Scientists spin a single molecule clockwise or counterclockwise on demand

Scientists spin a single molecule clockwise or counterclockwise on demand

Scanning tunneling microscopy (STM) image of a rotating europium (Eu) complex in gold foil. The dark spot on the disk indicates the single Eu atom. Credit: Argonne National Laboratory

Controlling the rotation of this molecule could lead to new technologies for microelectronics, quantum computing, and more.

You can easily spin a baseball in your hand by twisting your fingers. But it takes resourceful scientists with access to world-class science facilities to rotate an object that is only two billionths of a meter across. That’s a million times smaller than a raindrop.

Scientists at the US Department of Energy (DOE) Argonne National Laboratory report that they can accurately rotate a single molecule so small to order. The key ingredient is a single europium atom, a rare earth element. It rests at the center of a complex of different atoms and gives the molecule many potential applications.

“We can rotate this europium complex 60 or 120 degrees to the right or to the left,” said Saw Wai Hla, a physicist at the Center for Nanoscale Materials (CNM), a DOE Office of Science user facility in Argonne, and physics teacher. Ohio University professor. “The ability to control the movement of a rare earth complex like this could affect a wide spectrum of technologies.” That includes next-generation microelectronics, quantum technologies, catalysis to speed up reactions, light-to-electricity conversion, and more.

The term “rare earth” is misleading. Rare earth elements aren’t exactly rare, but they are critical materials used in many electronics devicessuch as cell phones, computer hard drives, solar panels, and flat screen monitors. The ability to rotate this europium molecule on demand could expand its applications into next-generation microelectronics running relatively low-power quantum computers and beyond.

Scientists spin a single molecule clockwise or counterclockwise on demand

Controlled rotation of the Eu complex on gold foil initiated by electrical power from the STM tip, top left. Europium complex before and after 120 degree rotation (b,c). The dashed circle indicates a negatively charged molecule. Credit: Argonne National Laboratory.

Rare earths easily combine with other elements in the earth’s crust. Therefore, it is difficult and expensive to produce pure rare earths for devices. They are also expensive to collect from waste that contains rare earths. The team’s europium complex would reduce the amount of rare earths needed for a particular device and would be much less expensive to manufacture in large quantities.

The key components of the complex are a single europium atom with Positive charge and two small molecules with negative charge. The europium atom is in the center of the complex, while one of the small molecules is on the side and the other on the bottom.

Because opposites attract, these positive and negative charges hold these components together without the need for a chemical bond. And the little molecule at the bottom anchors the complex to gold foil. This sheet acts as a table to hold the entire complex in one place, in the same way that a solid, flat surface is needed to spin a bottle.

“Normally, if you put a complex like ours with positive and negative charges on a sheet of metal, the charges dissipate,” Hla said. “So we were excited when that didn’t happen here. Our calculations indicated that the atoms in the complex surrounding the europium atom act as an insulator that prevents charges from dissipating to the gold foil.”

The two negatively charged molecules in the complex work together to act as a control unit. To cause rotation, the team applied electric power to a specific point in the complex through the tip of an instrument called a scanning tunneling microscope. This probe not only controls the rotation but can also visualize the complex for study.

At a temperature of 100 Kelvin (minus 208 Fahrenheit), the team’s complex rotates constantly. That rotation stops when they decrease the temperature to an ultracold 5 K. Applying electrical power starts the desired rotation of 60 or 120 degrees, clockwise or counterclockwise, depending on where the electric field is directed.






Rotating complex video. Credit: Argonne National Laboratory.

“Developing, manufacturing and testing this nanoscale complex would not have been possible without the one-of-a-kind instruments at CNM,” Hla said.

In addition, a beamline (XTIP) at the Advanced Photon Source, a DOE Office of Science user facility in Argonne, provided the high-brightness X-ray beam needed to establish that the single europium atom had a positive charge. . “XTIP is the world’s first beamline dedicated to the synchrotron X-ray scanning tunneling microscopy technique,” said Volker Rose, an Argonne physicist with a joint appointment at Ohio University.

“With the XTIP beamline we were able to characterize the elemental and chemical states of the europium-containing molecule,” said assistant physicist Nozomi Shirato. These data established that the single europium atom in the molecule has a positive charge of plus three and does not lose that charge when absorbed on the gold surface. This charge state retention is key to the ability to rotate the molecule.

“Our primary mission is to understand at the atomic level the properties of rare earths, which are critical materials for US industry,” Hla added. “This particular project could have a beneficial impact on many different technologies that now exist or could be developed.”

This research was published in nature communications.

More information:
Tolulope Michael Ajayi et al, Atomically Precise Control of Rotational Dynamics in Charged Rare Earth Complexes on a Metal Surface, nature communications (2022). DOI: 10.1038/s41467-022-33897-3

Citation: Scientists Rotate a Single Molecule Clockwise or Counterclockwise (December 21, 2022) Accessed December 22, 2022 at https://phys.org/news/2022 -12-scientists-molecule-clock-counterclock-demand.html

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