Kinetic mechanisms of the in situ electron beam-induced self-organization of gold nanoclusters in SiO2

Gold nanoclusters (NCs) were produced in thin SiO2 film by a sequential sputtering deposition procedure. In situ time-lapse studies of the NCs size distribution and morphology under 200 keV electron-beam irradiation have been performed using a transmission electron microscopy. Such a study has revealed the microscopic kinetic mechanisms of the NCs growth. In the 0-1620 s irradiation time range, the NCs growth process was found to be formed by two stages: in the 0-720 s time range, the main growth mechanism is demonstrated to be an electron beam-induced ripening of three-dimensional particles controlled by the Au diffusion in the SiO2 matrix. The application of the classical ripening theoretical model allowed us to derive the room-temperature Au diffusion coefficient in SiO2 under the electron-beam irradiation. In the 900-1620 s time range, the main growth mechanism is found to be a particle sintering in which neighbouring NCs form necks, by a partial deformation of their surfaces, through which the Au atomic diffusion occurs from the smaller NCs to the larger one. About the NCs morphology, three main classes of NCs were identified on the basis of their internal atomic structure, as a function of the irradiation time: FCC crystal structure, icosahedral-defect free structure and decahedral multi-twinned structure.