Interactive Microscopy of Hybrid Scattering Structures

这个项目的目标是了解电流如何在小型设备中流动，当它遇到大小与单个原子大小相同的障碍物时。这对于使计算机更快、更节能的电子设备小型化是很重要的，但当这些设备开始达到与组成原子之间的距离相当的尺寸时，也会产生新的问题。在这种尺寸体系下，像单个错位原子这样的微小缺陷——在过去可能无关紧要——突然之间就会变得非常重要。这个项目的重要性在于，它有助于精确地阐明不同原子尺度的物体如何影响小型设备中的电流，从而帮助技术成功地在最大程度上小型化。这里的难点在于需要在实际运行的器件内部对原子尺度结构进行成像，以确定原子尺度结构与器件性能之间的因果关系。这是通过扫描隧道显微镜完成的，根据量子力学的规则，它可以看到单个原子，也可以拍摄电子在尽可能小的障碍物周围流动的图像，比如水流。其他类型的显微镜被用于聚焦电子束和氦离子束，以有意地创造出非自然发生的原子尺度结构，从而有意地在尽可能小的距离上操纵电子设备的结构。该项目更广泛的影响在于其强大的教育和推广组成部分，以及它为研究生、本科生和高中生提供高水平的科学培训，为他们在STEM领域的职业生涯做好准备。研究人员和团队成员在各个层面开展了推广工作，包括为伯克利学校/大学合作推广实施计划创建纳米科学和技术教育材料，以及参与湾区学校科学计划。未被充分代表的少数族裔学生将通过伯克利夏季数学和科学荣誉学院项目在实验室获得为期5周的实习机会，并通过与加州大学高级学位项目的合作伙伴关系获得指导机会。本项目的主要目标是更好地理解二维材料中的电子在平衡（即零输运电流）和非平衡（非零输运电流）条件下如何在原子尺度上与不同结构相互作用。传统的制造和成像技术无法达到操作设备的原子尺度，因此在理解二维材料中的原子尺度结构如何改变设备功能方面出现了空白。该项目将通过开发新技术来合成二维设备中的原子精确结构，并在设备运行期间在原子尺度上对它们进行成像，从而帮助填补这一空白。一个中心问题是如何平衡电子性质的微观散射结构导致他们的非平衡响应在高电流密度和不同的器件条件下。具体目标包括对单层石墨烯场效应晶体管（FET）器件表面的点散射体、量子点和一维超晶格的这种行为的控制和可视化。利用新型透射电子显微镜（TEM）、扫描隧道显微镜（STM）和聚焦离子束合成技术，以前所未有的空间精度修饰氮化硼衬底，以设计石墨烯场效应晶体管封盖层的电子特性。该项目结合了主要研究人员的TEM，设备制造和扫描探针显微镜专业知识，探索一套独特的纳米级实验系统。这个项目的智力价值在于，它允许访问从未被探索过的物理机制，包括不同原子尺度散射体的非平衡性质，如库仑杂质、共振散射体和破坏亚晶格对称性的sp3缺陷。在石墨烯中探索了尽可能小的原子精确量子点，为可视化新型边缘状态行为以及电子透镜创造了机会。量子点波函数以前所未有的分辨率成像，使长期的理论预测得以验证。研究工程电各向异性系统的缺陷行为是二维材料研究的一个新前沿。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 AbstractThe goal of this project is to understand how electrical current flows in small devices where it encounters obstacles whose size is on the order of the size of a single atom. This is important for miniaturizing electrical devices in order to make computers faster and more energy efficient, but it also creates new problems as the devices begin to reach sizes comparable to the distance between constituent atoms. In this size regime tiny defects such as a single misplaced atom - which might not have mattered in the past - suddenly can become very significant. The importance of this project is that it helps to clarify precisely how different atomic-scale objects affect electrical current in small devices, thus helping technology to be successfully miniaturized to the greatest extent possible. The difficulty here is the need to image atomic-scale structure inside actual operating devices to determine the cause-and-effect relationship between atomic-scale structure and device performance. This is accomplished using a scanning tunneling microscope that can see single atoms and also image electrons as they flow around the smallest possible obstacles, like water in a stream, according to the rules of quantum mechanics. Other types of microscopes are used that involve focused electron beams and helium ion beams to intentionally create atomic-scale structures that are not naturally occurring and thus intentionally manipulate the structure of electrical devices over the smallest distances possible. The broader impacts of this project lie in its strong education and outreach components and the fact that it provides high-level scientific training to graduate students, undergraduates, and high school students, preparing them for careers in STEM fields. Outreach efforts are performed at all levels by the investigators and team members and include creation of educational materials on nanoscience and technology for the Berkeley School/University Partnership Outreach Implementation Plan, as well as participation in the Bay Area Science in Schools program. Underrepresented minority students will be offered 5-week internships in the laboratories through the Summer Math and Science Honors Academy program at Berkeley, as well as mentoring opportunities through partnership with the UC Leadership Excellence through Advanced Degrees Program.Technical AbstractThe main goal of this project is to better understand how electrons in 2D materials interact with different structures at the atomic-scale under both equilibrium (i.e., zero transport current) and nonequilibrium (non-zero transport current) conditions. Conventional fabrication and imaging techniques are unable to access the atomic-scale for operational devices and so a gap has opened up in the understanding of how atomic-scale structures in 2D materials alter device functionality. This project will help to fill that gap by developing new techniques to synthesize atomically-precise structures in 2D devices and also to image them at the atomic-scale during device operation. A central question that is addressed is how the equilibrium electronic properties of microscopic scattering structures lead to their nonequilibrium response under high current density and differing device conditions. Specific objectives include the control and visualization of this behavior for point scatterers, quantum dots, and 1D superlattices at the surfaces of single-layer graphene field-effect transistor (FET) devices. Novel transmission electron microscopy (TEM), scanning tunneling microscopy (STM), and focused ion beam based synthesis techniques are used to modify boron nitride substrates with unprecedented spatial precision to engineer the electronic properties of graphene FET capping layers. This project combines the principal investigators' TEM, device fabrication, and scanned probe microscopy expertise to explore a unique set of nanoscale experimental systems. The intellectual merit of this project lies in the fact that it allows access to physical regimes that have never been explored, including the nonequilibrium properties of different atomic scale scatterers such as Coulomb impurities, resonant scatterers, and sp3 defects that break sublattice symmetry. The smallest possible atomically-precise quantum dots are explored in graphene, creating opportunity to visualize new types of edge-state behavior as well as electron lensing. Quantum dot wavefunctions are imaged with unprecedented resolution, enabling long-standing theoretical predictions to be tested. Defect behavior is studied in systems with engineered electrical anisotropy, a new frontier in 2D materials research.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.