IMPURITY-SUPPRESSED SINTERING IN COPPER NANOPHASE MATERIALS

We use an ultrahigh-vacuum in-situ transmission electron microscope to study the behaviour of copper nanoparticles formed by inert-gas conde nsation onto unreactive substrates. We show that copper nanoparticles 'instantaneously' sinter upon contact in vacuo but that trace oxygen e xposure slows this sintering and alters particle structures. These res ults support a picture where particles grow primarily by Brownian coag ulation to produce a self-similar distribution. The model confirms the role of oxygen in inhibiting surface diffusion. The size distribution approaches the commonly reported log-normal distribution. Impurities such as oxygen may be desirable to limit agglomeration and to permit d ense nanoparticle compact formation.