Scanning tunneling microscopy reveals subsurface atomic structure
The figure (on the left) shows the magnetic state above the surface by means of its wave function (simplified) (green corrugated line), which penetrates under the graphene (small dark gray spheres) with magnetic iron (blue spheres). Electrons (small yellow spheres) “tunnel” of the tip of the magnetic scanning probe in this state. The green arrows indicate the electron spin, a quantum mechanical property of electrons linked to magnetic properties. From the image of the sample surface, two microscope images can be seen. The upper image shows a contrast between sample positions with different stacking sequences, while the lower image shows a map of local spin polarization, which is due to the density of spin at the buried interface. Credit: ACS Group – Chlenhoff
Scientists use scanning tunneling microscopy to understand how the electronic or magnetic properties of a material are linked to its atomic scale structure. However, when using this technique, they can normally study only the upper atomic layer of a material.
Professor Anika Schlenhoff and the postdoctoral researcher, Dr. Maciej Bazarnik, of the University of Münster’s Physics Institute (Germany) have now succeeded for the first time to use a modified measurement method for image of the structural and magnetic properties which are below the surface. The team studied an ultra-thin layer of a magnetic material (iron) under a layer of two-dimensional graphene. Research is published in the journal Nano ACS.
In conventional scanning tunnel microscopy, so -called electronic states on the surface of the sample are used for the measurement signal (the “tunnel current” which circulates between the point of the probe and the sample). However, in the resonance measurement variant used by the team, the states in front of the surface have been studied. Apparently contradictory, but known for some time, these special states can be used to study the transfer of electronic load at the interfaces buried inside the sample.
As researchers have now shown, these special states can be used to detect the local magnetic properties of an iron film covered by graphene. The physical reason is that the electronic states located above the surface penetrate under the graphene in the sample to the magnetic iron layer and themselves become magnetic by interaction with iron.
“This opens up new investigation possibilities,” explains Schlenhoff. “We can now use the same scanning tunneling microscope to study the upper layer of a layer system and an interfacial layer buried below their structural, electronic and magnetic properties. The two layers can be analyzed with a single and high spatial resolution which extends to the atomic scale.”
The team has also shown that their method can be used to obtain information on the local position of the layers compared to each other. For example, the position of the carbon atoms of the graphene varies locally compared to the underlying iron atoms due to different stacking sequences.
“The differences in vertical stack could not be resolved before for this material system using the conventional scanning tunnel microscopy,” explains Bazarnik.
It turns out now that states near the surface, which are used in resonant scanning tunnel microscopy, are sensitive to the stacking sequence and thus allow these differences to be visualized.
More information:
Maciej Bazarnik et al, image states of image on a 2D GR – ferromagnet hybrid: Improve the detection of spin and stacking, Nano ACS (2025). DOI: 10.1021 / ACSNANO.5C04475
Supplied by the University of Münster
Quote: Balayage tunneling microscopy reveals an underground atomic structure (2025, July 18) recovered on July 19, 2025 from https://phys.org/news/2025-07-scanning-tunneling-microscopy-reveals-subsurface.html
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