Credit: © 2008 NPG

Diffractive imaging, carried out by monitoring the passage of X-rays and electrons through a material, could potentially yield information about the three-dimensional structure of single nanoparticles on the atomic scale. However, sub-ångström resolution is not possible because weak coherent scattering cannot be detected by conventional diffraction imaging procedures. Now, Jian Zuo and colleagues1 at the University of Illinois at Urbana-Champaign report sub-ångström-resolution diffractive imaging of cadmium sulphide (CdS) quantum dots by integrating information from a low-resolution 'image' with the diffraction pattern generated by the passage of electrons through the sample.

The electron diffraction patterns were recorded inside a transmission electron microscope using an electron beam with a diameter of 40 nm and an energy of 200 keV. Notably, the CdS dots were supported by graphene or carbon nanotube substrates — which have a lattice mismatch with CdS — to minimize background diffraction signals and overlapping of diffraction peaks. Using this method, a four-fold improvement in the resolution of the CdS diffraction image was achieved, resolving the smallest separation between the Cd and S atomic columns of 0.84 ångströms.

As low-resolution images can be obtained from various sources, this technique provides a general method for the high-resolution, three-dimensional imaging of individual nanoparticles.