The control of surface properties is of utmost importance in almost all applications. Even with purely mechanical functional components, the question arises of how they can be glued, protected against corrosion or decoratively coated. This usually requires several process steps for surface finishing. A frequent pressing issue is that all manufacturing steps of the component leave marks on the surface – for example, residues of parting agents may cover localized spots or even more extensive areas. Already the search for suitable finishing processes often requires surface analysis to determine the status quo.
But even with established methods, surface analysis is time and again resorted to when problems such as failing bonds, peeling coatings, and lack of electrical conductivity suddenly occur. Here is where root cause analysis comes in to eliminate the source(s) of error.
The following imaging modalities and chemical methods are used both in establishing a finishing process and in damage analysis:
- X-ray photoelectron spectroscopy (XPS), also known as electron spectroscopy for chemical analysis (ESCA) for surface chemistry (the uppermost nanometers are detected);
- Scanning electron microscopy (SEM) for topography and morphology, often supplemented with energy-dispersive X-ray spectroscopy (EDX; X-ray microanalysis ) for the surface chemistry (information depth about one micrometer);
- Auger electron spectroscopy (AES) and imaging, layer composition of the uppermost nanometer, lateral resolution approximately 0.1 μm.
When examining a surface, we often realize that the selected analytical method provides only part of the information required and that another method of measurement would be expedient. By default, the sample would now have to be removed and fed to the other measuring method – and thereby the previously examined measuring point recovered again.
At Fraunhofer IGB, a new ESCA device (Kratos Axis Supra) is now available, which has been individually upgraded to include an SEM-EDX and an AES in addition to a latest-generation XPS. Ion scattering spectroscopy (ISS) for hydrogen detection is also available. It provides important information on the hydrogen content at a surface, which is especially useful in the case of polymer surfaces. The device also has an argon ion cluster source for the creation of depth profiles. This equipment enables us to investigate even most complex layer structures or damaged areas with high spatial resolution. Of course, the methods can also be used individually.