Theoretical Investigation of the Interfaces and Mechanisms of Induced Spin Polarization of 1D Narrow Zigzag Graphene- and <i>h</i>-BN Nanoribbons on a SrO-Terminated LSMO(001) Surface

Avramov, Paul,Kuzubov, Alexander A.,Kuklin, Artem V.,Lee, Hyosun,Kovaleva, Evgenia A.,Sakai, Seiji,Entani, Shiro,Naramoto, Hiroshi,Sorokin, Pavel B. American Chemical Society 2017 The Journal of physical chemistry A Vol.121 No.3

<P>The structure of the interfaces and the mechanisms of induced spin polarization of 1D infinite and finite narrow graphene- and h-BN zigzag nanoribbons placed on a SrO-terminated La1-xSrxMnO3 (LSMO) (001) surface were studied using density functional theory (DFT) electronic structure calculations. It was found that the pi-conjugated nanofragments are bonded to the LSMO(001) surface by weak disperse interactions. The types of coordination of the fragments, the strength of bonding, and the rate of spin polarization depend upon the nature of the fragments. Infinite and finite graphene narrow zigzag nanoribbons are characterized by the lift of the spin degeneracy and strong spin polarization caused by interface-induced structural asymmetry and oxygen-mediated indirect exchange interactions with Mn ions of LSMO support. Spin polarization changes the semiconducting nature of infinite graphene nanoribbons to half-metallic state with visible spin-up density of states at the Fermi level. The h-BN nanoribbon binding energy is weaker than graphene nanoribbon ones with noticeably shorter interlayer distance. The asymmetry effect and indirect exchange interactions cause spin polarization of h-BN nanoribbon as well with formation of embedded states inside the band gap. The results show a possibility to use one-atom thick nanofragments to design LSMO-based heterostructures for spintronic nanodevices with h-BN as an inert spacer to develop different potential barriers.</P>

DYNAMICAL ANALYSIS OF A VEHICLE TO TRAILER CONNECTION DURING BRAKING

Nikola Avramov 한국자동차공학회 2022 International journal of automotive technology Vol.23 No.4

In this paper the dynamical analysis of a vehicle to trailer connection during braking is presented. At first both the vehicles, motor vehicle and trailer are analysed as a separate vehicles, driving with same starting velocity and same braking force applied but no connection between them. Than the dynamic analysis is conducted for two types of connection, one rigid and second one with inertial brake between. The chronology of the study is to find the displacement of the vehicles as separate systems and to conduct the dynamic analysis of the two connections as a difference in the travel till zero velocity. The aim of the paper is to acknowledge the stiffness of the vehicle to trailer connection during braking.

Nuclear magnetic resonance and theoretical simulation study on Cs ion co-adsorbed with other alkali cations on illite

Baek, Woohyeon,Avramov, Paul V.,Kim, Yeongkyoo Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.489 No.-

<P><B>Abstract</B></P> <P>Illite is known to show highly selective Cs adsorption and can control the migration of Cs in a natural environment. However, the local environment and dynamic behavior of Cs with other ions on illite are not well known. To investigate this system, both NMR and theoretical calculation were used for the study of Cs with other alkali cations on the surface of illite. The order of selectivity for Cs adsorption on illite against other alkali cations is generally Li > Na > K > Rb. The fraction of Cs assigned to inner-sphere complexes as estimated by NMR is in the order of Na > K > Rb > Li, which is different from the order of Cs selectivity, and the difference becomes greater with decreasing Cs molar fraction in solution. This order of inner-sphere complex fraction of Cs is in good agreement with that found by theoretical calculation. The result of MD simulation shows the highest molarity peak for all competing alkali cations at 2–4 Å regardless of their fractions and species, but with different distribution and distance from the illite surface. Our results demonstrate that the Cs complexes on the surface of illite are highly dependent on the other hydrated competing alkali cations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This is the first report using both NMR and theoretical simulation for these systems. </LI> <LI> The fraction of inner-sphere complex Cs with other ions is in the order of Na > K > Rb > Li. </LI> <LI> The result from NMR is in good agreement with that found by theoretical calculation. </LI> <LI> Cs complexes on the illite surface are highly dependent on the other alkali cations. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Photo-Transformation Trajectories of Nitro-Spiropyran in Hybrid Compounds with [60]Fullerene

Pomogaev, Vladimir A.,Avramov, Pavel V.,Ruud, Kenneth American Chemical Society 2019 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.123 No.30

