Reliable chemical bath deposition of ZnO films with controllable morphology from ethanolamine-based solutions using KMnO4 substrate activation

Simple potassium permanganate solution treatment of various substrates (we discuss here mainly glass and plastic substrates) results in formation of a Mn–(hydroxy)oxide deposit on the substrate. This deposit, which can be totally invisible to both the eye and to a spectrophotometer, acts as an efficient seed layer that allows growth of ZnO by chemical bath deposition from alkaline solutions over a wide range of conditions under which the ZnO would not grow in the absence of the seed layer. The ZnO grows in the form of columns on top of a dense underlayer (formed in situ during the deposition), ca. 300 nm thick, of ZnO. The morphology (column shape, size and packing) can be controlled by the amount of the seed deposit. Since there is little or no homogeneous deposition in the solution, thick layers of ZnO (>5 µm) can be grown from a single deposition. Further control of the morphology is obtained by variation of the anion of the Zn salt. In addition to the very simple seeding method described here, the ethanolamine-based deposition bath used is highly reproducible and rapid (films of ca. 5 µm thick are obtained in ca. 30 min).