Boundary-Induced Vibrational Spectra Broadening in Nanostructures

Vibrational spectra are calculated and analyzed for nanostructures (including thin films, nanowires, and quantum dots) of yttria, an important laser host material. Lattice dynamics results show that vibrational spectra of nanocrystals are distinct from that of the bulk crystal, in the extended tails at low and high frequencies. This broadening of vibrational spectra is found to be resulted from the broadening of atomic spring constants at both surface and interior, especially at the surface. Molecular dynamics simulations are employed to further decompose the contributions of the surface and internal atoms, respectively. The results show explicitly that the surface spectra have evident tails and the interior spectra have moderate tails, confirming the results of lattice dynamics calculations.