Surface degradation of superconducting YBa2Cu3O7−δ thin films

The surface degradation of c-axis oriented YBa2Cu3O7−δ thin films due to air, CO2, N2, O2, and vacuum exposure has been studied with reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy, and contact resistivity measurements. The formation of an amorphous surface reaction layer upon exposure to air and CO2 is monitored with RHEED and correlated with an increase in contact resistivity. The contact resistivity of samples exposed to air increases with time t as ρc = (1.0 × 10−7 Ω cm2)e√t/640 min. Surfaces exposed to CO2 show a similar degradation while surfaces exposed to N2 showed a slightly different degradation mechanism. Vacuum exposed surfaces how little increase in contact resistivity, indicating no long-term surface oxygen loss.