Infinite-layer phase formation in the Ca1– x Sr x CuO2 system by reactive molecular beam epitaxy

We synthesized thin films of the thermodynamically unstable infinite-layer compound Ca1–xSrxCuO2 by reactive molecular beam epitaxy and established thermodynamic boundary conditions that allow for the minimization of impurity phases and defects. In particular, the choice of radio-frequency oxygen plasma as an oxidizing agent as well as diverse substrate materials has been found to limit the stability region in a way that is comparable to the synthesis temperature. We employed scanning transmission electron microscopy to gain microscopic information and feedback on the formation behavior of the infinite layer phase. Moreover, we find that minute variations of the oxidizing power coerce strong responses, i.e., termination of the formation of the infinite layer phase.