Focused ion beam FIB

The scanning electron microscope with focused ion beam, known as the FIB method, makes new insights possible under the surface of materials. In order to examine microscopic defects, point corrosion, cracks or artificial microstructures even underneath the surface and clarify the cause of defects where applicable, the location of a possible defect is first determined with the scanning electron microscope (SEM). Then the surface is cut open vertically using a finely focused ion beam with visual control. The material is removed on one side of the cut face with the ion beam so that looking diagonally at the cut face is subsequently possible. The benefit of using the FIB is that the cut face and be positioned with sub-micrometer accuracy so that even the smallest structures in the cross-section can be represented.

You will find the technical data of the FIB used by Fraunhofer IST here.

Cross-section through an ingrown particle

FIB cross-section through an ingrown particle.
© Fraunhofer IST

The simplest method to examine surfaces with the focused ion beam is to prepare cross-sections of the material being examined. This is then removed until the origin of a defect is discernible under the surface. A multilayer film system of alternating SiO2 and Ta2O5 layers is shown here. Under the surface, an overgrown particle with a diameter of approximately 2 µm that was overgrown during the coating process can be seen. The chemical composition of the particle can be determined using energy-dispersive X-ray spectrometry (EDX), allowing the source of the defects to be easily identified and avoided.

Cross-section through nylon textile material

Cross-section nylon textile
© Fraunhofer IST

This illustration shows the cross-section of a nylon textile material with a water-repellent coating. Even in such a challenging material, FIB sections with a cleanly defined cut face can be produced.

TEM lamella preparation

TEM lamella
© Fraunhofer IST

In addition to simple cross-sections, what are known as TEM lamella can also be prepared. These are wafer-thin slices cut vertically from the surface.

STEM image and EDX mapping of a low-E film system

STEM image and EDX mapping of low-E film system
© Fraunhofer IST

The lamella can be lifted from the surface with a micromanipulator and made even thinner until it becomes partially transparent for the electron beam. STEM (scanning transmission electron microscopy) images with an especially high resolution reveal the internal structure of the material, for example through crystal orientation contrasting. Here is a STEM image of a low-E layer system consisting of glass, 45 nm SiN, 45 nm ZnO, 12 nm Ag, 5 nm TiO2 and 45 nm ZnO. The lamella can also be chemically analysed using EDX with a spatial resolution of just 10 nm. This is an improvement of the spatial resolution by a factor of 50 compared to conventional cross-sections.

3D tomography

3D tomography is the third option for examinations using FIB. Rather than individual cuts, a whole series of cuts is made one after the other. This produces a 3D tomography of the microstructure on the microscale.