Periodic structures of randomly distributed Cu/Cu2O nanograins and periodic variations of cell voltage in copper electrodeposition

Potential-induced copper periodic micro-/nanostructures by electrodeposition on silicon substrate

We demonstrate the fabrication of large scale nano- and micropatterned copper periodic structures on a silicon substrate without imposed templates. In the electrodeposition process, we employ a periodic variation voltage in an ultrathin layer of concentrated CuSO(4) electrolyte. The pattern can be controlled by varying the frequency of the applied potential. We suggest that the observed periodic micro-/nanostructures are caused by the lag of the migrating ion concentration profile versus the applied voltage profile near the tip of the growth.

Layer-by-Layer Electrodeposition of Copper in the Presence of o-Phenanthroline, Caused by a New Type of Hidden NDR Oscillation with the Effective Electrode Surface Area as the Key Variable

Electrochemical deposition of copper (Cu) from aqueous acidic Cu2+ solutions with o-phenanthroline (o-phen) shows both potential and current oscillations, together with a (partially hidden) N-shaped negative differential resistance (N-NDR), indicating that the oscillations are classified into hidden N-NDR (or HN-NDR) oscillations. The color and the surface morphology of Cu deposits oscillate in synchronization with the potential and current oscillations. Microscopic inspection has shown that dense round Cu leaflets, which look gray, grow in the positive side of the potential oscillation or in the high-current state of the current oscillation, whereas thin Cu leaflets, which look black, grow in the opposite-side stages of the potential and current oscillations, thus finally resulting in a layered Cu deposit with the layer thickness of about 5 microm. The appearance of the NDR is explained to be due to adsorption of the reduced form of a [Cu(II)(o-phen)2]2+ complex, which suppresses the Cu electrodeposition. The increase in the effective electrode surface area by growth of thin Cu leaflets, on the other hand, causes a current increase that can hide the NDR. This NDR-hiding mechanism is of a new type and the present oscillation is regarded as a new-type of HN-NDR oscillator.