A team led by researchers from the Twin Cities at the University of Minnesota has discovered a pioneering one-step process for creating materials with special properties, metamaterials. Their results show the real possibility of designing similar self-assembled structures with the potential to create “custom-built” nanostructures for wide application in electronics and optical devices.
The research was published and appeared on the cover of this Dwarf Letters, A scientific journal published by the American Chemical Society.
In general, metamaterials are laboratory-made materials to provide specific physical, chemical, electrical, and optical properties that are impossible to find in materials found in nature. These materials can have unique properties, such as optical filters and medical devices, suitable for various aircraft soundproofing and infrastructure control applications. Typically these nanoscale materials are unlikely to be produced in a specialized clean room environment for days and weeks during the multi-step manufacturing process.
In this new study, a team at the University of Minnesota was studying a thin film material called strontium stannate or SrSnO3. During the study, they discovered an astonishing formation of nano-scale table models similar to metamaterial structures manufactured in an expensive multi-step process.
“At first we thought it must have been a mistake, but we soon realized that the periodic pattern is a mixture of two phases of the same material with different crystal structures,” said Bharat Jalan, lead author of the study and expert in materials synthesis. He holds a Shell Chair in the Department of Chemical Engineering and Materials Science at the University of Minnesota. “After consulting with colleagues at the University of Minnesota, the University of Georgia and New York City University, we realized that we could find something special that could have some special applications.”
The material was arranged spontaneously in an orderly structure as it changed from phase to phase. During a process called “primary structural phase transition,” the material was introduced into the mixed phase, with some parts of the system completing the transition and others not.
“These periodic nanoscale models are a direct result of the transition to the primary structural phase of this material,” said Richard James, a professor of aerospace engineering and mechanics at the University of Minnesota, author of the study and a professor at McKnight University. “For the first time, our work offers many opportunities to use reversible structural phase transformations with nanoelectronic and photonic systems.”
In fact, the team first demonstrated a process for obtaining a tunable nanostructure assembled to create metamaterials in a single step. The researchers tuned in to the ability to store the property of the electric charge within a single film using temperature and laser wavelength. The variable photonic crystal material was created with 99 percent efficiency.
Using high-resolution electron microscopes, the researchers confirmed the unique structure of the material.
“We saw that the boundaries between these crystallographic phases were sharply defined on an atomic scale, which is significant for a self-assembled process,” said Professor Andre Mkhoyan, author of the study, an expert in advanced electron microscopy and Ray D. and Mary T. Johnson / Mayon Plastics chair in the Department of Chemical Engineering and Materials Science at the University of Minnesota.
Researchers are exploring future applications that can be found on optical and electronic devices.
“When we started this research we never thought about these applications. We were driven by basic studies of material physics, “Jalan said.” Now, all of a sudden, it seems like we’ve opened up a whole new field of research, driven by the possibilities of many new and exciting applications. “
References: Abhinav Prakash, Tianqi Wang, Ashley Bucsek, Tristan K. Truttmann, Alireza Fali, Michele Cotrufo, Hwanhui Yun, Jong-Woo Kim, Philip J. Ryan, K. Andre Mkhoyan, Andrea Alù, Yohannes Abate, Richard D. James and Bharat Jalan, 2 December 2020, Dwarf Letters.
DOI: 10.1021 / acs.nanolett.0c03708
In addition to Jalan, the team included researchers from the University of Minnesota Abhinav Prakash, Ashley Bucs, Tianqi Wang, Tristan K. Truttmann, Hwanhui Yun, K. Andre Mkhoyan and Richard James; Researchers Alireza Fali and Yohannes Abate of the University of Georgia; Researchers Michele Cotrufo and Andrea Alù of New York City University; and researchers Jong-Woo Kim and Philip J. Ryan of the Argonne National Laboratory.
The research was primarily funded by the National Science Foundation (NSF) and the Air Force Office of Scientific Research (AFOSR) with additional support from the Minnesota Institute of the Environment, the Norwegian Centennial Chair Program and two Vannevar Bush Faculty grants. His work on the characterization of thin films at the University of Minnesota was supported by the U.S. Department of Energy. Parts of the research were conducted at the University of Minnesota’s Nano Center and Characterization Facility, which was funded in part by the National Science Foundation. The Argon National Laboratory did additional work at the U.S. Department of Energy’s Office of Science (Advanced Photon Source).