Materials on the edge: nanoscale understanding and control of interfacial and interaction-driven electronic properties of materials

今天的技术在很大程度上依赖于过去50-100年的材料。随着我们寻求解决人类挑战和推动未来技术，将需要新的材料和结构来支持这些应用。其中许多将属于“量子材料”的范畴，这种材料的性质与我们现在所依赖的金属、半导体和绝缘体有很大不同，为新的应用打开了许多可能性。以新的方式组合多种材料会带来更多的机会。然而，这些材料和结构的发展需要越来越详细地了解它们的电子态，这些电子态源于它们的原子级结构，它决定了电子和光学性质、反应性等。许多最令人兴奋的新兴材料是那些以各种方式“处于边缘”的材料：处于电子相变尖端的材料，处于化学稳定性边缘的材料，以及材料之间的界面，在这些界面上，电子性质可能与主体材料截然不同，具有最大的设计电子景观的潜力。仅举几个例子，包括形成有机光伏器件的光活性受体-供体界面的分子，用于能源和催化应用的吸附金属-有机络合物，原子工程石墨烯，以及具有不寻常电子状态的材料之间的界面，如拓扑材料和超导体。在每种情况下，对结构和局部环境的控制都是必不可少的，因为结构中的微小扰动(例如缺陷或结构无序)可能会对我们希望使用的结果性质产生巨大影响。 对这些新兴材料的研究需要能够将局部电子结构与原子和分子结构联系起来的工具，特别是在缺陷和界面主导所产生的性质的情况下。扫描探针显微镜(SPM)技术提供了原子尺度上的局部结构和电子信息。使用逐个像素的隧道光谱和静电力光谱以及揭示材料原子结构的成像方法，我们将把局部结构信息与这些关键表面和界面的电子态联系起来，以了解结构是如何驱动重要的性质的。为了扩展已经庞大的扫描探针显微镜技术工具箱，我们正在开发组合的光学-扫描探针显微镜方法，进行互补测量来研究界面上的电子态动力学，并建造新的仪器，这些仪器将与诸如角度分辨光电发射和输运测量等互补技术相联系。这些搭桥实验将提供SPM提供的原子尺度理解与大多数应用程序所基于的结果宏观尺度属性之间的迫切需要的联系。

Today's technologies largely rely on the materials of the past 50-100 years. As we seek to solve human challenges and propel futuristic technologies, new materials and structures will be required to underpin these applications. Many of these will fall into the category of “quantum materials”, where properties differ substantially from the metals, semiconductors and insulators we rely on now, opening up many possibilities for novel applications. Still more opportunities arise from combining multiple materials in new ways. However, development of these materials and structures requires increasingly detailed understanding of their electronic states, arising from their atomic-scale structure, which dictate electronic and optical properties, reactivity, and more. Many of the most exciting emerging materials are those that are, in a variety of ways, “on the edge”: materials on the cusp of electronic phase transitions, at the edge of chemical stability, and interfaces between materials where electronic properties can vastly differ from the bulk and there is the greatest potential to engineer electronic landscapes. Just a few examples of these include molecules that form photoactive acceptor-donor interfaces for organic photovoltaic devices, adsorbed metal-organic complexes for energy and catalysis applications, atomically engineered graphene, and interfaces between materials with unusual electronic states such as topological materials and superconductors. In each of these cases, control over the structure and local environment is essential as small perturbations in structure (e.g. defects or structural disorder) can have a dramatic influence on the resulting properties we hope to use. Investigation of these emerging materials requires tools that can connect the local electronic structure to the atomic and molecular structure, especially where defects and interfaces dominate resulting properties. Scanning probe microscopy (SPM) techniques provide both local structural and electronic information on the atomic scale. Using pixel-by-pixel tunnelling spectroscopy and electrostatic force spectroscopy alongside imaging methods that reveal the atomic structure of materials we will correlate local structural information with electronic states at these key surfaces and interfaces to understand how structure drives important properties. To expand the already vast toolbox of SPM techniques, we are developing combined optical-SPM methods, undertaking complementary measurements to investigate the dynamics of electronic states at interfaces, and building new instruments that will bridge to complementary techniques such as angle resolved photoemission and transport measurements. These bridging experiments will provide much-needed connection of the atomic-scale understanding provided by SPM to the resulting macro-scale properties most applications are built upon.