Many everyday objects and working materials have special surface finishes. Typically these come in the form of an added layer. Often defects arise when the layer is being made – to the detriment of function and durability. Thanks to modern “nano-analysis”, we can now explain the origin of these defects.
Despite the variety of materials available to us these days, almost all coating processes have problems getting layers to adhere to the base material. A number of processes can lead to a layer separating from the base, and sooner or later this will result in a component becoming faulty or breaking. Once a component is broken it is rarely possible to pinpoint the cause of the adherence problem. A new technique based on nanoanalysis now makes it possible to examine adherence problems before components become faulty.
Based in Constance, the Steinbeis Transfer Center for Nano Structures and Solid State Analytics has been working on a joint project with Oerlikon from Liechtenstein to examine multi-layer optical coatings. Once a multi-layer optical coating has been applied, each layer may be no thicker than 100 nm and although everything seems right, the coating contains tiny defects. The task lies in identifying the cause of these defects.
Defects can be found quickly using an electron microscope. Then a layer is carefully removed using a focused ion beam (FIB) which slices through the material. The images above show a section of material with two defects. The small defect on the left looked like a flat molehill. The one on the right looked like a speck sitting on the surface. Both were sliced open to look at the precise make-up inside the defect.
It turned out that both particles were on the component before it was coated as the layers added to the material could still be made out. The flat defect turned out to be a small speck measuring around 200 nm on the surface of the substrate. An EDX elemental analysis showed that it was a tiny grain of polish made out of lanthanum oxide that had not come off properly during cleaning.
An EDX analysis of the inside of the big defect uncovered a speck of steel. Bits of steel sometimes fly around when vacuum chambers are being produced. Slicing up small particles with an FIB makes it possible to analyze defects and take preventative measures.
Prof. Dr. Günter Schatz
Steinbeis Transfer Center Nano Structures and Solid State Analytics (Constance)
stz621@stw.de
Prof. Dr. Johannes Boneberg
Matthias Hagner
NEB “Euregio Nano-Center”, Lake Constance and The University of Constance