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Robust Plasma Focused Ion Beam System Uncovers “Weak Links”

A cutting-edge plasma-focused ion beam system, or FIB, with the capacity for in situ mechanical testing at temperatures between −130 and 1000 °C, will soon allow researchers from across the colleges and departments of Lehigh University to conduct experiments.

The new FIB system will be housed in Lehigh University’s state-of-the-art Health, Science, and Technology (HST) building. Image Credit: Doug Benedict/Academic Image.

Lehigh was recently given more than $1.2 million by the National Science Foundation to help with the cost of the new instruments. The grant is a component of the foundation’s Major Research Instrumentation program (MRI), which encourages the creation or purchase of machinery that would enhance engineering and science.

Lehigh University contributed a sizeable share of the cost-sharing to make the acquisition possible in addition to the NSF award. Such grants aim to have a major impact on research across a variety of fields.

We had 25 faculty members involved in this proposal, all of whom submitted projects requiring the FIB system, and many of them are associated with Lehigh’s Interdisciplinary Research Institutes. And they represent a range of disciplines, including materials science, mechanical engineering, chemical engineering, industrial engineering, bioengineering, physics, chemistry, and biology. There’s just such a high demand for a machine like this.

Masashi Watanabe, Professor, Materials Science and Engineering, Lehigh University

The FIB system is a micro-/nano-fabrication tool that is able to precision-machine samples in a rapid and efficient way, similar to woodworking, but at the micrometer or even nanometer level,” stated lead researcher Helen Chan, New Jersey Zinc Professor of Materials Science and Engineering

Helen Chan adds, “And the fixture that allows for in situ mechanical testing enables us to indent or pull or push on a material so we can simultaneously watch how the material fractures and deforms. Even more exciting, we can study the effect of temperature on the deformation process.”

One conceivable application is the investigation of microstructural constituents that may not be available in quantity. Assume a certain phase exists as fine, micron-sized dispersions within a matrix of another material.

The aggregation behavior of the dispersions and matrix could only be evaluated through bulk testing. Using the FIB method, however, a micromechanical sample could be machined so that only the volume of material within a single dispersion was examined.

According to Chan, the EBSD (electron backscattered diffraction) capability is fascinating because when some materials are stressed, a phase or orientation shift might occur, which is detectable by EBSD.

Chan details, “These changes are often highly localized, and hence difficult to observe in bulk samples. With in situ mechanical testing with EBSD analysis, we can observe these changes as a function of the stress and correlate with changes in the properties.”

Watanabe adds, “The biomaterials and polymer materials are so-called soft matters, which are quite challenging to observe inside of materials due to the softness nature of materials. One of the most effective approaches to fabricate or cut out such soft materials is cooling down to a liquid nitrogen temperature.

The FIB system to be installed is equipped with a cryo-stage and cryo-manipulators, which allows for the sectioning of soft materials at micrometer scales. Using the FIB system at cryo-temperatures, it is possible to apply for cross-sectioning of soft samples with ions for internal observation within the FIB or to prepare an electron-transparent thin specimen for further detailed observations at nanometer scales in transmission electron microscopy (TEM).

Masashi Watanabe, Professor, Materials Science and Engineering, Lehigh University

A focused ion beam milling equipment for germanium ions is now available at the university. According to Chan, the new FIB will operate on xenon ions, making it up to ten times faster, allowing for greater production of micromechanical test samples. Currently, researchers have a substantial limitation in producing enough such samples to enable statistically significant testing.

The new equipment also incorporates an ultra-high-speed electron camera for capturing EBSD patterns. which is extremely novel.

It will allow us to see the orientation, meaning the crystal structure of a particular sample. We’ll be targeting 2000 to 3000 patterns per second, which is incredibly fast. So during deformation, we’ll be able to see these crystal structure changes as they’re happening. This is very new. Nobody has done that.

Masashi Watanabe, Professor, Materials Science and Engineering, Lehigh University

According to Chan, such information will help researchers understand how cracks in structures form. There could be “weak links” in the microstructure that could be fixed with better processing.

Chan adds, “We would like to build into structures ‘crack stoppers’ that make it more difficult for cracks to propagate. The net result would be structures that exhibit higher toughness and longer lifetimes.

The group also includes mechanical engineering and mechanics faculty members Natasha Vermaak and John Coulter (Rossin College’s senior associate dean for research) and Loewy Professor of Materials Forming and Processing Wojciech Misiolek (chair of the Department of Materials Science and Engineering), expects the FIB system to be up and running by June.

The system will be housed in the university’s new Health, Science, and Technology (HST) building. In addition to world-class surface characterization and X-Ray diffraction and scattering equipment, the facility features cutting-edge virtual and augmented reality capabilities.

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