SXSPM Research | Highlights

Separating photo-excited signals from topography

In synchrotron X-ray STM, the STM tip 'sees' two current contributions; the conventional current relating to topography and the x-ray excited current caused by elements on the sample surface. The problem is that these signals are entangled, and the feedback loop of the STM that keeps the tunneling current constant, does not know which information is chemical and which is caused by sample topography. As a result, the STM tip can be lifted out of tunneling into the far field, resulting in images that provide incorrect information. And to make matters worse, this transition typically takes place without researchers noticing.

A way to fingerprint such near-to-far-field transitions is to monitor simultaneously tip and sample currents. However, controlling such transitions is obviously more useful than just detecting them. We have developed a topography filter - 'topo-filter' - that untangles the chemical and topographic signals, avoiding tip transitions. This 'easy-to-implement' topo-filter can also be applied to other variants of light-assisted STM such as laser STM. Research results have been published in Review of Scientific Instruments.