Credit: © 2008 APS

Light scattering is widely used to determine the physical properties of liquids, solids and gases. In most cases the scattered photons have the same energy as the incident light, but about one in ten million of the photons undergo Raman scattering, which means that they have less energy than the incident photons. Raman spectra contain a lot of information about the sample, but conventional Raman measurements are not well-suited for monitoring individual molecules at the nanometre scale.

Scanning probe microscopy, on the other hand, excels in probing the properties of materials at the nanoscale. These advantages have been combined with Raman spectroscopy before in a technique called tip-enhanced Raman spectroscopy (TERS), which has been used to measure both the topographic and chemical properties of molecules.

Now, Jens Steidtner and Bruno Pettinger of the Fritz Haber Institute in Berlin have performed TERS on a single brilliant cresyl blue molecule at the same time as performing tip-enhanced Raman imaging with a lateral resolution of ~15 nm. This is possible because the ultrahigh vacuum conditions in the experiment prevent photobleaching of the dye molecules.