The All-in molecule, composed of 4- to 8-membered rings, is produced via on-surface strain-driven synthesis from a helical precursor. The gold surface facilitates a reaction that would otherwise be impossible in solution. Using nc-AFM (grayscale image, scale bar: 0.5 nm), the molecular structure can be directly visualized in real space. Additional products derived from this precursor can be seen here.

Visualization  of charges in real space

Kelvin Probe Force Microscopy (KPFM), adapted from nc-AFM, enables the direct visualization of the charge distribution in single molecules and atoms. In this figure, you see a tripod-like molecule composed of four carbon rings arranged in a tetrakis (pyramidal) configuration, containing a halogen atom (Br or F). When the bond between the halogen and the ring is strong enough, the halogen can transfer some of its electron density and become slightly depleted of electrons, effectively acquiring a partial positive charge along the bond direction—a phenomenon known as the sigma-hole (top row). However, if the halogen is sufficiently electronegative (i.e., more electron-attracting), no sigma-hole will be observed. After a long struggle, we finally published this in Science.

Characterization of biomolecules

Biomolecules are typically non-conductive and highly three-dimensional, making STM characterization challenging. In this image, you can see two beta-cyclodextrins: one with its narrow rim pointing upwards and the other facing the gold surface. The high-resolution capabilities of nc-AFM allow for the assignment of each individual OH group in the molecule and reveal how atomic height variations influence image contrast. We published it recently in Nat. Comm.

Manipulation of single atoms and molecules