Research projects

The electrical resistance of materials or devices is often measured by the 4-point probe method to eliminate lead and contact resistance issues. In the recent decade, miniaturized versions, so-called nano­probes, have been develo­ped where four sharp tips are individually positioned by piezo-actuators and simultaneously imaged with a scanning electron micros­cope (see here for an example). However, the finite tip sharpness usually limits the minimal distance to about 100 nm.

We recently developed of a novel method which enables to detect how charged quasiparticles pro­pa­gate on length scales down to a few nm by remotely triggering the tautomerization of a single molecule with a scanning tunneling microscope (STM) (see here and the highlight in Nature Nanotechnology for further information).  In analogy to the 4-point nano­probe we coined it “mo­le­cu­lar nano­probe” (MONA).  In com­bi­na­tion with atom-by-atom-engi­neered inter­fero­meters, MONA al­lows to un­ra­vel the quan­tum-me­cha­ni­cal wave na­ture of hot elec­trons. Two inter­fero­meters can even be com­bined to build an energy-depen­dent selec­tor, which allows it to se­lec­tively switch one out of two mole­cules with­out chan­ging the po­si­tion of the STM tip. The MONA tech­nique may, in future, serve as a me­thod to map the charge den­sity dis­tri­bu­tion around an arbi­trary quasi­par­ticle in­jec­tion point.