The effects of defects in purple AuAl2 thin films

Sputter deposited thin films consisting of the intermetallic phase AuAl2 are known to display a different color than their bulk counterparts, gray or faint pink, instead of the intense purple the phase is famous for. Only after heat treatment is the typical color apparent. The reason for this behavior is assumed to be point defects in the film, a consequence of the deposition method. Heat treatment at 350 °C of 500 nm thin films results in a steady reduction in defects and the color becomes more intense. Ion irradiation by 3.5 MeV Au+ ions with fluences between 1012 and 5 × 1015 ions cm-2 reintroduces point defects in the material and thus gradually removes the color again. Interestingly, the color can be brought back to a very similar shade with subsequent thermal treatments, demonstrating reversibility in the process. The samples were investigated by means of X-ray diffraction, reflectometry, electron backscattered diffraction, scanning electron microscopy, light microscopy, transmission electron microscopy and resistivity measurements to obtain information about the correlation between color and the number of defects within the samples. The measured resistivity values were compared with values calculated using the combined Fuchs-Sondheimer/Mayadas-Shatzkes model. Vacancy concentrations were determined from the difference between the model and the measurements.