Competing quantum interactions cause individual molecules to stand up


Three-dimensional model of the standing PTCDA molecule (black, carbon atoms; red, oxygen atoms; white, hydrogen atoms) on two Ag adatoms (blue) on the Ag (111) surface (gray). Photo credit: University of Warwick

Nanoscale machines have many uses including drug delivery, single atom transistor technology, or memory storage. However, the machinery has to be assembled on a nanoscale, which is a major challenge for the researchers.

For nanotechnology engineers, the ultimate goal is to be able to assemble functional machines on a nano scale piece by piece. In the macroscopic world, we can just grab objects to assemble them. It is no longer impossible to “grab” individual molecules, but their quantum nature makes their reaction to manipulation unpredictable and limits the ability to put molecules together individually. This perspective has now come one step closer to reality, thanks to an international effort led by the Jülich Research Center of the Helmholtz Society in Germany, in which researchers from the Department of Chemistry at the University of Warwick are also involved.

As of today, November 10, 2021, in the magazine Scientific advancesAn international team of researchers has succeeded in uncovering the generic stabilization mechanism of a single standing molecule, which can be used for the rational design and construction of three-dimensional molecular devices on surfaces.

The scanning probe microscope (SPM) has brought the vision of manufacturing on a molecular scale closer to reality, as it offers the possibility of rearranging atoms and molecules on surfaces and thus creating metastable structures that do not form spontaneously. With the help of SPM, Dr. Christian Wagner and his team interact with a single standing molecule, perylene tetracarboxylic acid dianhydride (PTCDA), on a surface to investigate thermal stability and the temperature at which the molecule is no longer stable and reverts to its natural state where it is flat adsorbed on the surface. At -259.15 degrees Celsius, this temperature is only 14 degrees above absolute zero.

Competing quantum interactions cause individual molecules to stand up

STM images (−50 mV, 0.2 nA, 25 × 25 Å2) of all six observable azimuthal orientations of s-PTCDA, linked to the respective adatom dimers, D1 (blue) or D2 (purple). The central adatom (gray) is part of all dimers. In this way, three D2 dimers and six D1 dimers with azimuthal orientations that are identical in pairs can be formed. Photo credit: University of Warwick

Quantum chemical calculations carried out in collaboration with Dr. Reinhard Maurer from the Department of Chemistry at the University of Warwick were able to show that the subtle stability of the molecule results from the competition between two strong opposing quantum forces, namely the far-reaching attraction of the surface and the short-range restoring force from the anchor point between the molecule and the surface goes out.

Dr. Reinhard Maurer from the Department of Chemistry at the University of Warwick comments: “The balance of interactions, which keeps the molecule from falling over, is very subtle and a real challenge for our quantum chemical simulation methods, mechanisms that stabilize such unusual nanostructures, the project also posed to us helped to evaluate and improve the performance of our methods. “

Dr. Christian Wagner from the Peter Grünberg Institute for Quantum Nanosciences (PGI-3) at Forschungszentrum Jülich: “In order to use the fascinating quantum properties of individual molecules technically, we have to find the right balance: They have to be immobilized on a surface, but without making them too strong fix, otherwise they would lose these properties. Standing molecules are ideal in this regard. In order to measure how stable they actually are, we had to repeatedly set them up with a sharp metal needle and time how long they survived at different temperatures. “

Now that the interactions that lead to a stable standing molecule are known, future research can work to develop better molecules and molecule-surface connections to tune these quantum interactions. This can help increase the stability and the temperature at which molecules can be converted into standing arrays towards workable conditions. This raises the prospect of nanofabrication of machines on the nanoscale.

Visualization of designer quantum states in stable macrocycle quantum corals

More information:
Marvin Knol et al., The Stabilization Potential of a Standing Molecule, Scientific advances (2021). DOI: 10.1126 / sciadv.abj9751

Provided by the University of Warwick

Quote: Competing quantum interactions enable individual molecules to stand up (2021, November 10). Retrieved on November 10, 2021 from

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