Photocatalytic deposition of a gold nanoparticle onto the top of a SiN cantilever tip.

We propose a new technique for depositing a gold nanoparticle onto the tip of a dielectric support. We employed the photocatalytic effect of titanium dioxide for the deposition. When the titanium dioxide immersed in a solution including gold ions is subject to optical exposure, the excited electrons in the conduction band reduce gold ions into gold metal. Illumination by an evanescent wave generated with a total reflection configuration limits the deposition region to the very tip. In experiments we obtained 100-300 nm gold particles on SiN cantilever tips for atomic force microscopes. The contrast of evanescent interference fringes measured by a near-field scanning optical microscope with this gold nanoparticle probe has proved to be higher than that with a non-deposited SiN probe by a factor of 1.5.