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

非技术摘要：我们正在接近摩尔定律的不可避免的终点：即一个高密度集成电路上的晶体管数量每18个月到2年就会翻一番。这一趋势至少在50年来一直是现代技术社会生产力增长的引擎。为了延续这一趋势，一种令人兴奋的二维材料正在成为一个重大机遇。原子薄的层状材料，通常被称为二维材料，代表了与传统半导体（如硅）的根本背离，传统半导体包括当前的电子器件，模仿纸张而不是大的三维块。这种二维特性带来了不同寻常的特性，例如沿薄膜沿着方向的电阻极低，而垂直于薄膜方向的导电性却很差，这使得它非常适合用于极高性能的光学和电子电路。但是，与所有电子设备一样，材料之间的连接在制造它们的光学和电子设备的整体功能中起着核心作用。事实上，连接点通常是器件性能链中最薄弱的环节。在这个项目中，研究小组正在研究具有不同维度的不同材料界面处的物理和能量传输。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）以及新型二维化合物之间的连接。其目标是了解和增强跨结的能量和电荷传输，最终目标是大大提高电子和光学电路的性能。这种杂化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。该研究项目具有很强的教育成分，涉及研究生和本科生培训，以及为代表性不足的少数族裔高中生提供暑期研究机会。技术摘要：了解不同半导体材料之间的能量和电荷转移是实现利用不同接触材料的独特优势的器件的关键。在这种材料组合中可以共享或优化的感兴趣的特性包括有机物的电光振荡器强度和机械柔性，沿着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、二维过渡金属二硫属化物和无机量子威尔斯阱对于光电应用具有吸引力。然而，对这些物质系统之间形成的界面及其涌现特性的了解要少得多。三维有机和无机半导体与二维货车德瓦耳斯固体形成结的基本性质为研究界面物理提供了一个理想的平台。该团队研究了不同组成和维度的系统之间的三种独特的异质界面：（i）有机半导体-二维材料，（ii）无机半导体-二维材料和（iii）不同二维材料之间的横向异质结。稳态和时间分辨光谱测量（包括近场显微术沿着与传输测量）的组合用于获得在这些基本上未探索的界面处管理光子和电子的相互作用的物理学的基本认识，目标是开发基于跨界面的能量和电荷转移过程的观察的量子力学模型，杂化激发态的形成及其输运和非线性光学性质。预期的成果包括通过材料、界面特性、结构和薄膜形态的工程设计最终利用材料和维度的组合，并对其进行调整，以实现特定应用的优化性能。

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.