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，由于严格的合成限制，这些材料在很大程度上仍未被开发：在预测的447个稳定的三元氮化物中，只有不到一半被合成。这项研究开发并应用了一种新的合成方法，该方法基于对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到目前为止还没有被探索过，并提供了单晶氮化物合成的范例转变，为该方法的廉价扩展提供了一条明确的途径。现有前体材料的广泛资料库的应用允许合成范围广泛的三元甚至更复杂的氮化物。具有重要技术意义的氮化物将被合成，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就业做准备。为了促进科学和工程专业招收和留住女性、代表性不足的少数族裔和高危学生，大胆利用创新引领培养研究和科学工程师(建设者)倡议正在通过综合研讨会吸引和联系初中生、高中生和本科生，为更广泛的受众提供分层次的指导和教育机会。技术细节：已经提出了许多通过计算预测的具有有趣性质的稳定氮化物。由于合成工艺参数窗口有限，且在低于其分解温度的温度下氮或阳离子的溶解度不足，使得从溶液中合成它们的单晶受到了挑战。使用一种新的合成方法克服了这些限制，该合成方法基于从熔体中分解锂化氮化物前体。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力、氮气超压和温度梯度实现，而合金成分通过控制熔体成分实现。新开发的合成设备适用于至少100大气压和1000℃的操作。现场数据通过机器学习算法馈送，以连续自动控制合成条件，以产生目标材料组合物。这种方法不依赖于氮气通过气相熔剂的溶解和扩散，从而在快速、可扩展的氮化物单晶合成中产生了转化机会。学生们正在获得关于设备开发、现场技术、机器学习算法和最终的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NSF的法定使命，并通过使用基金会的智力优势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.