Deceptive “lattice spacings” in high-resolution micrographs of metal nanoparticles

Experimental HRTEM images of randomly oriented nanocrystals typically show fringes within the nanocrystals. Often these fringes are one-dimensional, although many appear to show two-dimensional resolution. In order to determine the tilt conditions necessary for the formation of one- and two-dimensional fringes in metal nanocrystals, simulations of HRTEM images of a 561-atom palladium nanoparticle were systematically carried out over an extensive range of tilts. The resultant images contained fringes that are deceptively like one- and two-dimensional lattice fringes. These fringes are, however, not simply related to the crystal structure of the particle, and “lattice spacings” measured from them will be in error. In addition, depending upon particle orientation, HRTEM images of a perfect nanoparticle can show details that may be erroneously interpreted as “relaxations”, “bent planes”, and even “twinned” areas.