Defects of ultrathin Cu films on Mo(1 1 0) studied by thermal helium desorption spectrometry

Abstract

Defects of ultrathin Cu films (3–200 Å) deposited on Mo(1 1 0) at room temperature by e-beam evaporation in ultra-high vacuum are investigated using thermal helium desorption spectrometry. The samples are analysed with both 75 and 1000 eV He+ implantation. Cu films transform into islands on annealing and the temperature of this transformation is strongly thickness dependent. Helium release from defects close to the surface of the Cu films (∼450 K), from monovacancies in as-deposited Cu film (50–200 Å), and from defects close to the interface (800–1050 K) are identified. Annealing of monovacancies is mainly responsible for reduction in helium trapping in a 20 Å Cu film prior to film islanding. There is an indication of retrapping of helium released from the first 5 Å layer of the film in the defects located in the overlayers (5–95 Å). Helium in the Cu films survives until the desorption temperature of the film (1200–1300 K).