Experimental insights on the stability of core–shell structure in single Sn/SnOx spherical nanoparticles during room temperature oxidation

• Study of room temperature Cabrera-Mott oxidation of spherical Tin nanoparticles. • Oxidation completes in timescale of minutes, no slower dynamics are observed. • Oxide shells have constant thickness of 4.6 ± 0.7 nm. • Although nominally possible, absence of nanoparticles smaller than 17 nm with core-shells structure. • Tin metallic core is unstable towards oxidation if smaller than 8 nm. Experimental insights on the dimensions and stability of Sn/SnOx core–shell structures formed by oxidation of tin nanoparticle surface at room temperature are presented. Oxidation completes within a few minutes, ruling out slow dynamics, and leads to oxide shells exhibiting a constant thickness of 4.6 ± 0.7 nm in all nanoparticles larger than approximately 17 nm. This is consistent with the self-limiting nature of the Cabrera-Mott oxidation model based on inward and outward drift of oxygen anions and metallic cations respectively. Since particles smaller than 17 nm range do not exhibit any core–shell structure and appear fully oxidized, we suggest that 8 nm is a critical dimension for the stability of the metallic tin core. In-situ evolution of core–shell structures under electron beam irradiation appears to further support this conclusion. In addition to surface curvature, size-related thermodynamic properties of tin may provide key insights into understanding these observations.