Nature Commun. 7, 10189 (2016)

Microscopists are fond of the saying 'seeing is believing'. And given the pervasive use of their technique across the natural sciences, few could blame them. However, many systems remain challenging to image, such as transparent, weakly bonded or extremely rough materials. Perhaps most notably, delicate structures such as biological samples can degrade under the energetic probes of traditional microscopy based on electrons or X-rays.

Scanning helium microscopy (SHeM) offers one way around this problem by providing a probe that is chemically, electrically and magnetically inert, and therefore non-destructive. For the most part, SHeM studies have focused on elastic scattering of the helium atoms, such that structural defects such as adsorbates or terraces on the surface of the sample usually dominate the imaging contrast. Chemical information has proven much harder to obtain.

By focusing on inelastic scattering processes — which have signals typically two or three orders of magnitude smaller than their elastic counterparts — Matthew Barr and colleagues have shown they contain important information about the chemical composition of a sample surface. The authors tested their technique on different metallic species, but in principle it is also applicable to more complex electronic and biological systems.