Scanning Quantum Dot Microscopy (SQDM)
Our single-molecule manipulation experiments have led us to the discovery of a new scanning probe technique that is able to image nanoscale variations of the electrostatic potential of surfaces with very high sensitivity and spatial resolution.
Scanning quantum dot microscope.
Copyright: 2015 APS
Scanning Quantum Dot Microscopy (SQDM) utilises the fact that a nanometer-sized molecule fixed with atomic precision to the tip apex of a low-temperature non-contact atomic force microscope (NC-AFM) [1, 2] acts as a quantum dot. Tunnelling of single electrons in and out of the quantum dot occurs when a sufficient electric bias voltage V is applied to the NC-AFM tip. The tunnelling changes the charge state of one of the molecular orbitals of the quantum dot between -e, 0 and +e, where e is the elementary charge [3]. The charging leads to abrupt jumps in the attractive electrostatic force acting from the surface on the tip. A sensitive mechanical resonator which continuously oscillates the quantum dot probe with sub-Ångstrom amplitudes responds to the abruptly changing force by sharp spikes in its oscillation frequency. Scanning the quantum dot probe at a constant height over the surface and adjusting V such that a particular frequency spike (0 → +e or 0 → -e) occurs, SQDM records maps of corresponding voltages V+ and V-, which finally yield the distribution of the electrostatic potential Φ over the scanned surface [4, 5]. We have developed a fast controller which tracks the spikes while scanning the surface, making SQDM an efficient und easy-to-use scanning probe technique [6].
Last updated: 4.10.2020
