Electronic and optical properties of polyanionic metal clusters

有限系统的物理和化学性质通常以简单的方式与颗粒尺寸成比例，并显示出特征趋势。相比之下，非常小的团簇在改变原子数量时表现出明显的量子尺寸效应。最近开发的实验方法产生的质量选择，聚阴离子金属簇在数字射频陷阱开辟了机会，研究（金属）纳米系统上尚未访问的潜在表面。一个令人兴奋的方面是形成一个排斥库仑势作为一个特征，从而形成一个障碍之间的相互作用电荷排斥和电子-电子的相关性。高于真空水平的结合能允许通过电子隧穿势垒使复合物松弛。相对于分子和富勒烯，具有离域电子的聚阴离子体系的光诱导动力学至今还没有从实验和理论上详细研究。除了库仑势垒的电子结构和可能的各向异性外，该项目还侧重于聚阴离子金属簇的光学活性，重点是集体激发。目前，等离子体振子模式的衰减和纳米颗粒中的单电子能级耦合仍在讨论中。我们将进行实验，使用可调谐激光脉冲，以及泵浦探测技术，以研究聚阴离子金属簇的物理性质，使用角分辨光谱作为现有的电子飞行时间诊断的扩展。 我们的目标是表征电子能级结构，光学响应和超快动力学。在光电子发射过程中，跃迁和内弛豫是必须考虑的相关衰变途径。在实验中，我们集中在铜，银和金团簇，因为它们代表模型系统，由于它们的等电子结构。由于它们的等离子体性质，贵金属团簇在技术应用上也很有趣。

The physical and chemical properties of finite systems often scale in a simple way with the particle size and show characteristic trends. In contrast, very small clusters show distinct quantum-size effects when changing the number of atoms. Recently developed experimental methods for generating mass-selected, polyanionic metal clusters in digital radio frequency traps have opened up opportunities to study (metallic) nanosystems on not yet accessible potential surfaces. An exciting aspect is the formation of a repulsive Coulomb potential as a characteristic feature, whereby a barrier is formed by the interplay between charge repulsion and electron-electron correlations. Binding energies above the vacuum level allows for a relaxation of the complex by electron tunneling through the barrier. In contrast to molecules and fullerenes, the photo-induced dynamics of polyanionic systems with delocalized electrons has not been studied in detail by experiment and theory so far. In addition to the electronic structure and possible anisotropies of the Coulomb barrier, the project focuses on the optical activity of polyanionic metal clusters with emphasis on thecollective excitations. Currently, the decay of the plasmon mode and the coupling to single-electron levels in nanoparticles is still under discussion. We will conduct experiments using tunable laser pulses, as well as the pump-probe technique in order to study the physical properties of polyanionic metal clusters, using angular-resolved spectroscopy as an extension of the already existing electrontime-of-flight diagnostics. We aim to characterize the electronic level structure, the optical response and the ultrafast dynamics. Tunneling and internal relaxation are relevant decay pathways, which have to be considered in the photoemission process. In the experiments we concentrate on copper, silver and gold clusters as they represent model systems due to their isoelectronic structure. Due to their plasmonic properties, the noble metal clusters are also interesting for technical applications.