In situ formation of silver nanoparticle layer by supramolecule-directed assembly

We report an in situ synthesis route for preparation of a layer of AgNPs (silver nanoparticles) on the silicon surface by employing an immobilized supramolecular layer as a directing agent. The AgNPs were immobilized and stabilized by a calix[7]hydroquinone monolayer which in turn was immobilized on the silicon surface by covalent layer-by-layer assembly. The calix[7]hydroquinone moiety served as a nano-reactor, container and template in the in situ synthesis process. AgNPs were formed by reduction of Ag ions by the hydroquinone form of the calix[7]arene. The AgNPs were obtained as plate-shaped particles with a diameter of about 10 nm and a height of less than 2 nm, and were stabilized and wrapped by calix[7]arene molecules. By repeated application of the redox properties of calix[7]arene, the size of the AgNPs can be adjusted continuously up to islands of 100 nm or larger. The process of in situ synthesis under controlled conditions, together with calibrated variation of particle size has the potential to serve as building blocks for electronic nano-devices. A significant advantage derived by this method of formation and assembly is its surfactant-free nature that enables access to the active surface of the nanoparticle.