Resolving bond angle of a plasmonic metamolecule

Plasmonic metamolecules have been found to have many peculiar properties. Applications in biological and materials science have also been demonstrated, such as reconfigurable 3D building blocks for complex nano architectures and imaging probes for high resolution sensing. In these applications, the fast detection of the bond angles of the sub-wavelength metamolecules is highly desired. However, the angle detection is not the same as orientation detection, since it has two orientations to be determined simultaneously while people only has to measure one orientation in the use of common orientation sensor. In this work, we propose and demonstrate a method to resolve the bond angle of a plasmonic metamolecule composed of three spherical nanoparticles. The detection of the bond angle is realized via the modulation depth analysis of polarization-resolved dark-field images. The underlying mechanism is found to be the opposite responses of the bonding mode and anti-bonding mode to the polarization variation of the incident light. In addition, the spectrally degenerate structures are further distinguished by the spot center localization method. This method will pave the way for real application of plasmonic metamolecules.