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. [Display omitted] •Cu layers were sputtered on glass and subsequently annealed at 300 °C in the air.•Formation of a crystalline structure of CuO prevailed due to annealing process.•Loss of adhesion and a higher cohesive strength manifested itself after annealing.•Annealing caused change from fcc structure (Cu) to monoclinic structure (CuO).•Thermodynamic calculations shown Cu2O is stable up to 23 nm and CuO above 22 nm.