How to cut brie cheese with a meat slicer, or how to ion mill soft materials.

Imagine, you sit down with some friends one afternoon and the host out does themselves with an impressive cheese platter. It’s got the works with the sharp cheddar to the smoked gouda and at the center a block of the softest brie cheese. And then your host hands you an electric turkey carver for cutting the cheese. Doesn’t really match the ambiance of a fancy cheese platter does it? But you’re an intrepid cheese fiend, and say to yourself “How hard can it be?”

When you're done cleaning all the brie from your shirt and the carpet surrounding you, the thought will definitely come that this was a lot harder than it should be and that the electric slicer was just not a good tool for that job. That the best option would be a knife or a cheese pick that would cut off a good gob of that brie. And you may be right: if your only goal was to take a random chunk of brie for your cracker then the electric slicer is overkill. But what if you wanted to take a really ultra thin precise cut of that brie? A regular cheese knife can’t do that, but maybe the slicer can…

In the world of material science there’s a similar challenge when it comes to cross sectioning soft materials like polymers, and hydrogels. Traditional approaches will typically involve either a scalpel/razor blade by hand but those are imprecise and can damage the delicate structures. You might opt for a microtome to automate the process and sure that does a bit better than by hand but you still will smear and disturb the internal structure. Then there’s the option of freezing/cryo-sectioning the material where the cold hardens the soft material allowing for more precise cuts. This works but again subjecting a soft delicate material to the process of freezing can disturb the internal structure due to ice crystal formation.

For semi-conductors and crystalline solids, focused ion beam (FIB) milling has been routinely employed for decades to etch and cut these hard materials. The FIB is like our electric carver: really precise and powerful for removing nanometer layers of material…provided it is hard enough to withstand the ion beam. The cool thing about FIB is that it can be combined with scanning electron microscopy (SEM) through FIB-SEM, a unique imaging approach to evaluate the internal structures of materials with nanometer resolution, and even in 3D.

Microstructure characterization with FIB-SEM is a natural for those harder materials, especially in the geoscience and energy material spaces. Soft materials, on the other hand, have been avoided due to the FIB resulting in high material loss as well as errant sample heating/ablation. Just like our brie, is it possible that the FIB milling process can work?

Here at digiM we’ve found the answer is a resounding yes…you just need to be clever with how you use your FIB. Rather than cranking the current of the ion beam super high to mill through tough materials, we opt for very low current that is orders of magnitude smaller than what you’d use for a tough material like silicon. Additionally we’ve developed an approach that takes into account the non-uniform ion intensity of the FIB, and is able to use the outer edge of the beam to precisely remove nanometers of soft material without heating the underlying object. It’s delicate work and has taken years of optimization to achieve this level of control at room temperature that is only now starting to be equaled with cryogenic FIB systems.

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Our pioneering work in this area has set us apart for soft polymer systems, such as microneedles, microspheres, implants, IUD, and extended release coatings. So next time you see that hunk of brie cheese, just remind yourself that with enough practice and a delicate touch you can absolutely cut your self the most precise slice of brie…or give us a call and we’ll cut it for you!

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