The influence of the choice of complexing ligand, zinc counter-ion, pH, ionic strength, supersaturation, deposition time and substrate on the nature of ZnO films grown from chemical baths (CBD) are discussed. There are significant differences between CBD and similar routes such as hydrothermal methods for ZnO films. Modelling of speciation and experimental results suggest that acicular ZnO morphologies are best obtained by limiting the concentration of one of either Zn2+ or OH- in the presence of a large excess of the other. The presence of a prior ZnO layer can facilitate nucleation at lower levels of supersaturation and enable size tailoring of ZnO columns. The point at which the substrate is introduced into the bath is crucial and can lead to a significant difference in both the width of the rods and optical transparency of the films. HR-TEM has yielded important structural information and a growth mechanism for single crystalline ZnO rods by CBD is described for the first time.

Base-catalyzed hydrolysis and condensation of zinc acetate dihydrate in alcoholic environments yields highly concentrated ZnO colloids with molarities near 3 M (50-70 wt % solid content) and particle sizes between 3 and 6 nm. These solutions were optimized to be stable against coagulation for several months and to yield optically transparent 0.8-2 ?m thick films of variable electronic conductivity in a single coating step. 2 atom % Al3+ or In3+, if present in these nanoporous air-sintered layers, produce a high free-carrier concentration of about 6 × 1019 cm-3 without noticeable changes in sheet resistance Rsh > 106 ? ?-1, whereas sintering under vacuum or N2/H2 (90/10)-atmosphere results in Rsh values around 150 ? ?-1. Furthermore, infiltration of small ZnO clusters into the porous films increases the refractive index from 1.8 to 2.2 and substantially lowers Rsh to values of about 20 ? ?-1. From Hall measurements, the charge-carrier concentration has been determined to be 2 × 1020 cm-3 and the corresponding electron mobility approaches values of about 9 cm2/V s. Electron microscopic investigations revealed that the ZnO/Al crystallites have a typical size of 10 ± 2 nm and are preferentially oriented with their (100) planes parallel to the substrate. Taking into account a preferential (002) orientation in physically deposited highly conductive ZnO/Al films, it appears that the chemical control of nanocrystallite boundaries is more decisive than their orientation within the films.