Enhanced oxidation of nanoparticles through strain-mediated ionic transport.

Geometry and confinement effects at the nanoscale can result in substantial modifications to a material's properties with significant consequences in terms of chemical reactivity, biocompatibility and toxicity. Although benefiting applications across a diverse array of environmental and technological settings, the long-term effects of these changes, for example in the reaction of metallic nanoparticles under atmospheric conditions, are not well understood. Here, we use the unprecedented resolution attainable with aberration-corrected scanning transmission electron microscopy to study the oxidation of cuboid Fe nanoparticles. Performing strain analysis at the atomic level, we reveal that strain gradients induced in the confined oxide shell by the nanoparticle geometry enhance the transport of diffusing species, ultimately driving oxide domain formation and the shape evolution of the particle. We conjecture that such a strain-gradient-enhanced mass transport mechanism may prove essential for understanding the reaction of nanoparticles with gases in general, and for providing deeper insight into ionic conductivity in strained nanostructures.

The growth of an ordered Mn layer on the Si(111)- 1 × 1-Ho surface.

The growth of ordered Mn layers on room temperature and liquid nitrogen cooled Si(111)- 1 × 1-Ho surfaces has been studied using scanning tunnelling microscopy. We have shown for 4 ML (monolayers) of Mn grown on a cooled Si(111)- 1 × 1-Ho surface that an ordered Mn layer is produced without any, or with only limited, silicide formation. This surface exhibits a [Formula: see text] low energy electron diffraction pattern. Significant variations in Mn island sizes have also been seen on the Si(111)-1 × 1-Ho and Si(111)-7 × 7 surfaces for Mn deposited at room temperature and at -180 °C.