Thermal properties of nanotubes and nanowires with acoustically stiffened surfaces.

A multilayer elasticity model is developed to investigate the effects of acoustically stiffened surfaces (increased surface moduli) on the specific heat and thermal conductivity of typical nanowire and nanotubes as a function of temperature. Changes in phonon dispersion are analyzed using approximated phonon dispersion relations that result from the solutions to the frequency equation of a vibrating elastic tube or rod. The results of the investigation indicate a 10% reduction in specific heat and a 2% decrease in lattice thermal conductivity at 50 K for a 10 nm outer diameter crystalline nanotube with an inner diameter of 5 nm when the average Young's modulus of the first three atomic layers on both the inner and outer free surfaces are increased by a factor of 1.87. In contrast, a 10 nm outer diameter nanowire composed of the same material and with an acoustically stiffened outer shell shows an approximate 30% increase in thermal conductivity and specific heat near 50 K. Our simplified model can potentially be extended to investigate the acoustic tuning of nanowires and nanotubes by inducing surface stiffening or softening via appropriate surface chemical functionalization protocols or coatings. [ABSTRACT FROM AUTHOR]