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

TL;DR

This paper introduces a post-fabrication platinum black coating technique for high-aspect-ratio silicon cantilevers, significantly reducing optical reflectivity while maintaining electrical conductivity, beneficial for optomechanical experiments.

Contribution

A novel electroplating method to apply platinum black on delicate micromechanical cantilevers, achieving low reflectivity without damaging the device.

Findings

Reflectivity reduced by a factor of 100 or more in the 0.3-1 μm range

Technique preserves electrical conductivity of the cantilever

Post-fabrication process does not damage delicate structures

Abstract

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 $475\,\mathrm{\mu m } \, \times 500\,\mathrm{\mu m } \, \times 10\,\mathrm{\mu m }$ Silicon/Gold cantilever, preserving its electrical conductivity but reducing its reflectivity in the $0.3 - 1\,\mathrm{\mu m}$ 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.