inc oxide (ZnO) is a beautiful material, with many applications. Believe it or not, it is used in cosmetic preparations such as sunscreen lotions. This material is a wide band gap semiconductor, which simply means that it behaves "almost" like an insulator. Electrochemistry can be used to determine the conditions under which one can deposit ZnO, starting from a dilute zinc nitrate aqueous solution. A while ago, Prof. Kristin Poduska's group found that, depending on the deposition conditions, one essentially ends up growing a "rectifying junction" or an "Ohmic junction",instead of a thin layer of resistive ZnO (as is predicted by the Pourbaix diagram --- which is a kind of phase diagram). This is because these electrochemical conditions enable deposition of not just ZnO, but some combination of Zn and ZnO in a sequential manner. The evidence suggests that electrodeposition of oxides is a much more complicated process than was previously thought!

People have been using ZnO electrodeposits to make devices such as solar cells, but the results have'nt been promising. Electrodeposition is attractive for making devices since it is much cheaper, less energy intensive, and easier to scale up to an industrial scale. Our results on these electrodeposits, suggest that there is substantial lateral heterogeneity in case of these oxide electrodeposits (which simply means neighboring regions of the electrodeposits behave quite differently). These heterogeneities can be probed using optical and electrical means. In fact, we find that such laterial heterogenity is intrinsic to ZnO electrodeposits. It is very likely that this heterogeneity is intrinsic to oxide electrodeposition in general (this statement is not yet verified!). Evidence suggests that lateral heterogeneities are the most likely culprits for the observed poor performance of devices made using ZnO electrodeposits.

For more details see: ECS Solid State Letters Vol. 1, P35-37 (2012). doi: 10.1149/2.002202ssl