Specific heat and thermal conductivity measurements for anisotropic and randommacroscopic composites of cobalt nanowires

Abstract

We report simultaneous specific heat(cp) and thermalconductivity (κ) measurements for anisotropic and random macroscopic composites of cobalt nanowires(Co NWs), from 300 to 400 K. Anisotropic composites of Co NW consist of nanowiresgrown within the highly ordered, densely packed array of parallel nanochannels in anodizedaluminum oxide. Random composites are formed by drop-casting a thin film of randomlyoriented Co NWs, removed from the anodized aluminum oxide host, within a calorimetriccell. The specific heat measured with the heat flow parallel to the Co NW alignment() and that for the random sample(cpR) deviate strongly in temperature dependence from that measured for bulk, amorphous, powdercobalt under identical experimental conditions. The thermal conductivity for random composites(κR) follows a bulk-like behavior though it is greatly reduced in magnitude, exhibiting a broadmaximum near 365 K indicating the onset of boundary–phonon scattering. The thermalconductivity in the anisotropic sample () is equally reduced in magnitude but increases smoothly with increasing temperature andappears to be dominated by phonon–phonon scattering.