Dilute Magnetic 2D-Semiconductors: Fundamentals for Device Applications

非技术描述磁性半导体是具有磁性的材料，也是半导体。它们可以用于非易失性存储器等应用中，并使基于自旋的电子产品能够应用于量子计算等应用中。然而，大多数半导体都是非磁性的。通过在传统半导体中掺杂磁性杂质，已经在制造磁性半导体方面取得了一些成功。通常只实现了较低的磁相变温度，限制了潜在的应用。这个项目将研究有可能达到室温磁性的二维(2D)磁性半导体。2D材料在平面上延伸，但只有几个原子厚。这种平面材料具有未来器件的潜力，因为二维晶体可以堆叠成原子尖锐的界面。2D材料对环境也很敏感，因此可以通过界面或外部刺激来调整它们的属性。在这项研究中，将研究2D材料中磁性掺杂剂的基本性质，以深入了解允许在这些材料中引入和调节磁性的机制。最终目标是开发可靠的方法来实现在室温以上工作的2D磁性半导体。这项研究有可能导致基于新型多功能材料的可调谐自旋电子器件的发展。重要的是，该项目为具有技术相关性的当代材料科学研究生提供培训，并将通过国际合作和研究活动拓宽他们的经验。技术说明该项目探索2D半导体MoS2和WSe2中的磁性掺杂。掺杂薄膜和单分子膜将通过低温分子束外延生长，以实现各种过渡金属掺杂的有效掺入。成功的掺杂和原子尺度的掺杂结构将通过扫描隧道显微镜和光谱进行研究，以深入了解控制局域磁矩的掺杂诱导缺陷态。通过系统地改变材料的加工条件，并通过磁测量和同步辐射x射线磁性圆二色谱研究材料的磁性能，研究了掺杂元素、结构和浓度对材料磁性能的影响。实验观测与理论密度泛函计算相关联。还研究了电荷转移掺杂对超薄膜磁性能的可调性。这项研究将深入了解掺杂的磁耦合机制以及二次缺陷在磁性调谐中的作用。这项研究利用材料系统的2D性质，既可以更好地了解稀磁半导体的一般机制，也可以利用其在范德华异质结构中原子锐利的界面来将磁性材料与具有不同量子属性的材料相结合，以及用于磁性器件结构。从根本上说，这项活动旨在确定磁性掺杂之间的磁耦合，以找出2D磁性稀释半导体中居里温度明显高于传统半导体的原因。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 DescriptionMagnetic semiconductors are materials with magnetic properties that are also semiconductors. They can be utilized in applications such as non-volatile memories and enable spin-based electronics with applications such as quantum computing. However, most semiconductors are non-magnetic. There has been some success in making magnetic semiconductors through doping conventional semiconductors with magnetic impurities. Usually only low magnetic transition temperatures have been achieved, limiting potential applications. This project will investigate two-dimensional (2D) magnetic semiconductors that have the potential to reach room temperature magnetism. 2D materials are extended in a plane but are only a few atoms thick. Such planar materials have potential for future devices because two-dimensional crystals can be stacked with atomically sharp interfaces. 2D materials are also sensitive to their environment and thus their properties can be tuned through interfaces or external stimuli. In this research the fundamental properties of magnetic dopants in 2D materials will be investigated in order to gain insight on the mechanisms that allow introduction and tuning of magnetism in these materials. The ultimate goal is to develop reliable approaches to realize 2D magnetic semiconductors that function above room temperature. The research has the potential to lead to the development of tunable spintronic devices based on new multifunctional materials. Importantly, this project provides training for graduate students in contemporary materials science with technological relevance and will broaden their experience through international collaborations and research activities.Technical DescriptionThis project explores magnetic dopants in the 2D-semiconductors MoS2 and WSe2. Doped films and monolayers will be grown by low temperature-molecular beam epitaxy to enable the efficient incorporation of various transition metal dopants. The successful doping and the atomic scale dopant-structures will be investigated by scanning tunneling microscopy and spectroscopy to gain insight on the dopant induced defect states that control the local magnetic moments. The role of dopant-element, structure, and concentration on the magnetic properties is investigated by systematically varying materials processing conditions and investigation of the magnetic properties by magnetometry and synchrotron x-ray magnetic circular dichroism studies. The experimental observations are correlated to theoretical density functional calculations. Tunability of the magnetic properties by charge transfer doping in ultrathin films is also studied. This study will give insight on the magnetic coupling mechanism of the dopants and the role of secondary defects in tuning of the magnetism. The study exploits the 2D nature of the material systems for both gaining better insight in the general mechanism for diluted magnetic semiconductors, as well as for the potential of exploiting their atomically sharp interfaces in van der Waals heterostructures for combining magnetic materials with materials with diverse quantum properties as well as for magnetic device structures. Fundamentally, this activity aims at determining the magnetic coupling between magnetic dopants to find the reason for the apparently higher Curie temperatures in 2D magnetic diluted semiconductors compared to traditional semiconductors.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.