Defects of ultrathin Cu films on Mo(110)studied by thermal helium desorption spectrometry

摘要

Defects of ultrathin Cu films (3-200 A) 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 A), 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 A Cu film prior to film islanding. There is an indication of retrapping of helium released from the first 5 _ layer of the film in the defects located in the overlayers (5-95 _ ). Helium in the Cu films survives until the desorption temperature of the film (1200-1300 K).