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Physicists Create One-Dimensional Noble Gas

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Using advanced transmission electron microscopy (TEM) methods, physicists at the University of Nottingham have successfully trapped atoms of krypton inside a carbon nanotube to form a one-dimensional gas.

Cardillo-Zallo et al. report on a nanoscale system consisting of endohedral fullerenes encapsulated within single-walled carbon nanotubes, capable of the delivery and release of krypton atoms on-demand, via coalescence of host fullerene cages under the action of the electron beam (in situ) or heat (ex situ). Image credit: Cardillo-Zallo et al., doi: 10.1021/acsnano.3c07853.

The behavior of atoms has been studied by scientists ever since it was hypothesized that they are the basic units of the Universe.

The movement of atoms has significant impact on fundamental phenomena such as temperature, pressure, fluid flow and chemical reactions.

Traditional spectroscopy methods can analyze the movement of large groups of atoms and then use averaged data to explain phenomena at the atomic scale.

However, these methods don’t show what individual atoms are doing at a specific point in time.

The challenge physicists face when imaging atoms is that they are very small, ranging from 0.1-0.4 nm, and they can move at very high speeds of around 400 m/s in the gas phase, on the scale of the speed of sound.

This makes the direct imaging of atoms in action very difficult, and the creation of continuous visual representations of atoms in real-time remains one of the most significant scientific challenges.

“Carbon nanotubes enable us to entrap atoms and accurately position and study them at the single-atom level in real-time,” said University of Nottingham’s Professor Andrei Khlobystov.

“For instance, we successfully trapped noble gas krypton (Kr) atoms in our study.”

“Because krypton has a high atomic number, it is easier to observe in a TEM than lighter elements. This allowed us to track the positions of krypton atoms as moving dots.”

“We used our state-of-the-art SALVE TEM, which corrects chromatic and spherical aberrations, to observe the process of krypton atoms joining together to form krypton pairs,” said University of Ulm’s Professor Ute Kaiser.

“These pairs are held together by the van der Waals interaction, which is a mysterious force governing the world of molecules and atoms.”

“This is an exciting innovation, as it allows us to see the van der Waals distance between two atoms in real space.”

“It’s a significant development in the field of chemistry and physics that can help us better understand the workings of atoms and molecules.”

The study authors utilized buckminsterfullerenes, which are football-shaped molecules consisting of 60 carbon atoms, to transport individual krypton atoms into test nanotubes.

The coalescence of buckminsterfullerene molecules to create nested carbon nanotubes helped to improve the precision of the experiments.

“Krypton atoms can be released from the fullerene cavities by fusing the carbon cages,” said Ian Cardillo-Zallo, a Ph.D. student at the University of Nottingham.

“This can be achieved by heating at 1,200 degrees Celsius or irradiating with an electron beam.”

“Interatomic bonding between krypton atoms and their dynamic gas-like behavior can both be studied in a single TEM experiment.”

The team was able to directly observe krypton atoms exiting fullerene cages to form a one-dimensional gas.

Once freed from their carrier molecules, krypton atoms can only move in one dimension along the nanotube channel due to the extremely narrow space.

The atoms in the row of constrained krypton atoms cannot pass each other and are forced to slow down, like vehicles in traffic congestion.

The scientists captured the crucial stage when isolated krypton atoms transition to a 1D gas, causing single-atom contrast to disappear in the TEM.

Nonetheless, the complementary techniques of scanning TEM (STEM) imaging and electron energy loss spectroscopy (EELS) were able to trace the movement of atoms within each nanotube through the mapping of their chemical signatures.

“By focusing the electron beam to a diameter much smaller than the atomic size, we are able to scan across the test nanotube and record spectra of individual atoms confined within, even if these atoms are moving,” said Professor Quentin Ramasse, Director of SuperSTEM, an EPSRC National Research Facility.

“This gives us a spectral map of the one-dimensional gas, confirming that the atoms are delocalized and fill all available space, as a normal gas would do.”

“As far as we know, this is the first time that chains of noble gas atoms have been imaged directly, leading to the creation of a one-dimensional gas in a solid material,” said University of Nottingham’s Professor Paul Brown.

“Such strongly correlated atomic systems may exhibit highly unusual heat conductance and diffusion properties.”

“Transmission electron microscopy has played a crucial role in understanding the dynamics of atoms in real-time and direct space.”

The findings appear in the journal ACS Nano.

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Ian Cardillo-Zallo et al. Atomic-Scale Time-Resolved Imaging of Krypton Dimers, Chains and Transition to a One-Dimensional Gas. ACS Nano, published online January 22, 2024; doi: 10.1021/acsnano.3c07853

Source : Breaking Science News

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