Electron irradiation effects on the nucleation and growth of Au nanoparticles in silicon nitride membranes

The formation of Au nanoparticles (NPs) in Auþ ion-implanted silicon nitride thin films and membranes was investigated as a function of post-implantation thermal treatments or room temperature electron irradiation at energies of 80, 120, 160, and 200 keV. The samples were characterized by Rutherford Backscattering Spectrometry and Transmission Electron Microscopy. High-temperature thermal annealing (1100 C, 1 h) resulted in the formation of Au particles with a mean diameter of 1.3 nm. In comparison, room-temperature electron irradiation at energies from 80 to 200 keV caused the formation of larger Au particles according to two growth regimes. The first regime is characterized by a slow growth rate and occurs inside the silicon nitride membrane. The second regime presents a fast growth rate and starts when Au atoms become exposed to the back free surface of the membrane. Realistic binary electron-atom elastic collision cross-sections were used to analyze the observed nanoparticle growth and membrane sputtering phenomena. The results obtained demonstrate that binary electron-atom elastic collisions can account for the microstructure modifications if the critical displacement energies for the sputtering of N and Si atoms are around 1463 eV, and the displacement energy for surface located Au atoms is approximately 1.2560.2 eV. Irradiation experiments using focused electron probes demonstrate that the process provides fine control of nanoparticle formation, resulting in well-defined sizes and locations. Published by AIP Publishing