Ultrafast Structural Dynamics in Materials at Atomic to Microscale Resolution

在未来的几年里，材料物理学的创新将取决于我们理解和控制材料结构与其性能之间的密切关系的能力，无论是处于平衡还是远离平衡。在美国能源部(DOE)最近的一份报告中，这一目标被认为是对基础科学的重大挑战。这需要新的工具，而PIS研究计划专注于开创性地开发仪器和方法，这些仪器和方法可以提供关于复杂材料的基本缺失信息，以及远离平衡的系统的结构和性质。这项研究计划预计将对所有传统科学学科(物理、化学、生物学)产生广泛影响。 特别是，麦吉尔的Siwick群的RF压缩超快电子衍射的最新发展使所提出的研究成为可能。射频压缩在仪器性能上的数量级提高为UED研究定义了一种新的最先进的技术，这项技术最近为几种材料的原子级结构动力学提供了前所未有的视角，并展示了通过超快光学诱导相变将来自晶格结构重组的动力学贡献与来自轨道占有率(或电荷密度)变化的动力学贡献区分开来的能力。结合Siwick实验室提供的最先进的超高速宽带反射率和蒙特利尔地区新的高级成像基础设施(基于两个独一无二的动态和超快透射电子显微镜)，PI拥有一套先进的表征方法，能够询问材料中接近细节水平的时间演变过程，这是我们用来研究材料平衡结构/性能的工具所提供的。通过这一提议，PI将利用这些突破性的工具和世界级的能力来测量相变过程中的材料结构和性能，以同时研究结构变化对材料功能的影响以及材料中光激发在其长度(Nm)、时间(fs-ps)和能量(MEV)的自然尺度上的动力学。 这些工具将被用来解决一些具有重大影响的目标问题，包括(但不限于)： 1.电子-电子关联、轨道选择和晶格扭曲在一大类强关联氧化物的金属-绝缘体转变中的各自作用。 2.从偶氮苯、电荷转移盐到蛋白质晶体等一系列光活性有机晶体的光诱导结构动力学。

In the coming years, innovation in materials physics will reside in our ability to understand and control the intimate relationships between the structure of materials and their properties, both at and far from equilibrium. This goal has been recognized as a Grand Challenge for the fundamental sciences in a recent US Department of Energy (DOE) report. This requires new tools, and the PIs research program is focused on the pioneering development of instruments and methods that can provide essential missing information on complex materials, and the structure and properties of systems far from equilibrium. This research program is expected to have a broad impact across all traditional scientific disciplines (Physics, Chemistry, Biology). In particular, the proposed studies are enabled by the very recent development of RF compressed ultrafast electron diffraction in the Siwick group at McGill. The orders of magnitude enhancement in instrumentation performance that RF compression provides has defined a new state-of-the-art for UED studies, a technique that has recently provided unprecedented views of atomic-level structural dynamics for several materials and demonstrated the ability to separate dynamical contributions that come from the reorganization of lattice structure from that which comes from changes in orbital occupancy (or charge density) through an ultrafast optically induced phase transition. Combined with the state-of-the-art ultrafast broadband reflectivity also available in the Siwick lab and the new Infrastructure for Advanced Imaging in the Montreal area (based on two one-of-a-kind dynamic and ultrafast transmission electron microscopes) the PI has at his disposal a suite of advanced characterization methods is capable of interrogating time-evolving processes in materials near the level of detail that is available from the tools we use to study the equilibrium structure/properties of materials. Through this proposal the PI will apply these breakthrough tools and world world-class capabilities to measure material structures and properties during transformations to study the effects of structural changes on material functionalities and the dynamics of optical excitation in materials on their nature scales of length (nm), time (fs–ps) and energy (meV) simultaneously. These tools will be employed to address a number of target problems of high impact, including (but not limited to): 1. The respective role of electron-electron correlations, orbital selection and lattice distortions in the metal-insulator transitions of a broad class of strongly correlated oxides. 2. Optically induced structural dynamics in a range of 'light active' organic crystals from azobenzenes and charge transfer salts to protien crystals.