CAREER: Raman Spectroscopy of Interlayer Phonons in van der Waals Heterostructures

职业：范德华异质结构中层间声子的拉曼光谱

• 批准号: 1760668
• 负责人: Rui He
• 金额: $ 43.74万
• 依托单位: Texas Tech University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-11 至 2022-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1760668&HistoricalAwards=false
• 关键词: CAREER; Raman; Spectroscopy; Interlayer; Phonons

Non-technical abstract:Van der Waals heterostructures are a new class of materials that could lead to new novel electronic and optoelectronic devices. These materials are formed by vertically stacking atomic layers such as graphene, hexagonal boron nitride, and transition metal dichalcogenide (e.g. molybdenum disulfide) layers. The forces between these layers are relatively weak. However, they can dramatically change the properties of the system and induce phenomena that are absent in individual layers. By stacking or epitaxially growing different atomic layers on one another, one may design and fabricate artificial materials with unprecedented optical, electronic, and vibrational properties that cannot be achieved in natural crystals. Raman spectroscopy, which is a direct, noninvasive, and sensitive optical probe, is used to explore the interlayer coupling, the interface effect, and the interaction between vibrations and charge carriers in these heterostructures. This research provides crucial guidance in designing novel electronic and optoelectronic devices using stacked atomic layers. The research activities have a powerful impact on the undergraduate students at the University of Northern Iowa. The principal investigator integrates the research topics into two existing courses. Undergraduates at all levels, including freshman students, are encouraged to participate. The principal investigator also uses departmental contacts with area high schools and collaborates with Physics Education faculty colleagues and the director of the Classic Upward Bound program to involve teachers and students at regional high schools. Engaging high school students and undergraduates in research is very important in advancing STEM (Science, Technology, Engineering, and Mathematics) education in young people.Technical abstract:This research explores fundamental physical properties of various van der Waals heterostructures using Raman spectroscopy of interlayer phonons (typically at low frequencies) and photoluminescence. The research projects include: (i) Develop an interlayer-phonon-based Raman technique to characterize the rotational angle and Moire wavelength of heterostructure superlattices. This study offers a simple method of characterizing Moire pattern features without using scanning tunneling microscopy; (ii) Explore the electronic, optical, and vibrational properties of complex multilayer van der Waals heterostructures and the indirect-direct gap transition in MoS2 bilayers intercalated with different middle layer materials. This research provides crucial guidance in designing novel electronic and optoelectronic devices using stacked van der Waals multilayers; (iii) Study van der Waals heterostructures that involve Dirac materials. In particular, the research team investigates the change in the electronic band structure of twisted bilayer graphene after it is placed or sandwiched between hexagonal boron nitride. This study probes the change in the electronic and vibrational properties of graphene at the hetero-interface; (iv) Probe the interaction between carriers and interlayer phonons in twisted bilayer graphene devices with a dual-gate. This study explores the Coulomb interaction between two charged graphene layers and the interlayer potential formed upon gating. The techniques and methods established in these research activities can be applied to heterostructures formed from any two-dimensional crystals stacked in any desired sequence.

非技术摘要：范德华异质结构是一类新型材料，可以产生新型电子和光电器件。 这些材料是通过垂直堆叠原子层形成的，例如石墨烯、六方氮化硼和过渡金属二硫属化物（例如二硫化钼）层。这些层之间的力相对较弱。 然而，它们可以极大地改变系统的属性并引发各个层中不存在的现象。通过相互堆叠或外延生长不同的原子层，人们可以设计和制造具有天然晶体无法实现的前所未有的光学、电子和振动特性的人造材料。拉曼光谱是一种直接、无创、灵敏的光学探针，用于探索这些异质结构中的层间耦合、界面效应以及振动和载流子之间的相互作用。这项研究为使用堆叠原子层设计新型电子和光电器件提供了重要指导。研究活动对北爱荷华大学的本科生产生了强大的影响。首席研究员将研究主题整合到两门现有课程中。鼓励各级本科生，包括新生，参加。首席研究员还利用与地区高中的部门联系，并与物理教育教员同事和经典向上发展项目主任合作，让地区高中的教师和学生参与进来。让高中生和本科生参与研究对于推进年轻人的 STEM（科学、技术、工程和数学）教育非常重要。技术摘要：本研究利用层间声子拉曼光谱探索各种范德华异质结构的基本物理性质（通常在低频）和光致发光。研究项目包括： (i) 开发基于层间声子的拉曼技术来表征异质结构超晶格的旋转角和莫尔波长。这项研究提供了一种无需使用扫描隧道显微镜即可表征莫尔图案特征的简单方法； (ii) 探索复杂多层范德华异质结构的电子、光学和振动特性以及插入不同中间层材料的 MoS2 双层中的间接-直接能隙跃迁。这项研究为使用堆叠范德华多层膜设计新型电子和光电器件提供了重要指导； (iii) 研究涉及狄拉克材料的范德华异质结构。研究小组特别研究了扭曲双层石墨烯放置或夹在六方氮化硼之间后电子能带结构的变化。这项研究探讨了异质界面处石墨烯电子和振动特性的变化； (iv) 探究双栅极扭曲双层石墨烯器件中载流子和层间声子之间的相互作用。这项研究探讨了两个带电石墨烯层之间的库仑相互作用以及选通时形成的层间电势。这些研究活动中建立的技术和方法可以应用于由以任何所需顺序堆叠的任何二维晶体形成的异质结构。