Barium titanate BaTiO3 (BTO) thin films were epitaxially grown at 225 degrees C on 2 x 1-reconstructed Ge(001) surfaces via atomic layer deposition (ALD). Approximately 2 nm of BTO film was grown directly on Ge(001) as an amorphous film. Electron diffraction confirmed the epitaxy of the BTO films after postdeposition annealing at 650 degrees C. Additional BTO layers grown on the crystalline BTO/Ge(001) film were crystalline as-deposited. X-ray diffraction indicated that the epitaxial BTO films had a c-axis out-ofplane orientation, and the abrupt BTO/Ge interface was preserved with no sign of any interfacial germanium oxide. Scanning transmission electron microscopy provided evidence of Ba atoms occupying the troughs of the dimer rows of the 2 x 1-reconstructed Ge(001) surface, as well as preservation of the 2 x 1-reconstructed Ge(001) surface. This study presents a low-temperature process to fabricate BTO/Ge heterostructures. (C) 2017 Elsevier B.V. All rights reserved.