Influence of doping with selected organic molecules on the magnetic and electronic properties of bare, surface terminated and defect patterned Ti₂C MXene monolayers

In this study, based on density functional theory, we examine the interaction between the bare, F-, OH-terminated as well as defect patterned Ti2C and selected neurotransmitter (NT) and amino acids (AA) such as dopamine, glutamate, glycine and serine. We found that these molecules are dissociated at a specific location in bare Ti2C monolayers and concomitantly they form Ti-H bonds. The adsorbed molecules give rise to significant charge transfer between the adsorbates and underlying substrates and generally the electronic energy states are affected, band gaps are tuned and magnetic moments are attained significantly. In particular, the bare antiferromagnetic-Ti2C monolayer undergoes an antiferromagnetic-ferromagnetic transition upon adsorption of the amino acids and nucleobase molecules due to bond dissociation of molecules. Moreover, the electronic and magnetic properties of bare Ti2C are crucially changed in the presence of a vacancy. While pristine Ti2C is an AFM semiconductor, mono- and di-vacancy structures become ferromagnetic semiconductors. When adsorbed by molecules, the defect patterned Ti2C is spin-polarized and hence the surface results in a metallic state. We also reveal that the Ti2C structure is transformed to the non-magnetic (NM) ground state in the presence of both F- and OH-surface termination groups. When adsorbed to these organic molecules on a terminated Ti2C surface, the binding of molecules to this surface is generally weak and arises from van der Waals interactions. We determine that the binding energy of dopamine, which is absorbed on bare Ti2C in equilibrium in a solvent, was found to be 2.31 eV and the magnetic moment per supercell was reduced to 2.91μB.