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

非技术描述：氮化物是一类令人着迷的功能材料，由于苛刻的合成限制，它在很大程度上仍未被探索：在447种预测的稳定三元氮化物中，只有不到一半被合成。本研究开发并应用了一种新的合成方法，该方法基于含氮前驱体的受控分解，从而驱动剩余氮化物材料的结晶。这种基于分解的方法迄今尚未被探索，并为单晶氮化物合成提供了一种范式转变，并为该方法的廉价缩放提供了明确的途径。应用广泛的现有前驱体材料库，可以合成各种三元甚至更复杂的氮化物。技术上重要的氮化物将被合成，为超硬材料、催化和（光电）电子器件提供材料。学生们正在接受设备开发、晶体合成和机器学习技术方面的培训，为他们在（单晶）材料合成和半导体行业的就业做好准备。为了促进女性、未被充分代表的少数族裔和有风险的学生在理工科领域的招聘和保留，“大胆利用创新引领研究和科学工程师（建设者）”倡议通过综合研讨会吸引和联系初高中和本科生，为更广泛的受众提供分层指导和教育机会。技术细节：已经提出了许多计算预测的具有有趣性质的稳定氮化物。由于有限的合成工艺参数窗口和氮或阳离子在低于分解温度下的溶解度不足，它们的溶液单晶合成受到挑战。利用一种基于熔体分解氮化锂前驱体的新合成途径克服了这些限制。前驱体的液化和受控分解导致结晶氮化物的沉积，并通过控制锂蒸气压、氮超压和温度梯度来实现，而合金成分通过控制熔体成分来实现。新开发的合成设备适用于至少100 atm和1000 c的操作，现场数据通过机器学习算法馈送，以连续和自动控制合成条件以产生目标材料成分。这种方法不依赖于氮通过气相通量的溶解和扩散，从而带来快速、可扩展合成氮化物单晶的变革机会。学生将获得有关设备开发、原位技术、机器学习算法和最终目标材料合成之间协同关系的深入实践经验。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.