Metal matrix interference layers

Production and testing of specimens (see also Etching) with interference layers.

The interference layer process in reflected-light microscopy is based on a polished sample surface that is applied with interference layers to apply reflection interference filters. Such a layer partly without any adsorption ahs the effect of weakening the light waves reaching the object surface by multiple reflections at the metal/layer and layer/air boundary surfaces. This leads to increased contrast between the structural components depending on the optical constants of two adjacent phases. This increase in contrast not only includes an increase in the difference of the intensity of the reflected light between two phases but also an increase in color contrast.

In comparison to conventional etching processes, this type of preparation offers the following advantages:

  • Exclusively, polished surfaces are examined. No topographicalchanges are applied by etching
  • Small particles remain (are not dissolved)
  • This is a detailed illustration of the true ratios

The process is also used for inspections with a micro probe as the sample surfaces have to be perfectly level for which reason chemical etching should be avoided. Applying the interference layer does not lead to any differences in height.

As preparation, the samples are polished, cleaned with alcohol and carefully dried. Then, the interference layer is applied by vapor deposition or spraying, also referred to as “sputtering”.

If the layer is applied by sputtering, cathode sputtering is used in a gas discharge chamber. The sample to be layered serves as anode while the layer material is the cathode. During electrical gas discharge, positively charged gas ions are created and accelerated by means of the voltage between anode and cathode to shoot at the cathode in order to split off atoms from its surface and spraying them in all directions. In this process, they come into contact with the sample surface and create the interference layer.