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 experime