Synthesis and Properties of Heterostructures Containing Magnetic 2d Layers Not Found As Bulk Compounds

非技术总结2010年诺贝尔物理学奖是因为在具有二维(2D)结构的化合物的单层中发现了主体化合物中没有的新性质而获奖。由此产生的科学领域-2D材料和被称为异质结构的2D材料堆积层-已经呈指数级扩大，因为理论家提出了新的奇异特性，实验者在单层和异质结构中发现了新的特性。目前，异质结构的制备是通过将块体材料裂解到单层极限并按设计的顺序堆积来完成的。这种方法仅限于作为可分解的大宗化合物的稳定的成分。需要新的合成方法，能够在晶片规模上制备异质结构，提供更广泛的组成层选择，并提供对纳米结构(组成层的堆积顺序和厚度)的控制。在该项目中，在材料研究部固态和材料化学与陶瓷计划的支持下，俄勒冈大学的David Johnson博士和他的研究小组将开发新的合成方法，以制备包含2D磁性成分层的异质结构，其结构和组成与孤立化合物相比在热力学上不稳定。目前正在测试三种不同的策略，这三种策略都使用具有与目标异质结构相匹配的目标组成轮廓的前体。该研究项目为研究生提供了沉积技术、薄膜表征技术以及2D异质结构中出现的物理现象的广泛技术背景。这种培训使他们能够在未来的各种职业中茁壮成长(高科技行业、学术界或国家实验室)。实习将为研究生提供一个“试驾”未来职业的机会，同时扩大他们的知识基础，从而培养出更多生产力的研究人员。让本科生参与这项研究，使他们能够应用课堂上学到的原则来解决研究挑战。提供本科生研究机会是增加学生将科学作为职业的数量和多样性的关键工具。技术总结在材料研究部固态和材料化学及陶瓷项目的支持下，俄勒冈大学的David Johnson博士和他的研究小组将开发合成方法，以制备包含2D磁性成分层的异质结构，其结构和组成与孤立化合物相比在热力学上不稳定。合成靶材包括二硒化物(TSE2)和岩盐结构的Pb2+NT1+mSe3+n+m层，其中T=铬、锰、铁和镍。三种合成策略正在测试中，它们使用具有目标局部组成和纳米结构的前体来控制成核和生长。一种策略是制备一种前体，其设计使一层结晶为2D薄片，由受控成分的无定形层隔开。由此得到的交错非晶层的2D形状因子和组成以及相邻晶层的结构将用于控制亚稳态成分层的形核和生长。第二种策略将是通过控制局部成分来形成所需结构的种子。第三种策略是使用相邻层的电荷转移来稳定目标结构。目标异质结构中的伴生成分对控制这些策略的反应途径至关重要，我们列出的潜在成分包括压电层(GeSE，SnSe)、拓扑绝缘层(Bi2Se3，Bi2Te3)、半导体层(PbSe，MoSe2，SnSe2)和/或超导(NbSe2)层。预计将有丰富的新材料集合，具有多样化和可调的紧急特性。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 SUMMARYThe 2010 Nobel prize in physics was awarded for the discovery of novel properties in monolayers of compounds with two dimensional (2D) structures that are not present in the bulk compounds. The resulting field of science - 2D materials and stacked layers of 2D materials known as heterostructures - has exponentially expanded as theorists proposed new exotic properties and experimentalists discovered new properties in monolayers and heterostructures. Currently the preparation of heterostructures is done by cleaving bulk materials to the monolayer limit and stacking them in designed sequences. This approach is limited to constituents that are stable as bulk compounds which are cleavable. New synthesis approaches are needed that enable preparation of heterostructures at a wafer scale, that provide a wider selection of constituent layers, and that provide control over the nanoarchitecture (stacking sequence and thickness of constituent layers). In this project, with the support of the Solid State and Materials Chemistry and Ceramics Programs in the Division of Materials Research, Dr. David Johnson and his research group at the University of Oregon, will develop new synthetic approaches to preparing heterostructures containing 2D magnetic constituent layers with structures and compositions that are not thermodynamically stable as isolated compounds. Three different strategies, all of which use precursors with targeted composition profiles that match that of the targeted heterostructures, are being tested. This research program provides a broad technical background for graduate students in deposition technologies, thin film characterization techniques, and physical phenomena that occur in 2D heterostructures. This training enables them to thrive in a variety of future careers (high tech industries, academia, or national laboratories). Internships will provide an opportunity for graduate students to “test drive” future careers while expanding their knowledge base, leading to more productive researchers. Engaging undergraduate students in this research enables them to apply principles learned in classes to solve research challenges. Providing undergraduate research opportunities is a critical tool to increase the number and diversity of students pursuing science as a career. TECHNICAL SUMMARYWith the support of the Solid State and Materials Chemistry and Ceramics Programs in the Division of Materials Research, Dr. David Johnson and his research group at the University of Oregon will develop synthetic approaches to preparing heterostructures containing 2D magnetic constituent layers with structures and compositions that are not thermodynamically stable as isolated compounds. Synthetic targets include diselenides (TSe2) and rock salt structured Pb2+nT1+mSe3+n+m layers, where T = Cr, Mn, Fe and Ni. Three synthesis strategies, which use precursors with targeted local composition and nanoarchitecture to control nucleation and growth, are being tested. One strategy is to prepare a precursor designed such that one layer crystalizes as 2D sheets separated by amorphous layers of controlled composition. The resulting 2D form factor and composition of the interleaved amorphous layers as well as the structure of adjacent crystalline layers will be used to control the nucleation and growth of the metastable constituent layers. A second strategy will be to seed nucleation of the desired structures by controlling local composition. A third strategy will be to use charge transfer from an adjacent layer to stabilize the targeted structures. The companion constituents in the targeted heterostructures will be critical to controlling the reaction pathways for each of these strategies, and our list of potential constituents include piezoelectric (GeSe, SnSe), topological insulating (Bi2Se3, Bi2Te3), semiconducting (PbSe, MoSe2, SnSe2) and/or superconducting (NbSe2) layers. A rich collection of new materials with diverse and tunable emergent properties is anticipated.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.