SINTERING OF SILVER AND COPPER NANOPARTICLES ON (001) COPPER OBSERVEDBY IN-SITU ULTRAHIGH-VACUUM TRANSMISSION ELECTRON-MICROSCOPY

The sintering of copper and silver nanoparticles with single crystal c opper substrates has been studied using a novel in-situ ultrahigh vacu um transmission electron microscope (UHV TEM). The system is equipped with a UHV DC sputtering attachment enabling metal nanoparticles to be generated in-situ and transferred directly into the microscope in the gas phase. In both cases, we find the particles to be of initially ra ndom orientation on the substrate. Upon annealing, however, the partic les reorient and assume the same orientation as the substrate. The pro cess apparently occurs by a mechanism involving sintering and grain gr owth. In the case of silver on copper, grain growth cannot occur since the metals are immiscible. Our observations show that, upon annealing , the particles wet the substrate surface and form epitaxially oriente d islands by surface diffusion and grain boundary migration. The post- anneal islands exhibit the orientation relationship (111)Ag parallel t o(001)cu, [110]Ag parallel to[110]Cu. (C) 1998 Acta Metallurgica Inc.