2D material in three dimensions — ScienceDaily

The carbon material graphene does not have a well-defined thickness, it simply consists of a single layer of atoms. It is therefore often referred to as a “two-dimensional material”. Trying to make it a three-dimensional structure may seem contradictory at first, but it is an important objective: if we want to exploit the properties of the graphene layer as well as possible, then we must integrate as much active surface as possible in limited volumes.

The best way to achieve this goal is to produce graphene on complex branched nanostructures. This is exactly what a cooperation between CNR Nano in Pisa, TU Wien (Vienna) and the University of Antwerp has achieved. This could help, for example, to increase the storage capacity per volume of hydrogen or to build chemical sensors with higher sensitivity.

From solid to porous

In the group of Professor Ulrich Schmid (Institute for Sensor and Actuator Systems, TU Wien), research has been carried out for years on how to transform solid materials such as silicon carbide into extremely fine porous structures in a precisely controlled manner. . “If you can control the porosity, many different material properties can be influenced by it,” says Georg Pfusterschmied, one of the authors of the current paper.

The technological procedures required to achieve this goal are challenging: “It is an electrochemical process that consists of several steps,” says Markus Leitgeb, a chemist who also works in Ulrich Schmid’s research group at TU Vienna. “We work with very specific etching solutions and apply tailor-made electric current characteristics in combination with UV irradiation.” This makes it possible to etch tiny holes and channels in certain materials.

Because of this expertise in making porous structures, Stefan Heun’s team from the Nanoscience Institute of the Italian National Research Council CNR turned to their colleagues at TU Wien. Pisa’s team was looking for a method to produce graphene surfaces in branched nanostructures to enable larger graphene surfaces. And the technology developed at TU Wien is perfectly suited for this task.

“The starting material is silicon carbide – a crystal of silicon and carbon,” explains Stefano Veronesi, who carried out the growth of graphene at CNR Nano in Pisa. “If you heat this material, the silicon evaporates, the carbon remains, and if you do it right, it can form a layer of graphene on the surface.”

An electrochemical etching process has therefore been developed at TU Wien which transforms solid silicon carbide into the desired porous nanostructure. About 42% of the volume is removed during this process. The remaining nanostructure was then heated under a high vacuum in Pisa so that graphene formed on the surface. The result was then examined in detail in Antwerp. This revealed the success of the new process: indeed, a large number of graphene flakes form on the surface with complex shapes of the 3D nanostructure.

Lots of surface in a compact form

“This allows us to use the advantages of graphene much more efficiently,” says Ulrich Schmid. “The original motivation for the research project was to store hydrogen: you can temporarily store hydrogen atoms on graphene surfaces and then use them for various processes. The larger the surface, the more hydrogen you can store is important.” But there are also many other ideas for using such 3D graphene structures. A large surface area is also a decisive advantage in chemical sensors, which can be used, for example, to detect rare substances in gases.

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Material provided by Vienna University of Technology. Note: Content may be edited for style and length.

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