Platinum Black for stray-light mitigation on high-aspect-ratio micromechanical cantilever

Microscopic devices are widely used in optomechanical experiments at the cutting-edge of precision experimental physics. Such devices often need to have high electrical conductivity but low reflectivity at optical wavelengths, which can be competing requirements for many commonly available coatings. In this manuscript, we present a technique to electroplate platinum with a highly convoluted surface on a $475\mu \mathrm{m}\times 500\mu \mathrm{m}\times 10\mu \mathrm{m}$ Silicon/Gold cantilever, preserving its electrical conductivity but reducing its reflectivity in the $0.3-1\mu \mathrm{m}$ range by a factor of $100$ or greater. The fact that the deposition can be done post-fabrication without damaging delicate structures makes this technique of interest to a potentially large range of experimental applications.