MXenes (pronounced max-eens) are ultra-thin materials only a few atoms thick, prized for their ability to conduct electricity, store energy, and interact with light. Yet, most previous studies examined MXenes as stacked thin films composed of many overlapping flakes, obscuring the true behaviors of individual layers.
"Measuring how single MXene flakes depolarize light enabled us to pinpoint structural intra-flake variations in thickness at the nano level," explained Dr. Andreas Furchner of Helmholtz-Zentrum Berlin (HZB). "We were excited to see how well the results match destructive techniques like STEM."
The study, led by Dr. Furchner in collaboration with Dr. Ralfy Kenaz from the Hebrew University of Jerusalem's Institute of Physics, unites the expertise of two leading research teams: Dr. Tristan Petit's group at HZB and Prof. Ronen Rapaport's group at Hebrew University. Together, they developed SME - a patented technique that acts as a kind of optical fingerprinting - to measure the optical, structural, and electronic properties of single MXene flakes with high precision and without causing damage.
Conventional ellipsometry, a cornerstone of materials characterization, cannot measure regions smaller than 50 microns, making it unsuitable for nanoscale structures. SME overcomes that barrier by shining light with defined polarization states onto microscopic flakes, then analyzing how the reflected light changes. From these reflections, researchers mapped the conductivity and optical behavior of individual flakes, revealing that thinner MXenes have higher electrical resistance - an essential factor in building stable, high-performance devices.
"What is truly outstanding with this work is that in less than one minute, we can directly measure the optical properties, thickness, structural properties, and conductivity of individual MXene flakes - all in a non-destructive way," said Dr. Kenaz, co-inventor of the SME technique. "Normally, these measurements require three different instruments, are time-consuming and destructive, and in the end, not as reliable as spectroscopic micro-ellipsometry."
Dr. Petit of Helmholtz-Zentrum Berlin noted that the technique opens the door to real-time materials monitoring: "This enables operando characterization that was previously only possible with synchrotron-based techniques such as scanning transmission X-ray microscopy. We now have a lab-based, high-throughput method to study how MXenes evolve in different environments."
MXenes are being investigated for use in ultrafast batteries, solar cells, water filtration, and flexible electronics. Understanding how their intrinsic properties change with thickness or exposure conditions is key to optimizing these applications.
"This work provides a roadmap for integrating MXenes into real technologies by offering a direct view of their intrinsic properties, without interference from stacked layers or impurities," said Prof. Rapaport. "By refining how we study these materials using our SME technique, we are paving the way for their use in optoelectronic devices, energy solutions, and beyond."
The breakthrough not only clarifies how MXenes behave at the atomic level but also establishes spectroscopic micro-ellipsometry as a powerful new tool for analyzing 2D materials. As Dr. Petit emphasized, "This is a powerful demonstration of how international collaboration and advanced physics can accelerate materials science. MXenes are just the beginning."
Research Report:Optical, Structural, and Charge Transport Properties of Individual Ti3C2Tx MXene Flakes via Micro-Ellipsometry and Beyond
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