Enhancement of superconductivity in cryogenically grown ultra thin Al film

Superconductivity in thin films can deviate significantly from bulk behavior, especially as dimensionality and disorder come into play. This is particularly true for aluminum, where critical temperature (T_C) and film morphology are highly sensitive to thickness and growth conditions. Here, we present an in-situ scanning tunneling microscopy (STM) study, performed at 78 K, of Al thin films grown on atomically clean Si(111) substrates by molecular beam epitaxy at cryogenic temperatures down to 6 K. The morphology is characterized across a wide range of coverages, from sub-monolayer up to 20 monolayers (ML). We also investigated the superconducting properties of cryogenically grown films after exposure to atmospheric conditions, as required for ex-situ transport measurements. To stabilize the films, we used different post-growth treatments, including low temperature and room temperature oxidation. The films show critical temperatures up to 3.1 K and critical fields above 5 T, which are significantly above the bulk values of 1.2 K and 0.01 T. Finally, we explore the potential of these ultrathin Al films as high kinetic inductance, low-loss elements suitable for integration in superconducting circuits.