New phenomena at the interface between 2D materials and liquids

该项目探索了两个非常不同的系统之间的界面：二维材料（2dm，例如石墨烯，单层碳；磷烯，单层磷；单层二硫化钼）和液体（例如：水，生物流体，乙醇）。该项目追求两个主要的科学目标。首先，通过可控地改变与2dm接触的液体的化学成分、介电常数和流速来修饰和研究2dm中电子之间的相互作用。这条研究路线有望揭示抑制2dm中电子散射的方法。更好地理解载流子散射，反过来，应该推进这些材料在未来电子设备中的潜在应用。该项目的第二个重点是使用2dm作为液体化学成分、流速和纳米级结构的超灵敏探针。更好地了解这些参数可以为更高效的水过滤器和能够记录单个神经元电活动的生物传感器铺平道路。该项目包括一个重要的教育组成部分。ppi继续参与“桥梁”项目，这是美国最成功的项目之一，旨在让少数族裔参与前沿研究，从而获得博士学位。通过参与范德比尔特大学本科生研究体验和范德比尔特大学暑期科学院项目，pi继续让本科生和高中生参与他们的研究。最后，该项目的多学科性质跨越了从凝聚态物质和计算物理到化学、生物学和成像等领域，有助于为博士研究生在科学和工业领域的成功职业生涯做好准备。技术描述本项目探索二维材料（2dm，如石墨烯，MoS2，磷烯）和液体（如水，己烷）之间的界面，以(i)研究和设计2dm微环境对其性质的影响，以及（ii）了解纳米厚界面液体层的行为。为了解决这些问题，pi开发了一种灵活的装置，可以将电接触的悬浮2dm放置在化学成分、电势、离子浓度和流速受控的液体中。通过电传输、霍尔效应和光学测量对2dm进行了询问，并通过最先进的电子显微镜和计算模型进行了研究。在项目的第一部分中，设置用于在2dm的哈密顿量中可控地“调优”多个参数。通过控制器件周围液体的介电常数，可以调节2dm中电子之间相互作用的有效强度。通过在离子液体和悬浮在其中的2dm之间施加电势，迄今为止无法达到的载流子密度达到1015 cm-2。在2dm中，通过在器件和液体之间施加大的电势来诱导缺陷。这些方法有望揭示2dm中的多种奇异现象，包括门控超导和激子坍缩。在项目的第二部分，2dm被用作超灵敏传感器来研究纳米厚的液体与固体接触界面层的性质。通过测量流动液体中的离子与石墨烯中的电子之间的库仑阻力所产生的电流，可以确定界面层的“滑移”速度。通过测量2DM/液电容，探测界面液层的介电常数。

NONTECHNICAL DESCRIPTIONThis project explores the interface between two very different systems: two-dimensional materials (2DMs, e.g.: graphene, single monolayer of carbon; phosphorene, a single layer phosphorus; monolayer molybdenum disulfide) and liquids (e.g.: water, biofluids, ethanol). The project pursues two main scientific goals. First, interactions between electrons in 2DMs are modified and studied by controllably changing the chemical composition, dielectric constant and flow velocity of liquids in contact with 2DMs. This line of investigation is expected to reveal the approaches to suppress electron scattering in 2DMs. Better understanding of carrier scattering, in turn, should advance potential applications of these materials in future electronic devices. The second thrust of the project employs 2DMs as ultrasensitive probes of chemical composition, flow velocity, and nanoscale structure of liquids. Better understanding of these parameters can pave the way towards more efficient water filters and biosensors capable of recording electrical activity of individual neurons. The project includes a significant educational component. The PIs continue their participation in the Bridge program, one of the most successful efforts in the nation to involve underrepresented minorities in cutting-edge research leading to the PhD degree. The PIs continue to involve undergraduates and high school students in their research through their participation in Vanderbilt's Research Experience for Undergraduates and Vanderbilt's Summer Science Academy programs. Finally, the multidisciplinary nature of the project spanning the fields from condensed matter and computational physics to chemistry, biology, and imaging helps preparing PhD students for successful careers in science and industry.TECHNICAL DESCRIPTIONThis project explores the interface between two-dimensional materials (2DMs, e.g. graphene, MoS2, phosphorene) and liquids (e.g. water, hexane) to (i) study and engineer the effects of the microenvironments of 2DMs on their properties, and (ii) understand the behavior of nanometer-thick interfacial liquid layers. To tackle these problems, the PIs developed a flexible setup that allows placing electrically contacted suspended 2DMs into liquids with controlled chemical composition, electrical potential, ionic concentration, and flow velocity. The 2DMs are interrogated via electrical transport, Hall effect, and optical measurements and studied through state-of-art electron microscopies and computational modeling. In the first part of the project, the setup is used to controllably "tune" multiple parameters in the Hamiltonians of 2DMs. The effective strength of interactions between electrons in 2DMs is tuned by controlling the dielectric constant of liquids surrounding the devices. Hitherto unattainable carrier densities up to 1015 cm-2 are achieved by applying an electric potential between ionic liquids and 2DMs suspended in them. Defects are induced in 2DMs by applying large electric potentials between devices and the liquid. These approaches are expected to reveal multiple exotic phenomena in 2DMs including gate-controlled superconductivity and excitonic collapse. In the second part of the project, the 2DMs are used as ultrasensitive sensors to study properties of a nanometer-thick interfacial layer of liquid in contact with a solid. By measuring the current induced by the Coulomb drag between ions in the flowing liquid and electrons in graphene, the "slip" velocity of the interfacial layer is determined. By measuring the 2DM/liquid capacitance, the dielectric constant of the interfacial liquid layer is probed.