Toward metal nanoarchitectonics: Shape-controlled synthesis and assembly of metal nanoparticles

There is much interest in the development of a "bottom-up" process as an alternative to the traditional lithographic procedures for producing devices with nanoscale features, where nanosized building blocks are first prepared and then assembled into useful devices. The two major challenges are addressed, namely the synthesis of nanoparticles with precisely controlled sizes and shapes, and rational organization of the prepared nanoscale building blocks. This work is concentrated mainly on noble metals such as gold, silver, and platinum, which are actively pursued for applications such as optical devices, sensors, and catalysts.; Several different methods for shape-controlled synthesis of metal nanoparticles are introduced. Anisotropic one-dimensional nanorods are produced by using cylinder-like reverse micelles as "soft templates", or using a photochemical reaction with the addition of foreign ions as the shape-controlling agent. Highly symmetric platonic shaped nanoparticles are produced via a modified polyol process, with the presence of surface passivating polymer poly (vinyl pyrrolidone). Bimetallic core-shell structured nanorods can be obtained by overgrowth on the synthesized nanorods. These shape control is achieved by controlling the early seed formation, and by subsequent growth of the particles in the presence of surface-passivating molecules and foreign ions to control the relative growth rate along different crystallographic directions.; Langmuir-Blodgett technique is a powerful tool for preparing large areas of ordered nanoparticles. Interparticle spacing can be controlled by compression, providing an effective method to tune the property of the nanoparticle assembly. Here, Langmuir-Blodgett assembly of anisotropic building blocks will be presented. Pressure-induced isotropic-nematic-smectic phase transitions as well as transformation from monolayer to multilayer are observed for Langmuir-Blodgett assembly of nanorods. Ordered arrays of silver nanowires have been prepared, which shows promise as substrates for surface enhanced Raman spectroscopy. Additionally, stripe micropattern formation induced by dewetting during film transfer has been observed.