Static and in situ TEM investigation of phase relationships, phase dissolution, and interface motion in Ag–Au–Cu alloy nanoparticles

Abstract Ternary nanoparticles of Ag–Au–Cu alloy were fabricated by physical vapor deposition of a ternary alloy source onto a heated amorphous carbon film in ultra-high vacuum. The as-cooled nanoparticles were studied using bright-field imaging, selected-area diffraction, energy-dispersive X-ray spectroscopy and high-resolution imaging in the transmission electron microscope (TEM). These analyses revealed the presence of two phases in the 20–50 nm diameter nanoparticles: a Ag-rich fcc α 1 phase and an ordered L1 2 phase (AuCu 3 prototype). The phases were found to have a cube-on-cube (or parallel) orientation relationship with α 1 –L1 2 interfaces that were parallel to {1 0 0}. In situ heating of the particles in the TEM showed that the α 1 –L1 2 {1 0 0} interface dissolved by steps one moire-fringe spacing high, consistent with recent theories of interface movement. In contrast to previous studies on the stability of ordered phases in Au–Cu alloys, the ordered L1 2 phase in the Ag–Au–Cu alloy remained at temperatures several hundred degrees higher than predicted from the equilibrium bulk phase diagram. This may be caused by elastic stabilization of the phase due to the small size of the particles and/or composition modulations induced by the surface.