&Bullet; physics 14, s64
A scheme that uses voltage to control the strength of a chemical bond allows the tip of an atomic force microscope to pluck a sheet of graphene from a substrate.
Today there are innumerable techniques for using atoms as microscopic “Legos” that can be put together to form complex nanostructures. Now a team led by Jörg Kröger from the Technical University of Ilmenau has expanded the nanomanipulation toolkit to include a technique for checking the strength of a single chemical bond  . By applying voltage to the bond, they showed that they could weaken or strengthen the interaction between an atom at the tip of an atomic force microscope and an atom in a sheet of graphene. The scheme could lead to methods for applying mechanical loads in nanomachines or investigating how the bond strength affects chemical reactions.
The new technology uses the behavior of polar covalent bonds that form between two atoms with different electron affinities, such as. B. the hydrogen and oxygen atoms in a water molecule. In such molecules, the binding electrons are unevenly distributed between the two atoms, so that an applied electric field can change the electron distribution, which affects the bond strength.
In their setup, the team placed the tip of an atomic force microscope probe on a layer of graphene. The tip was decorated with a gold atom that formed a bond with one of the carbon atoms of the graphene sheet. The team then applied a small voltage between the graphene sheet and the tip.
The team found that negative tension weakened the bond, while positive tension strengthened it. At the highest positive voltages, this gain was so great that when the tip was withdrawn, the gold atom stuck to the carbon atom and the tip acted like a crane pulling up the entire graphene layer. The team’s simulations showed that the effect originates from a stress-induced charge redistribution in the atomic orbitals of the atoms.
Matteo Rini is the editor of physics.
- M. Omidian et al., “Control of the electric field of a single atom polar bond”, Phys. Rev. Lett.126216801 (2021).