Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have engineered a new method to build MXenes, the ultra-thin materials used in next-generation high-tech applications, with near-perfect atomic order. By replacing traditional chemical etching with a molten salt and iodine vapor process, the team effectively eliminated the surface disorder that previously hampered electron flow.
MXenes, composed of stacked layers of transition metals and carbon or nitrogen, have been limited by the chaotic arrangement of atoms on their surfaces. Scientists previously relied on chemical etching, which left behind a random mix of oxygen, fluorine, or chlorine.
"This atomic disorder limits performance because it traps and scatters electrons, much like potholes slowing traffic on a highway," said Dr. Dongqi Li of TU Dresden.
Precision Synthesis via the GLS Method
The new technique, dubbed the GLS method, allows researchers to control the halogen atoms attached to the material's surface. By utilizing solid MAX phases combined with molten salts and iodine vapor, the team successfully produced clean, ordered MXene sheets from eight different base materials.
This structural precision led to dramatic performance gains. In tests focused on titanium carbide MXene, the team observed a 160-fold increase in macroscopic conductivity and a 13-fold boost in terahertz conductivity. Charge carrier mobility also improved nearly fourfold.
"The results were striking," said Li. "The chlorine-terminated MXene variant showed a 160-fold increase in macroscopic conductivity and a 13-fold enhancement in terahertz conductivity compared with the same material made by traditional methods."
Beyond raw conductivity, the ability to tailor surface composition offers significant potential for specific applications. Researchers noted that chlorine-terminated MXenes show strong absorption in the 14-18 GHz range, while bromine- and iodine-based variants respond to different frequencies.
This customization could inform the development of advanced radar-absorbing coatings and electromagnetic shielding. Dr. Mahdi Ghorbani-Asl of HZDR noted that these findings provide a clear path forward for material science.
"By combining theory with our experimental ability to precisely control surface terminations, we open a new path toward MXenes with improved stability and tailored functional properties," said Ghorbani-Asl. The team plans to continue experimenting with mixed halide salts to further refine the material's electronic and optical behavior.
