Anisotropic thermal properties of nanochanneled alumina templates

Anodic porous alumina templates contain highly ordered nanochannels that are frequently used for fabrication of thermoelectric nanowires. Thermal properties of the templates are of high interest in thermoelectric device applications. This paper reports the temperature-dependent, anisotropic thermal conductivity and thermal diffusivity of 55 μm thick anodic template Anodisc from Whatman, Inc. of 0.02 μm pore diameter and ∼30% porosity. The 3ω technique was employed to carry out measurements of the effective thermal conductivity and thermal diffusivity in the direction parallel to the nanochannels axis, while thermal anisotropy of the sample was estimated theoretically using the Maxwell model. Measured effective thermal conductivity is between 0.54 W/mK at 80 K and 1.3 W/mK at 300 K. Measured thermal diffusivity decreases from 2.1×10−6m2s−1 at 80 K to 1.08×10−6m2s−1 at 300 K. A photothermoelectric technique was employed to measure independently the components of the thermal diffusivity along the direction parallel to the nanochannels axis and in the plane perpendicular to this direction. Reasonable agreements were found between the results provided by the two characterization techniques.