Thermal stabilization of 2D and layered carbides through surface modification for functional high-temperature devices

About This Grant

NON-TECHNICAL ABSTRACT: The next generation of advances in dependable energy and space exploration technology in the United States will require scientists and engineers to develop functional devices capable of operating in extreme temperatures, high radiation, and chemically reactive environments. In addition to operating in extreme conditions, these devices will remain under the increasingly intense technological demand for miniaturization. Existing materials cannot satisfy these performance requirements. For example, the reliability of current state-of-the-art electronics (logic, memory, contacts, sensors, packaging), based on silicon technology, significantly degrades above 150 °C. Even proposed material solutions (e.g., silicon carbide) rely on thicker metallic contacts that are at best limited to ~350 °C. Layered, few-atom-thick two-dimensional (2D) structures can meet the miniaturization and performance requirements for these next-generation devices for extreme conditions. However, while there are high-temperature-capable 2D semiconductor and insulator candidates, no 2D conductors satisfy the stringent requirements for conductivity, interfacial stability, and thermal stability. This project advances the feasibility of ultra-thin next-generation extreme environment nanoelectronics by advancing the atomic-level design of 2D conductive sheets of transition metal carbides, known as MXenes, for extreme conditions. This is achieved via a synergistic combination of experiments, simulations, and modeling. To accelerate US-based innovation, all experimental and theoretical results produced, and models developed will be made available online to enable education, workforce development, and to develop new machine learning models for research. Undergraduate students on this project are being prepared for the future workforce to develop critical materials and devices for the advancement of US knowledge and technological capabilities. Further, to inspire the next-generation of the US workforce, a science-as-art competition called NanoArtography will be integrated to expand public outreach and education. As a part of this NanoArtography outreach, hands-on nanoart workshops involve training young students to color black-and-white electron microscopy images of 2D carbides to learn more about how nanomaterials appear at the nanoscale. TECHNICAL ABSTRACT: This project discovers new two-dimensional (2D) transition metal carbide (MXene) electrical conductors for next-generation functional devices operating under extreme conditions (> 1000 °C). This is accomplished through structural and compositional modification of their interior transition metal carbide/nitride chemistry and surface functionalities. To meet the future technical demands for device miniaturization and functionality while operating in extreme conditions, assemblies of 2D materials must be scientifically advanced in order to fabricate stable ultrasmall nanoelectronics capable of operation at high temperatures. While insulating and semiconductor 2D materials that can perform at ~500 °C are available, the metallic contacts critical to device performance have been comparatively overlooked. Current metallic conductors are comparatively thick (tens of nanometers or more) and cannot perform above ~300 °C. To address this gap, this project aims to enhance the thermal stability limits of 2D MXenes beyond current capabilities by altering their interior transition metal carbide core structure. Additionally, it aims to modify the surface of MXenes with halogen and chalcogen terminations through surface ligand exchange reactions to enhance MXenes’ stability as a 2D flake in high-temperature conditions (> 1000 °C). By pairing computational modeling with experimental validation, this project identifies and synthesizes MXene core compositions and surface chemistries that can reach these stability limits and experimentally benchmark the resulting high-temperature stable MXenes’ electrical and thermal properties as compared to other state-of-the-art materials for metallic conductors in extreme environmental conditions. 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.