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

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

In a paper not too long ago printed in Nature Nanotechnology, researchers from Drexel’s School of Engineering and Poland’s Warsaw Institute of Know-how and Institute of Microelectronics and Photonics reported a brand new approach to have a look at the atoms that make up MXenes and their precursor supplies, MAX phases, utilizing a way known 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 might clarify a few of their distinctive bodily properties. Additionally they demonstrated the existence of a wholly new subfamily of MXenes, known 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 greatest suited 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.

“Higher understanding of the detailed construction and composition of two-dimensional supplies will permit us to unlock their full potential,” mentioned Yury Gogotsi, Ph.D., Distinguished College and Bach professor within the School, who led the MXene characterization analysis. “We now have a clearer image of why MXenes behave the best way they do and can be capable to tailor their construction and due to this fact behaviors for necessary new purposes.”

Secondary-ion mass spectrometry (SIMS) is a generally used method to check strong surfaces and skinny movies and the way their chemistry adjustments with depth. It really 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 known as sputtering. The ejected ions are detected, collected and recognized primarily based on their mass and function indicators of the composition of the fabric.

Whereas SIMS has been used to check multi-layered supplies over time, the depth decision has been restricted analyzing the floor of a cloth (a number of angstroms). A workforce led by Pawel Michalowski, Ph.D., from Poland’s Institute of Microelectronics and Photonics, made a lot of enhancements to the method, 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 doable.

“The closest method for evaluation of skinny layers and surfaces of MXenes is X-ray photoelectron spectroscopy, which we’ve got been utilizing at Drexel ranging from the invention of the primary MXene,” mentioned Mark Anayee, a doctoral candidate in Gogotsi’s group. “Whereas XPS solely gave us a have a look at the floor of the supplies, SIMS lets us analyze the layers beneath the floor. It permits us to ‘take away’ exactly one layer of atoms at a time with out disturbing those beneath it. This may give us a a lot clearer image that will not be doable with another laboratory method.”

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

“We demonstrated the formation of oxygen-containing MXenes, so-called oxycarbides. This represents a brand new subfamily of MXenes—which is a giant discovery.” mentioned Gogotsi. “Our outcomes counsel that for each carbide MXene, there may be an oxycarbide MXene, the place oxygen replaces some carbon atoms within the lattice construction.”

Since MAX and MXenes signify a big household of supplies, the researchers additional explored extra advanced methods that embrace a number of metallic parts. They made a number of pathbreaking observations, together with the intermixing of atoms in chromium-titanium carbide MXene—which had been beforehand considered separated into distinct layers. They usually confirmed earlier findings, reminiscent of the whole separation of molybdenum atoms to outer layers and titanium atoms to the interior layer in molybdenum-titanium carbide.

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

“We will now management not solely the overall elemental composition of MXenes, but in addition know through which atomic layers the precise parts like carbon, oxygen, or metals are situated,” mentioned Gogotsi. “We all know that eliminating oxygen helps to extend the environmental stability of titanium carbide MXene and enhance its digital conductivity. Now that we’ve got a greater understanding of how a lot further oxygen is within the supplies, we will alter the recipe—so to talk—to supply MXenes that don’t have it, and in consequence extra secure within the surroundings.”

The workforce 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 method has confirmed to be efficient, Gogotsi plans to make use of it in future analysis, together with his latest $3 million U.S. Division of Power-funded effort to discover MXenes for hydrogen storage—an necessary step towards the event of a brand new sustainable vitality supply.

“In some ways, finding out MXenes for the final decade has been mapping uncharted territory,” mentioned Gogotsi. “With this new method, we’ve got higher steerage on the place to search for new supplies and purposes.”