Energy Dispersive X-ray Spectroscopy (EDS / EDX) quantifies elemental composition at every pixel within a scanned area of a micrograph. To make this measurement, EDS analyzes the characteristic x-rays emitted as the primary electron beam excites atoms in the outermost 10 to 100 nm of the sample. These characteristic x-rays are correlated to elements from B-U on the periodic table, and the intensity of each x-ray signal is used to compute the corresponding element’s atomic concentration.

Before EDS is performed, an SEM image is captured to calibrate the position and domain of the EDS measurement. Experts can either conduct a point-scan on a single pixel of the image, or run EDS analysis across a line or 2D area to evaluate how elemental composition varies across boundaries and regions of interest. Once the target area is set, EDS spectra are collected at every pixel, enabling 0D, 1D, and 2D mapping of elemental distribution.

EDS can also be combined with FIB-SEM tomography to generate 3D reconstructed volumes of elemental information.

EBSD on a FIB-SEM requires a specialized detector array similar to the camera system in a TEM. A phosphor screen, which fluoresces when excited by backscattered electrons, is positioned perpendicular to the pole piece of the electron column. The screen is paired with a CCD camera that captures diffraction patterns illuminated on the screen during measurement.

As the primary electron beam scans in the SEM, its interactions with sample atoms cause backscattered electrons to emit from various angles. Some of the backscattered electrons will exit the sample surface near to the characteristic Bragg Angle of the material. These special backscattered electrons diffract to produce a pattern when they strike the phosphor screen. TEM analysts would recognize the resulting diffraction patterns as Kikuchi bands: which correspond to all the distinct crystallographic planes present at each pixel. By indexing the Kikuchi bands, EBSD analysis can identify crystal structures and map their distribution within the scanned area.

For accurate crystal structure identification, it is paramount that the geometry of the primary beam and backscattered electron beams be precisely described. First, EBSD requires as flat a surface as possible on a crystalline sample. This face is then rotated to a high take-off angle relative to the primary electron beam (about 70 ⁰) to maximize diffraction contrast. As the EBSD patterns are collected, the system computationally indexes them using Miller Indices to identify the crystal structure present at each pixel. Once the scan is complete, EBSD yields a 2D map of the crystallographic domains, phase boundaries, and crystallinity in the scanned area.

FIB-SEM tomography is performed using automated Auto Slice and View ^TM software on Thermo Fisher Scientific DualBeam microscopes. This software facilitates serial ion-beam milling of thin layers from a cross-sectional face of a sample, capturing electron micrographs between each cut into the face*. Once the desired region of the sample has been milled and imaged, the software reconstructs a 3D model by stitching the collected 2-dimensional cross-sections into a composite volume. Once the 3D reconstruction is produced, it can be manipulated and analyzed to make dimensional measurements of internal structures and features of interest.

By combining FIB-SEM tomography with EDS or EBSD, analysts can investigate elemental distributions and crystallinity throughout a 3D reconstructed volume. This can be particularly useful in the analysis of alloys, porous materials, or integrated circuits and microprocessors.

* FIB-SEM tomography can cause higher-than-normal charge buildup in certain nonconductive samples. To mitigate this, it may be necessary to sputter coat the sample with a conductive metallic layer. Furthermore, depending on the shape and material of the sample, embedding the sample in resin may improve imaging resolution by fixing its position in a rigid mount.

Most FIB-SEM instruments available today use a liquid-metal ion source in the FIB column. Overwhelmingly, these systems use Gallium ions due to their excellent thermal, electromechanical, and vacuum properties. Plasma Focused Ion Beam (PFIB) Scanning Electron Microscopes instead use an inductively coupled plasma chamber to produce the ions for the FIB column. The plasma source enables finer control of the FIB accelerating voltage and substantially increased maximum current.

In the PFIB, multiple ion species are available including Xenon, Oxygen, and Carbon. These species produce distinct sputtering and milling effects when used on different sample materials. Critically, this empowers analysts with the flexibility to select a probe beam that minimizes risk of undesirable chemical reactions which may produce artifacts or cause damage to the sample. Among the available ion species, Xenon has been the most extensively studied and documented; however, Oxygen has shown substantial preliminary promise for biological and organic materials research.

All plasma ion species facilitate drastically increased sputter rates through higher maximum beam current: a Xe⁺ PFIB can remove material up to 60X faster than conventional Ga⁺ ion sources. In addition, improved ion-beam optics enable precision milling at accelerating energies as low as 2 kV to maximize operators’ control and reduce damage in sensitive samples.