Pursuing Innovative Substances for Future Electronic Gadgets
In the ever-evolving world of materials science, a groundbreaking discovery has been made by a team of scientists, led by Aleksandra Vojvodic and Zahra Fakhraai, at the MXenes Synthesis, Tunability and Reactivity (M-STAR) Center for Chemical Innovation. The team has expanded the predictions of machine learning to scan vast combinations of metals for MXenes, a type of two-dimensional material.
The M-STAR team has synthesised and characterised approximately 40 MAX-phase ceramics, the parent materials for MXenes. These efforts have led to the discovery of a method to incorporate up to nine metals into the composition of MXenes.
The composition of each layer in both MAX and MXenes has been experimentally determined through studies using time of flight secondary ion mass spectroscopy. The findings suggest that chaos can be constructive in the world of MXenes, as adding more elements can make it easier to manipulate the system for greater versatility.
The resistivity and emissivity of MXenes have been found to shift as disorder increases, according to the Fakhraai Group's findings. The functional groups present in the MXenes are critical, contributing to the material's properties and stability beyond that provided by layering of the metals and carbon.
Zahra Fakhraai's lab is probing stability and conductivity in disordered MXenes, focusing on how surface chemistry shapes performance. The Vojvodic Lab, in collaboration with De-en Jiang at Vanderbilt, has pinpointed the crossover point, where fewer than six metals result in order, and at six or seven, entropy dominates.
The Vojvodic Lab ran density functional theory simulations to calculate formation energies and stability across different combinations and surface terminations of MXenes. The Fakhraai Group used atomic force microscopy and spectroscopic ellipsometry to map the structure and probe the optical and electronic properties of MXenes.
For MXenes with few metals (up to six), some metals tend to segregate into distinct layers. Group 6 atoms like molybdenum often occupy the surface, while Group 4 atoms like titanium settle in the middle. Once more than seven metals are present in MXenes, entropy dominates, leading to fully disordered atomic arrangements.
This project, supported by the NSF's M-STAR Center, relied on close collaboration among graduate students and postdocs across multiple institutions for several years. The work received support from various grants and awards, including those from the National Science Foundation, the Department of Energy, the National Science Centre of Poland, the Vagelos Institute for Energy Science and Technology, the Korea Institute for Advancement of Technology, and unspecified other sources.
This discovery opens up new possibilities for the development and application of MXenes, offering a more versatile and adaptable material for various industries. The team's work continues to push the boundaries of what is possible in the field of materials science.
