Physicists make molecular vibrations more detectable

In this micrograph, lead phthalocyanine particles appear on the surface of a superconducting lead in the form of a tetrahedral clover. The vibrations of these particles were studied in the new method. Credit: Jan Homberg

In molecules, atoms vibrate with distinct 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 image individual particles, their vibrations have so far been difficult to detect.

Physicists at Kiel University (Christian-Albrechts-Universität zu Kiel, CAU) have invented a method by which vibration signals can be amplified by a factor of 50. Moreover, they have significantly increased the frequency accuracy. The new method will improve understanding of interactions in molecular systems and other simulation methods. The research team has now published the results in the journal physical review messages.

The discovery by Dr. Jan Homberg, Dr. Alexander Wiseman and Professor Dr. Richard Berndt of the Institute of Experimental and Applied Physics is based on a special quantum mechanical effect called “inelastic tunneling”. In a scanning tunneling microscope, electrons passing through a molecule on their way from a metal tip to the substrate surface can release energy into or take energy from the molecule. this is energy exchange It occurs in parts determined by the properties of the molecule in question.

Credit: Christian Albrechts, Kiel University

Usually, this The transfer of energy It rarely happens and is therefore difficult to measure. In order to amplify the measurement signal and achieve high-frequency accuracy at the same time, the CAU team used a special property of molecules on the superconductors they discovered earlier: appropriately arranged, molecules A condition appears in the spectra that looks like a needle, very high and very sharp – the so-called Yu-Shiba Rusinov resonance.

Physicists make molecular vibrations more detectable

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

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

Making and breaking chemical bonds in ‘nano-confined’ single molecules

more information:
Jan Homberg et al, Resonance-enhanced vibrational spectroscopy of molecules on a superconductor, physical review messages (2022). DOI: 10.1103/ PhysRevLett.129.116801

Provided by Christian Albrechts University in Kiel

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