The discovery of superconductivity in bilayer nickelates has brought an important new perspective to the research field of unconventional superconductivity in strongly correlated oxide materials. To date two material systems have been identified to host superconductivity: infinite-layer Nichelates and bilayer Ruddlesden-Popper (RP) La3Ni2O7[1, 2]. While superconductivity in bulk La3Ni2O7 was initially observed under high pressure, recent studies have demonstrated superconducting behavior in epitaxial thin films at ambient pressure [3, 4]. Despite this progress, the synthesis of superconducting bilayer nickelate thin films remains challenging because of the metastable nature of the Ruddlesden- Popper phase and the stringent requirements on stoichiometry, strain, and oxygen content.

In this work, we investigate chemical substitution as a route to stabilize superconductivity in bilayer nickelate thin films. Ca and Sm substituted La3Ni2O7 thin films were synthesized by ozone-assisted molecular beam epitaxy (MBE) on LaSrAlO4(001) substrates. Remarkably, superconducting behavior is observed directly in the as-grown films without the low-temperature post-annealing treatments commonly employed to induce superconductivity in bilayer nickelates.

A superconducting La2.85Ca0.15Ni2O7 thin film was successfully obtained in the as-grown state. X- ray diffraction measurements indicate a highly ordered crystal structure and full epitaxy with the underlying substrate. Electrical transport measurements reveal a superconducting transition near 45K. The superconducting properties remain stable under ambient conditions for several weeks and can be further preserved by storage in liquid nitrogen.

In addition, a series of La3-xSmxNi2O7 thin films (x=0.6-1.2) was synthesized. Structural characterization reveals a systematic evolution of the crystal structure with increasing Sm concentration. Electrical transport measurements demonstrate a strong dependence of the electronic properties on Sm substitution. All Sm-substituted samples exhibit either partial or full superconducting transitions in the as-grown state without additional thermal treatments, with the most pronounced transition observed for x=1.2 near 25K.

These results demonstrate that chemical substitution and ozone-assisted MBE provide an effective pathway for stabilizing superconducting behavior in bilayer nickelates thin films.