The experiments conducted at TU Wien lie in this complicated in-between world: Extremely little pieces of gold, including a couple of thousand atoms and with a size in the order of ten nanometres, are bombarded with extremely charged ions. This makes it possible to alter the sizes and shape of these gold pieces in a targeted manner. The outcomes reveal: What happens in the procedure can not merely be imagined like the impact of a golf ball in a sand bunker– the interaction of ion and gold piece is a lot more subtle.
Energy transferred by ion bombardment
” We work with multiply-ionized xenon atoms. Approximately 40 electrons are eliminated from these atoms, so they are extremely electrically charged,” states Prof. Richard Wilhelm from the Institute of Applied Physics at TU Wien. These extremely charged ions then struck small gold islands put on an insulating substrate– and after that different things can take place: The gold islands might end up being flatter, they can melt, they can even evaporate. “Depending on how extremely our ions are electrically charged, we can set off various effects,” says Gabriel Szabo, first author of the current research study, who is presently dealing with his argumentation in Richard Wilhelms group.
The extremely charged ions hit the small gold nuggets at raised speed– at around 500 kilometers per second. It is remarkably not the force of the effect that alters the gold islands. The process is entirely various from the effect of a golf ball in a stack of sand, or the accidental effect of a tennis ball in a well embellished birthday cake.
” If you shoot uncharged xenon atoms at the gold islands with the same kinetic energy, the gold islands remain virtually unchanged,” states Gabriel Szabo. “So the definitive factor is not the kinetic energy, however the electrical charge of the ions. This charge also carries energy, and it is transferred exactly at the point of effect.”
Changes in the electronic structure
As soon as the exceptionally strongly favorably charged ions struck the nano gold piece, they snatch electrons away from the gold. In a large piece of gold, this would have no substantial impact: Gold is an exceptional conductor, the electrons can move freely, and more electrons would be supplied from other locations of the gold nugget.
” The charge energy of the affecting ion is transferred to the gold, hence the electronic structure of the entire nano-gold things is tossed totally out of balance, the atoms begin to move and the crystal structure of the gold is destroyed,” describes Richard Wilhelm. “Depending on just how much energy you deposit, it might even happen that the whole nano-gold piece melts or is vaporised.”
The results of the ion bombardment can then be studied in an atomic force microscopic lense: Depending on the charge of the ions, the height of the gold pieces is reduced to a lower or greater degree, Gabriel Szabo reports: “Just as our models had actually also anticipated, we can control the impact of the ions on the gold– and not by the speed we give our projectiles, however rather by their charge.”
Improved control and deeper understanding of such processes is necessary for making a variety of nanostructures. “Its a method that allows you to selectively modify the geometry of especially small structures. Thats simply as intriguing for the production of microelectronic components as it is for so-called quantum dots– small structures that enable extremely specific custom-made electronic or optical impacts due to their quantum physical properties,” says Richard Wilhelm.
And it is another insight into the world of small however not yet small things– into the multifaceted intermediate world between quantum physics and solid-state physics, which can just be comprehended by keeping quantum and many-particle phenomena in mind at the same time.
Recommendation: “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.
While nano gold structures can no longer be regarded as an inexhaustible tank of electrons, larger gold structures can take on brand-new electrons to change those that are lost.
These extremely charged ions then struck little gold islands placed on an insulating substrate– and then various things can happen: The gold islands may become flatter, they can melt, they can even evaporate.” If you shoot uncharged xenon atoms at the gold islands with the very same kinetic energy, the gold islands remain almost unchanged,” says Gabriel Szabo. As quickly as the extremely highly favorably charged ions struck the nano gold piece, they snatch electrons away from the gold. In a large piece of gold, this would have no substantial result: Gold is an excellent conductor, the electrons can move easily, and more electrons would be supplied from other areas of the gold nugget.
Highly charged ions struck tiny gold nuggets on an insulating surface. Credit: ucyborg.com/studio
Tiny structures made of gold can be particularly controlled by ion barrage at the Vienna University of Technology (TU Wien)– surprisingly, the definitive factor is not the force of the effect.
Scientists at TU Wien have actually discovered a way to control the geometry of small gold particles by bombarding them with extremely charged ions. While nano gold structures can no longer be regarded as an inexhaustible tank of electrons, bigger gold structures can take on brand-new electrons to change those that are lost.
Usually, we need to decide in physics: Either we handle big things– such as a metal plate and its product properties, or with tiny things– such as private atoms. There is also a world in between: The world of small but not yet tiny things, in which both results of the macroscopic world and impacts of the tiny world play a function.
