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We detail the physical mechanisms that govern the directivity of a single particle antenna coupled with an electric dipole emitter. It is well known that the size of the particle plays an important role in the directivity properties, and that small particles tend to collect the emitted light whereas large particles tend to act as reflectors. However, we demonstrate that the directivity can be extremely sensitive to the distance between the dipolar emitter and the particle, and that a particle can either higly reflect or collect light, depending on its distance with the emitter. We derive an analytical model that perfectly explains this unexpected sensitivity.

plasmonics; nanoantennas; directivity; dipole