Nano Gold Nuggets Melted by Extremely Charged Ions Reveal a New World Between Macroscopic and Microscopic Physics


Highly Charged Ions Hit Tiny Gold Nuggets

Extremely charged ions hit tiny gold nuggets on an insulating floor. Credit score:

Tiny buildings manufactured from gold may be particularly manipulated by ion bombardment on the Vienna College of Know-how (TU Wien) – surprisingly, the decisive issue will not be the drive of the influence.

Researchers at TU Wien have discovered a method to management the geometry of tiny gold particles by bombarding them with extremely charged ions. By altering the dimensions and form of the particles, the researchers say it’s doable to create new sorts of nanostructures, together with quantum dots. The extremely charged ions knock electrons away from the gold, altering the particles’ digital buildings and inflicting their atoms to maneuver. Whereas nano gold buildings can not be considered an inexhaustible reservoir of electrons, bigger gold buildings can tackle new electrons to interchange these which are misplaced.

Usually, we’ve to select in physics: Both we take care of massive issues – resembling a steel plate and its materials properties, or with tiny issues – resembling particular person atoms. However there may be additionally a world in between: The world of small however not but tiny issues, during which each results of the macroscopic world and results of the microscopic world play a job.

The experiments performed at TU Wien are situated on this difficult in-between world: Extraordinarily small items of gold, consisting of some thousand atoms and with a diameter within the order of ten nanometres, are bombarded with extremely charged ions. This makes it doable to vary the form and dimension of those gold items in a focused method. The outcomes present: What occurs within the course of can not merely be pictured just like the influence of a golf ball in a sand bunker — the interplay of ion and gold piece is far more delicate.

Vitality transferred by ion bombardment

“We work with multiply-ionized xenon atoms. As much as 40 electrons are faraway from these atoms, so they’re extremely electrically charged,” says Prof. Richard Wilhelm from the Institute of Utilized Physics at TU Wien. These extremely charged ions then hit small gold islands positioned on an insulating substrate – after which various things can occur: The gold islands might change into flatter, they’ll soften, they’ll even evaporate. “Relying on how extremely our ions are electrically charged, we will set off completely different results,” says Gabriel Szabo, first writer of the present examine, who’s at present engaged on his dissertation in Richard Wilhelm’s group.

The extremely charged ions hit the tiny gold nuggets at elevated velocity — at round 500 kilometers per second. Nonetheless, it’s remarkably not the drive of the influence that modifications the gold islands. The method is totally completely different from the influence of a golf ball in a pile of sand, or the unintended influence of a tennis ball in a properly embellished birthday cake.

“In case you shoot uncharged xenon atoms on the gold islands with the identical kinetic power, the gold islands stay virtually unchanged,” says Gabriel Szabo. “So the decisive issue will not be the kinetic power, however the electrical cost of the ions. This cost additionally carries power, and it’s deposited precisely on the level of influence.”

Adjustments within the digital construction

As quickly because the extraordinarily strongly positively charged ions hit the nano gold piece, they snatch electrons away from the gold. In a big piece of gold, this could haven’t any important impact: Gold is a superb conductor, the electrons can transfer freely, and extra electrons could be provided from different areas of the gold nugget. However the nano-gold buildings are so small that they’ll not be considered an inexhaustible reservoir of electrons. It’s exactly right here that one enters the intermediate world between macroscopic steel and tiny atomic clusters and their

The effects of the ion bombardment can then be studied in an atomic force microscope: Depending on the charge of the ions, the height of the gold pieces is reduced to a lesser or greater extent, Gabriel Szabo reports: “Just as our models had also predicted, we can control the impact of the ions on the gold —  and not by the speed we give our projectiles, but rather by their charge.”

Improved control and deeper understanding of such processes is important for making a wide variety of nanostructures. “It’s a technique that allows you to selectively edit the geometry of particularly small structures. That’s just as interesting for the creation of microelectronic components as it is for so-called quantum dots — tiny structures that allow very specific tailor-made electronic or optical effects due to their quantum physical properties,” says Richard Wilhelm.

And it is another insight into the world of small but not yet tiny things — into the multifaceted intermediate world between quantum physics and solid-state physics, which can only be understood by keeping quantum and many-particle phenomena in mind at the same time.

Reference: “Charge-State-Enhanced Ion Sputtering of Metallic Gold Nanoislands” by Gabriel L. Szabo, Benedykt R. Jany, Helmut Muckenhuber, Anna Niggas, Markus Lehner, Arkadiusz Janas, Paul S. Szabo, Ziyang Gan, Antony George, Andrey Turchanin, Franciszek Krok and Richard A. Wilhelm, 22 March 2023, Small.
DOI: 10.1002/smll.202207263

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