Copper nanoparticles grown under hydrogen: Study of the surface oxide

Copper nanoparticles with sizes between 10 nm and 50 nm were grown by condensation in hydrogen at pressures from 10 Pa to 1200 Pa. The crystallite size ranged from 10 nm to 25 nm using the Scherrer method. X-ray diffraction showed the reflections of metallic copper occasionally mixed with an oxidized phase (CuO or Cu₂O). As shown by TEM examination, the smaller particles that did not exceed 25 nm exhibited faceted morphologies whereas the bigger ones had ovaled-spherical forms sometimes containing twins. X-ray photoelectron spectroscopy revealed that the nanoparticles consist of a copper core, completely surrounded by a Cu₂O shell, which is oxidized to CuO at the surface layer.