Transmission electron microscopy observation of oxide layer growth on Cu nanoparticles and formation process of hollow oxide particles

Abstract

The growth of a Cu2O layer on Cu nanoparticles at 323–373 K was investigated by transmission electron microscopy to elucidate the influence of voids formed at the Cu/Cu2O interface on the oxidation rate. The thickness of the Cu2O formed on Cu nanoparticles with an initial diameter of 10 to ∼35 nm was measured as a function of oxidation time. During the initial oxidation stage until the oxide film is about 2.5 nm thick, the oxide film on nanoparticles of 10 to ∼35 nm in diameter grows rapidly at an almost consistent rate. After that, however, the growth rate of smaller nanoparticles decreases drastically compared with that of larger ones, suggesting that the voids formed near the Cu/Cu2O interface prevent Cu atoms from diffusing outward, because the volume ratio of voids to inner Cu in the case of smaller nanoparticles is considerably higher than that for larger ones at the same oxidation time.