Electrodeposition Growth of Oriented ZnO Deposits in Ionic Liquid Media

ZnO is a material of great interest for microelectronics because it offers a panel of attractive physical properties. It has been grown for decades as thin films from a wide variety of physical-chemical deposition techniques, most of them leading to films oriented with the polar direction perpendicular to the substrate. Here we report the electrodeposition of ZnO in ionic liquids (EMImTFSI (1-ethyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide), BMPTFSI (1-Butyl-1-Methylpyrrolidinium bis(trifluoromethylsulfonyl)imide) or BMImTf (1-butyl-3-methylimidazolium trifluoromethanesulfonate)), together with the feasibility of manipulating the growth orientation of the ZnO deposits by adding the proper co-solvent to ionic liquid. We establish solvent dielectric constant as a key parameter to tailor the deposit growth direction. Moreover, via the use of Electrochemical Quartz Crystal Microbalance (EQCM) measurements, we determine the importance of the competition between Zn2+ and O2 reduction to properly trigger the transport phenomena leading to the growth of ZnO. This work provides insight which can be implemented to the growth of other binary and ternary oxides deposits in ionic liquid media, a field still poorly explored.