News from the NNI Community - Research Advances Funded by Agencies Participating in the NNI

Researchers from Florida State University, the Shanghai Institute of Microsystem and Information Technology, and Wuhan University have revealed how various physical manipulations of graphene, such as layering and twisting, impact its optical properties and conductivity. The researchers found that the optical conductivity of twisted bilayer graphene is not heavily impacted by such manipulations and instead depends more on how the material's geometry structure changes by interlayer twisting. To conduct the study, the team captured images of plasmons – tiny waves of energy that happen when electrons in a material move together – that appeared in various regions of the twisted bilayer graphene.

Researchers from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory, the University of California at Berkeley, the Massachusetts Institute of Technology, Arizona State University, and the National Institute for Materials Science in Tsukuba, Japan, have captured direct images of a new quantum phase of an electron solid – the Wigner molecular crystal. Whereas Wigner crystals are characterized by a honeycomb arrangement of electrons, Wigner molecular crystals have a highly ordered pattern of artificial “molecules” made of two or more electrons. The scientists formed a nanomaterial, called a “twisted tungsten disulfide moiré superlattice,” and doped it with electrons, which filled each 10-nanometer-wide unit cell of the material with just two or three electrons. In a surprising result, these filled unit cells formed an array of moiré electron molecules throughout the superlattice – resulting in a Wigner molecular crystal.  

Researchers from New York University; the Center for Functional Nanomaterials (CFN), a U.S. Department of Energy Office of Science user facility at Brookhaven National Laboratory; and the National Institute for Materials Science in Tsukuba, Japan, have used a special robotic system to assemble very large pieces of atomically clean two-dimensional materials into stacks. These materials, called graphene heterostructures, consist of sheets just a few atoms thick, have record-setting dimensions – as large as 7.5 square millimeters, which is very large in the world of microelectronics. The robotic assembly tool helped the scientists discover a new interface cleaning mechanism that combines mechanical and thermal forces. Overall, this study opens a new opportunity to develop a more effective process to make large and clean layered heterostructure devices.

Researchers from the Massachusetts Institute of Technology and the University of Udine in Italy have created a new type of three-dimensional transistor using a unique set of ultrathin semiconductor materials. It features vertical nanowires only a few nanometers wide, which can deliver performance comparable to state-of-the-art silicon transistors while operating efficiently at much lower voltages than conventional devices. The transistor’s extremely small size would enable more of these 3D transistors to be packed onto a computer chip, resulting in fast, powerful electronics that are also more energy-efficient. “This is a technology with the potential to replace silicon, so you could use it with all the functions that silicon currently has, but with much better energy efficiency,” says Yanjie Shao, the scientist who led this study.

Flame aerosol synthesis is used to create nanoparticles that serve as key ingredients in inks and air filters. While effective, this technique has limitations, including challenges with manipulating the flame, achieving precise control over the size and distribution of nanoparticles, and cost. Two new studies, from researchers at the University at Buffalo; the U.S. Department of Energy’s Lawrence Berkeley National Laboratory, Brookhaven National Laboratory, and Lawrence Livermore National Laboratory; and the National Synchrotron Radiation Research Centre in Taiwan have addressed these shortcomings. The studies center on a unique flame aerosol system that is versatile, easy-to-use and cost-effective. In one of the studies, the system was used to create metal-organic frameworks, which are porous nanomaterials; in the other study, the researchers showed that the system could be used to create high-entropy ceramic nanomaterials.

Cornell University researchers have made headway into understanding how twisted bilayer graphene becomes a superconductor. In 2023, the scientists developed a theoretical formalism to compute the highest possible superconducting transition temperature in any material obtained by stacking and twisting two-dimensional materials. For the current work, the scientists applied this theoretical formalism to twisted bilayer graphene. “One of the remarkable properties of twisted bilayer graphene is the associated tunability,” said Debanjan Chowdhury, one of the scientists involved in this study. “You have unprecedented control over temperature and the twist angle – the tiny electric fields that are applied to switch the material from being an insulator versus a superconductor – making it very easy to explore all sorts of exciting regimes in this material.”

Researchers from Drexel University, the University of Pennsylvania, and Accenture Labs (San Francisco, CA), and Corporal Michael J. Crescenz Veterans Affairs Medical Center (Philadelphia, PA) have built a textile energy grid that can be wirelessly charged. The grid was printed on nonwoven cotton textiles with an ink composed of MXene, a type of nanomaterial that is both conductive and durable enough to withstand the folding, stretching, and washing that clothing endures. The proof-of-concept represents an important development for wearable technology, which, at present, requires complicated wiring and is limited by the use of rigid, bulky batteries that are not fully integrated into garments.

Researchers at William & Mary have measured the strength and stretchability of minuscule nanofibrils present in the silk spun by the southern house spider. The core of a spider silk strand is composed of two distinct warps that form helical loops around a central foundation fiber. The tiniest fibers, nanofibrils, are spun into a mesh that surrounds those supporting structures. The researchers found that the nanofibrils in the southern house spider’s silk could stretch 11 times their original length, more than twice the amount of any spider silk previously tested. "As amazing as spider silk as a whole is, looking at these tiny fibrils, they are even stretchier,” said Hannes Schniepp, one of the scientists involved in this study.

Researchers from Northwestern University and the University of California, Los Angeles, have developed a new strategy that prevents frost formation before it begins. The researchers discovered that tweaking the texture of any surface and adding a thin layer of graphene oxide prevents frost from forming on the surface for one week, or potentially even longer. This is 1,000 times longer than current, state-of-the-art anti-frosting surfaces. As an added bonus, the new scalable surface design also is resistant to cracks, scratches, and contamination.

Researchers at the Massachusetts Institute of Technology have designed tiny particles that can be implanted at a tumor site, where they deliver two types of therapy: heat and chemotherapy. In a study of mice, the researchers showed that this therapy completely eliminated tumors in most of the animals and significantly prolonged their survival. To create a microparticle that could deliver both of these treatments, the researchers combined an inorganic material called molybdenum disulfide nanosheets with one of two drugs: doxorubicin or violacein. To make the particles, molybdenum disulfide and the drug are mixed with a polymer called polycaprolactone and then dried into a film that can be pressed into microparticles of different shapes and sizes. Once injected into a tumor site, the particles remain there throughout the treatment, and an external near-infrared laser is used to heat up the particles.