In the quest for new 2D materials outperforming graphene, research on other more advanced 2D materials has greatly intensified. The purpose of this proposal is to clarify what key factors of the band structures and Fermi surfaces affect the electronic transport properties of a new class of two-dimensional (2D) transition metal carbides and nitrides called MXene. These semiconducting stacked Mn+1Xn (M is a transition metal and X is either carbon or nitrogen) nanosheets are emerging materials with a large technological impact for applications in Li-ion batteries, super-capacitors, fuel, and solar cells, water splitting as well as in 2D-based electronics, and transistors.
The ultimate objective is to be able to tune and optimize the semiconducting and electronic transport properties of MXenes by investigating the influence of the functional -O, -OH, -OH2, and -F termination species Tx, and intercalated ions (Li, Na, and K) at the interfaces between stacked Mn+1Xn nanosheets. In particular, we investigate how the stacked Mn+1Xn layers in MXene should optimally be terminated to optimize the catalytic processes in applications such as gas sensors and hydrogen production.
In this project, relaxations and SCF calculations using VASP, WIEN2k, and OCEAN DFT codes are made for the novel 2D MXene materials with different types of termination species. The calculations are compared to existing experimental data produced in fruitful collaboration with Post. Doc. Joseph Halim, who defended his thesis at IFM at the end of 2018.
Presently, we are working on several publications and need more time to finish the calculations.
The first DFT results were published in the papers:
1. Chemical Bonding of Termination Species in 2D Carbides Investigated through Valence Band UPS/XPS of Ti3C2Tx MXene; Lars-Åke Näslund, Mikko Mikkela, Esko Kokkonen, and Martin Magnuson; 2D Materials 8, 045026 (2021). DOI: https://doi.org/10.1088/ 2053-1583/ac1ea9
2. Local chemical bonding and structural properties in Ti3AlC2 MAX phase and Ti3C2Tx MXene probed by Ti 1s X-ray absorption spectroscopy; Martin Magnuson and Lars-Åke Näslund; Phys. Rev. Research 2, 033516 (2020). DOI: https://doi.org/10.1103/PhysRev Research.2.033516
3. Chemical Bonding in Carbide MXene Nanosheets; M. Magnuson, J. Halim and L.-Å. Näslund; J. Elec. Spec. 224, 27-32 (2018). DOI: https://doi.org/10.1016/j.elspec.2017. 09.006.
For 2022, we have obtained several new beamtimes in an international competition for XAS, XPS, XES/RIXS, and ARPES to measure MXenes and related 2D materials at the MAX IV synchrotron in Lund. Therefore, it is important to be able to directly compare the measurements with calculated results. My Ph.D. student Gabriel Nzulu also produces experimental data from MAX IV that needs to be supported by the same type of DFT calculations.