Researchers are investigating new ways of artificially assembling two-dimensional (2D) materials and identifying so-called 2.5D materials (A new era of 2.5D materials) with unique physical properties. Japanese researchers researched the latest developments and applications of 2.5D materials in the journal Science and Technology of Advanced Materials.
“The 2.5D concept symbolizes the freedom of composition, materials, angles and space commonly used in 2D materials research,” explains Hiroki Ago, a scientist and lead author of nanomaterials at Kyushu University in Japan. 2D materials, such as graphene, consist of a layer of atoms and are used in applications such as flexible touch panels, integrated circuits and sensors.
Recently, new methods have been introduced that allow the artificial stacking of 2D materials vertically, in a plane or at rotated angles, regardless of their composition and structure. This is due to the ability to control Van der Waals forces: weak electrical interactions between atoms and molecules, similar to attracting dust to a microfiber cloth. It is now also possible to integrate 2D materials with other material dimensions, such as ions, nanotubes and bulk crystals.
The most common method of producing 2.5D materials (A new era of 2.5D materials) is chemical vapor deposition (CVD), which applies one layer, one atom or molecule at a time to a solid surface. Commonly used building blocks for 2.5D materials include graphene, hexagonal boronitride (hBN) (a compound used in cosmetics and aviation) and transition metal dichalcogenides (TMDC) (nanolayer semiconductor).
Using the CVD method, the researchers selected a bilayer of graphene, the simplest form of a 2.5D material (A new era of 2.5D materials), using a copper-nickel foil with a relatively high concentration of nickel as a catalyst. Thanks to nickel, carbon is highly soluble, which gives researchers more control over the number of graphene layers. When the electric field is placed vertically over two layers of graphene, a hole in the strip opens, which means that its conductivity can be turned on and off. This is a phenomenon that is not observed with single-layer graphene because it has no bandgap and always persists. By tilting the stacking angle by one degree, the researchers found that the material had become superconducting.
Similarly, another group in the United Kingdom and the United States found that a layer of graphene and hBN results in a quantum Hall effect, a conductive phenomenon with a magnetic field that creates potential differences. Others have shown that accumulations of TMDC excitons (electrons associated with their other holes in the color state) capture overlapping lattice patterns. This can lead to applications in storage devices. New robotic assembly techniques also make it possible to create more complex vertical structures, including a layered heterostructure consisting of, for example, 29 alternating layers of graphene and hBN. Some studies have used nanospaces created between layers of 2.5D material to penetrate molecules and ions to improve the electrical, magnetic and optical properties of the host material.
To date, for example, scientists have found that graphene disrupts ferric chloride when inserted between its stacked layers, while the penetration of lithium ions leads to a faster rate of dispersion (how much faster the molecules disperse in one place) than graphite. electric conductor. used in batteries. This means that the material can be used in high-performance rechargeable batteries.
In addition, the researchers found that the penetration of aluminum chloride molecules between two graphene plates leads to the formation of new crystal structures that are completely different from the bulk crystals of aluminum chloride. More research is needed to understand why this is happening and what applications it may have. “There are many opportunities to explore this new 2.5D concept,” Ago said.
Future applications of 2.5D materials include solar cells, batteries, flexible devices, quantum devices and very low power devices.
The next steps should include machine learning, in-depth learning and materials informatics to further improve the design and synthesis of 2.5D materials.
