Ahmad Ranjbar

Electronic properties and applications of MXenes: a theoretical review

The recent chemical exfoliation of layered MAX phase compounds to novel two-dimensional transition metal carbides and nitrides, the so-called MXenes, has brought a new opportunity to materials science and technology. This review highlights the computational attempts that have been made to understand the physics and chemistry of this very promising family of advanced two-dimensional materials, and to exploit their novel and exceptional properties for electronic and energy harvesting applications.

OH terminated two-dimensional transition metal carbides and nitrides (MXenes) as ultralow work function materials

MXenes are a set of two-dimensional transition metal carbides and nitrides that offer many potential applications in energy storage and electronic devices. As an important parameter to design new electronic devices, we investigate the work functions of bare MXenes and their functionalized ones with F, OH, and O chemical groups using first-principles calculations. From our calculations, it turns out that the OH terminated MXenes attain ultralow work functions between 1.6 and 2.8 eV. Moreover, depending on the type of the transition metal, the F or O functionalization affects increasing or decreasing the work functions. We show that the changes in the work functions upon functionalizations are linearly correlated with the changes in the surface dipole moments. It is shown that the work functions of the F or O terminated MXenes are controlled by two factors: the induced dipole moments by the charge transfers between F/O and the substrate, and the changes in the total surface dipole moments caused by surface relaxation upon the functionalization. However, in the cases of the OH terminated MXenes, in addition to these two factors, the intrinsic dipole moments of the OH groups play an important role in determining the total dipole moments and consequently justify their ultralow work functions.

Nearly free electron states in MXenes

Using a set of first-principles calculations, we studied the electronic structures of two-dimensional transition metal carbides and nitrides, so called MXenes, functionalized with F, O, and OH. Our projected band structures and electron localization function analyses reveal the existence of nearly free electron (NFE) states in a variety of MXenes. The NFE states are spatially located just outside the atomic structure of MXenes and are extended parallel to the surfaces. Moreover, we found that the OH-terminated MXenes offer the NFE states energetically close to the Fermi level. In particular, the NFE states in some of the OH-terminated MXenes, such as

Chemical engineering of adamantane by lithium functionalization: A first-principles density functional theory study

\mathrm{T}{\mathrm{i}}_{2}\mathrm{C}{(\mathrm{OH})}_{2},\mathrm{Z}{\mathrm{r}}_{2}\mathrm{C}{(\mathrm{OH})}_{2},\mathrm{Z}{\mathrm{r}}_{2}\mathrm{N}{(\mathrm{OH})}_{2},\mathrm{H}{\mathrm{f}}_{2}\mathrm{C}{(\mathrm{OH})}_{2},\mathrm{H}{\mathrm{f}}_{2}\mathrm{N}{(\mathrm{OH})}_{2},\mathrm{N}{\mathrm{b}}_{2}\mathrm{C}{(\mathrm{OH})}_{2}

Theoretical prediction of two-dimensional functionalized MXene nitrides as topological insulators

, and

Large-Gap Two-Dimensional Topological Insulator in Oxygen Functionalized MXene

\mathrm{T}{\mathrm{a}}_{2}\mathrm{C}{(\mathrm{OH})}_{2}

First-principles study of structural stability, magnetism, and hyperfine coupling in hydrogen clusters adsorbed on graphene

, are partially occupied. This is in remarkable contrast to graphene, graphane, and

Topological insulators in the ordered double transition metals M 2 ′ M ″ C 2 MXenes ( M ′ = Mo , W; M ″ = Ti , Zr, Hf)

\mathrm{Mo}{\mathrm{S}}_{2}

Geometrical indications of adsorbed hydrogen atoms on graphite producing star and ellipsoidal like features in scanning tunneling microscopy images: Ab initio study

, in which their NFE states are located far above the Fermi level and thus they are unoccupied. As a prototype of such systems, we investigated the electron transport properties of

Correlation between entanglement and spin density in nitrogen-vacancy center of diamond

\mathrm{H}{\mathrm{f}}_{2}\mathrm{C}{(\mathrm{OH})}_{2}