Nanodentures and Mechanical Electrodynamics: Three-Dimensional Relative Orientation of Plasmonic Nanoarches from Absorption Spectra

We propose a general theme, labeled mechanical electrodynamics, where the relative three-dimensional (3-D) orientation of particles with nontrivial geometries is tracked based on the details of the absorption spectrum beyond a one-dimensional (1-D) distance dependence. Specifically, we simulate absorption spectra of a subwavelength denture-like nanostructure with freely moving parts. The nanodentures are made of two gold nanoarches that either open and dose or rotate about a single arch base (hinge rotation). We show how the absorption spectrum for the nanodentures changes depending on orientation and position. There is a similar to 0.1-0.2 eV shift in absorbance peak frequencies as the denture closes, corresponding to an increased coupling between the two gold arches, while a hinge rotation results in a depletion of one absorbance peak (1.48 eV) with the simultaneous emergence of a new absorbance peak at lower frequencies (0.88 eV). The unique spectral signature of each position and orientation of the nanodentures points to a variety of applications. One will be experimentally tracking and measuring orientation and position of plasmonic-coupled nanoparticles using simple methods such as UV-vis or IR spectral analysis. Additionally, the denture structure will tune in and out of different plasmon resonance frequencies, or turn "on and off," depending on its orientation. The simulations were performed efficiently by the recent near-field (NF) approach, which is a time-dependent Poisson algorithm that shares a lot of the machinery of full-fledged Maxwell equations but allows for much larger time steps and therefore can treat large systems.