Metal-insulator Transitions in 2D and 3D Refractory Nitrides

这个项目是由两个材料研究部门共同资助的：(I)陶瓷和(Ii)电子和光子材料。非-技术描述：这个项目研究的新材料有望结合两个关键性质：高温稳定性和电半导体。这些特性的结合对于各种应用是非常有前景的，例如，将汽车发动机的废热转换为电力的设备，用于移动应用的低功率设备(大幅增加电池充电周期之间的时间)，以及用于具有增强数据带宽的移动通信的高速开关和过滤设备。在本研究中，通过在真空沉积过程中结合所需的原子来合成两种特定的材料。这两种材料以前从未被合成过，但理论上被预测具有可能导致上述应用的所需电子性质。该项目确定了制造这些新材料的工艺，并通过实验量化了相关材料的性能，以确定它们的潜在应用。学生接受半导体和国防工业的职业培训。技术细节：这项研究项目研究未探索的过渡金属氮化物中的金属-绝缘体转变。这是由最近的两个理论预测所推动的：(I)TiMgN_2具有稳定的有序相，禁带宽度为1.1 eV；(Ii)绝缘的CrN在~4 nm厚度的层中形成了2D电子气。该项目使用外延薄膜生长、电子传输测量和光学表征技术来证实这些预测，并研究金属-绝缘体转变的组成和量子限制空间。这两种材料体系被用作开发包括三元化合物在内的氮化物和具有良好的光电和热电性能的界面材料的起点。该项目通过提供过渡金属氮化物的一系列新应用，从极端环境的耐火半导体到高温热电和光电材料，再到新的压电式和自旋电子式薄膜，有可能开创“半导体过渡金属氮化物”的新研究领域，对涂料行业产生潜在的变革性影响。研究生和本科生以及高中实习生都接受了薄膜沉积和电子表征方法的培训，这些方法在涂层和半导体行业中非常重要。

This project is co-funded by two Division of Materials Research programs: (i) Ceramics, and (ii) Electronic and Photonic Materials.NON-TECHNICAL DESCRIPTION: This project studies new materials which are expected to combine two key properties: high-temperature stability and electrically semiconducting. The combination of these properties is very promising for various applications, including, for example, devices that convert waste-heat from automobile engines to electricity, low-power devices for mobile applications which dramatically increase the time between battery recharging cycles, and high-speed switching and filtering devices for mobile communication with enhanced data bandwidth. In this research, two specific materials are synthesized by combining the required atoms in a vacuum deposition process. Both of these materials have never been synthesized before, but have been theoretically predicted to exhibit desired electronic properties that may lead to the aforementioned applications. The project determines the process for making these new materials and experimentally quantifies the relevant materials properties to determine their potential applications. Students are trained for careers in the semiconductor and defense industries.TECHNICAL DETAILS: This research project studies metal-insulator transitions in unexplored transition-metal nitrides. It is motivated by two recent theoretical predictions: (i) TiMgN2 exhibits a stable ordered phase with a 1.1 eV bandgap and (ii) insulating CrN forms a 2D electron gas for layers of ~4 nm thickness. The project employs epitaxial thin film growth, electron transport measurements, and optical characterization techniques to confirm these predictions and study the composition and quantum-confinement space for the metal-insulator transitions. The two material systems are used as starting points to develop nitrides including ternaries and interface materials with promising opto- and thermo-electric properties. This project has the potential to create a new research field of "semiconducting transition-metal nitrides" with potential for transformative impact on the coatings industry by providing a range of new applications for transition-metal nitrides, ranging from refractory semiconductors for extreme environments to high-temperature thermoelectric and optoelectronic materials to new piezoelectric and spintronic thin films. Graduate and undergraduate students as well as high-school interns are trained on thin film deposition and electronic characterization methods which are very important in the coating and semiconductor industries.