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

该提案是响应纳米尺度科学与工程招标（NSF 01-157，类别NIRT）而收到的。这个项目的目标是探索在纳米尺度上限制自旋极化电荷的问题，在零维（量子点样）半导体几何形状中。该方法是在III-V和ii - vi基磁性半导体（如GaMnAs或ZnMnSe）中实现这一目标，这些磁性半导体受到纳米级调制磁场的影响。这些材料的巨大塞曼分裂特性有望表现出纳米级调制，从而导致自旋极化态的紧密局域化。这个想法是通过三种方式在磁性半导体（MS）中产生纳米级的场调制：(1)通过在MS表面沉积的光刻图纹铁磁（FM）层（例如，亚微米Co/Pt多层光盘）；通过在MSs上沉积和图案化超导（SC）覆盖层，当磁通量绕过由于迈斯纳效应导致的纳米级SC“障碍”时，实现磁场调制；通过使用无图案的SC薄膜，在MS/SC界面的场调制是通过Abrikosov涡旋晶格实现的，其“晶格常数”-因此zeeman诱导的量子点分离-可以由外部磁场控制。在图像化之前，SC薄膜要么外延沉积，在与MS层相同的分子束外延（MBE）室中；或者通过溅射来移位。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，涉及圣母大学、普渡大学和芝加哥大学的研究人员。此外，由George Crabtree博士领导的Argonne国家实验室超导和磁性小组将合作提供磁输运，近场磁光测绘，以及STM和（最终）SC-MS混合结构的自旋极化STS测绘。该项目涉及材料科学中具有高技术相关性的主题领域的基础研究问题。该计划的一个重要特点是通过培养学生在一个基础和技术上重要的领域的研究和教育的整合。除了培养纳米科学方面的研究生外，本科生还将通过高级项目和NSF REU计划参与研究。预计还将在大四和研究生一年级开设一门关于纳米科学的定期学分课程。该项目结合了实验和理论，汇集了来自物理学、电气工程和材料科学的研究人员。这些活动旨在通过前沿研究环境的独特教育经历，培养本科生、研究生和博士后强大的技术、沟通和组织/管理技能。各机构之间的跨学科研究和实地考察将促进教育和培训进程。该项目由DMR/CMP、DMR/EM和ECS/EPDT部门/项目共同支持

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.***