Nanohalos: A manifestation of electron channelling in gold nanoparticles

We discuss interesting haloing effects observed in experimental images of gold nanoparticles obtained using aberration-corrected scanning transmission electron microscopy (STEM) employing the low-angle annular dark-field (LAADF) imaging mode. The LAADF images contained bright rings of intensity (halos) with a diameter equal to or smaller than the diameter of the nanoparticle, the diameter varying as a function of the defocus of the STEM probe. Numerical simulations reveal that the halos are only present if the nanoparticles are imaged down a zone axis. Since the halos were observed in nearly all experimental images, this suggests that the nanoparticles become oriented along crystal zone axes during imaging.

► Haloing effects were observed in experimental LAADF images of gold nanoparticles.
► The diameter of the halos varied as a function of the defocus of the STEM probe.
► Halos are only present if the nanoparticles are imaged down a zone axis.
► Halos were ubiquitous, suggesting orientation along zone axes during imaging.