CRC 1636/1: Controlling chemical reactions by propagating surface plasmon polaritons (SP A06)

In this project, the potential of propagating surface plasmon polaritons (pSPPs) to influence and steer chemical reactions will be explored. The central idea is to spatially separate the optical excitation of plasmons from the site where the reaction takes place and to study the interplay of light and plasmon fields with reagents in various geometries.
The spatial separation of laser excitation from the reaction site guarantees that the reaction is driven exclusively by plasmonic near fields (hypothesis H3) and not by laser-deposited heat or direct optical excitation of molecules. We aim at driving simple model reactions by plasmons and at efficient plasmon-induced chemical structuring of the surface at the nanoscale. We will investigate quasi-2D and quasi-1D geometries including thin metal-polymer heterostructures laterally patterned by nano-lithography (focused ion beam (FIB), atomic force microscope (AFM)), as well as nano-wires and particles prepared by colloidal chemistry. Quantitative theoretical modelling of the envisioned structures and effects will guide the selection and optimization of geometries and will provide interpretative support. Specifically, modelling will include the role of non-local material properties as well as the role of surface roughness on the plasmonic near field. In addition, modelling will include the transition from continuous-wave pSPPs to ultrafast pSPP wavepackets (so-called SPP bullets) and their impact on the aforementioned model reactions in the near-field.
Together we shall combine our experience to drive chemical reactions such as grafting to the metal surface and C-C coupling reactions and polymerization by pSPPs. Such reactions have been demonstrated at plasmonic nanoparticles under direct laser illumination. Here we shall use pSPPs in quasi-1D and quasi-2D geometries. We want to selectively steer polymerization vs. grafting by appropriate control of the light fields, which is our interpretation of hypothesis. Scanning near-field optical microscopy (SNOM) will be used to map the near field intensity pattern excited at the nano-patterned metals. Synthesis will be conducted in-situ under specially modified optical microscopes coupled with the required irradiation set-up. Stokes and anti-Stokes-Raman microscopy will characterize the chemical transformations and monitor the local release of heat. Atomic force microscopy (AFM) will be used to investigate nanoscale polymerization processes.