About the cover
The cover shows a detail from Through the Looking Glass, a large-scale glass artwork by TED Fellow Kate Nichols, which uses silver nanoparticles as 'paint'. The colours arise from oscillations of electrons in the metal particles, called localized surface plasmon resonances. The plasmonic properties of these particles make them attractive for a variety of imaging, sensing and renewable-energy technologies. But it is the particles less than 10 nanometres in diameter that may be most relevant to many natural and engineered systems. As particles approach the quantum regime, our knowledge of how their plasmonic properties change becomes rather hazy. Jonathan Scholl and colleagues investigate the plasmonic properties of individual silver nanoparticles with dimensions in the quantum size regime. Using electron microscopy and spectroscopy, they correlate a particle's plasmon resonance with its size and geometry for diameters ranging from 20 nm to less than 2 nm. The results demonstrate the quantum-mechanical nature of small metallic nanospheres, with direct applications to catalytically active and biologically relevant nanoparticles. Cover credit: Kate Nichols, Alivisatos Lab, Univ. California, Berkeley, www.katenicholsstudio.com/ Photo: Donald Felton.