Resonant optical nanoantennas hold great promise for applications in physics and chemistry. Their operation relies on their ability to concentrate light on spatial scales much smaller than the wavelength. In this work, we mechanically tune the length and gap between two triangles comprising a single gold bow-tie antenna by precise nanomanipulation with the tip of an atomic force microscope. At the same time, the optical response of the nanostructure is determined by means of dark-field scattering spectroscopy. We find no unique single antenna resonance. Instead, the plasmon mode splits into two dipole resonances for gap sizes on the order of a few tens of nanometres, governed by the full three-dimensional shape of the antenna arms. This result opens the door to new nano-optomechanical devices, where mechanical changes on the nanometre scale control the optical properties of artificial structures.
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