Role of Ti out-diffusion from a Pt/Ti bi-layer on the crystalline growth of (Ba,Sr)TiO3: A transmission electron microscopy investigation

We investigated the influence of the Ti out-diffusion in Pt/TiOx/SiO2/Si substrates (0 ≤ x ≤ 2), having different thicknesses of Pt and TiOx layers, on the crystalline growth of (Ba,Sr)TiO3 (BST) deposited by pulsed laser deposition. By means of X-ray diffraction and transmission electron microscopy, we show that the orientation of BST clearly depends on the presence and quantity of Ti having migrated up to the Pt surface, and on its possible oxidation prior to BST deposition, which was controlled by the atmosphere (vacuum or oxygen) of the pre-heating stage of the BST deposition process. Whereas BST has no preferential orientation if grown on a bare Pt surface, a strong (111) orientation of BST is obtained for a limited diffusion of titanium oxides on the Pt surface just before BST deposition. However, the (111) orientation is lost if this seeding titanium oxide layer on Pt is too thick just before BST deposition. Also, the formation of protrusions was evidenced at the BST/Pt interface and associated with the oxidation of Ti within the Pt layer.