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

本项目由材料研究部的两个项目共同资助：(i)陶瓷和（ii）电子与光子材料。非技术描述：该项目研究的新材料有望结合两个关键特性：高温稳定性和电半导体。这些特性的组合对于各种应用非常有前景，包括，例如，将废热从汽车发动机转化为电力的设备，用于移动应用的低功耗设备，大大增加了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交换和过滤设备。在本研究中，通过在真空沉积过程中组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合成过，但理论上预测它们会表现出所需的电子特性，可能会导致上述应用。该项目确定了制造这些新材料的过程，并通过实验量化了相关材料的特性，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：本研究项目研究未开发的过渡金属氮化物中金属绝缘体的转变。这是由两个最近的理论预测驱动的：(i) TiMgN2表现出稳定的有序相，具有1.1 eV的带隙；（ii）绝缘CrN在~ 4nm厚度的层上形成二维电子气体。该项目采用外延薄膜生长、电子输运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氮化物的起点，包括三元化合物和具有良好光电和热电性能的界面材料。该项目有可能创造一个新的研究领域“半导体过渡金属氮化物”，通过为过渡金属氮化物提供一系列新的应用，从极端环境的耐火半导体到高温热电和光电子材料，再到新型压电和自旋电子薄膜，对涂料行业产生变革性影响。研究生和本科生以及高中实习生接受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工业中非常重要。

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.