Phys. Rev. Lett. 115, 026101 (2015)

Kelvin probe force microscopy (a version of atomic force microscopy) is currently the most promising in terms of the mapping of the electrostatic potential at the single-atom and single-molecule levels. However, it is very sensitive to the distance between the conducting tip and the surface under investigation, which can make it less reliable. Stefan Tautz and colleagues now present an alternative approach, where a quantum dot is attached to the end of the tip. Quantum dots are sometimes referred to as artificial atoms, as they exhibit distinct energy levels, which shift in the presence of electrostatic gating. The team follows these changes when the tip is close to the target atom or molecule, allowing them to map the field around their target in three dimensions with high sensitivity. The ability to detect the electrostatic potential while away from the surface (the authors report a 6 nm distance), can be useful for the characterization of rougher samples.