Thermal Properties of Nanotubes and Nanowires With Acoustically Stiffened Surfaces

Abstract

A core-shell elasticity model is employed to investigate the effect of a nanowire and nanotube’s increased surface moduli on specific heat, ballistic thermal conductance, and thermal conductivity as a function of temperature. Phonon confinement is analyzed using approximated phonon dispersion relations that result from solutions to the frequency equation of a vibrating rod and tube. The results indicate a maximum 10% decrease in lattice thermal conductivity and ballistic thermal conductance near 160 K for a 10 nm outer diameter nanotube with an inner diameter of 5 nm when the average Young’s Modulus of both the inner and outer free surfaces is increased by a factor of 1.53. In the presence of the acoustically stiffened surfaces, the specific heat of the nanotube is found to decrease by up to 20% at 160 K. Near room temperature, changes in thermal properties are less severe. In contrast, a 10 nm outer diameter nanowire composed of similar material exhibits up to a 12% maximum increase in thermal conductivity at 600 K, a 25% increase in ballistic thermal conductance at 400 K, and a 48% increase in specific heat at 470 K when its outer free surface is acoustically stiffened to the same degree. Our simplified model may be extended to investigate the acoustic tuning of nanowires and nanotubes by inducing surface stiffening or softening via appropriate surface chemical functionalization and coatings.