What is FIB-SEM?

Compared to conventional scanning electron microscopy (SEM) imaging, FIB-SEM 3D nano-tomography adds a “cutting” tool in the form of a focused ion beam (FIB). Due to its heavy ionic mass, FIB removes a small amount of material, exposing the surface underneath. Repetitive FIB milling simultaneous with SEM imaging produces a stack of images which can be reconstructed into a 3D volume. The combination of these techniques, focused ion beam scanning electron microscopy, serves as a powerful tool to analyze and quantify internal microstructures.

FIB can remove layers at the nanometer scale, allowing for a completely clean cross sectioned surface to be prepared for SEM imaging. 

Below, a cross section of the polymer membrane of a drug pellet sample was prepared using two methods: conventional freeze cleave and FIB polishing. The resulting cross-sectioned SEM images are dramatically different. Due to mechanical fracturing, residual surface topology remains on the cleaved sample, and obscures the internal microstructure. In comparison, the FIB cross section reveals microporosity accurately, and allows for both qualitative and quantitative assessment.

Most importantly, FIB-SEM produces 3D volumes at a nanometer scale, which can be applied in image analysis and image-based simulation.

Sample Preparation

FIB-SEM typically runs with a resolution of 3–50 nm. Assuming an image produced has 2000x2000 pixels along X and Y directions, its field of view might be about 6 – 100 micrometers in size. This size is very small compared to other imaging techniques. Hence, it is critical to ensure that imaged volumes are representative. 

For microscopic imaging, sample representativeness is critical, yet often difficult to verify. A larger sample can be as unrepresentative as a high-resolution small sample. When using FIB-SEM microscopy, we work closely with our clients to guarantee that a representative sample volume will be imaged at the most appropriate resolution. The sample will be prepared to ensure both optimal image quality and budgetary responsibility. 

Artifact Management

Regardless of successful an imaging experiment is, there are always artifacts. FIB-SEM imaging can take a few hours to a few days. A sample with gas or liquid contents can react to electron and ion beams, which can cause undesirable effects. 

DigiM manages imaging artifacts in three ways:

  1. Artifacts are mitigated during imaging experiments, such as charging, re-deposition, and sample stability.
  2. A suite of software algorithms has been developed to correct artifacts, such as curtaining, stage drifting, and intensity variation.
  3. Fundamental understandings of these artifacts are leveraged to design new experiments and study dynamic responses of such samples under electron and ion beam excitations.  

Example of DigiM’s artifact corrections are shown below.

Presentations and Publications

  1. Tracey, J., Lin, S., Jankovic, J., Zhu, A., Zhang, S. (2019). Iterative Machine Learning Method for Pore-Back Artifact Mitigation in High Porosity Membrane FIB-SEM Image Segmentation. Microscopy and Microanalysis. Download here.
  2. Zhang, S., Byrnes, A. P., Jankovic, J., & Neilly, J. (2019). Management, Analysis, and Simulation of Micrographs with Cloud Computing. Microscopy Today, 27(2), 26-33. Read here.
  3. DigiM FIB-SEM Curtaining Removal. DigiM Technology Highlight. February 25, 2015. Request a Copy.
  4. Zhang, S. (2014). Integrated Material Characterization and Property Prediction Using 3D Image-based Analytics and Modeling. Presented at TMS 2014 Annual Meeting in San Diego, CA (February 16-20, 2014).