Size dependent spinodal decomposition in Cu-Ag nanoparticles

Abstract Nanoparticles are of considerable interest, owing to their size-dependent properties, different from those of bulk materials. For revealing internal atomic processes in them, individual nanoparticles of Cu-Ag alloys were grown by direct current (DC) magnetron sputtering. Phase-separation during growth in Cu-Ag particles was found to be size- and composition-dependent. Particles below 5 nm in diameter grow as a solid solution of the components for all compositions (15–80 at.% Ag). In the low Ag content range (15 and 30 at.% Ag) phase-separation occurs only for particles above 5 nm in diameter. The separation into Cu-rich and Ag-rich domains, when observed, takes place by spinodal decomposition for all particle sizes. In particles undergoing incomplete coalescence, phase-separation occurs even if the diameter of the colliding particles is below 5 nm. In the higher Ag content range (60–80 at.%), however, no phase-separation is observed until coalescence sets in. Lattice parameter measurements in alloy particles of 30 at.% Ag revealed that the miscibility gap in individual particles varies between 70 and 90 at.%. Calculation of the composition dependence of the critical length for spinodal decomposition provided quantitative explanation for the observed phenomena.