Electron-irradiation-induced sputtering of gold atoms from isolated nanometer-sized particles of Al₂Au

Electron irradiaion effect on nanometer-sized Al2Au particles has been studied using transmission electron microscopy. Particles of Al2Au in sizes of around 25 nm in diameter have been irradiated with 200 keV electrons at room temperature. In bright field images, no appreciable changes in the size and in the microstructure of Al2Au particles have been detected. However, careful analyses of the chemical concentration by the quantitative measurement of intensities of Debye–Scherrer rings using imaging plates show that gold atoms in Al2Au particles were selectively removed by 200 keV electron irradiation. In separate annealing experiments, on the other hand, it is observed that aluminum atoms in Al2Au compound particles were preferentially evaporated with increasing temperature. Based upon these results, it is concluded that the selective removal of gold atoms in nanometer-sized Al2Au particles was induced not by heat-induced-evaporation of gold atoms but by knock-on displacement during 200 keV electron irradiation. It is suggested that the threshold energy for gold atom sputtering from Al2Au nanoparticles is as low as less than 1.9 eV.