ABSTRACT – We show that the different bond orders of individual carbon-carbon bonds in polycyclic aromatic hydrocarbons and fullerenes can be distinguished by noncontact atomic force microscopy (AFM) with a carbon monoxide (CO)–functionalized tip. We found two different contrast mechanisms, which were corroborated by density functional theory calculations: The greater electron density in bonds of higher bond order led to a stronger Pauli repulsion, which enhanced the brightness of these bonds in high-resolution AFM images. The apparent bond length in the AFM images decreased with increasing bond order because of tilting of the CO molecule at the tip apex.
The bonds at centre appear shorter than those at the edges, as more electrons are present in them
IBM has refined their method to precisely measure the structural details of a single molecule. With their technique, they managed to measure very subtle differences in the distribution of electrons within the molecule’s bonds. How subtle? We’re talking 3 picometers or 0.000000000003 meters. That’s one-hundredth the diameter of an atom!
Because the team is able to measure bond lengths to within 3 picometers, they have a much more accurate picture of the electron properties throughout these molecule. They’ve even started testing other carbon grid molecules to see how the electronic properties of the whole molecule become distorted by other kinds of atoms or irregularities.
Why is that important? Because the electronic properties of this lattice is what makes gives carbon nanotubes their superconductive properties and sensor abilities. Understanding how even the littlest changes can cause electrons to change the way they are distributed in the molecule is of utmost importance if carbon nanotubes are going to useful and reliable in future technologies.
The technique developed by IBM uses atomic force microscopy or AFM with a single carbon monoxide (CO) at the tip that interacts with the molecule being probed