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质之间的密切关系的能力，无论是在平衡状态还是远离平衡状态。 在美国能源部（DOE）最近的一份报告中，这一目标被认为是基础科学面临的巨大挑战。 这需要新的工具，PI研究计划的重点是开拓性的开发仪器和方法，可以提供复杂材料的基本缺失信息，以及远离平衡的系统的结构和特性。 该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，拟议的研究是由麦吉尔大学Siwick小组最近开发的RF压缩超快电子衍射实现的。 射频压缩提供的仪器性能的数量级增强已经为UED研究定义了一个新的最新技术水平，这种技术最近为几种材料提供了前所未有的原子级结构动力学视图，并证明了将来自晶格结构重组的动力学贡献与来自轨道占有率变化的动力学贡献分开的能力（或电荷密度）通过超快光学诱导相变。结合Siwick实验室和蒙特利尔地区新的高级成像基础设施中也提供的最先进的超快宽带反射率（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，能够询问时间-材料的演变过程接近我们用来研究材料平衡结构/性质的工具所提供的细节水平。 通过这项提案，PI将应用这些突破性的工具和世界一流的能力来测量材料结构和性能，同时研究结构变化对材料功能的影响以及材料中光激发的动力学对长度（nm），时间（fs-ps）和能量（meV）的自然尺度的影响。 ** 这些工具将用于解决一些具有高影响力的目标问题，包括（但不限于）：*1.电子-电子关联、轨道选择和晶格畸变在一类强关联氧化物的金属-绝缘体转变中的各自作用。（注2） 从偶氮苯和电荷转移盐到蛋白质晶体的一系列“光活性”有机晶体中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.