N. S. Eliseeva

Theoretical study of the magnetic properties of ordered vacancies in 2D hexagonal structures: Graphene, 2D-SiC, and h-BN

The magnetic properties of vacancies in 2D hexagonal structures—graphene and 2D-SiC and h-BN monolayers—have been studied. It has been found that a local magnetic moment exists in all listed systems in the presence of vacancies. However, in 2D hexagonal silicon carbide, the local magnetic moment appears only in the presence of silicon vacancy. In addition, the effect of the distance between vacancies in a monolayer on transitions between the ferromagnetic and antiferromagnetic states has been revealed.

Mobility of vacancies under deformation and their effect on the elastic properties of graphene

The effect of isolated vacancies on the elastic properties of a graphene sheet has been investigated by the ab initio density functional method. An almost inverse linear dependence of the Young’s modulus on the concentration of vacancies has been revealed. The height of potential barriers for the motion of vacancies in various directions has been calculated as a function of various independent applied strains. The velocity of vacancies at various temperatures has been calculated as a function of applied strains using the transition state theory.

Contact-induced spin polarization of monolayer hexagonal boron nitride on Ni(111)

Hexagonal boron nitride (h-BN) is a promising barrier material for graphene spintronics. In this Letter, spin-polarized metastable de-excitation spectroscopy (SPMDS) is employed to study the spin-dependent electronic structure of monolayer h-BN/Ni(111). The extreme surface sensitivity of SPMDS enables us to elucidate a partial filling of the in-gap states of h-BN without any superposition of Ni 3d signals. The in-gap states are shown to have a considerable spin polarization parallel to the majority spin of Ni. The positive spin polarization is attributed to the π-d hybridization and the effective spin transfer to the nitrogen atoms at the h-BN/Ni(111) interface.

Possibility of a 2D SiC Monolayer Formation on Mg(0001) and MgO(111) Substrates

The geometrical characteristics of a 2D SiC monolayer on Mg(0001) and MgO(111) plates regarded as potential materials for growing two-dimensional silicon carbide were studied. The most favorable positions of the atoms of 2D SiC on the substrates were determined. In the 2D SiC/Mg(0001) system, unlike in 2D SiC/MgO(111), the deviation of the carbon atom from the silicon carbide monolayer was insignificant (0.08 Å). Consequently, magnesium can be used as a substrate for growing two-dimensional silicon carbide. The use of MgO(111) is not recommended because of a significant distortion of the 2D SiC surface.

Theoretical Study of the Lithium Diffusion in the Crystalline and Amorphous Silicon as well as on its Surface

Using the PAW DFT-GGA method and numerical solving of master equation the diffusion rates of lithium atoms inside both crystal and amorphous silicon of LixSi (x= 0..0.5) composition have been calculated for different temperatures. It is shown the diffusion rate for amorphous silicon is ~10 times greater than that for the crystal silicon. For both structures the rate is increased by 1.5-2 orders of magnitude while the lithium concentration is increased up to 0.5 value. This should result in that the LixSi/Si interface will be sharp. This fact has been further confirmed using molecular dynamic calculations based on Angular Dependent Potential (ADP) model. Also binding energies of Li atoms lying on different sites of Si (001) surface as well as the potential barriers for the atom jumps both along the surface and in the subsurface layers have been calculated. The data show the Li atoms move along the surface very easily but their jumps into subsurface layers are very difficult due to the high potential barrier values.

Theoretical study of sorption and diffusion of lithium atoms on the surface of crystalline silicon and inside it

The energy of the sorption and diffusion of lithium atoms on the reconstructed (4 × 2) (100) silicon surface in the process of their transport into near-surface layers, as well as inside crystalline silicon, at various lithium concentrations have been investigated within the density functional theory. It has been shown that single lithium atoms easily migrate on the (100) surface and gradually fill the surface states (T3 and L) located in channels between silicon dimers. The diffusion of lithium into near-surface silicon layers is hampered because of high potential barriers of the transition (1.22 eV). The dependences of the binding energy, potential barriers, and diffusion coefficient inside silicon on distances to the nearest lithium atoms have also been examined. It has been shown that an increase in the concentration of lithium to the Li0.5Si composition significantly reduces the transition energy (from 0.90 to 0.36 eV) and strongly increases (by one to three orders of magnitude) the lithium diffusion rate.

Calculating the energy of vacancies and adatoms in a hexagonal SiC monolayer

It is noted that the development of semiconductor SiC-electronics is prevented by a low quality of grown silicon carbide single crystals. It is found that structural defects of a substrate penetrating into an epitaxial layer upon subsequent homoepitaxial growth can considerably degrade a device’s characteristics. We investigate the effect of the deformation of a hexagonal SiC monolayer on vacancy stability and material properties, and study the processes of silicon and carbon adatom migration over a surface of SiC.

Theoretical investigation of the atomic and electronic structure of LixBC3 intercalated compounds

LixBC3 intercalated compounds with various configurations are studied for their possible application as electrode materials for lithium current sources. For this purpose, the band structure and the density of states were calculated for each structure, and energy stability and possible deformations due to a change in the unit cell volume during intercalation are investigated.

Features of the structure and properties of β-FeSi 2 nanofilms and a β-FeSi 2 /Si interface

The electronic, geometric, and magnetic structure of nanofilms of the β phase of iron disilicide FeSi2 with the (001), (100), and (010) surfaces have been simulated through density functional calculations. A substantial reconstruction of the (001) surface terminated with silicon atoms has been observed, which was accompanied by an increase in the surface symmetry and appearance of “squares” of silicon atoms. Analysis of the electron density of states (DOS) and spin DOS projected on the contributions of layers of atoms (LSDOS) indicates that all plates have metallic properties. The main contribution near the Fermi level comes from the surface iron layers and it decreases rapidly with an increase in the distance from the surface of the plate. Analysis of the calculated effective magnetic moments of atoms shows that the surface layers in the plates have a significant magnetic moment, in particular, iron layers on the (001) surface (1.89 μB/atom). The moments of atoms decrease rapidly with an increase in their distance from the surface. The electron and geometric regions of a (001)Si/FeSi2 interface have been studied. Analysis of the LSDOS shows that the surface conducting state mainly determined by the contribution from the near-surface silicide layers is implemented in this region. The possibility of the formation of the perfect and sharp Si/FeSi2 interface has been demonstrated.

Theoretical investigation of the adsorption and diffusion of hydrogen on the surface and in the bulk of the intermetallic compound Mg2Ni

The intermetallic compound Mg2Ni as a potential material for hydrogen storage has been investigated theoretically. The sorption and diffusion of a hydrogen atom in the bulk and on the surface of this material, as well as the step-by-step process of dissociative chemisorption of a H2 molecule on the surface, have been considered. The dependence of the sorption energy of atomic hydrogen on the structural characteristics of the intermetallic compound Mg2Ni has been analyzed.