Focused Ion-Beam (FIB)

In a Focused Ion-Beam (FIB) instrument, a beam of heavy ions, typically Ga+, is used to bombard a target material, thereby sputtering atoms from the target surface. The Ga+ ions are generated by a liquid meal ion source (LMIS), which is a small Ga reservoir connected to a tungsten needle. Upon heating the reservoir, Ga flows to the tip of the needle, forming a small point source. A strong electric field applied to the needle tip then extracts ions from this source.

The FIB can be used for i) imaging, ii) site specific milling and iii) metal deposition and patterning. Since the FIB is a scanning ion microscope, raster scanning the ion-beam across a sample surface generates secondary electrons and secondary ions that may be collected for image formation of the sample surface. When striking the sample surface, the primary ion-beam also sputters material, thereby facilitating site specific milling.

The FIB is nowadays usually combined with a scanning electron microscope (SEM) into a combined FIB-SEM workstation, allowing for easy site specific sputtering of material. The FIB-SEM has been extensively used in materials research during the past two decades. The major applications at Chalmers Materials Analysis Laboratory have been to produce high quality cross sectional cuts of materials normal to the sample surface to study, e.g. interfaces and bulk matter. It is also commonly used for site specific TEM sample preparation by thin foil extraction through the lift-out technique.

The process of making cross sectional cuts can also be extended to render 3D information from a material. By serial sectioning, a so-called “slice and view” procedure, a cross section normal to the sample surface is first exposed and an image recorded. Then another small slice is cut from the material to expose a new cross section which is imaged. Repeating this procedure results in a stack of images that can be recombined to render a full 3D volume of the material. Depending on the imaging mode, both structural and chemical information may be obtained.

Chalmers Materials Analysis Laboratory has two FIB-SEMs, a Tescan GAIA3 and a FEI Versa3D LoVac DualBeam. Both instruments are equipped with a Ga ion source for material sputtering, a GIS for platinum deposition and an Omniprobe for TEM thin foil extraction by the lift-out technique. The GAIA3 instrument is equipped with detectors and software for 3D EDX and EBSD analysis, equipment for cryo applications as well as micro manipulators for in-situ studies. The SEM unit on both the GAIA and the Versa also allows for imaging in low vacuum mode and the Versa is also equipped with a detector for wet-STEM imaging.