A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 2 2 1 3 NEW ERA OF 2.5D MATERIALS Nanomaterials researchers at Kyushu University in Japan are investigating new ways to artificially stack 2D materials, introducing so-called 2.5D materials with unique physical properties. A common method for fabricating 2.5D materials is chemical vapor deposition (CVD). Routinely used building blocks for 2.5D materials include graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenides (TMDCs). Using the CVD method, researchers selectively synthesized a bilayer of graphene, the simplest form of a 2.5D material, using a copper-nickel foil with relatively high nickel concentration as a catalyst. When an electrical field was applied vertically across the bilayer of graphene, it opened a band gap, meaning that its conductivity can be turned on and off. This is a phenomenon that is not observed in monolayer graphene because it has no band gap and stays on all the time. By tilting the stacking angle one degree, scientists found that the material became superconducting. Future applications of 2.5D materials include solar cells, batteries, flexible devices, quantum devices, and devices with very low energy consumption. The next steps will utilize machine learning to further advance the design and synthesis of 2.5D materials. www.kyushu-u.ac.jp/en/. PREDICTING MATERIAL EFFECTIVENESS Penn State, State College, researcher and materials science pro- fessor Zi-Kui Liu, FASM, developed a new cross phenomena theory that goes beyond the phenomenological scientific approach, where observations in experiments are made to describe the relationship of phenomena to each other based on what is observed. The new theory involves what Liu calls zen- tropy theory. Zentropy considers how entropy occurs over multiple scales within a system by integrating quantum mechanics, statistical mechanics, and experimental measurements of thermodynamics. This novel theory of cross EMERGING TECHNOLOGY Natron Energy Inc., Santa Clara, Calif., and Clarios International Inc., Milwaukee, are collaborating to manufacture the first mass-produced sodium-ion batteries with production to begin in 2023. Natron’s batteries are now used in data centers and telecom networks. Future applications may include electric vehicles and grid energy storage. www.natron.energy. BRIEF phenomena can be used by researchers to guide experimental discovery and provide a theoretical understanding of experimental observations. According to Liu, this could enable researchers to predict the best ways to develop new materials with emergent behavior via quantum mechanics and statistical mechanics. Emergent behavior in a system refers to characteristics of the whole that are greater than the sum of its parts. Liu pointed to one example based on an ultrasound transducer— the hand-held part of an ultrasound machine—that is used to detect a fetal heartbeat in the womb. The next step will be researching how this novel theory of cross phenomena can be used as a predictive tool to enable more efficient discovery of materials with emergent behaviors including superconductivity, ferroelectricity, and ferromagnetismfor applications in energy conversion, refrigeration, and sensors. psu.edu. Using a stacking method, it is now possible to create 2.5D materials with unique physical properties that can be used in solar cells and quantum devices. Heat from the Sun results in various examples of cross-phenomena such as evaporation of water and photosynthesis for growth of trees and crops. Courtesy of Elizabeth Flores-Gomez Murray. Cross-phenomena Zentropy
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