Diffusion-controlled electrochemical growth of porous zinc oxide on microstructured electrode band arrays

Abstract

Films of zinc oxide were prepared by electrochemical deposition at constant electrode potential from an oxygen-saturated aqueous zinc-chloride solution on rotating microband electrode arrays of gold or silver on SiO 2 /Si wafers. Porous ZnO films were obtained by deposition in the presence of the xanthene dye eosinY as a structuredirecting agent. The electrode size, the gap width, the number of electrode bands, the deposition time, and the rotation rate were varied. The growth of ZnO was monitored by the observed current, and the films were subsequently characterized by profilometry and by scanning electron and confocal laser microscopy. Strongly enhanced growth was observed at the edges of the electrode bands. This was explained by models of hemi-cylindrical diffusion revealing inhomogeneous mass transport to the electrodes. The models were extended to processes of electrochemical deposition. A model for diffusion-limited growth on microstructured electrode band arrays is proposed and applied to the present results.

Ultramicroelectrode Studies of Self-Terminated Nickel Electrodeposition and Nickel Hydroxide Formation upon Water Reduction

“…The increase in brightness at the electrode edge during diffusion-limited reduction of Ni 2+ (Video S2; Figure 2b) reflects enhanced electrodeposition due to higher Ni 2+ flux. 32,73 At potentials negative of the spike near −1.40 V (Videos S1 and S2; Figure 2a,b), the electrode surface gradually appeared more granular. Homogeneous precipitation of bulk Ni(OH) a Cl 2−a •xH 2 O, which will be referred to as Ni(OH) 2 •xH 2 O, and the resulting change in optical density could perturb the light path from the electrode surface; indeed, at extended times at −1.50 to −1.60 V, a circular, light gray gel formed, with a larger diameter at higher overpotentials (Video S2; Figure 2b).…”

Modeling of Dendrite Formation as a Consequence of Diffusion-Limited Electrodeposition

“…It has been observed, e.g., for the deposition of copper, 1 metallic lithium [2][3][4][5][6][7][8][9][10] or zinc oxide. 11,12 Whereas solutions were found already for the deposition of copper and metallic lithium, for zinc oxide no technique exists to control or at least predict the growth of dendrites. In the field of electrochemical copper deposition on microstructures Moffat et al developed impressive ways to suppress preferred growth on edges to fill trenches and vias.…”

“…The electrochemical deposition of ZnO from an oxygen-containing aqueous electrolyte containing eosinY as structure-directing agent and electrocatalyst was found to be limited by the diffusion of oxygen toward the electrodes. 12 The underlying reactions can by expressed by 1 and 2 and summarized by 3: 50…”

“…A lower current density or, in case of an electrochemical deposition, a lower growth rate is observed. As reported earlier the diffusion profiles can be distinguished roughly in three consecutive steps: 12,51 at the beginning of a reaction each electrode band can be treated separately, then the overlap has to be considered and finally the diffusion profile can be described as planar. Aoki et al derived an equation for the boundary diffusion layer δ N at single planar (without any elevation above the insulating surroundings) band electrodes (Eq.…”

Dynamic Electrolyte Spreading during Meniscus-Confined Electrodeposition and Electrodissolution of Copper for Surface Patterning

“…Since δ 2 > δ 1 , the local current density will be higher, and the electrodeposition will occur preferentially at the tip of the asperities rather than in the vicinity of the interior TPCL, as shown in Figure (b). Such nonuniform diffusion layer thickness-induced inhibition of electrodeposition at specific locations has been observed for microelectrode or nanoelectrode arrays , and dendrite formation during electrodeposition as well as for subconformal electrodeposition on structured surfaces . It is to be noted that even though the A SL and γ SL change at the SL interface, predominantly near the tip of asperities (due to continued electrodeposition), the TPCL movement does not occur.…”