Researchers at the Nanoscience Center at the University of Jyvaskyla, Finland and the University of Guadalajara in Mexico, have developed a method to simulate and visualize the electron currents induced by a magnetic field inside of gold nanoparticles. The method facilitates the precise analysis of magnetic field effects inside complex nanostructures in nuclear magnetic resonance measurements and establishes quantitative criteria for the aromaticity of nanoparticles. The work was published on 04/30/2021 as an Open Access article in Nature communications.
According to classical electromagnetism, a charged particle moving in an external magnetic field experiences a force that makes the particle’s path circular. This fundamental law of physics is used, for example, in the design of cyclotrons that function as particle accelerators. When nano-sized metal particles are placed in a magnetic field, the field induces a current of electrons flowing inside the particle. The circulating current in turn creates an internal magnetic field which opposes the external field. This physical effect is called magnetic shielding.
The strength of the shielding can be studied using nuclear magnetic resonance (NMR) spectroscopy. Internal magnetic shielding varies greatly on an atomic length scale even within a nanoscale particle. Understanding these variations at the atomic scale is only possible by using the theory of quantum mechanics of the electronic properties of each atom constituting the nanoparticle.
Today, the research group of Professor Hannu Häkkinen of the University of Jyväskylä, in collaboration with the University of Guadalajara in Mexico, has developed a method to calculate, visualize and analyze the currents of electrons circulating in the interior of complex 3D nanostructures. The method has been applied to gold nanoparticles with a diameter of only about one nanometer. The calculations shed light on unexplained experimental results from previous NMR measurements in the literature regarding how the magnetic shielding inside the particle changes when a gold atom is replaced by a platinum atom.
A new quantitative measure to characterize the aromaticity inside metal nanoparticles has also been developed based on the total integrated force of the shielding electron current.
“The aromaticity of molecules is one of the oldest concepts in chemistry, and it has traditionally been linked to ring-shaped organic molecules and their delocalized valence electron density which can develop circulating currents. in an external magnetic field. However, the generally accepted quantitative criteria for the degree of aromaticity were lacking. Our method now gives a new tool to study and analyze the electron currents at the resolution of an atom within of any nanostructure, in principle. Peer reviewers of our work have viewed this as a significant breakthrough in the field, ”says Professor Häkkinen who coordinated the research.
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