Focused ion beam

What is the focused ion beam used for?

FIB enables the creation of high-resolution digital images of solid surfaces. This can be achieved with FIB alone or, more commonly, in combination with scanning electron microscopy (FIB-SEM) or transmission electron microscopy (FIB-TEM). These methods find applications in mapping the surface topography of all kinds of solid materials, including semiconductors, thin films, and naturally occurring substrates. In microelectronics and nanotechnology, FIB can also be used to alter samples through the deposition of very thin material layers on top of them.

How does the focused ion beam work?

The focused ion beam is created using a heated liquid metal, like gallium, and a tungsten needle. When these come into contact, a strong electric field is created, which will ionize the gallium atoms and create ions. Then, using a series of electrically charged “lenses”, the ions can be accelerated and directed towards a specific target, effectively creating a “beam” of ions. This beam can then be directed toward the surface of a sample, where it can be used to image, etch, and prepare the sample for further analysis.

Suitable samples

FIB-SEM and FIB-TEM are suitable for most hard solid samples, whether they are metals, glasses, semiconductors, or thin films. The FIB can, however, damage some softer sample types to the point of no longer being able to gather useful data. This may be overcome by flash-freezing the sample before milling (cryo-FIB), after which cryo-SEM or cryo-TEM can be performed.

Differences between FIB-TEM and FIB-SEM

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are two techniques that are used to image samples on a very small scale. Both work in a similar manner, with the key difference being the scale that they work on. TEM can image surfaces on a far smaller scale than SEM, making it more suitable for very in-depth analysis. SEM, on the other hand, can produce larger images, making it more useful for ‘whole picture’ analysis.

In both cases, a FIB can be used to prepare the samples beforehand. In the case of FIB-TEM, the sample must be electron-transparent for the analysis to work. Therefore, the FIB is used to etch a tiny, under 100 nm thick layer of the material so that it can be accurately studied through TEM.

In the case of FIB-SEM, the FIB is usually incorporated directly into the SEM process, allowing the sample to be cut as the probe scans. This allows for several images to be prepared together, which can then be used to construct a more comprehensive 3D image of the analyzed area.

Advantages and limitations of FIB sample preparation

The main advantage of applying FIB to SEM and TEM is that it enhances both techniques in a way that allows for more valuable data to be collected, whether by cutting a very thin cross-section of the sample or allowing for full 3D images to be prepared through tomography. In both cases, FIB enables gathering more versatile results than could be gathered through electron microscopy alone.

The downside to incorporating FIB is that it introduces a destructive element to the process. Both SEM and TEM are inherently non-destructive, meaning that the sample is not usually damaged during imaging. The application of a focused ion beam will irreparably cut the sample, which means that it cannot be restored post-analysis. Furthermore, FIB can be too damaging for some sample types, leading them to break in ways that can affect the results.

Need a FIB-TEM or FIB-SEM analysis?

Measurlabs offers high-quality laboratory services that make use of focused ion beam technology. Do not hesitate to contact our electron microscopy experts using the form below to discuss your analysis needs.