Researchers from Imperial College London, in collaboration with Politecnico di Torino, Politecnico di Milano, and Istituto Italiano di Tecnologia, have published a study in Nature npj 2D Materials and Applications detailing how oxidation affects the electrical properties of titanium carbide (Ti₂CTₓ) MXene. This discovery establishes a direct link between oxidation, material thickness, and electrical behaviour, paving the way for the rational design of MXene-based electronic devices with precisely controlled conducting, semiconducting, or insulating characteristics.
MXenes, a family of atomically thin materials, are highly attractive for printable electronics due to their metallic conductivity and solution processability. They can be formulated into inks and deposited over large areas using scalable techniques like spray coating and inkjet printing, facilitating the creation of flexible and wearable electronic devices. However, MXenes are prone to oxidation when exposed to air, which alters their structure and electrical properties. While the impact of oxidation on MXene performance has been known, the precise mechanism influencing electrical charge transport remained unclear until now.
The research team investigated Ti₂CTₓ, the thinnest titanium-based MXene. Using advanced microscopy and electrical measurements under various temperatures and fields, they tracked charge movement from individual MXene flakes to interconnected printed films. They found that oxidation transforms single-layer MXene flakes into electrical insulators. Conversely, thicker flakes retain conductivity as their oxidised outer layers act as a protective shield, preserving a metallic core. This creates a network of metallic regions separated by thin insulating barriers that dictate electrical charge flow.
Dr Felice Torrisi, lead researcher from the Department of Chemistry and Centre for Processable Electronics at Imperial College London, stated, "Our work shows that oxidation is not simply a degradation process but a powerful design parameter for printed electronics. By understanding how oxidation affects electrical transport, we can engineer MXene films with properties tailored for specific applications."
The study indicates that the degree of oxidation determines whether printed MXene films function as conductors or semiconductors. This insight offers a practical method for tuning future device performance by controlling flake thickness, ink formulation, and processing conditions. The findings could accelerate the development of printed technologies such as flexible antennas, transparent electrodes, and wearable sensors and photodetectors. The team also proposes a framework that could be integrated with machine-learning tools to expedite the discovery and optimisation of printable electronic materials.
"By linking oxidation directly to charge transport across multiple length scales, we can now identify the key parameters needed to design MXene electronic devices with targeted performance", confirmed Dr Torrisi. The researchers believe these design principles can be extended to other air-sensitive two-dimensional materials, fostering the next generation of scalable, flexible, and wearable electronic technologies.
