Normal and abnormal grain growth in nanostructured gold film

Thin nanostructured gold films were deposited on SiO2 by the sputtering technique at roomtemperature. Films of different thicknesses were deposited ranging from 2 to 16 nm. The filmmorphology as a function of the thickness was analyzed by microscopic techniques such as atomicforce microscopy and transmission electron microscopy. These analyses allowed us to clarify thegrowth mechanism of the gold nanograins forming the film: in a first stage of growth 2–6 nmnormal grain growth proceeds; then 8–16 nm the grain surface energy anisotropy drives thegrowth of abnormal large gold grains by annihilation of the normal ones. During the abnormalgrowth other normal grain continue to growth. The normal grain size distribution is showed to bea monomodal log-normal distribution that evolves toward larger mean grain radius continuouslyfollowing a scaling law. By determination of the grain growth exponent, the kinetic mechanismresponsible of the grain growth is demonstrated to be the gold atomic diffusion on grain boundaries.By fitting the experimental data using established theoretical models, the room-temperature goldgrain boundary coefficient diffusion and mobility were derived. The abnormal grain grows, manifestitself as a bimodal grain size distribution: with the log-normal distribution of the normal grain size,a second Gaussian grain size distribution rises, shifting toward lower size increasing the filmthickness. The abnormal grain growth continues until all the abnormal grain boundaries meet eachother.