Credit: © 2009 NPG

Conventional electron microscopes can provide atomic-scale information about a material's structure and bonding, but not its electromagnetic field. Now, the field structure inside and close to nanostructures can be observed using a technique called photon-induced near-field electron microscopy (PINEM), developed by Ahmed Zewail and co-workers at California Institute of Technology1.

PINEM works by exciting a nanostructure using very intense photon pulses from a laser, at the same time as bombarding the nanostructure with electron packets. If the electron packets arrive at exactly the same time as the photon pulse, the electrons gain or lose energy in discrete amounts. In fact, Zewail and colleagues found that each electron can absorb more than eight photons, despite interacting with the nanostructure for only a few hundred attoseconds. This interaction is greatly enhanced by the evanescent (decaying) electric field created by exciting the nanostructure.

By selecting only those electrons that gained energy from the photons, the researchers built up images of evanescent electric fields evolving in space and time in carbon nanotubes and silver nanowires. They found that the fields can extend outwards up to 50 nm on either side of the nanostructures.

This impressive new method extends the principles of optical near-field imaging, and will allow exploration of interfacial fields at the atomic scale.