide peaks of each component decreased with time, as each metal reacted with atmospheric oxygen; as with the pure metals, the Co component of the alloy was the more reactive.

The chemical and morphological properties of CoNi alloy nanoparticles, formed by co-evaporation onto freshly cleaved highly oriented pyrolytic graphite (HOPG) surfaces, have been studied by ToF-SIMS, XPS, SEM and AFM.Figure optionsDownload high-quality image (106 K)Download as PowerPoint slideResearch highlights
► CoNi alloy nanoparticles are formed by co-evaporation onto HOPG surfaces.
► Even under UHV, the NPs react with residual gases to form surface contaminants.
► The Co component of the alloy is the more reactive.
► Alloying increases the reactivity of Ni.