Mixed self-assembled monolayers (SAMs) with different ratios of –OH to –CH3 groups were used to modify the surface free energies of the Si substrates from 64 to 29 mN m–1. The TiO2 thin films were grown on the mixed SAM-coated Si substrates by atomic layer deposition (ALD) from titanium isopropoxide and water. A two-dimensional growth mode is observed on the SAMs-coated substrates possessing high surface free energies. As the surface free energy decreases, a three-dimensional growth mode begins to dominate. These observations indicate that the mixed SAMs can control the growth modes of the atomic layer deposition by modifying of the surface free energies of the substrates.