D. I. Bazhanov

Structure and electronic properties of zirconium and hafnium nitrides and oxynitrides

The atomic structure, stability and electronic properties of zirconium and hafnium nitrides and oxynitrides (MN, M3N4, and M2N2O; M=Zr, Hf) have been studied using first-principles density functional theory calculations. It is found that the orthorhombic Pnam structure of M3N4, which was observed experimentally for zirconium nitride, is more stable for this stoichiometry than the cubic spinel and rock-salt-type structures. The calculated band structures and electronic densities of states demonstrate that both the MN and M3N4 phases of zirconium and hafnium nitrides in the rock-salt-type structure are characterized by metallic properties, while the orthorhombic structure of the M3N4 phase exhibits an insulating behavior in agreement with experimental observations. The formation of nitrogen vacancies in the insulating M3N4 phase converts it into the metallic MN phase. Calculations of Zr2N2O and Hf2N2O in the cubic Bixbyite-type and hexagonal P3–ml crystal structures predict that these materials are insulato...

Stress, strain and magnetostriction in epitaxial films

The application of the cantilever bending technique to stress measurements at surfaces and in epitaxial films is elucidated. The role of elastic anisotropy in quantitative cantilever curvature analysis is discussed. The stress in Co monolayers is measured during epitaxial growth on Cu(001). The Co-induced stress is found to oscillate with a period of one atomic layer. Simultaneous stress and medium-energy electron diffraction identify maximum stress for filled Co layers. Strain relaxation in Co islands leads to the reduced stress contribution of 2.9 GPa in the partially filled top layer as compared to 3.4 GPa for the filled layers. The cantilever technique is also applied to measure magnetoelastic properties of nanometre thin epitaxial films. Our measurements reveal that the magnetoelastic-coupling coefficients in epitaxial Fe, Co and Ni films differ from the respective bulk values. It is proposed that the epitaxial misfit strain is of key importance for this peculiar magnetostrictive behaviour of ultrathin films.

Stress oscillations in a growing metal film

The stress in Co monolayers has been measured during epitaxial growth on Cu(0 0 1). The Co-induced stress is found to oscillate with a period of one atomic layer. Simultaneous stress and medium energy electron diffraction identify maximum stress for filled Co layers. Strain relaxation in Co islands leads to a reduced stress contribution of 2.9 GPa in the partially filled top layer as compared to 3.4 GPa for the filled layers. The corresponding variation of the elastic energy is 1 meV per Co atom. Atomic scale calculations reveal that the size-dependent mesoscopic mismatch is the driving force for stress relaxation in Co islands. 2002 Elsevier Science B.V. All rights reserved.

Emergence of giant magnetic anisotropy in freestanding Au/Co nanowires

The emergence of giant magnetic anisotropy was found in evenly mixed Au/Co nanowires. First principles molecular dynamics calculations revealed the large values of magnetic anisotropy energy of about ∼130 meV per Co atom in Au/Co nanowires. It was established that the emergence of giant magnetic anisotropy is due to (dxy,dx2) band splitting caused by the strong spin-orbit interaction between gold and cobalt atoms in the wire. It is also shown that the energy of the magnetic anisotropy depends strongly on the geometry and composition of the wire.

Impact of strain on the surface properties of transition metal carbide films: First-principles study

The effect of in-plane lattice strain on the atomic and electronic properties of low-index transition metal (M=Ti, Nb, and Ta) carbide surfaces is studied by first-principles molecular dynamics calculations using a pseudopotential plane-wave technique. The most stable cubic rock-salt phase is considered for carbides. The first-principle study of various [(001), (110), and metal-terminated (111)] carbide surfaces reveals that both compressive and tensile strains strongly affect surface relaxation and electronic properties (work function values and band structures). The most stable (001) carbide surfaces exhibit rumpling between transition metal and carbon atoms in the topmost surface layers, which depends on the applied strain. The work function (WF) for the metal-terminated (111) surfaces varies monotonically, rather strongly depending on the applied strain (the range of variation reaches about 1 eV), while the WF for the (001) surface varies nonmonotonically with a much smaller resulting variation over t...

Effect of stretching-contraction deformations on the magnetic ordering state of mixed Pd-Fe nanowires

The performed ab initio calculations indicate the possibility of forming stable, uniformly mixed Pd-Fe nanowires. The effect of stretching-contraction deformations on the electronic structure of Pd-Fe nanowires has been revealed. Using the calculation results, a transition from ferromagnetic to antiferromagnetic state in a uniformly mixed Pd-Fe nanowire subjected to tension has been predicted.

Atomic and electronic structure of mixed Au-Co nanowires: Ab initio molecular dynamics study

The atomic and electronic structure of uniformly and nonuniformly mixed Au-Co nanowires have been studied using the ab initio molecular dynamics method. The effect of elastic stretching/contraction deformations on the stability and electronic properties of mixed Au-Co nanowires has been studied. It is established that Co dimers are formed in a nonuniformly mixed nanowire. The formation of CO2 dimers results in a non-uniform distribution of the electron density and interactomic distances along the wire and leads to accelerated rupture of the wire between Au atoms under stretching. Only a uniformly mixed Au-Co nanowire composed of regularly alternating Au and Co atoms is stable under stretching up to large interactomic distances.

Effect of hydrogen on the formation of the atomic structure of linear carbon chains: An ab initio approach

An ab initio study of the features of the formation of the atomic structure of carbon chains, which are structural parts of films of linear carbon chains, has been performed using the electron density functional theory. It has been shown that the formation and stabilization of experimentally observed kinks of carbon chains require the presence of hydrogen impurities in the chamber during the synthesis of linear carbon chains. The kinks of a carbon chain are formed in the process of the adsorption of hydrogen atoms on a chain. The optimal kink angle of carbon chains has been determined. The stability of kinks of carbon chains has been estimated as a function of the length of linear fragments. An additional mechanism has been proposed for the formation of kinks in carbon chains owing to the joining of short carbon chains with hydrogen ends.

First-principles investigation of the structure and electronic properties of CdS/CdSe/CdS and CdS/CdTe/CdS quantum wells using a slab approximation

The structure and electronic properties of CdS, CdSe, and CdTe thin films and multilayer CdS/CdSe/CdS and CdS/CdTe/CdS heterostructures simulating quantum wells of these compositions are performed using density functional theory and a slab approximation. Various crystal modifications and various crystallographic surfaces of the specified compounds are considered. In the calculations, the GGA approximation for the exchange-correlation functional (PW91) and ultrasoft pseudopotentials are used. For the systems in study, the work functions are calculated for various surfaces. The calculated structural data are in good agreement with experiments. The calculated surface reconstruction can be qualitatively described as an inward displacement of cadmium atoms into the surface crystal layer and an outward displacement of chalcogen atoms. The calculated surface energies indicate that the (110) surface formation energy is lower than the (100) surface formation energy. The calculated work functions decrease in the sequence CdS > CdSe > CdTe, while the calculated work functions for multilayer structures are between the corresponding values for the pure components of the structure.

Magnetic properties of mixed Co–Cu clusters on Cu(001)

The aim of this article is to present ab initio calculations of the effect of intermixing at Co/Cu interface on magnetic properties of small Co islands. We find that coating of Co islands with Cu atoms reduce magnetic moments. The spin polarization of Cu atoms near Co islands is revealed. RKKY interaction between Co impurities in Cu layers is calculated.