The electrical resistance of materials or devices is often measured by the 4-point probe method to eliminates 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.
In a just accepted article, we describe the development 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 molecules with a scanning tunneling microscope (STM). 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 the future, serve as a method to map the charge density distribution around an arbitrary quasiparticle injection point. more