Real-time investigation of surface plasmon plariton propagation in nanoscale plasmonic phase structures

该项目的主要目标是实时研究a)传播表面等离子激元（SPP）与相位操纵材料的基本相互作用机制；b)用亚波长分辨率观察其相关的辐射和非辐射损失。尽管最近在功能纳米等离子体器件的发展方面取得了重大进展，但由于固有的损耗，它们的广泛应用仍然步履蹒跚。虽然提出了几种损耗补偿方法，但对等离激元波与材料的基本相互作用过程引起的阻尼的微观来源仍缺乏详细的了解。指令SPP输运只能通过电子束光刻、离子束蚀刻工艺、自组装纳米掩膜或这些方法的复杂组合的体积结构来实现。这些结构旨在单独控制SPP振幅的横向分布，而不对SPP相位产生直接影响。为此，我们引入了无地形等离子体相结构（PPS）的新概念，增加了空间指数变化作为新的控制参数，同时避免了凹凸处的散射损失。这为今后等离子体结构的设计提供了更大的自由度。利用聚焦离子束装置将镓局部纳米级离子注入单晶/多晶金薄膜中，产生等离子体相结构。与纯介质波导中折射率的变化类似，由离子注入剂量/深度控制的介电函数的空间变化允许对SPPs的传播行为进行泰勒化。这种方法可能为PPS开辟一条更有效、更复杂的控制PPS的途径。为了设计最佳的SPP操纵设计，必须在纳米尺度上对动态电子和光学特性进行彻底的表征。利用时间分辨和能量分辨光电子能谱仪（PEEM）研究了材料的电子特性及其在离子注入下的变化。得到的时间分辨和横向分辨光电子能谱用于区分非辐射通道的不同激发机制。光学性质，另一方面，将研究的时间分辨近场显微镜（SNOM）。为了解决金属孔径探头透射率极低的固有问题，我们将实现新型白光纳米显微镜。在悬臂顶端的介电球作为米氏散射体，应该显示出极高的传输和宽带宽。这为实现飞秒时间分辨率和50纳米空间分辨率铺平了道路，这将使新材料的动态光学特性的局部表征成为可能。

The main goal of this project is the real-time investigation of a) the fundamental interaction mechanism of propagating surface plasmon polaritons (SPP) with phase manipulative materials and b) its associated radiative and non-radiative losses observed with sub-wavelength resolution. Despite the recent significant steps in the development of functional nanoplasmonic devices, their widespread implementation still limps because of inherent losses. Several methods for loss compensation were proposed, but a detailed understanding of the microscopic origin of damping caused by the fundamental interaction processes of plasmon waves and material is still lacking. The directive SPP transport has been realized only by volumetric structuring with electron beam lithography, ion beam etch processes, self-assembled nanomasking or a complex combination of such methods. These structures are intended to solely control the lateral distribution of the SPP amplitude without a direct influence on the SPP phase. For this additional purpose we introduce the new concept of topography-free plasmonic phase structures (PPS), adding the spatial index variation as new control parameter and simultaneously avoiding scattering losses at asperities. As a result, a higher degree of freedom in the design of future plasmonic structures is gained. Plasmonic phase structures are generated by local nanoscale ion implantation of gallium into thin homogeneous layers of mono/polycrystalline gold films with a focused ion beam apparatus. In analogy to the variation of the refractive index in pure dielectric waveguides, the spatial variation of the dielectric function, controlled by the ion implantation dose / depth, allows to taylor the propagation behaviour of SPPs. This way might open the route for PPS with the perspective of a more effective and sophisticated control of SPPs. In order to engineer the optimal SPP manipulation design, a thorough characterization of the dynamical electronic as well as optical properties has to be performed on the nanoscale. The electronic properties of the material and their modification under ion implantation will be probed with time- and energy-resolved photoelectron spectromicroscopy (PEEM). The obtained time- and lateral-resolved photoelectron spectra are used to distinguish between different excitation mechanisms of non-radiative channels. The optical properties, on the other hand, will be investigated by time-resolved near-field microscopy (SNOM). To solve the inherent problem of extremely low transmission of metallic aperture probes, we are going to implement the new white light nanoscope. A dielectric sphere at the tip apex of a cantilever acts as a Mie scatterer and is supposed to show an extremely high transmission with a broad bandwidth. This paves the way to achieve femtosecond time resolution together with a 50 nm spatial resolution, that will make the local characterization of the dynamical optical properties of the new material possible.