Nanoparticles Imaged In Space And Time

A new electron microscopy technique, called ultrafast spectrum imaging, is capable of mapping electric fields across and around nanomaterials over time (Science, DOI: 10.1126/science.1213504). When photons of light strike a metal nanostructure, the object’s electrons oscillate collectively. This wave, known as a plasmon, generates a localized electric field that enables the tiny structure to be used as a photovoltaic component or as a sensor for nearby molecules. Being able to map the electric field, says Philip E. Batson, a physicist at Rutgers University, should enable scientists to design more efficient nanomaterials. A research team led by California Institute of Technology’s Ahmed H. Zewail demonstrated the new method by investigating triangular silver nanoparticles on a graphene surface. After exciting the nanoparticles with a green femtosecond laser beam, the researchers probed the materials’ response with a 10-nm-diameter ultrafast electron beam. They repeated the process at multiple spots on and around the nanoparticles to generate electric field maps. Future improvements to their setup should enable the researchers to resolve electric fields on an atomic scale, they say.