NIRT: Formation and Properties of Spin-Polarized Quantum Dots in Magnetic Semiconductors by Controlled Variation of Magnetic Fields on the Nanoscale

该提案是响应纳米科学与工程招标，NSF 01-157，类别NIRT。这个项目的目标是探索在纳米尺度上，在零维（量子点状）半导体几何结构中限制自旋极化电荷的问题。该方法是在基于III-V和II-VI的磁性半导体（例如GaMnAs或ZnMnSe）中进行这一操作，该磁性半导体受到在纳米尺度上调制的磁场的影响。这些材料的巨大塞曼分裂特性预计将表现出纳米尺度的调制，导致自旋极化态的紧密局域化。该想法是以三种方式在磁性半导体（MS）中产生这种纳米级场调制：（1）通过沉积在MS表面上的光刻图案化铁磁（FM）层（例如，亚微米Co/Pt多层盘）;通过在MS上沉积和图案化超导（SC）覆盖层，其中当磁通量由于迈斯纳效应而绕过纳米级SC“障碍物”时实现磁场调制;以及通过使用未图案化的SC膜，其中MS/SC界面处的场调制经由Abrikosov涡旋晶格实现，它的“晶格常数”--以及塞曼诱导的量子点分离--可以由外部磁场控制。在图案化之前，SC膜将在与MS层相同的分子束外延（MBE）室中外延沉积;或者通过溅射非原位沉积。该项目的关键方面是：理论，材料生长，光刻，表征和自旋电子概念的发展。该项目是高度合作的，涉及圣母院，普渡大学和美国大学的研究人员。IL在芝加哥。此外，由乔治克拉布特里博士领导的阿贡国家实验室的超导和磁性小组将通过提供SC-MS混合结构的磁输运、近场磁光映射以及STM和（最终）自旋极化STS映射进行合作。该项目解决了材料科学领域的基础研究问题，具有高度的技术相关性。该计划的一个重要特点是通过在一个基本和技术上重要的领域对学生进行培训来整合研究和教育。除了培养纳米科学的研究生外，本科生还将通过高级项目和NSF REU计划参与研究。预计还将在高年级和研究生一年级开设关于纳米科学的定期学分课程。该项目结合了实验和理论，并汇集了来自物理，电气工程和材料科学的研究人员。活动旨在通过前沿研究环境所带来的独特教育体验，在本科生和研究生以及博士后中培养强大的技术，沟通和组织/管理技能。各组织之间的跨学科研究和实地访问将加强教育和培训进程。该项目由DMR/CMP，DMR/EM和ECS/EPDT部门/计划共同支持。

This proposal was received in response to the Nanoscale Science and Engineering solicitation, NSF 01-157, category NIRT. The goal of this project is to explore the issues of confining spin-polarized charges on the nano-scale, in zero-dimensional (quantum-dot-like) semiconductor geometries. The approach is to do this in III-V- and II-VI-based magnetic semiconductors (such as GaMnAs or ZnMnSe) subjected to a magnetic field that is modulated on the nano-scale. The giant Zeeman splitting characteristic of these materials is expected to exhibit nano-scale modulation resulting in tight localization of spin-polarized states. The idea is to produce such nano-scale field modulation in a magnetic semiconductor (MS) in three ways: (1) by lithographically-patterned ferromagnetic (FM) layers deposited on the MS surface (e.g., sub-micron Co/Pt multilayer discs); by depositing and patterning superconducting (SC) overlayers on the MSs, where the magnetic field modulation is achieved as the magnetic flux by-passes the nano-scale SC "obstacles" due to the Meissner effect; and by using unpatterned SC films, where the field modulation at the MS/SC interface is achieved via the Abrikosov vortex lattice, whose "lattice constant"-and thus the Zeeman-induced quantum dots separation-can be controlled by an external magnetic field. Prior to patterning, the SC films will either be deposited epitaxially, in the same molecular beam epitaxy (MBE) chamber as the MS layers; or ex-situ, by sputtering. Key aspects of the project are: theory, materials growth, lithography, characterization, and development of spintronic concepts. The project is highly collaborative involving researchers at Notre Dame, Purdue, and U. IL at Chicago. Additionally, the Superconductivity and Magnetism Group at Argonne National Laboratory, led by Dr. George Crabtree, will collaborate by providing magneto-transport, near-field magneto-optical mapping, as well as STM and (eventually) spin-polarized STS mapping of the SC-MS hybrid structures. %%% The project addresses basic research issues in a topical area of materials science with high technological relevance. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. In addition to training graduate students in nano-science, undergraduates will also participate in research through senior projects and the NSF REU program. It is also expected that a regular for-credit course on nano-science at the senior and first-year-graduate level will be developed. The project combines experiment and theory, and brings together researchers from physics, electrical engineering, and material science. Activities are designed to develop strong technical, communication, and organizational/management skills in undergraduate and graduate students and postdoctorals through unique educational experiences made possible by a forefront research environment. Cross-disciplinary research and site visits between organizations will enhance the education and training process. The project is co-supported by the DMR/CMP, DMR/EM, and ECS/EPDT Divisions/Programs.***