  We propose using short-period superlattices as substrates to control the
vibrational relaxation dynamics of adsorbate overlayers. The mass modulation of
superlattices creates both band gaps and large spectral enhancements in the
phonon density of states. These modifications can dramatically alter the
coupling between vibrational modes of the adsorbate overlayer and the substrate
lattice, thereby significantly affecting the lifetime of adsorbate modes.
