Phonons in Epitaxial DySi_{2}: From the Bulk to Self-Organized Nanoislands and Nanowires

Using nuclear inelastic scattering on ^{161}Dy, we determined the Dy-partial phonon density of states of epitaxial DySi_{2} in bulk and self-organized nanoislands and nanowires (NWs) on vicinal Si(001) surface. Compared to the bulk, the nanoislands exhibit softening of the crystal lattice, which is further enhanced in the NWs and significantly affects their thermodynamic and elastic properties. Our ab initio calculations reveal that the origin of this effect is the vibrations of Dy atoms located at the surfaces of the nanoislands and the NWs as well as forming a (2×4) reconstruction on the Si(001) surface between the NWs. The results demonstrate that, opposite to the widely accepted anisotropic lattice mismatch model, the NWs form with their length along the [0001] direction of the strained hexagonal unit cell with lattice parameters close to the Si(001) surface.