Researchers from IBM have succeeded in ‘seeing’ the distribution of charge within a single X-shaped molecule.
Taking advantage of the workings of atomic-force microscopy (AFM), Fabian Mohn and his colleagues at IBM Research Zurich managed to map the distribution of charge in a molecule of naphthalocyanine on a bed of sodium chloride.
In AFM, a needle-like tip is moved across the object being imaged, and the attractive force between the object and the tip is then measured. Researchers have previously exploited this technique to determine the structure of individual molecules and their electron density (see Feeling the shapes of molecules).
Mohn’s team used a version of AFM called ‘Kelvin prove-force microscopy’ that measures the potential difference between the microscope tip and the molecule being looked at. Using this, they created amazingly detailed maps of the charge density around a naphthalocyanine molecule, which is shaped like an ‘X’.
From left to right, the first two images show the potential difference of the molecule in two slightly different states, the third shows the average of these and the fourth a theoretically calculated image of the same molecule.
Using this technique it could even be possible to see how charge is redistributed in a single molecule when bonds are broken and formed, the researchers write in Nature Nanotechnology.