Size and frequency dependence of effective thermal conductivity in nanosystems

A single phenomenological expression is proposed to describe thermal transport in a wide variety of nanoscale devices. Size and frequency dependence is studied for some nanosystems from the diffusive to the ballistic regimes. In a single expression we obtain the effective thermal conductivity of cross-plane thin layer experiments where the device has a size limitation in the direction of the flux, and nanowire and in-plane experiments where the size limitation is in a transversal direction from the flux in terms of the effective size of the device. For nonzero frequencies, the size dependence has a maximum which becomes narrower at higher frequencies. For a given size, the effective thermal conductivity decreases for increasing frequency. These features may be limited in the design of nanoscale devices, because of the accumulation of dissipated heat. (C) 2008 American Institute of Physics.