Ultramicrotomy is a technique for cutting cross-sections of material which was originally used by biologists for soft tissue analysis. With only a few changes to accommodate the hard dielectric coatings and substrates, the technique may be used to prepare specimens of optical multilayer devices for cross-sectional transmission electron microscopy (XTEM).
The ultramicrotome, mounted on a vibration damped table, is capable of cutting uniform 40 nm thick cross-sections of materials with a diamond knife. An epoxy embedded sample is cycled past the knife at a controlled rate and advanced by a precise, preset distance on each pass. As each section is cut, it comes off the knife edge to a reservoir of water where, while floating, it can be picked up on a TEM grid.
Artifacts generated by this mechanical technique for preparing thin cross-sections are readily apparent yet easy to disregard. TEM analysis of these cross-sections provides direct imaging of real samples for accurate feature and thickness measurement and direct chemical and crystalline structure analysis.