<P>Photo- and thermo- isomerization trajectories of various conversion pathways between nitro-spiropyran and its <I>trans</I>-<I>trans</I>-<I>cis</I> merocyanine form were produced and the role of <I>n</I>π* states was investigated along the corresponding potential energy surface calculated using the ωB97XD functional and the cc-pVDZ basis set. The nondissociative <I>n</I>π* states on the photoisomerization trajectories can switch from/to the dissociative photoactive ππ* state at two intersections between their energy surfaces. The photochromic properties inherited in hybrid compounds of nitro-spiropyran-containing [60]fullerene are interpreted due to a reversible “dual energy bypass” ππ*↔<I>n</I>π* mechanism in terms of both adiabatic absorption and highly effective nonadiabatic dissipative transitions between the excited states of the photochromic fragment, that prevents energy loss through the [60]fullerene and in this way keeps the photochromic properties intact.</P> [FIG OMISSION]</BR>

Features of Electronic, Mechanical, and Electromechanical Properties of Fluorinated Diamond Films of Nanometer Thickness

Kvashnin, A. G.,Avramov, P. V.,Kvashnin, D. G.,Chernozatonskii, L. A.,Sorokin, P. B. American Chemical Society 2017 The Journal of Physical Chemistry Part C Vol.121 No.51

<P>Electronic, elastic, and electromechanical properties of the quasi-two-dimensional diamond films of cubic and hexagonal symmetry with fluorinated surfaces were studied using electronic band structure calculations in the framework of density functional theory Perdew–Burke–Ernzerhof and self-consistent GW methods. Predicted two-dimensional elastic constants and acoustic velocities of the films coincide well with available experimental data. It was found that both methods predict drastically different dependencies of the band gaps, electromechanical responses, and charge carrier effective masses upon the films’ thicknesses.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2017/jpccck.2017.121.issue-51/acs.jpcc.7b07946/production/images/medium/jp-2017-07946z_0005.gif'></P>

Novel hybrid C/BN two-dimensional heterostructures

Kvashnin, Dmitry G,Kvashnina, Olga P,Avramov, Pavel V,Sorokin, Pavel B,Kvashnin, Alexander G IOP 2017 Nanotechnology Vol.28 No.8

<P>Here we present an investigation of new quasi-two-dimensional heterostructures based on the alternation of bounded carbon and boron nitride layers (C/BN). We carried out a theoretical study of the atomic structure, stability and electronic properties of the proposed heterostructures. Such ultrathin quasi-two-dimensional C/BN films can be synthesized by means of chemically induced phase transition by connection of the layers of multilayered h-BN/graphene van der Waals heterostructures, which is indicated by the negative phase transition pressure in the calculated phase diagrams (<I>P</I>, <I>T</I>) of the films. It was shown that the band gap value of the C/BN films spans the infrared and visible spectrum. We hope that the proposed films and fabrication method can be considered as a possible route to obtain nanostructures with a controllable band gap in wide energy range. This makes these materials potentially suitable for a variety of applications, including photovoltaics, photoelectronics and more.</P>

A key role of tensile strain and surface termination in formation and properties of La_0.7Sr_0.3MnO₃ composites with carbon nanotubes

Kovaleva, Evgenia A.,Kuzubov, Alexander A.,Avramov, Pavel V.,Kholtobina, Anastasia S.,Kuklin, Artem V.,Tomilin, Felix N.,Sorokin, Pavel B. Elsevier 2017 Computational materials science Vol.139 No.-

<P><B>Abstract</B></P> <P>Atomic and electronic structure of LSMO-based composites with carbon nanotubes were studied by means of density functional theory with respect to the termination of LSMO surface. The deformation of the tubes caused by the lattice mismatch with the substrate leads to a major change in their electronic structure. The surface terminated with Mn-O layer provides much stronger interaction with carbon nanotubes than Sr-O terminated one does. The interaction with transition metal atoms is essential for spin polarization of the nanotube while no spin injection was observed for Sr-O-supported tubes.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Inheritance of Photochromic Properties of Nitro-Substituted and Halogenated Spiropyrans Containing the Pyrrolidino[60]fullerene

Pomogaev, Vladimir A.,Barachevsky, Valery A.,Tuktarov, Airat R.,Avramov, Pavel V.,Artyukhov, Victor Ya. American Chemical Society 2018 The journal of physical chemistry. A, Molecules, s Vol.122 No.2

