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

非技术摘要该项目是研究新的合成和表征人工结构的层状化合物的科学和信息技术的应用。人工层状化合物（ALC）由4至7种元素组成，这些元素通过原子层定制原子层，从而形成在自然界中或通过其他已知合成方法不可用的纳米级化合物。它们对应于一种新的铁磁材料原型，这种铁磁材料可以被设计成具有未来量子信息技术所需的新型可调电子和磁性功能。研究将集中在探索ALC的合成和表征，研究原子尺度的结构，并探测电子和磁性。目标是实现具有所需性质和功能的ALC，阐明结构和性质之间的性质和相互作用，并开发通过原子尺度合成来控制和微调这些性质的方法。潜在的影响是显著的，因为这项工作可以建立一种途径，用于实现和控制一类新材料中的电子和磁效应。这项工作不仅将探索可以很容易地集成到当今硅基技术中的新材料，而且还可以使人们对这些复杂人工材料的基本过程有一个全面的了解。教育是这项工作的另一个关键目标。学生将接受从合成到表征的广泛的跨学科前沿活动的培训，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，迫切需要对人力资源和专业知识进行投资。技术摘要该项目是研究新的MBE合成和表征的超短周期（USP）超晶格（SL）组成的半金属和半导体Heusler化合物在Si/Ge衬底上。USP（定义为组成化合物的一到两个连续单元尺寸）对应于一种新的铁磁SL原型。这样的原型使能带结构和界面状态的非平衡工程，但尚未进行实验探索。其目的是实现更强大的和可调的铁磁半金属（HM）伴随着一个大的和可调的单轴垂直磁各向异性（PMA）。这种功能性和可调谐性的组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理想的。研究将集中在探索MBE的合成和表征，研究结构和化学顺序，并探测电子态，自旋极化和磁性。我们的目标是实现强大的和可调的铁磁HM在SL与至少一个非HM成分，并阐明少数自旋间隙和相关现象的性质，实现PMA在所有的赫斯勒SL，并阐明结构，磁性和界面状态之间的性质和相互作用，并开发手段来控制和微调自旋相关的状态和磁各向异性。这项工作的潜在影响是显著的，因为它可以建立一个途径，实现和控制自旋极化效应和磁性的Si兼容外延系统。这项工作不仅将探索新的自旋极化材料，可以很容易地集成到硅基平台，但也可以导致在这些复杂的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关键目标。学生将接受从合成到表征的广泛的跨学科活动的培训，而个人将专注于几种先进的技术。该奖项反映了NSF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.