Supercritical water (SCW) serves as a medium alone for fragmenting silver (Ag) aggregates and organizes the resulting Ag nanoparticles into chain-like nanowires and nanobanners. A variety of 1D and 2D nanostructured assemblies were formed from the nanoparticles by variations in pressure, temperature, and time. The size distribution of Ag nanoparticles is controllable in the range of 2-20 nm. Under appropriate conditions, the SCW medium allows the merging of Ag nanoparticles to form Ag nanowires with diameters of similar to60 rim, and nanobanners of triangle-shaped morphology with lengths of several hundred mum. (C) 2003 Elsevier B.V. All rights reserved.