Figure 9.

Scanning Electron Microscopy images of a collection of tapered micro-channels fabricated using (a-c) two consecutive steps of deep reactive ion etching (Bosch) followed by anisotropic etching to taper the tip. The diffusion constraints produced by the narrow geometry channel produces non-uniformities and residue accumulation at the tip. The use of four consecutive steps (d-f) leads to a wider channel entrance that facilitates diffusion, producing tapers with a more uniform size range and geometry.