Nanocluster nucleation and growth kinetic and mechanistic studies: a review emphasizing transition-metal nanoclusters

A review of the literature of kinetic and mechanistic studies of transition-metal nanocluster nucleation and growth is presented; the focus is on nucleation processes. A brief survey of nucleation theory is given first, with an emphasis on classical nucleation theory, as this is the logical starting point of transition-metal nanocluster nucleation and growth studies. The main experimental methods for following nanocluster formation are examined next--dynamic light scattering, UV-visible spectroscopy, electron microscopy, and X-ray spectroscopies--with special attention paid to their strengths and weaknesses. Several specific examples of transition-metal nanocluster formation are then given, beginning with LaMer's classic sulfur sol system and including the Finke-Watzky mechanism of slow continuous nucleation A-->B followed by fast autocatalytic surface growth A+B-->2B. Finally, brief overviews of semiconductor nanoparticle preparations, solid-state nucleation studies-emanating from Avrami's work--and protein agglomeration mechanistic studies are also provided, as these processes are relevant, conceptually and in a general sense, to the field of transition-metal nanocluster nucleation and growth mechanisms.