Phonon propagation in isotopic diamond superlattices

The out-of-plane thermal conductivity and elastic constant of epitaxial [100] $^{12}\mathrm{C}/^{13}\mathrm{C}$ superlattice diamonds with layer thicknesses 1, 30, 100 nm are evaluated by picosecond ultrasound spectroscopy. measured constants the superlattices equivalent to those single-layer diamond thin films. This result confirms our success in synthesizing specimens few defects at interfaces. Therefore, phonon transport behavior is governed mass difference, not interfacial defects. lower than that a pure $^{12}\mathrm{C}$ isotope film. We estimated lattice using dynamics calculation, attributing lowered decrease group velocity superlattices. further consider effect mini-umklapp scattering superlattice, which explains dependence on thickness. reveal becomes significant only for an because high Debye temperature large relative difference.