CAREER: Fundamentals and synthesis of new compositions and shapes/microstructures of 3D and 2D carbides, nitrides and carbonitrides (MAX phases and MXenes)

NON-TECHNICAL SUMMARY This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).

The discovery of new, and better, materials can lead to advances in new and innovative technologies, for example centered around batteries, sensors, and magnets. This materials discovery together with understanding their characteristics, such as their structure and properties, and how these factors can be influenced during their preparation are therefore of utmost importance for our economy and society securing the country’s prosperity.

With this CAREER award, Professor Christina Birkel at Arizona State University will investigate materials that contain different metals and either carbon or nitrogen (or both), called carbides or nitrides (carbonitrides), respectively. These materials offer a huge playground for the discovery of new types of materials with useful properties since the researchers (i) mix and match different elements, and (ii) produce them in different shapes.

The creation of (hollow) spheres, films, or wires paves the way to even more areas where these materials can be utilized. One can, for example, envision to integrate the wires into fabrics and produce wearable electronics that monitor sweat levels or produce energy on-the-go. Furthermore, the team can break these layered solids down into atomically thin sheets, which is less than one-billionth of a meter (less than a nanometer).

Reaching this type of size regime, special physical phenomena occur that are not accessible in the larger structures. All of these new types of materials are an ideal platform to connect to and educate the public, local high-school and campus communities (through seminars and student involvements), and to increase the impact and visibility of Materials Science and Chemistry within Arizona, the US and worldwide (through winter schools and social media).

Prof. Birkel will develop an inclusive program to strengthen education, mentoring and recruitment efforts through being role models and creating future role models in STEM (science, technology, engineering, and math). TECHNICAL SUMMARY

With this CAREER award, Professor Christina Birkel at Arizona State University will synthesize new members as well as new shapes and microstructures of the three- and two-dimensional layered compounds that belong to the families of MAX phases and MXenes. The main target materials are: (i) (Carbo)nitrides, because they are scarce and therefore much less explored than the respective carbides yet hold promise for improved mechanical stability (solid solution strengthening) and higher conductivities (additional electron of the nitrogen) and (ii) Cr-, Mn- and Mo-containing phases, because of intriguing magnetic (Cr, Mn) and catalytic behavior (Mo) whose investigations are still in their infancy.

This proposal has a strong and distinguishing focus on wet chemical-assisted techniques which (i) benefit from intimate mixing of the precursors on the atomic/molecular scale and with that typically reduced reaction times and temperatures (this leads to MAX phase particles instead of the typical bulky structures and can also stabilize metastable phases), and (ii) allow for advanced processing of the liquid/gel precursor mixture into additional shapes, e.g. wires and hollow microspheres, that would not be possible with powders used in solid-state reactions. To evaluate their stability/degradation and functional properties, the materials will be subject to mechanical testing (nanoindentation) and calorimetry as well as electronic/magnetic transport and catalytic measurements.

The outcome of this proposal will be the synthesis of entirely new types of structural and functional materials and will lay the groundwork for various application-based areas, such as construction (self-healing materials, refractory materials), energy technologies (magnetocalorics, catalysts, sensors), consumer electronics (coatings) and electronic textiles (“smart”/functional fabrics). These materials are an ideal platform to connect to and educate the public, local high-school and campus communities (through seminars and student involvements), and to increase the impact and visibility of Materials Science and Chemistry within Arizona, the US and worldwide (through winter schools and social media).

The team develops an inclusive program to strengthen education, mentoring and recruitment efforts through being role models and creating future role models in STEM with the goal to break down barriers and demonstrate that there is space in science for everyone.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.