Single Molecule Sensors For Ultra-High Resolution Microscopy
Using single molecule sensors, scientists in Jülich have mapped electric fields with unprecedented precision. The ultrahigh-resolution images provide information on the distribution of charges in the electron shells of single molecules and even atoms. The technique is relevant for diverse scientific fields, including investigations into biomolecules and semiconductor materials.
“Our method is the first to image electric fields near the surface of a sample quantitatively with atomic precision on the sub-nanometre scale,” said research group leader Ruslan Temirov. Such electric fields surround all nanostructures like an aura. Their properties provide information, for instance, on the distribution of charges in atoms or molecules.
Electric Field Maps With Unprecedented Nanometer Resolution
The research paper, published on Physical Review Letters and titled “Scanning Quantum Dot Microscopy,” is freely available. “We have reported a scanning probe technique that is able to provide truly three-dimensional, so far elusive, maps of the electrostatic potential field with nanometer resolution,” reads the conclusion of the paper.
The scientists “have pushed the capabilities of force microscopy to a new level by attaching a single molecule at the sharp end of an STM probe and exploiting it as a quantum dot capable of sensing electrostatic fields,” notes a review of the work.
To achieve ultra-high resolution, the scientists attached a single molecule – a quantum dot – to the tip of an atomic force microscope. Quantum dots are tiny structures, measuring no more than a few nanometres across, which due to quantum confinement can only assume certain, discrete states comparable to the energy level of a single atom. The molecular quantum dot terminating the tip of the microscope is very sensitive to electric fields, and allows the electrostatic potential to be mapped out around a target atom or molecule.
“Because the whole molecular balance is so small, comprising only 38 atoms, we can create a very sharp image of the electric field of the sample,” explains researcher Christian Wagner.
It’s a bit like a camera with very small pixels.
A patent is pending for the method, which is particularly suitable for measuring rough surfaces, for example those of semiconductor structures for electronic devices or folded biomolecules. “In contrast to many other forms of scanning probe microscopy, scanning quantum dot microscopy can even work at a distance of several nanometres. In the nanoworld, this is quite a considerable distance,” says Wagner.
The technique has only been applied in high vacuum and at low temperatures so far, but the scientists believe that future versions of the technique could be used in less extreme conditions.
“The increased sensitivity offered by this technique could be used to characterize rough surfaces, adsorbed materials on semiconductors, or artificial nanostructures,” says reviewer Philip Moriarty, University of Nottingham. “There are also fascinating possibilities for combining quantum dot microscopy with single-atom or single-molecule positioning, in which a scanning probe is used to construct nanostructures element-by-element.”
Images from Forschungszentrum Jülich.