Strong electric field enhancement in the interparticle gap of resonators formed by two spherical Au nanoparticles occurs for polarization of the incoming light parallel to the dimer axis. This enhancement exhibits a strong dependence on gap width and is the basis of surface‐enhanced Raman scattering or tip‐enhanced Raman scattering. The enhancement factor as a function of gap width can be readily calculated solving Maxwellapos;s equations. However, the derived dependence is difficult to verify experimentally, in particular, because of the large uncertainty in determining the interparticle gap value, which is typically one or two orders of magnitude smaller than the diameters of the Au spherical nanoparticles forming the resonator. We demonstrate that a much more reliable verification of the predicted interparticle gap dependence of the electric field enhancement is possible using an approach analogous to triangulation in surveying and mapping.

Far-field effects depending on microscopic structure, tip, and environment dominate tip-enhanced optical spectra of 2D materials such as MoS2.

Detection of nanoparticles gets more and more relevant in various fields of application, e.g., semiconductor technology, medicine or biology. A fast and universal detection method of nanoparticles is essential for these leading-edge technologies. Classical imaging methods struggle with the resolution of nanoparticles smaller than the diffraction limit. Established optical near-field methods are complex and time consuming. We demonstrate that using Coherent Fourier Scatterometry can overcome most of these challenges. For this purpose, we study the optical response of gold nanosphere arrangements on silicon wafers. In particular, we examine arrays of particles arranged in geometrical structures such as lines, squares, triangles, and L-shapes. The dimensions of these structures are in the order or even smaller than the Airy diameter. Correlations between the geometry of the particle arrangement and the intensity distributions in the Fourier plane are characterized by applying different analyzing methods. Thus, it is possible to distinguish between different structures and, furthermore, to extract their geometrical orientations. In addition, gold nanostructures of defined shape, but different sample thicknesses top-down fabricated on silicon are also investigated. These nanostructure shapes studied comprise the same geometries as mentioned above as well as spirals with a diameter comparable to the spot size of the used microscope objective.

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