TiO₂ as diffusion barrier at Co/Alq₃ interface studied by x-ray standing wave technique

Nano-scale diffusion at the interfaces in organic spin valve thin films plays a vital role in controlling the performance of magneto-electronic devices. In the present work, it is shown that a thin layer of titanium dioxide at the interface of Co/Alq₃ can act as a good diffusion barrier. The buried interfaces of Co/Alq₃/Co organic spin valve thin film has been studied using x-ray standing waves technique. A planar waveguide is formed with Alq₃ layer forming the cavity and Co layers as the walls of the waveguide. Precise information about diffusion of Co into Alq₃ is obtained through excitation of the waveguide modes. It is found that the top Co layer diffuses deep into the Alq₃ resulting in incorporation of 3.1% Co in the Alq₃ layer. Insertion of a 1.7 nm thick barrier layer of TiO₂ at Co/Alq₃ interface results in a drastic reduction in the diffusion of Co into Alq₃ to a value of only 0.4%. This suggests a better performance of organic spin valve with diffusion barrier of TiO₂. (paper)