Last Friday, April 17^th, PhD student Jaap Kautz and postdoc Johannes Jobst received the Dutch Vacuum Society’s annual prize (NeVac Prize). Jaap and Johannes, both in the group of Sense Jan van der Molen at Leiden, developed a new method to study electrical conductivity in two-dimensional materials. Their technique is based on Low Energy Electron Microscopy (LEEM) and hence does not require local probes.

Charge transport measurements form an essential tool in condensed matter physics. The usual approach is to contact a sample by two or four probes, measure the resistance and derive the resistivity, assuming homogeneity within the sample. A more thorough understanding, however, requires knowledge of local resistivity variations. Jaap and Johannes have presented a new way to determine spatial potential maps of a current-carrying sample, using low-energy electron microscopy (LEEM). In this type of electron microscopy, the image intensity depends sensitively on the local electron landing energy. For a sample under a lateral voltage bias, however, this local landing energy will depend on position, and hence also the local image intensity will. In other words, the local intensity provides information about the local voltage. This is the key to the new technique developed, coined low-energy electron potentiometry (LEEP).

Specifically, Jaap and Johannes probed the in-plane potential distribution in a layered quasi-two-dimensional (2D) sample (single to triple layer graphene) under bias. Interestingly, for such a layered material, the accuracy of LEEP is enhanced, since one can make use of sharp quantum resonances. These come about when the incoming electrons are in sync with unoccupied interlayer graphene states. Interestingly, the method is straightforwardly extendable to other quasi-2D systems, most prominently to the upcoming class of layered van der Waals materials.

For more information on the NeVac Prize, click here.

For more information on the Van der Molen group, follow this link.

Jaap Kautz