Credit: © 2009 Wiley

Like other colloidal noble-metal nanoparticles, silver nanoparticles have several applications in catalysis and surface-enhanced Raman scattering, and their plasmon wavelength can be tuned by the shape of the particles. Several methods to make silver nanoparticles with different shapes and sizes exist, but in practice it is difficult to arrest the growth of the particles at the desired stage because the reaction is so fast. Furthermore, the products are unstable and gradually evolve into more stable forms with different optical properties. Researchers at the University of California at Riverside now report that simple ultraviolet (UV) irradiation can tune the optical properties of silver nanoplates by reconstructing the shape of the particles1.

Yadong Yin and co-workers irradiated fully grown silver nanoplates with UV light and monitored changes in the shapes and optical properties using electron microscopy and spectroscopy methods. The as-grown triangular silver nanoplates gradually became thicker and more rounded, and their plasmon peaks were blue-shifted with different irradiation times. Coating the nanoplates with poly(vinylpyrrolidone) made them stable at room temperature for at least three months. Although the exact mechanism remains unclear, it is thought that the shape transformation is due to the migration of surface atoms from the highly energetic sharp corners of the triangular plates to the surface of the plate, resulting in a more stable rounded structure.

This 'backward tuning' method is expected to be a simple way to prepare stable silver nanoplates with tunable plasmon resonance.