How to fire projectiles through materials without breaking anything
Graphical abstract. Credit: Nano Letters (2022). DOI: 10.1021/acs.nanolett.2c03894

Spectacular micro-explosions can happen when charged particles are shot through thin layers of material. The reasons for this have been explained.

It sounds like a trick, but some materials can be shot through without holes. It is possible at the level of individual particles. In the last few years, different research groups have conducted different experiments with different results.

There is a detailed explanation of why some materials and others are different. For the processing of thin membranes, which are supposed to have tailor-madenano-pores in order to trap, hold or let through very specific atoms or Molecules, this is interesting.

Graphene is one of the ultra-thin materials.

Prof. Lemell says that there is a wide range of ultrathin materials that only have a few atomic layers. Graphene is a material made of a single layer of carbon atoms. Molybdenum disulfide is one of the ultrathin materials being researched today.

In Prof. Friedrich Aumayr's research group at the Institute of Applied Physics, such materials are bombarded with highly charged ion projectiles. They strip noble gases of their electrons by taking atoms. The ion with 30 to 40 times the electrical charge is created. The high energy ion particles hit the thin layer of material.

According to Anna Niggas, an experimental physicist at the Institute of Applied Physics, this results in different effects depending on the material. A hole with a diameter of a few nanometers is formed when the materiallayer around the impact site is completely destroyed.

The electron's speed.

When an ion hits the material, it attracts a larger amount of electrons and takes them with it. The material layer has a positive charged region left.

The effect is dependent on how fast electrons can move. The electron mobility of graphene is very high. There is a local positive charge that can be balanced quickly. The electrons flow in from somewhere else.

The electrons can't be supplied in time from outside to the impact site in other materials. At the impact site, the positively charged atoms from which the projectile has taken their electrons, repel each other, they fly away.

The model we have developed allows us to estimate well in which holes are formed and in which they are not, and this depends on the electron mobility in the material and the charge state of the projectile.

The model shows that the high speed of the projectile doesn't matter to the atoms that are knocked out of the material. In this process, not all of the electric repulsion is transferred to the sputtered atoms, but a large portion of the energy is absorbed in the remaining material.

The simulations and the experiments were done in Austria. The resulting deeper understanding of atomic surface processes can be used to tailor membranes. One can build amolecular sieve or hold certain atoms in a controlled way. It's possible to use such materials to remove CO 2 from the air. We now have control over the manipulation of materials at the atomic level. "This provides a whole new tool for manipulating ultrathin films in a precise way for the first time."

Alexander Sagar Grossek and his team created a model for the formation of apores in two-dimensional materials. The title is "acs.nanolett.2c03894."

Journal information: Nano Letters