Tuesday, October 4, 2022

Secondary ion mass spectrometry reveals atoms that make up MXenes and their precursor supplies

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A brand new approach utilizing secondary-ion mass spectrometry has given Drexel researchers a contemporary take a look at the two-dimensional supplies they’ve been learning for greater than a decade. Credit: Drexel University

Since the preliminary discovery of what has grow to be a quickly rising household of two-dimensional layered supplies—referred to as MXenes—in 2011, Drexel University researchers have made regular progress in understanding the complicated chemical composition and construction, in addition to the bodily and electrochemical properties, of those exceptionally versatile supplies. More than a decade later, superior devices and a brand new method have allowed the crew to look throughout the atomic layers to raised perceive the connection between the supplies’ kind and performance.

In a paper just lately printed in Nature Nanotechnology, researchers from Drexel’s College of Engineering and Poland’s Warsaw Institute of Technology and Institute of Microelectronics and Photonics reported a brand new approach to take a look at the atoms that make up MXenes and their precursor supplies, MAX phases, utilizing a method referred to as secondary ion mass spectrometry. In doing so, the group found atoms in areas the place they weren’t anticipated and imperfections within the two-dimensional supplies that would clarify a few of their distinctive bodily properties. They additionally demonstrated the existence of a wholly new subfamily of MXenes, referred to as oxycarbides, that are two-dimensional supplies the place as much as 30% of carbon atoms are changed by oxygen.

This discovery will allow researchers to construct new MXenes and different nanomaterials with tunable properties finest fitted to particular purposes from antennas for 5G and 6G wi-fi communication and shields for electromagnetic interference; to filters for hydrogen manufacturing, storage and separation; to wearable kidneys for dialysis sufferers.

“Better understanding of the detailed structure and composition of two-dimensional materials will allow us to unlock their full potential,” stated Yury Gogotsi, Ph.D., Distinguished University and Bach professor within the College, who led the MXene characterization analysis. “We now have a clearer picture of why MXenes behave the way they do and will be able to tailor their structure and therefore behaviors for important new applications.”

Secondary-ion mass spectrometry (SIMS) is a generally used approach to check strong surfaces and skinny movies and the way their chemistry modifications with depth. It works by taking pictures a beam of charged particles at a pattern, which bombards the atoms on the floor of the fabric and ejects them—a course of referred to as sputtering. The ejected ions are detected, collected and recognized based mostly on their mass and function indicators of the composition of the fabric.

While SIMS has been used to check multi-layered supplies through the years, the depth decision has been restricted analyzing the floor of a cloth (a number of angstroms). A crew led by Pawel Michalowski, Ph.D., from Poland’s Institute of Microelectronics and Photonics, made a lot of enhancements to the approach, together with adjusting the angle and vitality of the beam, how the ejected ions are measured; and cleansing the floor of the samples, which allowed them to sputter samples layer by layer. This allowed the researchers to view the pattern with an atom-level decision that had not been beforehand attainable.

“The closest technique for analysis of thin layers and surfaces of MXenes is X-ray photoelectron spectroscopy, which we have been using at Drexel starting from the discovery of the first MXene,” stated Mark Anayee, a doctoral candidate in Gogotsi’s group. “While XPS only gave us a look at the surface of the materials, SIMS lets us analyze the layers beneath the surface. It allows us to ‘remove’ precisely one layer of atoms at a time without disturbing the ones beneath it. This can give us a much clearer picture that would not be possible with any other laboratory technique.”

As the crew peeled again the higher layer of atoms, like an archaeologist fastidiously unearthing a brand new discover, the researchers started to see the delicate options of the chemical scaffolding throughout the layers of supplies, revealing the surprising presence and positioning of atoms, and numerous defects and imperfections.

“We demonstrated the formation of oxygen-containing MXenes, so-called oxycarbides. This represents a new subfamily of MXenes—which is a big discovery.” stated Gogotsi. “Our results suggest that for every carbide MXene, there is an oxycarbide MXene, where oxygen replaces some carbon atoms in the lattice structure.”

Since MAX and MXenes characterize a big household of supplies, the researchers additional explored extra complicated methods that embrace a number of metallic components. They made a number of pathbreaking observations, together with the intermixing of atoms in chromium-titanium carbide MXene—which have been beforehand regarded as separated into distinct layers. And they confirmed earlier findings, akin to the whole separation of molybdenum atoms to outer layers and titanium atoms to the inside layer in molybdenum-titanium carbide.

All of those findings are essential for creating MXenes with a finely tuned construction and improved properties, in response to Gogotsi.

“We can now control not only the total elemental composition of MXenes, but also know in which atomic layers the specific elements like carbon, oxygen, or metals are located,” stated Gogotsi. “We know that eliminating oxygen helps to increase the environmental stability of titanium carbide MXene and increase its electronic conductivity. Now that we have a better understanding of how much additional oxygen is in the materials, we can adjust the recipe—so to speak—to produce MXenes that do not have it, and as a result more stable in the environment.”

The crew additionally plans to discover methods to separate layers of chromium and titanium, which can assist it develop MXenes with engaging magnetic properties. And now that the SIMS approach has confirmed to be efficient, Gogotsi plans to make use of it in future analysis, together with his latest $3 million U.S. Department of Energy-funded effort to discover MXenes for hydrogen storage—an essential step towards the event of a brand new sustainable vitality supply.

“In many ways, studying MXenes for the last decade has been mapping uncharted territory,” stated Gogotsi. “With this new approach, we have better guidance on where to look for new materials and applications.”

Titanium carbide flakes obtained by selective etching of titanium silicon carbide

More data:
Paweł P. Michałowski et al, Oxycarbide MXenes and MAX phases identification utilizing monoatomic layer-by-layer evaluation with ultralow-energy secondary-ion mass spectrometry, Nature Nanotechnology (2022). DOI: 10.1038/s41565-022-01214-0

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Drexel University

Secondary ion mass spectrometry reveals atoms that make up MXenes and their precursor supplies (2022, September 23)
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