Attosecond time-resolved streaking spectroscopy as a probe of strong field effects at the solid-vacuum interface of layered materials

在固体真空界面附近的强电磁场可以动态地改变表面性质，并可能用于控制界面上的电荷转移过程的子周期时间尺度。这种强场控制的实施需要两个，原子长度尺度上的实际场分布的完整知识和在这个大规模扰动多体系统中发生的复杂过程的理解。目前，在界面附近的原子尺度的局部动态场分布是未知的。这个问题是解决在本项目中，旨在提高对强IR场在接口的行动的基本过程的理解，也解决了有关的光电子过程的动态开放的问题。为了实现这些目标，采用固体表面的阿秒条纹光谱。由单个阿秒XUV脉冲激发的光电子通过衬底-真空界面传播，并与同时存在的强红外条纹场相互作用。确定所观察到的光电子延迟的基本机制和过程仍在争论中，还没有完整的理论模型。在这个项目中，过渡金属二硫属化物形成层状货车德瓦尔斯晶体和其他层状材料被用来定位发射的核心级光电子的原子精度的起源。实验结果表明，界面附近原子尺度的局域场分布对光电子拖尾有很强的影响。使用这种层状材料和单货车德瓦尔斯晶体单层的进一步实验将提供对这种工作假设的检验。对条纹效应的角度依赖性的系统研究应提供有关局部条纹场影响的基本信息。

Strong electromagnetic fields in the vicinity of the solid-vacuum interface can dynamically change surface properties and might serve to control interfacial charge transfer processes on a sub-cycle time-scale. The implementation of such strong field control requires both, the complete knowledge of the actual field distribution on an atomic length scale and the understanding of the complex processes occurring in this massively perturbed many-body system. Presently the atomic-scale local dynamic field distribution in the vicinity of the interface is unknown. This issue is addressed in the present project that aims to improve the understanding of the fundamental processes governing the action of strong IR fields at interfaces and also addresses open questions concerning the dynamics of the photoemission process. To achieve these goals attosecond streaking spectroscopy at solid surfaces is employed. Photoelectrons excited by a single attosecond XUV pulse propagate through the substrate-vacuum interface and interact with the simultaneously present intense IR streaking field. The fundamental mechanisms and processes determining the observed delays in photoemission are still under debate and no complete theoretical model is available yet. In this project transition metal dichalcogenides forming layered van der Waals crystals and other layered materials are employed to localize the origin of the emitted core level photoelectrons with atomic precision. The experiments conducted up to now indicate that the photoelectron streaking is strongly affected by the atomic scale local field distribution close to the interface. Further experiments using such layered materials and single van der Waals crystal monolayers will provide a test of this working hypothesis. The systematic investigation of the angular dependence of the streaking effect shall provide essential information on the impact of local streaking fields.