<P>The photophysical and isomerization properties of hybrid molecular compounds that consist of photochromic nitro-substituted and halogenated spiropyran derivatives bonded to the surface of the [60]fullerene cage through the pyrrolidine bridge were investigated using various functionals and basis sets of TD-DFT and semiempirical quantum-chemical approaches. The role of <I>n</I>π* states formed by the lone pairs of substituents in changing of the electronic structure and photochromic properties of spiropyran derivatives was evaluated. The S<SUB>ππ</SUB>(spiropyran) → intermediate <I>n</I>π* states → S<SUB>ππ</SUB>(merocyanine) channel for phototransformation of the hybrid compound containing a nitro-substituted spiropyran moiety was established and compared with similar systems of halogenated spiropyrans attached to the [60]fullerene bulk where photoinduced isomerization does not process due to high probability of internal conversion from the excited electronic state localized on the spiropyran fragment to the states of the pyrrolidino[60]fullerene.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcafh/2018/jpcafh.2018.122.issue-2/acs.jpca.7b08374/production/images/medium/jp-2017-08374s_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp7b08374'>ACS Electronic Supporting Info</A></P>

Direct observation of site-selective hydrogenation and spin-polarization in hydrogenated hexagonal boron nitride on Ni(111)

Ohtomo, M.,Yamauchi, Y.,Sun, X.,Kuzubov, A.,Mikhaleva, N.,Avramov, P.,Entani, S.,Matsumoto, Y.,Naramoto, H.,Sakai, S. Royal Society of Chemistry 2017 Nanoscale Vol.9 No.6

<P>We report the structural analysis and spin-dependent band structure of hydrogenated boron nitride adsorbed on Ni(111). The atomic displacement studied by using the normal incidence X-ray standing wave (NIXSW) technique supports the H-B(fcc):N(top) model, in which hydrogen atoms are site-selectively chemisorbed on boron atoms and N atoms remain on top of Ni atoms. The distance between the Ni plane and nitrogen plane did not change after hydrogenation, which implies that the interaction between Ni and N is 3d-pi orbital mixing (donation and back-donation) even after hydrogenation of boron. The remaining pi* peaks in near-edge X-ray absorption fine structure (NEXAFS) spectra are a manifestation of the rehybridization of sp(2) into sp(3) states, which is consistent with the N-B-N bonding angle derived from NIXSW measurement. The SPMDS measurement revealed the spin asymmetry appearing on hydrogenated h-BN, which was originated from a p related orbital with back donation from the Ni 3d state. Even though the atomic displacement is reproduced by the density functional theory (DFT) calculation with the H-B(fcc):N(top) model, the experimental spin-dependent band structure was not reproduced by DFT possibly due to the self-interaction error (SIE). These results reinforce the site-selective hydrogenation of boron and pave the way for efficient design of BN nanomaterials for hydrogen storage.</P>

Two-dimensional hexagonal CrN with promising magnetic and optical properties: A theoretical prediction

Kuklin, A.,Kuzubov, A.,Kovaleva, E.,Mikhaleva, N.,Tomilin, F.,Lee, H.,Avramov, P. Royal Society of Chemistry 2017 Nanoscale Vol.9 No.2

<P>Half-metallic ferromagnetic materials with planar forms are promising for spintronics applications. A wide range of 2D lattices like graphene, h-BN, transition metal dichalcogenides, etc. are non-magnetic or weakly magnetic. Using first principles calculations, the existence of graphene-like hexagonal chromium nitride (h-CrN) with an almost flat atomically thin structure is predicted. We find that freestanding h-CrN has a 100% spin-polarized half-metallic nature with possible ferromagnetic ordering and a high rate of optical transparency. As a possible method for stabilization and synthesis, deposition of h-CrN on 2D MoSe2 or on MoS2 is proposed. The formation of composites retains the half-metallic properties and leads to the reduction of spin-down band gaps to 1.43 and 1.71 eV for energetically favorable h-CrN/MoSe2 and h-CrN/MoS2 configurations, respectively. Calculation of the dielectric functions of h-CrN, h-CrN/MoSe2 and h-CrN/MoS2 exhibit the high transparency of all three low-dimensional nanomaterials. The honeycomb CrN may be considered as a promising fundamental Half-2D material for a variety of potential applications of critical importance.</P>