Materials that consist of multiple ultra-thin layers are an exciting new area of research.
Scientists have investigated a combination of graphene andmolybdenum disulfide. Two layers of material come into contact and then adhere to each other under the influence of weak van der Waals forces. Graphene is a very good conductor, molybdenum disulfide is a semiconductor, and this combination could be interesting for the production of new types of storage devices, scientists say.
However, for certain applications, the geometrythe material must be specially processed at the nanometer scale - for example, to alter chemical properties by adding additional types of atoms or to control the optical properties of a surface. Surfaces can be modified using an electron beam or conventional ion beam. However, in a two-layer system, there is always a problem - the ion beam acts on both layers simultaneously, even if in the problem it is worth changing only one layer.
When an ion beam is used for surface treatment, usually the impact force of the ions will affect the material. However, the scientists' new method uses relatively slow ions that are multiply charged.
“Here it is necessary to distinguish between two different formsenergy. On the one hand, there is kinetic energy, which depends on the speed at which the ions impact the surface. On the other hand, there is potential energy, which is determined by the electrical charge of the ions. In ion beams, kinetic energy plays a decisive role, but for scientists it is potential energy that is especially important.
There is an important difference between these twoforms of energy: while kinetic energy is released in both layers of a material when penetrating a layer system, potential energy can be distributed very unevenly between the layers.
Molybdenum disulfide reacts very strongly tohighly charged ions. A single ion entering this layer can remove tens or hundreds of atoms from the layer. Only a hole remains, which is very clearly visible under an electron microscope. On the other hand, the graphene layer, into which the projectile hits immediately after impact, remains intact: most of the potential energy has already been released.
The same experiment can also be reversed. The strongly charged ion first hits the graphene and then onto the molybdenum disulfide layer. In this case, both layers remain intact: graphene provides the ion with the electrons needed to electrically neutralize it in a fraction of a second. The electron mobility in graphene is so high that the impact point also immediately “cools down”. The ion traverses the graphene layer without leaving a permanent trail. After that, it can no longer cause significant damage to the molybdenum disulfide layer.
This gives scientists a new method of targetedcontrol surfaces. Now it is possible to add nanopores on the surface without damaging the substrate material underneath. This will help you create geometric structures that were previously impossible. You can create "masks" of molybdenum disulfide, perforated exactly as desired, to which certain metal atoms are then deposited. This opens up completely new possibilities for monitoring the chemical, electronic and optical properties of surfaces.
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