Formation and Ordering of Gold Nanoparticles at the Toluene−Water Interface

Microscopic measurements that provide direct information in nanometer length scales are essential to obtain a proper understanding of the interfacial reactions that form nanostructured materials. We present here the results of a synchrotron X-ray scattering study of the formation and ordering of gold nanoparticles at the toluene−water interface through a reduction reaction. The observed X-ray reflectivity and diffuse scattering data show the formation of a monolayer of "magic clusters" at the water−toluene interface. Each cluster consists of 13 nanoparticles with about 12 Å diameter, similar to Au-55 nanoparticles, with about an 11 Å organic layer and an in-plane cluster−cluster separation of 180 Å. The electron density profile of the monolayer of these clusters exhibits three layers of nanoparticles as a function of depth that evolves with time.