In-vacuum projection of nanoparticles for on-chip tunneling spectroscopy.

Starting with a discussion of the percolation problem applied to the trapping of conducting nanoparticles between nanometer-spaced electrodes, we show that a good strategy to trap a single nanoparticle between the electrodes is to prepare chips with low coverage of nanoparticles to avoid percolating current paths. To increase the probability of trapping a single nanoparticle, we developed a new method where nanoparticles are projected in-vacuum on the chip, followed by a measure of the tunnel current, in a cycle that is repeated up to a few thousand times until a preset threshold value is reached. A plot of the tunneling current as a function of time allows discriminating between the two possible current paths, i.