Ultrafast local structural and electronic dynamics in chiral thin films

改变薄膜材料的手性的超快过程在不同的领域中具有重要的应用，例如液晶排列的膜和用于自旋电子学和光学数据存储的薄层。这种手性膜经常显示出在微观长度尺度上的圆二色性（CD）的显著不均匀性和具有来自线性二色性（LD/LD '）、圆双折射（CB）和线性双折射（LB/LB'）的隐藏贡献的表观CD信号。此外，局部有利的膜的结构顺序有很大的影响，其手性响应。理解这种手性系统的动力学需要超快的时间分辨率和高的空间分辨率。因此，在这个建议中，我们将实施两种新的方法，手性敏感的时间分辨显微镜：基于椭圆偏振的超快宽带瞬态圆二色性显微镜和超快瞬态圆偏振发光显微镜，两者都具有衍射限制的空间分辨率。使用稳态Müller矩阵显微镜的薄膜表征将提供关于CD、LD/LD '、CB和LB/LB'贡献方面的偏振变化的完整信息。本文的主要研究内容之一是手性有机薄膜结构动力学的时间分辨CD光谱。这些包括聚集诱导的异质性的超快局部响应的手性共聚物薄膜和photoswitch-driven超分子重排在预对准的双相。另一部分将讨论无机和混合无机-有机系统的空间分辨手性动力学，特别是钙钛矿激发化合物的手性薄膜以及未掺杂和掺杂的相变材料。在这里，我们的目标是了解自旋去极化的动力学，即钙钛矿材料的局部“手性记忆”。这一结果与自旋电子学的未来应用有关。我们还研究了低维钙钛矿的空间动力学，这是嵌入在液晶，以提高其手性光学响应。此外，我们将使用圆偏振作为相变材料中超快信息存储的“附加维度”。薄膜显示出强大的“非CD”的贡献，也将使用超快米勒矩阵光谱。

Ultrafast processes changing the chirality of thin-film materials have important applications in diverse fields, such as films of liquid crystal arrangements and thin layers for spintronics and optical data storage. Such chiral films frequently show substantial inhomogeneities in circular dichroism (CD) on a microscopic length scale and apparent CD signals with hidden contributions from linear dichroism (LD/LD'), circular birefringence (CB) and linear birefringence (LB/LB'). In addition, the locally favored structural order of the films has a strong impact on their chiral response. Understanding the dynamics of such chiral systems requires both ultrafast time resolution and high spatial resolution. In this proposal, we will therefore implement two new methods for chirality-sensitive time-resolved microscopy: ellipsometry-based ultrafast broadband transient circular dichroism microscopy and ultrafast transient circularly polarized luminescence microscopy, both with diffraction-limited spatial resolution. The thin-film characterization using steady-state Müller matrix microscopy will provide complete information regarding polarization changes in terms of the CD, LD/LD', CB and LB/LB' contributions. One of the main investigations in this proposal deals with the time-resolved CD spectroscopy of the structural dynamics in chiral organic thin films. These include the aggregate-induced heterogeneity of the ultrafast local response in chiral copolymer thin films and photoswitch-driven supramolecular rearrangements in pre-aligned cholesteric phases. Another part will address the spatially resolved chiral dynamics of inorganic and hybrid inorganic-organic systems, specifically chiral thin films of perovskite-inspired compounds as well as undoped and doped phase-change materials. Here we aim to understand the dynamics of spin depolarization, i.e. the local "chiral memory" of perovskite materials. The result is relevant to future applications in spintronics. We also investigate the spatial dynamics of low-dimensional perovskites, which are embedded in cholesteric liquid crystals, in order to enhance their chiral optical response. Furthermore, we will use circular polarization as an "added dimension" for ultrafast information storage in phase-change materials. Thin films showing strong "non-CD" contributions will be also characterized using ultrafast Müller matrix spectroscopy.