The effect of the presence of Zn2+ ions on the adsorption of octadecylphosphonic acid (ODPA) on nanocrystalline ZnO films has been studied by means of Quartz Crystal Microbalance (QCM) technique and complementary exsitu analysis of film properties. Phosphonic acid moiety has sufficient acidity, even in organic solvents, to cause dissolution of ZnO. Dissolved Zn2+ ions form complexes with the ODPA molecules in the solution, leading to the deposition of thick and undefined precipitation layers. Our results indicate that the formation of such precipitation layers could be prevented by the addition of appropriate amounts of Zn2+ ions into the deposition solution. Bi-functional monomolecular linkers with phosphonic acid head-groups are excellent candidates for application-specific functionalization of nanostructured ZnO films as well as ZnO nanoparticles. The results presented here demonstrate a straight forward method to increase the film quality