Reactivity and passivation for Bi adatoms on YBa2Cu3O6.9 and Bi2Ca1+xSr2−xCu2O8+y

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Abstract
X‐ray photoemission spectroscopy was used to examine the reactivity of clean YBa2Cu3O6.9 and Bi2Ca1+xSr2−xCu2O8+y surfaces with adatoms of vapor‐deposited bismuth. For YBa2Cu3O6.9, depositions ≤8 Å of Bi induce O 1s, Cu 2p3/2, and Bi 4f line‐shape changes due to BiO bonding, limited oxygen loss from the substrate, partial conversion of Cu2+ to Cu1+, and growth of Bi metal. For coverages greater than 8 Å, there is no reaction and only Bi metal growth is observed. For Bi deposition onto Bi1Ca1+xSr2−xCu2O8+y, there is minimal reaction with only subtle O 1s and Cu 2p3/2 line‐shape changes and the nucleation and growth of Bi metal starting at low coverages (≥2 Å). Comparison shows that Bi is less reactive than other metals, except Ag and Au, and that Bi2Ca1+xSr2−xCu2O8+y is more stable toward Bi deposition than YBa2Cu3O6.9.