"One in a million"‑ atomic resolution electron spectroscopy puts faces to individual atoms
The whereabouts and destiny of a single impurity atom in a material is being unveiled using ultra‑high spatially resolved electron spectroscopy. Following a recent demonstration in which the elemental nature of individual atoms in single‑layer materials was identified using advanced imaging techniques in new‑generation transmission electron microscopes (Krivanek et al., Nature 464, 571, 2010.), we report how the capability of such microscopes can be increased further still, by adding atomic resolution electron energy loss (EEL) spectroscopy, enabling the bonding state of single impurity atoms to be measured. This combination of techniques is a most powerful tool for nano‑technology. Here multi‑walled carbon nanotubes and few‑layer graphene were ion‑implanted with atom species including light elements (e.g., boron), which due to their similarity in atomic number to carbon cannot indubitably be 'seen' by imaging. EEL spectroscopy shows up not only atomic locations of these elements, but also how the element resides electronically in its atomic environment. By monitoring the fate of individual ion‑implanted impurity atoms we show that carbon‑based nano‑materials, which bear enormous promise for nano‑electronics, can be successfully doped to densities larger then one atom nm^‑2 via ion‑implantation, an established routine in device mass‑production in semiconductor industries.
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LQ12292
Cooling off friction
The atomic scale roots of friction have been the focus of researchers in the
past ever since the invention of the friction force microscope. A
fundamental process, envisioned already back in the early 20th century by
Ludwig Prandtl, is the atomic stick‑slip phenomenon: The atoms of the
sliding contacts first stick together until enough lateral force is applied
to make them jump (or 'slip') suddenly to the neighboring atomic lattice
site. One decade ago Gnecco et al. (Phys.Rev.Lett. 84, 1172(2000)) predicted
that temperature can strongly influence this process: Thermal energy will
tend to induce premature jumps in effect reducing the jump inducing force,
and therefore friction. Our work now provides direct experimental proof that
this notion is indeed true by presenting measurements of atomic friction on
graphite as a function of surface temperature from ambient down to cryogenic
temperatures. While the concept is shown to hold in principle some
corrections are proposed concerning an unexpected temperature dependence of
the attempt frequency of the slip process.
