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6 NEUTRONS VERIFY NEW TOPOLOGICAL MATERIAL A team led by researchers at the University of California, Los Angeles re- cently discovered the first intrinsic fer- romagnetic topological insulator—and the scientists have now used neutrons at the DOE’s Oak Ridge National Labo- ratory (ORNL), Tenn., to help verify their finding. Topological insulators act as insulators on the inside while allowing electrons to flow across their surfac- es. Their ferromagnetic counterparts are not as well known, but are thought to hold useful properties for quantum technology. The researchers discovered the new topological insulator—consisting of manganese, bismuth, and tellurium atoms—by stacking ferromagnetic mo- lecular layers. To confirm the material’s intrinsic nature, they used the High Flux Isotope Reactor at ORNL. “Neutron dif- fraction’s high contrast can distinguish magnetic manganese atoms from oth- ers,” says ORNL’s Huibo Cao, co-author on the study. “It is well-suited for the new two-dimensional material and its magnetism.” ucla.edu , ornl.gov. RESEARCH TRACKS SCIENTISTS FINE- TUNE HYBRID PEROVSKITES Researchers from MIT, Cambridge, Mass., and Northwestern Uni- versity, Evanston, Ill., worked together to fine- tune the electronic prop- erties of hybrid per- ovskite materials. The materials are considered hybrid because they con- tain inorganic compo- nents like metals, plus organic molecules with elements such as carbon and nitrogen, organized into nanoscale layers. The team showed that by vary- ing the composition of the organic lay- ers, they could tune the color of light absorbed by the perovskite as well as the wavelength at which the material emitted light. “Until now, most exper- imental and theoretical evidence indi- cated that the organic layers simply act as inert spacers whose only role is to separate the electronically active inor- ganic layers,” says Professor Will Tisdale of MIT. “These new results show that we can teach the organic layer to do much more.” Perovskites, first discovered as naturally occurring minerals in the Ural Mountains nearly 200 years ago, have been thoroughly investigated after it was determined they could turn light into usable electricity. How- ever, perovskite solar cells are far less dura- ble and stable than sil- icon-based versions in outdoor conditions due to their sensitivity to heat and moisture. Scien- tists recently found that splitting the traditional 3D structure of perovskites into many thin layers— ranging from a few atoms to dozens— improves stability and performance. In layered perovskites, the inorganic lay- er absorbs light and produces charges that are required to produce electrical energy. The organic layers are typically insulating and act like walls, preventing the light-generated charges from mov- ing out of the inorganic layer. The Northwestern-MIT collabo- ration began after a chance encounter at a 2018 conference. The Stupp labo- ratory at Northwestern had previous- ly performed pioneering work on the synthesis of inorganic-organic hybrid materials for potential applications in energy and medicine, while MIT’s Tis- dale group specializes in using lasers to probe the properties of nanomaterials. These interests overlapped perfectly, as the Stupp group developed the hy- brid perovskite structures and the Tis- dale group performed the spectroscop- ic measurements necessary to confirm the interactions within the systems. In the future, the ability to fine-tune the electronic properties of these materi- als could be applied to various optical or electronic sensors as well as solar cells and light detectors. web.mit.edu , northwestern.edu. Researchers performed single-crystal neutron diffraction using the HB-3A four circle diffractometer to confirm the first intrin- sic ferromagnetic topological insulator. Courtesy of Genevieve Martin/ORNL. 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 0 Left: Scanning electron microscope image of film fragments. Right: Elemental mapping indicates creation of hybrid perovskites. Courtesy of MIT .