Ultra-short-period superlattices of half-metallic and semiconducting Heusler alloys by combinatorial molecular beam epitaxy

该项目旨在为信息技术的科学和应用研究人工结构层状化合物的新合成和表征。人工层状化合物（ALC）由4到7个元素组成，原子层被原子层剪裁，从而形成纳米级化合物，这在自然界或其他已知的合成方法中是不可用的。它们对应于一种新的铁磁材料原型，可以被设计成具有未来量子信息技术所需的新型可调谐电子和磁性功能。研究将集中在探索ALC的合成和表征，研究其原子尺度结构，以及探测其电子和磁性能。目标是实现具有期望性质和功能的ALC，阐明结构和性质之间的性质和相互作用，并通过原子尺度合成开发控制和微调这些性质的方法。潜在的影响是重大的，因为这项工作可以为在一类新的材料中实现和控制电子和磁效应建立一条途径。这项工作不仅将探索可以很容易地集成到今天的硅基技术中的新材料，而且还可以导致对这些复杂人工材料的基本过程的一般理解。教育是这项工作的另一个主要目标。学生将接受广泛的跨学科前沿活动的培训，从合成到表征，而个人将专注于几种最先进的技术。这些领域在科学和技术上至关重要，特别是对于未来的先进技术，为了保持美国在这些领域的领导地位，对人力资源和专业知识的投资是至关重要的。技术概述：该项目是研究在Si/Ge衬底上由半金属和半导体Heusler化合物组成的超短周期（USP）超晶格（SLs）的新型MBE合成和表征。USP（定义为组成化合物的一到两个原始细胞大小）对应于铁磁SLs的新原型。这种原型可以实现带结构和界面状态的非平衡工程，但尚未在实验中进行探索。目的是实现具有更大的可调谐单轴垂直磁各向异性（PMA）的铁磁半金属（HMs）。这种功能和可调性的结合在任何目前已知的材料中都不存在，但对于未来的量子信息技术来说是非常可取的。研究将集中在探索MBE的合成和表征、结构和化学顺序、电子态、自旋极化和磁性等方面。目标是在具有至少一个非hm成分的SLs中实现鲁棒和可调谐的铁磁磁畴，并阐明少数自旋间隙和相关现象的性质，在所有Heusler SLs中实现PMA，阐明结构，磁性和界面状态的性质和相互作用，并开发控制和微调自旋依赖状态和磁各向异性的方法。这项工作的潜在影响是显著的，因为它可以为硅相容外延系统中自旋极化效应和磁性的实现和控制建立一条途径。这项工作不仅将探索可以很容易地集成到硅基平台上的新型自旋极化材料，而且还可以导致对这些复杂人工材料的基本过程的一般理解。教育是这项工作的另一个主要目标。学生将接受从合成到表征的广泛跨学科活动的培训，而个人将专注于几种先进技术。这些领域在科学和技术上都是至关重要的。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。

NON-TECHNICAL SUMMARYThe project is to investigate novel synthesis and characterization of artificially structured layered compounds for the science and applications of information technologies. The artificial layered compounds (ALC) consist of 4 to 7 elements tailored atomic layer by atomic layer thus forming nanoscale chemical compounds that are not available in nature or by other known synthesis methods. They correspond to a new archetype of ferromagnetic materials, which can be engineered to possess novel tunable electronic and magnetic functionalities desired for future quantum information technologies. The research will be focused on exploring the synthesis and characterization of the ALC, investigating the atomic scale structures, and probing the electronic and magnetic properties. The objectives are to realize the ALC with the desired properties and functionalities, elucidate the nature and interplay between structures and properties, and develop means to control and fine-tune these properties through atomic scale synthesis. The potential impact is significant, because the work can establish a pathway for realizing and controlling the electronic and magnetic effects in a new class of materials. The work will not only explore novel materials that can be readily integrated into today's silicon-based technologies, but also can lead to general understanding of the fundamental processes in these complex artificial materials. Education is another key objective of the work. Students will be trained in a wide range of interdisciplinary cutting-edge activities from synthesis to characterization, while the individuals will specialize in several state-of-the-art techniques. These areas are of critical importance scientifically and technologically, especially for future advanced technologies, and in order to maintain the leadership role of the US in these areas, investments in human resources and expertise are critically needed. TECHNICAL SUMMARYThe project is to investigate novel MBE synthesis and characterization of ultra-short-period (USP) superlattices (SLs) consisting of half-metallic and semiconducting Heusler compounds on Si/Ge substrates. USP (defined as one to two primitive-cell size of the constituent compounds) corresponds to a new archetype of ferromagnetic SLs. Such an archetype enables non-equilibrium engineering of band structures and interfacial states but has not been explored experimentally. The aim is to realize more robust and tunable ferromagnetic half-metals (HMs) accompanied by a large and tunable uniaxial perpendicular magnetic anisotropy (PMA). This combination of functionalities and tunability is not present in any currently known materials but is extremely desirable for future quantum information technologies. The research will be focused on exploring the MBE synthesis and characterization, investigating the structural and chemical order, and probing the electronic states, spin polarization, and magnetism. The objectives are to realize robust and tunable ferromagnetic HMs in SLs with at least one non-HM constituent, and elucidate the nature of the minority spin gap and related phenomena, realize PMA in the all Heusler SLs, and elucidate the nature and interplay between structure, magnetism, and interfacial states, and develop means to control and fine-tune spin-dependent states and magnetic anisotropy. The potential impact of the work is significant, because it can establish a pathway for realizing and controlling spin polarized effects and magnetism in Si-compatible epitaxial systems. The work will not only explore novel spin polarized materials that can be readily integrated onto Si-based platform, but also can lead to general understanding of fundamental processes in these complex artificial materials. Education is another key objective of the work. Students will be trained in a wide range of interdisciplinary activities from synthesis to characterization, while the individuals will specialize in several advanced techniques. These areas are of critical importance scientifically and technologically.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.