Nov 5 2019
A research team, which included scientists from the University of Strasbourg in France, and their colleagues from the research centers in Jülich, Germany, and San Sebastián, Spain, has successfully detected the magnetic moments of nanoscale structures with unparalleled spatial resolution.
Topographic image of a small island of Cobalt on a Copper surface (size 25 nm by 25 nm). Nc marks the molecules used for functionalizing the tip. The tiny square marks the area of a zoom-in which is shown enlarged in the top left corner and which shows the different magnetic interaction fields from different Cobalt atoms in the layer. (Image credit: Forschungszentrum Jülich/Markus Ternes)
With the help of a scanning tunneling microscope, the researchers effectively made the magnetic moments visible in atomic-level resolution. A scanning tunneling microscope is an instrument that has been customarily used in the science field for many years.
By placing a tiny molecule, comprising nickel atom, at the tip of the microscope, the researchers made the tip sensitive to magnetic characteristics.
The results of the study, reported in the current issue of Science, provide new opportunities to gain a significant understanding of atomic-scale structures and for designing upcoming atomic-scale devices such as quantum simulators and nanoscale storage devices.
To study the world of individual molecules and atoms, researchers employ microscopes that are not dependent on electrons or a ray of light but instead observed as a definitive version of a similar record-player.
These devices, called scanning probe microscopes, “read” the grooves produced by molecules and atoms on the supporting surface. They achieve this by using the end of a sharp needle as a tip.
To detect the proximity between the surface and the tip, the researchers used a small electrical current that begins to flow when both the tip and the surface are merely separated by a fraction of a nanometer, or in other words, millionths of a millimeter. By regulating the tip to maintain this distance, topographic imaging can be performed by scanning the surface.
The fundamental concept of such microscopes has already been developed in the 1980s. But it was only during the last 10 years that researchers in numerous laboratories learned to widen the capabilities of these instruments by ingeniously developing the ultimate end of their probing tips.
For instance, by linking a tiny molecule such as hydrogen or carbon monoxide, they achieved an unparalleled increase in spatial resolution in which the molecule’s flexibility made even chemical bonds perceptible.
Likewise, the authors of the latest publication in Science also exclusively designed the apex of the tip to bring an innovative function to the sharp tip: They made the tip sensitive to magnetic moments by positioning a molecule, comprising one nickel atom or the so-called quantum molecular magnet, at the apex.
Such a molecule can be brought easily and electrically into different magnetic states in a way that it behaves just like a small magnet. While the ground state of the molecule effectively lacks a magnetic moment, its excited states certainly have a magnetic moment that senses close-by moments with excellent sensitivity and unparalleled spatial resolution.
This breakthrough has a very high significance. Now, for the first time, this technique can be used to image surface structures along with their magnetic characteristics in atomic resolution.
Furthermore, the use of a molecule as an active sensor not only makes it highly reproducible but also easy to apply in devices used by other teams across the world operating in the domain. Moreover, “dark” magnetic moments of intricate magnetic structures, which are often hard to quantify, become accessible. This breakthrough is significant for interpreting their internal structure.
Another benefit is also provided by the new technique. Since the ground state of the molecular sensor is non-magnetic, the measurement promotes only a mild back-action onto the system being studied—significant to prevail volatile states at the nanoscale.
To sum up, this latest study has allowed researchers to broaden their nanoscale toolbox with a novel tool sensitive to the magnetic characteristics. This aspect will be crucial for upcoming applications spanning from nanoscale memory-devices to new applications or materials in the area of quantum computing and simulation.