A microscope creates images with nanometre resolution by exposing samples to single ions.

In electron and ion microscopy, increasing a sample's exposure time can improve the signal-to-noise ratio and result in clearer images, but this can damage or contaminate the sample. To avoid this, Georg Jacob at the University of Mainz in Germany and his colleagues used an electric-field 'trap' to release calcium ions one by one.

Each ion, either transmitted or blocked by the sample, corresponds to a pixel. By controlling the release of the ions, the team calculated when those coming from the source and through the sample should arrive at the detector. This allowed the team to turn the detector on only during those times, reducing the number of detected 'noise' ions.

The microscope showed a fivefold increase in the signal-to-noise ratio, and could potentially cut noise signals by a factor of one million, compared with current methods. It also pinpointed the position of a 1-micrometre hole in a diamond sample with a precision of 2.7 nanometres.

Phys. Rev. Lett. 117, 043001 (2016)