Physicists make molecular vibrations more detectable

Kiel physicists are making molecular vibrations easier to detect

In this microscopic image, the lead phthalocyanine molecules appear as a four-leaf clover on a superconducting lead surface. The new method was used to study the vibrations of these molecules. Photo credit: Jan Homberg

In molecules, the atoms vibrate with characteristic patterns and frequencies. Vibrations are therefore an important tool to study molecules and molecular processes such as chemical reactions. Although individual molecules can be imaged with scanning tunneling microscopes, their vibrations have so far been difficult to detect.

Physicists from the CAU (Christian-Albrechts-Universität zu Kiel, CAU) have now invented a method with which the vibration signals can be amplified by a factor of 50. They have also significantly 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 specialist journal Physical Verification Letters.

The discovery of dr. Jan Homberg, Dr. Alexander Weismann and Prof. Dr. Richard Berndt from the Institute for Experimental and Applied Physics is based on a special quantum mechanical effect, the so-called “inelastic tunneling”. Electrons that pass a molecule on their way from a metal tip to the substrate surface in the scanning tunneling microscope can give off energy to the molecule or absorb energy from it. This exchange of energy occurs in portions determined by the properties of each molecule.

Source: Christian-Albrechts-University of Kiel

Normally, this transfer of energy occurs infrequently and is therefore difficult to measure. In order to amplify the measurement signal and at the same time achieve high frequency resolution, the CAU team used a previously discovered special property of molecules on superconductors: Appropriately arranged, the molecules in the spectra show a state that appears needle-like, very high and extremely sharp – the so-called Yu-Shiba-Rusinov resonance.

Kiel physicists are making molecular vibrations easier to detect

The model shows the molecular assembly on a lead substrate. Photo credit: Jan Homberg

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

Making and breaking chemical bonds in single “nano-confined” molecules

More information:
Jan Homberg et al, Resonance-Enhanced Vibrational Spectroscopy of Molecules on a Superconductor, Physical Verification Letters (2022). DOI: 10.1103/PhysRevLett.129.116801

Provided by the Christian-Albrechts-University in Kiel

Citation: Physicists Make Molecular Vibrations More Detectable (2022 September 21) Retrieved September 21, 2022 from

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