A corus line: nanophase diagrams of miscible bimetallic nanoparticles

To this day, the variety in chemical ordering within gas-phase deposited nanoparticle (NP) samples is not fully understood. On the one hand, energetic arguments point toward specific, uniquely defined configurations. On the other hand, kinetically controlled phenomena (NP coalescence, adatom decoration, ripening) account for emergent energetically unfavourable orderings but cannot capture all cases. Here, we present a simple, fundamental nanothermodynamics argument that can potentially explain inverted core/shell-like structures even within the same bimetallic NP deposits. Specifically, we propose that surface segregation of one or the other constituent may be identified using nanophase diagrams, whose morphologies change with NP size due to differences in the melting point depression between different elements. Hence, we rename the equivalent of liquidus/solidus lines in bulk diagrams to shellus/corus, to give an intuitive explanation of the phenomenon. Our study can provide fundamental insight to the cluster-beam deposition community, guiding experimental fabrication of binary alloy NPs.