Microscopic theory for nanoparticle-surface collisions in crystalline silicon

We present an atomic-scale description for the impact of silicon nanospheres onto a silicon substrate under various temperature conditions. In spite of the relatively low impacting kinetic energies considered, of below 1 eV /atom, the process exhibits a rich behavior. The rigid Hertzian model is valid for speeds below ∼500 ms, while a quasiellipsoidal deformation regime is encountered at larger speeds. No nanoparticle bouncing was observed. For speeds up to ∼1000 ms the result is the deposition of a crystalline Si nanostructure and creation of a long-lived coherent surface phonon. Higher speeds result in a rapid attenuation of the coherent phonon due to an unexpected partial cubic diamond→β -tin phase transformation occurring in the particle.