Physicists make molecular vibrations more detectable

Physicists make molecular vibrations more detectable

In this microscope image, lead phthalocyanine molecules on a superconducting lead surface appear as four-leaf clovers. The vibrations of these molecules were studied with the new method. Credit: Jan Homberg

In molecules, atoms vibrate with characteristic patterns and frequencies. Therefore, vibrations are an important tool for studying molecules and molecular processes such as chemical reactions. Although scanning tunneling microscopes can be used to visualize individual molecules, their vibrations have so far been difficult to detect.

Physicists at the University of Kiel (Christian-Albrechts-Universität zu Kiel, CAU) have now invented a method by which vibration signals can be amplified by a factor of up to 50. In addition, they have greatly increased the frequency resolution. The new method will improve the understanding of interactions in molecular systems and other simulation methods. The research team has now published the results in the journal Physical Review Letters.

The discovery by Dr. Jan Homberg, Dr. Alexander Weismann and Prof. Dr. Richard Berndt from the Institute of Experimental and Applied Physics is based on a special quantum mechanical effect, the so-called “inelastic tunneling”. Electrons passing through a molecule on their way from a metal tip to the surface of the substrate in the scanning tunneling microscope can either release energy to the molecule or take energy from it. This energy exchange takes place in portions determined by the properties of the respective molecule.

Credit: Christian-Albrechts-University of Kiel

Normally, this energy transfer occurs only rarely and is therefore difficult to measure. To amplify the measurement signal and simultaneously achieve high-frequency resolution, the CAU team used a special property of molecules on superconductors that they had previously discovered: properly arranged, the molecules show a state in the spectra that looks like of a needle, very high and extremely sharp — the so-called Yu-Shiba-Rusinov resonance.

Kiel physicists make molecular vibrations more detectable

The model shows the molecular arrangement on a lead substrate. Credit: Jan Homberg

The experiments were supported by the theoretical work of Troels Markussen of the Synopsis software company in Copenhagen.

Making and breaking chemical bonds in simple “nanoconfined” molecules.

More information:
Jan Homberg et al, Resonance-enhanced vibrational spectroscopy of molecules on a superconductor, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.129.116801

Provided by Christian-Albrechts-University of Kiel

Citation: Physicists make molecular vibrations more detectable (2022, September 21) Retrieved September 22, 2022, from

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