Improved tip performance for scanning near-field optical microscopy by the attachment of a single gold nanoparticle

Nanometer-size optical probes are gaining increasing interest in near-field optical microscopy. Optimization of the probe shape is still a challenging research and development issue. Here, we propose to improve the optical properties of a fiber-based probe by attachment at the tip apex of one single gold particle of 60 nm diameter. This probe produces an enhancement of the light throughput, both in the near and the far fields, a homogenization of the diffracted light polarization, and a higher accuracy of the topographic sensitivity. In this letter, the chemical procedure for the fixation of one single gold particle on the apex of a standard tip for scanning near-field microscopy is described. Far-field as well as near-field measurements with this probe are performed, showing improvement of the light distribution in excellent agreement with the theory. (C) 2000 American Institute of Physics. [S0003-6951(00)05315-8].