Metal Diborides: Investigating the Structure, Processing, and Properties of a New Class of Two-Dimensional Materials

Arizona State University, Scottsdale AZ

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: Metal diborides are a class of ceramic materials with the chemical composition MB2, where M can be many different metals. They have a common structure of stacked sheets of boron separated by layers of metal atoms. Examples of the diverse, outstanding properties of these materials include superconductivity in magnesium diboride and resistance to extremely high temperatures in titanium diboride and zirconium diboride. Metal diborides also find application in ballistic armor and heat shields for spacecraft. However, conventional methods of preparing metal diborides result in thick, brittle materials that do not take advantage of the flexible, two-dimensional (2D) nature of their constituent boron sheets. The PIs recently developed a method to directly generate substantial amounts of 2D metal diborides composed of single- to few-layer atomically thin sheets. This project is focused on studying in detail the structure, properties, processing, and performance of this new class of 2D ceramics. Few-layer metal diborides suspended across porous surfaces or incorporated into polymers are tested for their improved mechanical properties. Thin films of the 2D metal diborides are investigated for their potential as lightweight and flexible superconductors. Overall, these studies aim to exploit the exceptional properties of the metal diborides in applications not possible using conventional materials processing techniques and to improve their performance in their conventional areas of use. The educational goals of this project are the training of graduate and undergraduate students in advanced materials research, incorporation of research results into the PIs' interdisciplinary courses for graduate and undergraduate students, and outreach to students and families in the general public through open house science events and at-home virtual science kits. TECHNICAL DETAILS: This project is focused on understanding in detail the structure and properties of 2D sheets of metal diborides prepared using solution-phase processing and micromechanical cleavage techniques. The structure and composition of these 2D materials are studied down to the atomic scale by aberration corrected transmission electron microscopy, scanning tunneling microscopy, electron energy loss spectroscopy, and energy dispersive X-ray spectroscopy. Mechanical measurements across different length scales, starting from individual microscopic sheets of 2D metal diborides to macroscopic polymer composites reinforced by 2D metal diborides, are being studied using atomic force microscopy and tensile testing equipment. Solution-processed, flexible thin films of the 2D metal diboride MgB2 are being investigated for their potential superconducting behavior. This research project is thus providing new fundamental knowledge of the electronic and mechanical properties of the metal diborides once they are only a few atomic layers thick. The improved understanding of the properties and processing of 2D metal diboride ceramics is facilitating their integration into stretchable and flexible forms unavailable to their conventional bulk counterparts, and yielding new application areas for these compounds in structurally reinforced polymer composites and bendable superconductors.