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 | A P R I L 2 0 2 1 7 PROCESS TECHNOLOGY ONE-STEP METAMATERIALS PROCESS While studying a thin-film material called strontium stannate (SrSnO3), researchers at the University of Minnesota Twin Cities, Minneapolis, discovered a groundbreaking one-step process for creating metamaterials. They demonstrated the realistic possibility of designing similar self-assembled structures with the potential of creating built-to-order nanostructures with wide applications in electronics and optical devices. In the new work, researchers studied a thin-film material called strontium stannate. During their research, they noticed the surprising formation of checkerboard patterns at the nanoscale similar to the metamaterial structures fabricated in the costly, multistep process. “At first we thought this must be a mistake, but soon realized that the periodic pattern is a mixture of two phases of the same material with different crystal structures,” says researcher Bharat Jalan. The material had spontaneously organized into an ordered structure as it changed from one phase to another. During a first-order structural phase transition process, the material moved into a mixed-phase in which some parts of the system completed the transition and others did not. The team then demonstrated a process for the first-ever self- assembled, tunable nanostructure to create metamaterials in just one step. They were able to tune the ability to store electrical charge property within a single film using temperature and laser wavelength, effectively creating a variable photonic crystal material with 99% efficiency. Using high-resolution electron microscopes, the researchers confirmed the unique structure of the material. They are now looking to future applications for their discovery in optical and electronic devices. twin-cities.umn.edu. GRAPHENE FUNCTIONALIZATION An international research team has demonstrated a new pro- cess to modify the structure and properties of graphene. This chem- ical reaction, photocycloaddition, modifies the bonds between atoms using ultraviolet light. Although graphene has outstanding physical, optical, and mechanical properties, it currently has limited use in electronics. “No other material has properties similar to graphene, yet unlike semiconductors used in electronics, it lacks a band gap. In electronics, this gap is a space in which there are no energy levels that can be occupied by electrons. Yet it is essential for interacting with light,” says Professor Federico Rosei of the Institut National de la Recherche Scientifique’s (INRS) Énergie Matériaux Télécommunications Research Centre in Quebec City, Canada. The multidisciplinary group of researchers from Canada, China, Denmark, France, and the U.K. succeeded in modifying graphene so as to create a band gap. According to Rosei, current research is rather fundamental but could have repercussions over the next few years in optoelectronics, such as in the fabrication of photodetectors or in the field of solar energy. “These include the manufacture of high-performance photovoltaic cells for converting solar energy into electricity, or the field of nanoelectronics, for the extreme miniaturization of devices,” he added. www. inrs.ca/en. Checkerboard patterns surprisingly formed at the nano scale of thin films, similar to structures fabricated in costly, multistep processes. Courtesy of Jalan Group/University of Minnesota. Researchers from Kanazawa University, Japan, report a major improvement in recovering silver and palladium ions from aqueous acidic waste. Recovery of the metals in elemental, metallic form is straightforward—simply burn the extraction material and collect the remaining metal after further heating. www.kanazawa-u.ac.jp. BRIEF Magnified experimental and simulated scanning tunneling microscopy images of the molecule network on graphene. Courtesy of INRS.
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