Creation and Ordering of Oxygen Vacancies at WO3−δ and Perovskite Interfaces

Changes in the structure and composition resulting from oxygen deficiency can strongly impact the physical and chemical properties of transition-metal oxides, which may lead to new functionalities for novel electronic devices. Oxygen vacancies (VO) can be readily formed to accommodate the lattice mismatch during epitaxial thin film growth. In this paper, the effects of substrate strain and oxidizing power on the creation and distribution of VO in WO3−δ thin films are investigated in detail. An 18O2 isotope-labeled time-of-flight secondary-ion mass spectrometry study reveals that WO3−δ films grown on SrTiO3 substrates display a significantly larger oxygen vacancy gradient along the growth direction compared to those grown on LaAlO3 substrates. This result is corroborated by scanning transmission electron microscopy imaging, which reveals a large number of defects close to the interface to accommodate interfacial tensile strain, leading to the ordering of VO and the formation of semi-aligned Magneli phases....