X-ray photoelectron spectroscopy and transmission electron microscopy study of internally oxidized Nb–Ru coatings

This study investigates the internal oxidation of Nb–Ru multilayer coatings with a cyclically gradient chemical concentration distribution along the growth direction after annealing in a 1% O 2 –Ar atmosphere at 600 °C for 1 h. X-ray photoelectron spectroscopy and transmission electron microscopy were used to analyze the oxidation behavior of Nb–Ru coatings. The results show that Nb oxidized preferentially in a Nb–Ru coating and partial Nb atoms oxidized to Nb 5 + , Nb 4 + , and Nb 2 + , but Ru remained in a metallic state. After annealing, the microstructure evolved to a laminated structure consisting of alternative crystalline Nb 2 O 5 and Ru layers.