Synchrotron sheds light on damaging impact of inspection technique

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Focused Ion Beam Milling (FIB), a widely used technique that enables scientists to manipulate and study materials at the nano-scale may have dramatic unintended consequences, according to researchers at Oxford University.

FIB uses a tiny beam of highly energetic particles to cut and analyse materials smaller than one thousandth of a strand of human hair and has become an essential tool for a number of applications including microscopy, researching high performance alloys for aerospace engineering, nuclear and automotive applications and for prototyping in micro-electronics and micro-fluidics.

Above: schematic showing FIB in action (Credit: Oxford University)

Whilst the technique was previously understood to cause structural damage within a thin surface layer of the material being cut it was assumed that its effects would not extend beyond this thin damaged layer. However, the Oxford University research, published in Scientific Reports, reveals that FIB can in fact dramatically alter a material’s structural identity.

The team studied the damage caused by FIB using a technique called coherent synchrotron X-ray diffraction. This relies on ultra-bright high energy X-rays, available only at central facilities such as the Advanced Photon Source at Argonne National Lab, USA, with whom the Oxford team collaborated.

These X-rays were used to probe the 3D structure of materials at the nano-scale and revealed that even very low FIB doses, previously thought negligible, have a dramatic effect.

Argonne National Laboratory's Advanced Photon Source

Felix Hofmann, Associate Professor in Oxford’s Department of Engineering Science and lead author on the study, said: "Our research shows that FIB beams have much further-reaching consequences than first thought, and that the structural damage caused is considerable.

"It affects the entire sample, fundamentally changing the material. Given the role FIB has come to play in science and technology, there is an urgent need to develop new strategies to properly understand the effects of FIB damage and how it might be controlled."

The team is now looking to build on its work to gain a better understanding of the damage formed and how it might be removed.

“We have gone from using the technique blindly, to working out how we can actually see the distortions caused by FIB. Next we can consider approaches to mitigate FIB damage,” said Hofmann. “Importantly the new X-ray techniques that we have developed will allow us to assess how effective these approaches are. From this information we can then start to formulate strategies for actively managing FIB damage.”