The Zeiss Crossbeam 550L FIB features an Oxford EDS detector for chemical element analysis, and an EBSD detector for characterizing crystal orientation phases. Both techniques can be used in parallel with 3D acquisition.
A cryogenics system enables work to be carried out at very low temperatures on samples sensitive to the ambient atmosphere under the beam (Quorum). It features a cold transfer system between the device and a controlled atmosphere glove box.
The microscope is also coupled to a Raman spectrometer (Renishaw).
A vacuum transfer system is provided between a glove box and the microscope.
Extraction of a slide for TEM microscopy
To work on a bulk material using transmission electron microscopy, it must be thin enough for the electron beam to pass through it, and for the information transmitted not to be degraded by the thickness of the observed zone. Before the advent of the FIB, this was a complicated task performed by mechanical or chemical means, or by exposure to an ion beam. These methods are very approximate to achieve a correct thickness and, most importantly, to target a very specific area in a block, with the naked eye or by optical means.
The FIB machining precision now makes it possible to cut a material and extract a section a hundred nanometers thick. The extraction location is pinpointed on the sample using electronic imaging, allowing the removal of a section from the exact spot intended for analysis. First, a thick section is removed from the material. It is then welded onto a nanomanipulator by ion-beam organometallic deposition (platinum), transported and welded onto a copper grid compatible with the MET Nant’Themisobject holder. Final thinning is achieved with the ion beam.
Observation of a section
In most abrasion operations, the sample surface is perpendicular to the ion beam and inclined at 54° to the electron beam. This arrangement enables the electron column to be used to observe the sidewall of an ion beam trench, provided that the observation is not hindered by the opposite wall. By choosing the shape of the hole to open up the perspective for the electron column (an opening that can be compared to that of a slope to access an underground garage), we make it possible to observe a cut in the depth of the sample. This is done exactly where needed, and without any prior sample preparation (whereas, without an ion column, the sample should be cut and polished before being fed into the machine).
3D reconstruction
The abrasion capacity of the ion beam is precise enough to remove a very thin layer of material (down to about ten nanometers). By repeating this operation a large number of times over the same surface, we explore a volume of the sample whose depth is proportional to the number of layers removed. By taking an electronic image of the surface each time a layer is removed, we get a collection of images. Stacked one on top of the other, these images reflect the internal morphology of the abraded volume.
3D reconstruction software processes this collection of images to obtain an in-depth visualization of the sample. The software can be used to extract numerical data (e.g. porosity or volume occupied by a phase) and generate graphical representations.
Observation and cold machining
Some materials are damaged by the beam or by the vacuum in the column of scanning electron microscopes. This mainly concerns samples containing water, but also materials referred to as “fragile”. The double-beam microscope is equipped to observe these materials at cold temperature, thanks to a QUORUM system that freezes a sample in liquid nitrogen before introducing it into a preparation chamber, connected to the microscope by an airlock.
A system of circulating cooled nitrogen gas in a liquid nitrogen dewar maintains the sample at -140°C in the preparation chamber, under the protection of a trap cooled to -170°C (to trap residual contaminants). The chamber is equipped with knives to break the sample and then metallize it after possible sublimation. The sample is then introduced into the microscope for observation on a support cooled in the same way as in the preparation chamber, and similarly protected by a cold trap.
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The FIB was financed by the 2015-2020 State-Region Plan Contract (CPER).
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