Self-assembly of mixed-metal oxide arrays; biodegradable thin-film devices; hexagonal boron nitride films.
Researchers from North Carolina State University and Iowa State University demonstrated a technique for self-assembling electronic devices. The proof-of-concept work was used to create diodes and transistors with high yield and could be used for more complex electronic devices.
“Our self-assembling approach is significantly faster and less expensive [compared to existing chip manufacturing techniques],” said Martin Thuo, a professor of materials science and engineering at NC State, in a press release. “We’ve also demonstrated that we can use the process to tune the bandgap for semiconductor materials and to make the materials responsive to light – meaning this technique can be used to create optoelectronic devices.”
D-Met fabricated patterns produce components for potential use in microelectromechanical systems (MEMS). (Credit: Julia Chang)
The process, called a directed metal-ligand (D-Met) reaction, starts with liquid metal particles that are placed next to a mold. For their proof-of-concept, the researchers used Field’s metal, an alloy of indium, bismuth, and tin. A solution containing ligands that are made up of carbon and oxygen is poured onto the liquid metal, which harvests ions from the surface of the liquid metal and holds them in a specific geometric pattern.
The solution flows across the liquid metal particles and is drawn into the mold, where the ion-bearing ligands begin assembling themselves into more complex, 3D structures. The structures form an array as the liquid evaporates. The mold is then removed and the array heated to break up the ligands, forming semiconductor metal oxides wrapped in graphene sheets.
“The nature of the D-Met technique means you can make these materials on a large scale – you’re only limited by the size of the mold you use. You can also control the semiconductor structures by manipulating the type of liquid used in the solution, the dimensions of the mold, and the rate of evaporation for the solution,” said Thuo, in the release. “This work demonstrated the creation of transistors and diodes. The next step is to use this technique to make more complex devices, such as three-dimensional chips.” [1]
Researchers from TUD Dresden University of Technology created biodegradable electronic substrates based on the structure of leaves. The method, which the researchers call ‘Leaftronics,’ adapts the quasi-fractal lignocellulose structures in natural leaves, which serve as a scaffold for a leaf’s living cells, to reinforce biodegradable solution-processed polymer films.
The team demonstrated that lignocellulose-reinforced polymer films can withstand the manufacturing process for soldered circuitry and can support thin-film devices like OLEDs. They said that the smoothness of the films enables deposition of ultra-thin layers of materials and allows for high-performance thin-film electronics to be fabricated on the substrates.
“What we see is that the embedded, natural quasi-fractal structure seems to thermomechanically stabilize polymer films without compromising their biodegradability,” said Rakesh Nair, a postdoctoral scientist at TUD, in a statement.
Once the devices have reached the end of their life cycle, the substrates can be easily decomposed in soil or processed in biogas plants, allowing for the extraction of electronic components or precious materials for recycling.
The researchers have also applied the technique to create metallized antimicrobial meshes for water purification. [2]
Researchers from King Abdullah University of Science and Technology (KAUST), Nanyang Technological University, Massachusetts Institute of Technology (MIT), and University of Texas at Austin found a way to grow high-quality films of the 2D insulator hexagonal boron nitride (hBN) which is suitable for industrial-scale production.
The method adapts a chemical vapor deposition (CVD) process that produces hBN on a copper foil by decomposing an ammonia borane precursor. This normally results in triangular islands of hBN, with nitrogen atoms on the edges. But by adding a trace of oxygen during the growth process, the islands form hexagonally, with three nitrogen edges and three boron edges. “Hexagonal islands have fewer defects, making the final film more uniform and reliable,” said Xixiang Zhang, a professor in the Material Science Program at KAUST, in a press release.
The team used the method to grow a 25 x 70 mm film of hBN, and they believe larger areas should be possible. “The process is now limited by the CVD system or substrate size, so it is suitable for industrial production,” said Bo Tian, a postdoctoral researcher at Nanyang Technological University, in a release. The researchers are studying the CVD growth mechanism of hBN in more detail to further increase the film size and quality. [3]
[1] Julia J. Chang et al., Guided Ad infinitum Assembly of Mixed-Metal Oxide Arrays from Liquid Metal. Mater. Horiz., 2024. https://doi.org/10.1039/D4MH01177E
[2] Rakesh R. Nair et al., Leaftronics: Natural lignocellulose scaffolds for sustainable electronics. Sci. Adv. 10, eadq3276 (2024). https://doi.org/10.1126/sciadv.adq3276
[3] Li, J., Samad, A., Yuan, Y. et al. Single-crystal hBN Monolayers from Aligned Hexagonal Islands. Nat Commun 15, 8589 (2024). https://doi.org/10.1038/s41467-024-52944-9
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