Synthesis of Cu(OH)2 and CuO nanotubes arrays on a silicon wafer

We report the synthesis of copper hydroxide (Cu(OH)2) and cupric oxide (CuO) nanotubes arrays on a silicon wafer. It is the first time, to the authors' knowledge, that Cu(OH)2 and CuO tubes have been synthesized on another substrate than a copper foil. Monocrystalline Cu(OH)2 tubes were grown, on a homogeneous copper layer previously evaporated on the top of the wafer, by oxidation of this copper layer in two successive alkaline solutions containing Na(OH) and (NH4)2S2O8 each. The first solution is used to control the tubes morphology and density on the wafer and the second one to accelerate the tubes growth. By changing the first solution concentration, lengths between 3.5 μm and 6.6 μm were obtained and a mean external diameter close to 100 nm could be reached. For such a low external diameter, the internal diameter was equal to 75 nm. An annealing at 200 °C during 1 h under static air leads to the dehydration of Cu(OH)2 tubes into CuO ones. The morphology of the tubes before and after annealing is almost identical, so it is possible to obtain CuO nanotubes with a mean external diameter around 100 nm. This value is much smaller than the diameters of several hundred nanometers published up to now for CuO tubes. After annealing, the presence of Cu2O, due at least partially to a diffusion phenomenon at the interface copper layer/CuO, has been detected.