Annealing of Cu nanolayers on glass: Structural, mechanical and thermodynamic analysis

Thin Cu nanolayers were deposited on glass substrates by magnetron sputtering. Consequent post-deposition annealing at 300 °C under atmospheric conditions served to form stable oxide layers. X-ray Photoelectron Spectroscopy (XPS) demonstrated that as-sputtered Cu layers on glass were composed of Cu0, Cu1+ and Cu2+ oxidation states and had fcc structure according to X-ray diffraction (XRD). As-sputtered Cu layers on glass further showed a crack-like structure with islands on Scanning electron (SEM) and Atomic force microscope (AFM) images and similar properties to bulk Cu such as low sheet electrical resistance (102 Ω) and a typical surface plasmon resonance band in UV–Vis spectra (650 nm). Owing to annealing, Cu layers on glass demonstrated dramatic changes and a loss of bulk Cu behaviour. XPS and XRD analysis confirmed that annealing caused the formation of CuO, which had a monoclinic structure. Both the annealed and as-sputtered Cu layers on glass acquired more hydrophobic character with aging time (from 65° to 103°). Nanoindentation measurements revealed that annealing produces softer layers with pronounced loss of adhesion and a higher cohesive strength. Thermodynamic calculations confirmed our experimental data. Cu layers on glass have a huge potential in photovoltaics, catalysis and antibacterial surfaces.