Probing Fundamental Magneto-Electronic Properties of Two-Dimensional Metal Halides

非技术总结：研究人员最近学会了如何生产被称为二维（2D）材料的原子薄材料，因为它们在两个维度（即长度和宽度）上扩展，但在原子尺度上仅限于第三维度（即深度）。由于在原子薄极限下的一系列优异性能和新物理特性，二维材料已经引起了基础研究和原型器件开发的极大兴趣。到目前为止，化学惰性二维材料已经得到了最广泛的研究，因为它们可以在最小的进一步预防措施下在环境条件下进行加工。然而，二维材料家族还有数百个额外的成员，由于其高化学反应性，在制备和处理电子测试样品方面带来了挑战，因此尚未得到充分开发。为了解决这一知识差距，该项目开发了封装和相关的样品制备方案，以表征化学反应性2D材料的基本特性。特别令人感兴趣的是二维金属卤化物，因为理论上预测它们具有与下一代计算和量子技术相关的独特电子和磁性组合。这些研究成果通过一系列教育和推广活动广泛传播给不同的受众，包括帮助低收入、第一代和/或代表性不足的少数民族学生进入大学并完成学业的Illuminate，以及组织参观养老院进行互动科学演示和示范的Science with Seniors。技术总结：层状范德华过渡金属卤化物是最具化学活性的二维（2D）材料之一。由于它们的高化学反应性，对大块金属卤化物的实验研究很少，传统上需要惰性环境和/或真空设备。然而，理论模型预测许多层状金属卤化物由于低解理能和面内结合强度大而可机械剥落，这表明如果确定合适的钝化和加工条件，可以在二维极限下探索它们。该项目开发了原子层沉积封装层，允许在环境条件下处理、加工和测试二维金属卤化物。在原子层沉积之前，二维金属卤化物被有机缓冲层钝化，从而最大限度地减少电荷捕获和散射，从而允许探测内在特性。利用横向场效应晶体管、垂直异质结构和霍尔棒电极阵列，研究了二维金属卤化物的电子、磁性和光学特性之间的相互作用，并将其表征为温度的函数。通过阐明基本电荷输运现象，如量子化异常霍尔效应，这项工作为将二维金属卤化物纳入先进磁电子应用（包括自旋电子器件、量子技术和非易失性存储器）的新兴努力提供了指导。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。

Nontechnical Summary:Researchers have recently learned how to produce atomically thin materials that are referred to as two-dimensional (2D) materials since they are extended in two dimensions (i.e., length and width) but are confined in the third dimension (i.e., depth) at the atomic scale. Due to a range of superlative properties and new physics in the atomically thin limit, 2D materials have attracted significant interest for fundamental studies and prototype device development. Thus far, chemically inert 2D materials have been the most widely studied since they can be processed in ambient conditions with minimal further precautions. However, the family of 2D materials has hundreds of additional members, which have been underexplored due to their high chemical reactivities that introduce challenges in preparing and handling samples for electronic testing. To address this knowledge gap, this project develops encapsulation and related sample preparation protocols to enable characterization of the fundamental properties of chemically reactive 2D materials. Of particular interest are the 2D metal halides since they are theoretically predicted to possess unique combinations of electronic and magnetic properties that are relevant to next-generation computing and quantum technologies. These research results are widely disseminated to diverse audiences through a series of education and outreach activities including Illuminate, which assists and enables low-income, first-generation, and/or underrepresented minority students to attend and complete college, and Science with Seniors, which organizes visits to retirement homes for interactive science presentations and demonstrations.Technical Summary:Among the most chemically reactive two-dimensional (2D) materials are the layered van der Waals transition metal halides. Due to their high chemical reactivity, experimental studies of bulk metal halides are rare and have traditionally required an inert environment and/or vacuum equipment. However, theoretical models have predicted many layered metal halides to be mechanically exfoliatable due to low cleavage energies and large in-plane bond strength, suggesting that they could be explored in the 2D limit if suitable passivation and processing conditions were identified. This project develops atomic layer deposition encapsulation layers that allow 2D metal halides to be handled, processed, and tested in ambient conditions. Preceding atomic layer deposition, the 2D metal halides are passivated with organic buffer layers that minimize charge trapping and scattering, thus allowing intrinsic properties to be probed. The interplay among the electronic, magnetic, and optical properties of 2D metal halides is characterized as a function of temperature using lateral field-effect transistors, vertical heterostructures, and Hall bar electrode arrays. By elucidating fundamental charge transport phenomena such as the quantized anomalous Hall effect, this work provides guidance to emerging efforts to incorporate 2D metal halides into advanced magneto-electronic applications including spintronic devices, quantum technologies, and non-volatile memory.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.