Collaborative Research: OP-Interface States and Excitons at Heterojunctions Between Two and Three Dimensional Materials Systems

非技术摘要：摩尔定律不可避免地要走到尽头了。摩尔定律是指高密度集成电路上晶体管的数量每18个月到2年就会翻一番。至少50年来，这一趋势一直是现代技术社会生产力增长的引擎。为了扩展这一趋势，一类令人兴奋的二维材料正在成为一个重大机遇。原子薄层材料，通常被称为二维材料，代表了对传统半导体（如硅）的彻底背离，这种半导体包括当前的电子设备，模仿纸张而不是大的三维块。这种二维特性导致了不寻常的特性，例如沿薄片的电阻非常低，但垂直于薄片的导电性很差。这使得它非常适合用于极高性能的光学和电路。但是，就像在所有电子设备中一样，材料之间的连接在制造光学和电子设备的整体功能中起着核心作用。事实上，结通常是器件性能链中最薄弱的环节。在这个项目中，研究小组正在研究不同维度的不同材料界面的光物理和能量传输。具体来说，该团队探索了有机半导体、传统无机半导体（如硅和砷化镓）和新型二维化合物之间的连接。其目标是了解和增强能量和电荷在结之间的传输，最终目标是大大提高电子和光学电路的性能。这种混合材料的潜在应用包括太阳能收集、发光二极管和安全量子信息技术。这个研究项目有很强的教育成分，包括研究生和本科生的培训，以及为少数民族高中学生提供的暑期研究机会。技术摘要：了解不同半导体材料界面间的能量和电荷传递是实现利用不同接触材料独特优势的器件的关键。在这些材料组合中可以共享或优化的特性包括超高光学振荡器强度和有机物的机械柔韧性，以及在有限维无机半导体中发现的非常大的电荷迁移率和量子离域。正是这些方面使得有机分子、二维过渡金属二硫族化合物和无机量子阱在光电应用中具有吸引力。然而，人们对这些材料系统之间形成的界面及其涌现特性知之甚少。三维有机和无机半导体与二维范德华固体形成结的基本性质为研究界面物理提供了理想的平台。该团队研究了不同组成和维度系统之间的三种独特类型的异质界面：(i)有机半导体-二维材料，（ii）无机半导体-二维材料，（iii）不同二维材料之间的横向异质结。结合稳态和时间分辨光谱测量，包括近场显微镜和传输测量，用于获得控制光子和电子在这些很大程度上未被探索的界面上相互作用的物理的基本欣赏，目标是建立基于观察界面上的能量和电荷转移过程的量子力学模型。杂化激发态的形成及其输运以及非线性光学性质。预期的结果包括通过材料工程、界面特性、结构和薄膜形态及其调谐来实现特定应用的优化性能，从而最终开发材料和尺寸的组合。

Non-technical abstract: We are reaching the inevitable end of Moore's Law: the scaling law that says the number of transistors on a dense integrated circuit will double every 18 months to 2 years. This trend has been the engine of productivity growth of modern technological societies for at least 50 years. To extend this trend, an exciting class of two-dimensional materials is emerging as a major opportunity. Atomically thin layered materials, often called two dimensional materials, represent a radical departure from conventional semiconductors such as silicon that comprise current electronic devices, mimicking sheets of paper as opposed to large three dimensional blocks. This two dimensionality leads to unusual properties such as exceptionally low resistance along the sheet, yet poor conduction perpendicular to it. This makes it ideal for use in extremely high performance optical and electrical circuits. But, as in all electronic devices, junctions between materials play a central role in the overall functioning of the optical and electronic devices out of which they are made. In fact the junction is often the weakest link in the device performance chain. In this project, the research team is investigating the photophysics and energy transport at interfaces of dissimilar materials with different dimensionality. Specifically, the team explores junctions between organic semiconductors, traditional inorganic semiconductors such as silicon and gallium arsenide, and the new class of two dimensional compounds. The goal is to understand and enhance the energy and charge transport across the junctions, ultimately with the goal of vastly improving the performance of electronic and optical circuits. The potential applications of such hybrid materials include solar energy harvesting, light emitting diodes and secure quantum information technologies. This research project has a strong educational component that involves graduate and undergraduate student training, as well as summer research opportunities for underrepresented minority high school students. Technical Abstract: Understanding energy and charge transfer across interfaces between widely dissimilar semiconductor materials is key to realizing devices that exploit the unique advantages of the different contacting materials. The properties of interest that can be shared, or optimized in such materials combinations include ultrahigh optical oscillator strengths and mechanical flexibility of organics, along with the very large charge mobilities and quantum delocalization found in limited dimensional inorganic semiconductors. It is precisely these aspects that make organic molecules, two dimensional transition metal dichalcogenides and inorganic quantum wells attractive for optoelectronic applications. However, much less is known about interfaces that form between these material systems and their emergent properties. The fundamental nature of three dimensional organic and inorganic semiconductors forming junctions with two dimensional van der Waals solids presents an ideal platform to investigate interface physics. The team investigates three unique classes of heterointerfaces between systems of different composition and dimensionality: (i) organic semiconductor - two dimensional materials, (ii) inorganic semiconductor - two dimensional materials and (iii) lateral heterojunctions between dissimilar two dimensional materials. The combination of steady state and time resolved spectroscopic measurements including near field microscopies along with transport measurements are used to gain a fundamental appreciation of the physics governing the interplay of photons and electrons at these largely unexplored interfaces with the goal to develop quantum mechanical models grounded on observation of the energy and charge transfer processes across the interfaces, the formation of hybrid excited states and their transport as well as nonlinear optical properties. The anticipated outcomes include the ultimate exploitation of combinations of materials and dimensionalities through engineering of materials, interface properties, structures, and film morphologies and their tuning to achieve optimized performance for a particular application.