Spatially-Resolved Electronic and Magnetic Structure of 2D Van der Waals Materials and Heterostructures

二维范德华材料和异质结构的空间分辨电子和磁性结构

• 批准号: 1809145
• 负责人: Randall Feenstra
• 金额: $ 40万
• 依托单位: Carnegie-Mellon University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-07-01 至 2022-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1809145&HistoricalAwards=false
• 关键词: Spatially; Resolved; Electronic; Magnetic; Structure

Non-technical Description: In this project, a class of materials known as "two-dimensional (2D) Van der Waals materials" are being studied. These materials consist of individual sheets (planes) of atoms, with the sheets bonded to each other with only very weak bonds (Van der Waals type bonds). In such materials, the electrons move mainly within a sheet, producing special properties for the electron orbitals (that is, the "quantum states" of the electrons). It is very interesting from a fundamental physics point of view to study these orbitals of the electrons, and the orbitals have potential application in electronic devices such as low-power, high-speed transistors. An instrument known as a low-temperature scanning tunneling microscope (LT-STM), recently installed at Carnegie Mellon University and funded through the NSF Major Research Instrumentation program, is being used for the research. With this instrument, the individual atoms on the top atomic plane of the material are imaged, and the electron orbitals are also imaged. The research also includes: (i) study of magnetic properties of the materials, using a magnetic "probe" in the LT-STM instrument; and (ii) assembling of stacks of atomic sheets, containing different types of atoms in one sheet to the next. Forming such "heterostructures" leads to new type of orbitals for the electrons, again with potential application in variety of electronic devices. The project personnel are involved in graduate and undergraduate student training on this unique LT-STM instrument operation, as well as in assisting external users, and demonstration on nanoscience to visiting middle school children.Technical Description: Initial studies are focusing on transition metal dichalcogenide (TMD) materials, such as MoS2 and WSe2. Typically in heterobilayers composed of atomic layers of two different materials, the lattices in the two layers are rotationally aligned, but nevertheless an interference pattern forms due to the different lattice constants (separation between atoms) in the two layers. This pattern is found to have a large influence on the electronic states in the heterobilayer. In particular, states near the valence and conduction band edges are found to be confined within the unit cell of the interference patterns, i.e. analogous to confined states of "quantum dots". The relatively large size of the unit cell (about 10 nm) leads to strong confinement of the lowest energy states, leading to a very flat (width of less than 1 meV) electronic bands that are split off from the usual valence and conduction band edge. New types of physics phenomena may be manifest in these materials at low temperature, due to instabilities arising from the large density of states of the flat bands; conceivably, the confined states of the heterobilayers could find application, e.g., in quantum computing. The research effort utilizes low-temperature spin-resolved scanning tunneling microscopy and spectroscopy to investigate the band structures of a variety of two-dimensional materials, including heterostructures, that exhibit magnetic, superconducting and charge density wave phenomena. The spin-resolved scanning tunneling microscope offers unique opportunities for the students involved and benefits other research projects by being available to external users.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.

非技术说明：在该项目中，正在研究一类被称为“二维（2D）货车范德瓦尔斯材料”的材料。这些材料由单个原子片（平面）组成，这些原子片仅以非常弱的键（货车范德华型键）彼此键合。在这样的材料中，电子主要在薄片内移动，产生电子轨道的特殊性质（即电子的“量子态”）。从基础物理学的角度来看，研究电子的这些轨道是非常有趣的，并且这些轨道在电子器件中具有潜在的应用，例如低功率，高速晶体管。一种被称为低温扫描隧道显微镜（LT-STM）的仪器，最近安装在卡内基梅隆大学，并通过NSF主要研究仪器计划资助，正在用于研究。使用这种仪器，材料顶部原子平面上的单个原子被成像，电子轨道也被成像。研究还包括：（i）使用LT-STM仪器中的磁性“探针”研究材料的磁性;以及（ii）将原子片堆叠起来，在一个片中包含不同类型的原子。形成这种“异质结构”导致电子的新型轨道，再次具有在各种电子器件中的潜在应用。项目人员参与了研究生和本科生关于LT-STM仪器操作的培训，以及协助外部用户，并向来访的中学生演示纳米科学。技术说明：初步研究集中在过渡金属二硫属化物（TMD）材料，如MoS 2和WSe 2。通常，在由两种不同材料的原子层组成的异质双层中，两层中的晶格是旋转对齐的，但是由于两层中不同的晶格常数（原子之间的间隔）而形成干涉图案。这种模式被发现有很大的影响，在异质双层的电子状态。特别是，发现价带和导带边缘附近的状态被限制在干涉图案的晶胞内，即类似于“量子点”的受限状态。相对大尺寸的晶胞（约10 nm）导致最低能量状态的强约束，导致从通常的价带和导带边缘分裂的非常平坦（宽度小于1 meV）的电子带。由于平带的大态密度引起的不稳定性，在低温下这些材料中可能会出现新类型的物理现象;可以想象，异质双层的受限态可能会得到应用，例如，在量子计算中。研究工作利用低温自旋分辨扫描隧道显微镜和光谱学来研究各种二维材料的能带结构，包括异质结构，这些材料表现出磁性，超导和电荷密度波现象。自旋分辨扫描隧道显微镜为参与的学生提供了独特的机会，并通过向外部用户提供而使其他研究项目受益。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Unexplored MBE growth mode reveals new properties of superconducting NbN

• DOI: 10.1103/physrevmaterials.5.024802
• 发表时间: 2020-08
• 期刊: Physical Review Materials
• 影响因子: 3.4
• 作者: J. Wright;Celesta S. Chang;D. Waters;Felix Lüpke;R. Feenstra;L. Raymond;R. Koscica;G. Khalsa;D. Muller;H. Xing;D. Jena

Proximity-induced superconducting gap in the quantum spin Hall edge state of monolayer WTe2

• DOI: 10.1038/s41567-020-0816-x
• 发表时间: 2020-03-16
• 期刊: NATURE PHYSICS
• 影响因子: 19.6
• 作者: Lupke, Felix;Waters, Dacen;Hunt, Benjamin M.
• 通讯作者: Hunt, Benjamin M.

Formation of graphene atop a Si adlayer on the C-face of SiC

• DOI: 10.1103/physrevmaterials.3.084006
• 发表时间: 2019-05
• 期刊: Physical Review Materials
• 影响因子: 3.4
• 作者: Jun Li;Qingxiao Wang;Guowei He;M. Widom;L. Nemec;V. Blum;Moon J. Kim;P. Rinke;R. Feenstra

Acquisition and analysis of scanning tunneling spectroscopy data—WSe 2 monolayer

扫描隧道光谱数据的采集和分析——WSe 2 单层

• DOI: 10.1116/6.0000684
• 发表时间: 2021
• 期刊: Journal of Vacuum Science & Technology A
• 影响因子: 2.9
• 作者: Feenstra, Randall M.;Frazier, Grayson R.;Pan, Yi;Fölsch, Stefan;Lin, Yu-Chuan;Jariwala, Bhakti;Zhang, Kehao;Robinson, Joshua A.
• 通讯作者: Robinson, Joshua A.