MXene as a frame for 2D water films shows new properties
Cooling down the MXene with enclosed water (left) leads to the formation of amorphous ice clusters (right), significantly increasing the distance between the MXene layers and the formerly metallic MXene becomes a semiconductor. When heated, the clusters dissolve, the distance between the layers decreases and the sample becomes metallic again. © HZB
An international team led by Dr. Tristan Petit and Prof. Yury Gogotsi has investigated MXene with confined water and ions at BESSY II. In the MXene samples, a transition between localised ice clusters to quasi-two-dimensional water films was identified by increasing temperature. The team also discovered that the intercalated water structure drives a reversible transition from metallic to semiconducting behaviour of the MXene film. This could enable the development of novel devices or sensors based on MXenes.
Water still has unknown sides. When water is forced into two dimensions by enclosing it in appropriate materials, new properties, phase transitions, and structures emerge. MXenes as a class of materials offer a unique platform for exploring these types of phenomena: MXenes consist of transition metal carbides and nitrides with a layered structure whose surfaces can help them absorb water easily. The water forms an extremely thin film between the individual layers.
A team led by Dr Tristan Petit, HZB, and Yury Gogotsi, Drexel University, USA, has investigated a series of MXene samples containing enclosed water and different ions at BESSY II using various analytical methods.
X-ray structural analysis revealed the formation of amorphous ice clusters in the enclosed water, which increases the distance between the MXene layers. The previously metallic MXene film then becomes a semiconductor. “When heated above 300 K, the clusters dissolve again, restoring the distance between the layers and their metallic behaviour,” says Petit. This metal-semiconductor transition is therefore reversible, unless the water layer is removed. Further X-ray investigations using different techniques revealed unique characteristics in the water hydrogen bond networks.
‘In the next step, we need computer-aided modelling to improve our understanding of the formation of amorphous ice and its impact on electronic transport,’ says Katherine Mazzio, who is co-first author of the study. She concludes that MXene is ideal for investigating the phase changes of confined water, providing new insights into how water behaves at the nanoscale. The use of MXene as a material for energy storage and catalysis is already being discussed, and the role of confined water on the unique MXene properties for these applications is currently being investigated.
- Materials chemistry shapes the future of catalysisThe synthesis of materials can serve as a tool for developing smart, adaptive electrocatalysts. This rapidly evolving field of research involves in-situ analytics, data-driven discoveries and autonomous robotics. These new approaches could accelerate the discovery of long-lasting and efficient catalysts for future energy conversion and the decarbonisation of the chemical industry. A recent article by Dr Prashanth Menezes and his team in the renowned journal Angewandte Chemie provides an overview of this research.
- Imaging Ellipsometry for Process Control of Thin-Film DevicesA German–Israeli research team led by Dr. Andreas Furchner has demonstrated how imaging ellipsometry enables non-destructive characterisation and quality control of microstructured MXene thin films during device fabrication. The authors used two complementary ellipsometry approaches for precise, multi-scale access to key material properties. The work positions imaging ellipsometry as a powerful platform for monitoring thin-film uniformity, device integrity, and functionality throughout processing, including critical lithographic steps. The study was published in Applied Physics Letters and selected as an Editor’s Pick.
- Spintronics at BESSY II: Real-time analysis of magnetic bilayer systemsSpintronic devices enable data processing with significantly lower energy consumption. They are based on the interaction between ferromagnetic and antiferromagnetic layers. Now, a team from Freie Universität Berlin, HZB and Uppsala University has succeeded in tracking, for each layer separately, how the magnetic order changes after a short laser pulse has excited the system. They were also able to identify the main cause of the loss of antiferromagnetic order in the oxide layer: the excitation is transported from the hot electrons in the ferromagnetic metal to the spins in the antiferromagnet.