CAREER: Nitride Synthesis via Controlled Decomposition of Precursors under Moderate Pressure

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NON-TECHNICAL DESCRIPTION: Nitrides are a fascinating class of functional materials that remain largely unexplored due to demanding synthesis constraints: of the 447 predicted stable ternary nitrides, less than half have been synthesized. This research develops and applies a novel synthesis approach based on controlled decomposition of a nitrogen-containing precursor thereby driving the crystallization of the remaining nitride materials. This decomposition-based approach is hitherto unexplored and offers a paradigm shift in single crystal nitride synthesis with a clear path towards inexpensive scaling of the method. Application of an extensive library of existing precursor materials allows for synthesis of a wide range of ternary and even more complex nitrides. Technologically important nitrides will be synthesized providing materials for super-hard materials, catalysis and (opto-)electronic devices. Students are being trained in equipment development, crystal synthesis, and machine learning techniques preparing them for employment in (single crystal) material synthesis and semiconductor industries. To promote recruitment and retention of female, underrepresented minority and at-risk students in science and engineering, the Boldly Utilizing Innovation to Lead in Developing Engineers for Research and Science (BUILDERS) initiative is engaging and connecting middle/high school and undergraduate students via synthesis workshops providing hierarchical mentorship and educational opportunities for the broader audience. TECHNICAL DETAILS: Many computationally predicted stable nitrides with intriguing properties have been proposed. Their single crystal synthesis from solution is challenged due to limited synthesis process parameter windows and insufficient solubility of nitrogen or cations at temperatures below their decomposition temperature. These limitations are overcome using a new synthesis pathway based on decomposition of lithiated nitride precursor from a melt. Liquification and controlled decomposition of the precursor results in the deposition of a crystalline nitride and is achieved via controlling the lithium vapor pressure, nitrogen overpressure and temperature gradients, while alloy composition is achieved via control of the melt composition. The newly developed synthesis equipment is suitable to operate up to at least 100 atm and 1000 C. In situ data is fed through a machine learning algorithm to continuously and automatically control synthesis conditions to yield targeted material compositions. This approach does not rely on dissolution and diffusion of nitrogen through the flux from the gas phase leading to transformative opportunities in rapid, scalable synthesis of nitride single crystals. Students are obtaining in-depth, hands-on experience about the synergistic relationships between equipment development, in situ technologies, machine learning algorithms and resulting targeted material synthesis.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.