ULISSE - Using Electrostatic Interactions to Control Supramolecular Self-Assembly at Surfaces

纳米技术研究对当代社会的一个主要承诺是，下一代分子级设备将比基于当前技术的设备更快、更通用、更节能。有机分子是未来纳米级器件制造的最佳候选材料之一。它们的化学结构可以很容易地修改，这表明精心设计的分子原则上可以自发地组装成任何想要的结构，而不需要自上而下的干预。相应地，在分子自组装领域，通过设计分子之间的化学连接来优化是一个被广泛探索的概念，尽管在某种程度上，由于键合的短程特性，其范围受到了限制。最近的研究表明，通过远程静电相互作用的贡献，控制有机分子的电荷状态可能为确定更大尺度上的组装特征提供进一步的直接处理。然而，尽管它对纳米制造有潜在的影响，这种可能性实际上仍未被探索。与此同时，分子有机材料的电子特性也吸引了大量且不断增长的兴趣。事实上，有机电子学目前是一个蓬勃发展的领域，对社会具有战略意义的新型发光和光能量转换应用正在研究中，早期设备正在生产中。同样，这些器件的一些关键特性是由发生在纳米尺度上的过程决定的，并且涉及静电相互作用。在金属表面和沉积在其上的有机分子层之间的电荷转移是已知的，例如，控制金属-有机接触的导电特性。然而，对于如何正确地模拟这种金属-有机界面，尚未达成共识，设备设计通常是一个反复试验的过程。本项目将研究有机分子与金属衬底之间的电荷转移过程及其与自组装的联系。利用理论和实验，我们将研究这些过程是否可以通过适当选择分子、底物和覆盖物来预测和控制。这项工作将有助于理解分子自组织的基本原理，并揭示控制金属-有机界面能级排列的基本机制。至关重要的是，整体将远远大于部分的总和。也就是说，从电荷转移开始，追求自组装路线，我们将确定带电分子之间的远程力是否可以驱动新型超分子结构的自发形成。这将代表一种预测和控制装配的新工具。相反，从观察到的组装开始，追求有机电子路线，我们将研究特定的分子连锁模式是否可以揭示电荷转移的发生。这将为获取金属-有机界面电子特性的宝贵信息提供一条新途径。电子结构计算、光电发射光谱实验、分子动力学模拟和扫描隧道显微镜成像将贯穿整个研究。这将把两个战略研究领域联系起来，这两个领域可以相互极大地受益，即超分子组装的纳米制造和分子电子学，这是第一次在一个基于英国的综合项目中。

A major promise made by Nanotechnology Research to contemporary society is that next-generation molecular-scale devices will be faster, more versatile and more energy efficient than the ones based on current technology. Organic molecules are among the best candidate bricks for future nanoscale device fabrication. Their chemical structure can be easily modified, suggesting that carefully designed molecules could in principle assemble spontaneously into any desired structure, with no need of top down intervention. The optimisation by design of the chemical linkage between molecules has been, correspondently, an extensively explored concept in the molecular self-assembly field, albeit in some way limited in its scope by the short-range character of the bonding. Very recent research suggests that controlling the state of charge of organic molecules may provide a further direct handle to determine the assembly features on larger scales, through the contribution of long-range electrostatic interactions. However, this possibility is still virtually unexplored, in spite of its potential impact on nanofabrication. The electronic properties of molecular organic materials are, meanwhile, also attracting a massive, and ever growing, interest. Indeed, Organic Electronics is currently a booming field, with novel light-emission and light-energy conversion applications of strategic importance for society being investigated and early devices being produced. Once more, some crucial properties of these devices are determined by processes occurring at the nanometre scale and involve electrostatic interactions. Charge transfer between a metal surface and a layer of organic molecules deposited on it is known, e.g., to control the electric conduction properties of a metal-organic contact. However, no consensus has been reached yet on how to model such metal-organic interfaces properly, and device design is often a trial-and-error process.The present project will study charge transfer processes between organic molecules and metallic substrates, and their connection with self-assembly. Using both theory and experiment, we will investigate if these processes can be predicted and controlled by appropriate choices of molecules, substrates and coverages. The work will be useful for both understanding fundamental principles of molecular self-organisation and for unravelling the fundamental mechanisms that govern energy level alignment at metal-organic interfaces. Crucially, the whole will be much more than the sum of the parts. Namely, starting from charge transfer and pursuing the self-assembly route, we will determine if long-range forces between charged molecules can drive the spontaneous formation of novel classes of supramolecular structures. This would represent a novel tool for predicting and controlling the assembly. Conversely, starting from the observed assembly and pursuing the Organic Electronic route, we will investigate if specific molecular linkage patterns can reveal the occurrence of charge transfer. This would provide a novel route to precious information on the electronic properties of metal-organic interfaces. Electronic structure calculations, photoemission spectroscopy experiments, molecular dynamics simulations, and scanning tunnelling microscopy imaging will be used throughout the investigation. This will link two strategic fields of research which can greatly benefit from each other, namely nanofabrication by supramolecular assembly and molecular electronics, for the first time in an integrated UK-based project.