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.

Interactions of selected organic molecules with a blue phosphorene monolayer: self-assembly, solvent effect, enhanced binding and fixation through coadsorbed gold clusters.

In this paper we investigate the interaction between a pristine blue phosphorene monolayer and selected organic molecules like amino acids and nucleic acid bases. These molecules are bound to the substrate by a weak van der Waals interaction leading to their physisorption. When isolated, they tend to orient themselves parallel to the surface and are located in flat minima with very low libration frequencies; thus the electronic structures of the substrate and physisorbed molecules are not affected except for relative shifts. Even though the regular self-assembly of these molecules on the pristine blue phosphorene cannot be realized under this weak interaction, only their irregular coating of the substrate can occur due to increased intermolecular coupling. In a solvent like water, the weak binding energy is further decreased. Gold adatoms and gold clusters can form strong chemical bonds with pristine blue phosphorene and modify its electronic and magnetic state depending on the coverage. While full coverage of a blue phosphorene monolayer by gold adatoms leads to instabilities followed by clustering, relatively lower coverage can attribute very interesting magnetic and electronic states, like a spin gapless semiconductor. When bound to the gold clusters already adsorbed on the blue phosphorene monolayer, amino acid and nucleic acid base molecules form relatively strong chemical bonds and hence can be fixed to the surface; they are reoriented to gain self-assembly character and the whole system acquires new functionalities.

Two dimensional ruthenium carbide: structural and electronic features.

The design and realization of novel 2D materials and their functionalities have been a focus of research inspired by the successful synthesis of graphene and many other 2D materials. In this study, in view of first principles calculations, we predict a novel 2D material ruthenium carbide (RuC) in graphene-like honeycomb hexagonal lattice with planar geometry. Phonon dispersion spectra display a dynamically stable structure. Comprehensive molecular dynamics calculations confirm the stability of the structure up to high temperatures as ≈1000 K. The system is a narrow gap semiconductor with a band gap of 53 meV (345 meV) due to GGA-PBE (HSE) calculations. Band gap exhibits significant changes by applied strain. Elastic and optical properties of the system are examined in monolayer form. RuC/RuC bilayer, RuC/graphene and RuC/h-BN heterostructures are also investigated. By calculating the phonon dispersion it is verified that RuC bilayer is the most stable in AA type-stacking configuration where Ru and C atoms of both layers have identical lateral coordinates. The effects of atomic substitutions on electronic band structures, acting as p-type and n-type doping, are revealed. A novel 3D RuCLi structure is also predicted to be stable and the isolation of its monolayer forms are discussed. Ruthenium carbide, as a 2D material which is dynamically and thermally stable, holds promise for applications in nanoelectronics.