New approach permits researchers to scrape past the floor of nanomaterials


    Sep 23, 2022

    (Nanowerk Information) 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 strategy have allowed the staff to look throughout the atomic layers to raised perceive the connection between the supplies’ kind and performance. In a paper not too long ago revealed in Nature Nanotechnology (“Oxycarbide MXenes and MAX phases identification utilizing monoatomic layer-by-layer evaluation with ultralow-energy secondary-ion mass spectrometry”), 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 means to have a look at the atoms that make up MXenes and their precursor supplies, MAX phases, utilizing a method 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 completely 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. using secondary-ion mass spectrometry to look at MXenes A brand new approach utilizing secondary-ion mass spectrometry has given Drexel researchers a contemporary have a look at the two-dimensional supplies they’ve been learning for greater than a decade. (Picture: Drexel College) 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. “Higher understanding of the detailed construction and composition of two-dimensional supplies will enable us to unlock their full potential,” stated Yury Gogotsi, PhD, 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 vital new purposes.” Secondary-ion mass spectrometry (SIMS) is a generally used approach to check stable surfaces and skinny movies and the way their chemistry modifications with depth. It really works by capturing 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 based mostly on their mass and function indicators of the composition of the fabric. Whereas SIMS has been used to check multi-layered supplies through the years, the depth decision has been restricted inspecting the floor of a cloth (a number of angstroms). A staff led by Pawel Michalowski, PhD, from Poland’s Institute of Microelectronics and Photonics, made plenty 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 doable. “The closest approach for evaluation of skinny layers and surfaces of MXenes is X-ray photoelectron spectroscopy, which we have now been utilizing at Drexel ranging from the invention of the primary MXene,” stated 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 can provide us a a lot clearer image that might not be doable with every other laboratory approach.” Because the staff 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 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 brand new subfamily of MXenes – which is an enormous discovery!” stated 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 symbolize a big household of supplies, the researchers additional explored extra advanced programs that embody a number of steel parts. They made a number of pathbreaking observations, together with the intermixing of atoms in chromium-titanium carbide MXene — which have been beforehand considered separated into distinct layers. They usually confirmed earlier findings, equivalent 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 vital for growing MXenes with a finely tuned construction and improved properties, based on Gogotsi. “We are able to now management not solely the whole elemental composition of MXenes, but in addition know through which atomic layers the precise parts like carbon, oxygen, or metals are positioned,” stated Gogotsi. “We all know that eliminating oxygen helps to extend the environmental stability of titanium carbide MXene and improve its digital conductivity. Now that we have now a greater understanding of how a lot extra oxygen is within the supplies, we are able to alter the recipe – so to talk – to provide MXenes that would not have it, and in consequence extra secure within the atmosphere.” The staff additionally plans to discover methods to separate layers of chromium and titanium, which can assist it develop MXenes with enticing 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. Division of Power-funded effort to discover MXenes for hydrogen storage – an vital step towards the event of a brand new sustainable vitality supply. “In some ways, learning MXenes for the final decade has been mapping uncharted territory,” stated Gogotsi. “With this new strategy, we have now higher steerage on the place to search for new supplies and purposes.”


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