8 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 | J A N U A R Y / F E B R U A R Y 2 0 2 3 According to the researchers, they expected MAPbI3 to behave like an insulator when they exposed it to terahertz light. What they found, however, was that there was a lot of variation in light scattering along the boundary between the grains. This wide variation sheds light on the material’s degradation problem, and the findings could be useful for improving and manipulating it in the future. “We believe that the present study demonstrates a powerful microscopy tool to visualize, understand, and potentially mitigate grain boundary degradation, defect traps, and materials degradation,” says Wang. “A better understanding of these issues may enable developing highly efficient perovskite-based photovoltaic devices for many years to come.” ameslab.gov. TESTING | CHARACTERIZATION LAW OF FRICTION DISCOVERY A new method to measure the interfacial shear between two atomic layers was established by researchers at New York University’s Tandon School of Engineering. The findings also uncovered that the measured quantity is inversely related to friction, following a new law. The researchers say their work could lead to more efficient manufacturing processes, greener vehicles, and an overall more sustainable world. Studying bulk graphite and epitaxial graphene films grown with different stacking orders and twisting, researchers measured the hard-to-access interfacial transverse shear modulus of an atomic layer on a substrate. Results revealed that the modulus is largely controlled by the stacking order and the atomic layer-substrate interaction and demonstrated its importance in controlling and predicting sliding friction in supported 2D materials. The experiments showed a general reciprocal relationship between friction force per unit contact area and interfacial shear modulus for all the graphite structures the scientists investigated. “The interaction between a single atomic layer of a material and its substrate governs its electronic, mechanical, and chemical properties,” explains lead researcher Elisa Riedo. “Gaining insight into that topic is important, on both fundamental and technological levels, in finding ways to reduce the energy loss caused by friction. Our results can be generalized to other 2D materials as well,” Riedo continues. “This presents a way to control atomic sliding friction and other interfacial phenomena, and has potential applications in miniaturized moving devices, the transportation industry, and other realms.” engineering.nyu.edu. NEW MICROSCOPE EXAMINES SOLAR CELL MATERIAL A new characterization tool developed by researchers at the DOE’s Ames National Lab in Iowa is helping scientists gain insight into a possible alternative material for solar cells. The research team, led by senior scientist Jigang Wang, developed a microscope that uses terahertz waves to collect data on material samples. The team then used their microscope to explore methylammonium lead iodide (MAPbI3) perovskite, a material that could potentially replace silicon in solar cells. The main challenge to using MAPbI3 for this application is that it degrades easily when exposed to elements like heat and moisture. Triangular holes make this material more likely to crack from left to right. Courtesy of N.R. Brodnik et al./Phys. Rev. Lett. 9T Labs AG, Zurich, is collaborating with Purdue University, West Lafayette, Ind., to research and test the potential to build structural aerospace composite applications at scale with 9T’s additive fusion technology. Purdue’s Composite Manufacturing and Simulation Center will provide the tools and resources to analyze, simulate, and test composite performance. 9tlabs.com. BRIEF In this artistic rendering of how atomic shear is measured, a nanoscale tip pulls atoms so they slide on top of others. Courtesy of Martin Rejhon. In this visualization of a microscope tip exposing material to terahertz light, the colors on the material represent the lightscattering data, while the red and blue lines represent terahertz waves.
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