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

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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.