Nanotechnology  

Researchers have shown how to switch a particular transition metal oxide, a lanthanum nickelate (LaNiO3), from a metal to an insulator by making the material less than a nanometer thick.

Researchers from Cornell University and Brookhaven National Laboratory have shown how to switch a particular transition metal oxide, a lanthanum nickelate (LaNiO3), from a metal to an insulator by making the material less than a nanometer thick.

Ever-shrinking electronic devices could get down to atomic dimensions with the help of transition metal oxides, a class of materials that seems to have it all: superconductivity, magnetoresistance and other exotic properties. These possibilities have scientists excited to understand everything about these materials, and to find new ways to control their properties at the most fundamental levels.

This discovery paves the way for making advanced nanoscale electronic devices from oxides.

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The team of researchers, which published its findings in Nature Nanotechnology, includes lead researcher Kyle Shen, associate professor of physics; first author Phil King, a recent Kavli postdoctoral fellow at Cornell now on the faculty at the University of St. Andrews; Darrell Schlom, the Herbert Fisk Johnson Professor of Industrial Chemistry; and co-authors Haofei Wei, Yuefeng Nie, Masaki Uchida, Carolina Adamo, and Shabo Zhu, and Xi He and Ivan Božović.

Using an extremely precise growth technique called molecular-beam epitaxy (MBE), King synthesized atomically thin samples of the lanthanum nickelate and discovered that the material changes abruptly from a metal to an insulator when its thickness is reduced to below one nanometer. When that threshold is crossed, its conductivity – the ability for electrons to flow through the material – switches off like a light, a characteristic that could prove useful in nanoscale switches or transistors, Shen said.

Using a one-of-a-kind system at Cornell, which integrates MBE film growth with a technique called angle-resolved photoemission spectroscopy (ARPES), King and colleagues mapped out how the motions and interactions of the electrons in the material changed across this threshold, varying the thickness of their oxide films atom by atom.

The researchers discovered that when the films were less than 3 nickel atoms thick, the electrons formed an unusual nanoscale order, akin to a checkerboard.

The results demonstrate the ability to control the electronic properties of exotic transition metal oxides at the nanometer scale, as well as revealing the striking cooperative interactions that govern the behavior of the electrons in these ultrathin materials. Their discovery paves the way for making advanced new electronic devices from oxides.


SOURCE  Cornell University

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 Nanotechnology  

Researchers have developed a new approach to designing novel nanostructured materials through an inverse design framework using genetic algorithms. The study is the first to demonstrate the application of this methodology to the design of self-assembled nanostructures, and could help speed up the materials discovery process. It also shows the potential of machine learning and "big data" approaches.

Researchers at Columbia Engineering, led by Chemical Engineering Professors Venkat Venkatasubramanian and Sanat Kumar, have developed a new approach to designing novel nanostructured materials through an inverse design framework using genetic algorithms. The study, published in the Early Online edition of Proceedings of the National Academy of Sciences (PNAS), is the first to demonstrate the application of this methodology to the design of self-assembled nanostructures, and shows the potential of machine learning and “big data” approaches embodied in the new Institute for Data Sciences and Engineering at Columbia.

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“Our framework can help speed up the materials discovery process,” says Venkatasubramanian, Samuel Ruben-Peter G. Viele Professor of Engineering, and co-author of the paper. “In a sense, we are leveraging how nature discovers new materials—the Darwinian model of evolution—by suitably marrying it with computational methods. It’s Darwin on steroids!”

Using a genetic algorithm they developed, the researchers designed DNA-grafted particles that self-assembled into the crystalline structures they wanted. Theirs was an “inverse” way of doing research. In conventional research, colloidal particles grafted with single-stranded DNA are allowed to self-assemble, and then the resulting crystal structures are examined. “Although this Edisonian approach is useful for a posteriori understanding of the factors that govern assembly,” notes Kumar, Chemical Engineering Department Chair and the study’s co-author, “it doesn’t allow us to a priori design these materials into desired structures. Our study addresses this design issue and presents an evolutionary optimization approach that was not only able to reproduce the original phase diagram detailing regions of known crystals, but also to elucidate previously unobserved structures.”

The researchers are using “big data” concepts and techniques to discover and design new nanomaterials—a priority area under the White House’s Materials Genome Initiative—using a methodology that will revolutionize materials design, impacting a broad range of products that affect our daily lives, from drugs and agricultural chemicals such as pesticides or herbicides to fuel additives, paints and varnishes, and even personal care products such as shampoo.

“This inverse design approach demonstrates the potential of machine learning and algorithm engineering approaches to challenging problems in materials science,” says Kathleen McKeown, director of the Institute for Data Sciences and Engineering and Henry and Gertrude Rothschild Professor of Computer Science. “At the Institute, we are focused on pioneering such advances in a number problems of great practical importance in engineering.”

Venkatasubramanian adds, “Discovering and designing new advanced materials and formulations with desired properties is an important and challenging problem, encompassing a wide variety of products in industries addressing clean energy, national security, and human welfare.” He points out that the traditional Edisonian trial-and-error discovery approach is time-consuming and costly—it can cause major delays in time-to-market as well as miss potential solutions. And the ever-increasing amount of high-throughput experimentation data, while a major modeling and informatics challenge, has also created opportunities for material design and discovery.

The researchers built upon their earlier work to develop what they call an evolutionary framework for the automated discovery of new materials. Venkatasubramanian proposed the design framework and analyzed the results, and Kumar developed the framework in the context of self-assembled nanomaterials. Babji Srinivasan, a postdoc with Venkatasubramanian and Kumar and now an assistant professor at IIT Gandhinagar, and Thi Vo, a PhD candidate at Columbia Engineering, carried out the computational research. The team collaborated with Oleg Gang and Yugang Zhang of Brookhaven National Laboratory, who carried out the supporting experiments.

The team plans to continue exploring the design space of potential ssDNA-grafted colloidal nanostructures, improving its forward models, and bring in more advanced machine learning techniques. “We need a new paradigm that increases the idea flow, broadens the search horizon, and archives the knowledge from today’s successes to accelerate those of tomorrow,” says Venkatasubramanian.



SOURCE  Columbia Engineering

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