Thin film annealing and alloying of a Au/Cu two-layer system studied by positron annihilation spectroscopy

• We performed in situ CDBS on a Au/Cu two-layer system during tempering.
• Depth dependent CDBS revealed that the initial Au film was replaced by an alloy.
• By ab initio calculations the alloyed film was identified as Au0.7Cu0.3.
• In the initial phase of intermixing annealing of the Au film was observed.
• Afterwards homogenization of Au and Cu due to bulk diffusion was detected.

The high temperature behavior of a Au(d = 180 nm)/Cu(d = 480 nm) two-layer system was studied by Positron Annihilation Spectroscopy (PAS). Therefor defect sensitive and element specific Coincident Doppler Broadening Spectroscopy (CDBS) with a monoenergetic positron beam was applied. In situ CDBS during isothermal tempering at 633 K for 7 h enabled the observation of both annealing of the Au film and alloying of Au and Cu. The changes in the recorded spectra could be separated into two stages: In the first stage, annealing in the Au film was detected, whereas in the second stage intermixing of Au and Cu atoms was observed. The intermixing zone was found to be homogeneous up to a depth of more than 180 nm. In addition, ab initio calculations were performed in order to determine the composition of the alloyed film, which was found to be Au0.7Cu0.3.