Coalescence behaviour of amorphous and crystalline tantalum nanoparticles: a molecular dynamics study

Porous films of tantalum (Ta) and its oxides exhibit numerous properties suitable for high surface area applications, mainly in the semiconductor and bio-implant industries. Such films can be developed by Ta nanoparticle deposition using DC magnetron sputtering with gas aggregation. In order to engineer films of desirable properties, accurate control and in-depth understanding of the processes and parameters of nanoparticle growth, deposition and coalescence are crucial. Of utmost importance is to control the film's porosity, since it determines many of the other physical properties. To this end, we performed a number of classical Molecular Dynamics simulations to study the coalescence of two or more Ta nanoparticles. Temperature, relative size and crystallographic orientation, defect content, degree of crystallinity and deposition rate effects were taken into account, and a mapping of the sintering processes was acquired. A broad range of possible interaction mechanisms were observed, from simple nanoparticle reorientation in order to achieve epitaxial configuration, to atomic adsorption, neck formation, twinning within the nanoparticles and full consolidation into a single, larger nanoparticle. The parameters studied are directly linked to experimental deposition parameters; therefore, fitting them accordingly can lead to growth of films with bespoke properties.