Imaging light atoms on graphene

Graphene makes a nearly ideal substrate for transmission electron microscopy (TEM). Composed of a honeycomb carbon lattice just one atom thick, it is the thinnest, most transparent support possible for adsorbed atoms and molecules. But it’s also strong and conductive, able to trap the atoms long enough for good images to be captured and yet suffer minimal charging effects from the electron beam. Researchers from the University of California, Berkeley, and Lawrence Berkeley National Laboratory have taken advantage of those properties to reveal individual hydrogen and carbon adatoms that appear as if suspended in free space. In order to enhance the signal-to-noise ratio, the team summed multiple scans. As pictured here, carbon (black) and hydrogen (gray) adatoms show up as dark spots on a bright background, and atomic vacancies created from electron irradiation appear as white spots. The visualization of the low-contrast light atoms allowed the team to follow the dynamics of individual adsorbed atoms and organic molecules in real time for several minutes. The demonstration presents a straightforward way of using TEM to study both atomic-scale chemical diffusion and reactions that occur under electron irradiation. (J. C. Meyer, C. O. Girit, M. F. Crommie, A. Zettl, Nature 454 , 319, 2008 http://dx.doi.org/10.1038/nature07094 .)