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This study employs atomic-resolution scanning tunneling microscopy and spectroscopy to characterize 1.5 unit-cell-thick (La,Pr)₃Ni₂O₇ ultrathin films grown on SrLaAlO₄. Through low-temperature ultrahigh vacuum sample transfer, an ordered √2×√2 surface reconstruction is preserved, and a U-shaped spectrum with two gap scales (approximately 14 and 20 meV) and a flat zero-bias conductance is observed in the tunneling spectra, indicating a nodeless superconducting gap. In contrast, if the sample is exposed to ultrahigh vacuum for a longer time during transfer without cooling, although the surface reconstruction and a transport superconducting onset temperature above 40 K are maintained, the tunneling spectrum becomes V-shaped, and the wide-energy spectrum shows that oxygen deficiency mixes spectral weight related to density waves. By comparing samples with different transfer times, it is determined that controlling the oxygen content is necessary to obtain an intrinsic superconducting gap, providing atomic-scale observational evidence for the intrinsic nodeless superconducting gap in bilayer nickelate ultrathin films.

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