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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>
Kuklin, Artem V.,Kuzubov, Alexander A.,Kovaleva, Evgenia A.,Lee, Hyosun,Sorokin, Pavel B.,Sakai, Seiji,Entani, Shiro,Naramoto, Hiroshi,Avramov, Paul Elsevier 2017 Journal of magnetism and magnetic materials Vol.440 No.-
<P><B>Abstract</B></P> <P>Induced spin polarization of π-conjugated carbon and <I>h</I>-BN low dimensional fragments at the interfaces formed by deposition of pentacene molecule and narrow zigzag graphene and <I>h</I>-BN nanoribbons on MnO<SUB>2</SUB>-terminated LSMO(001) thin film was studied using GGA PBE+U PAW D3-corrected approach. Induced spin polarization of π-conjugated low-dimensional fragments is caused by direct exchange with Mn ions of LSMO(001) MnO-derived surface. Due to direct exchange, the pentacene molecule changes its diamagnetic narrow-band gap semiconducting nature to the ferromagnetic semiconducting state with 0.15eV energy shift between spin-up and spin-down valence bands and total magnetic moment of 0.11μ<SUB>B</SUB>. Direct exchange converts graphene nanoribbon to 100% spin-polarized half-metal with large amplitude of spin-up electronic density at the Fermi level. The direct exchange narrows the <I>h</I>-BN nanoribbon band gap from 4.04 to 1.72eV in spin-up channel and converts the <I>h</I>-BN ribbon semiconducting diamagnetic nature to a semiconducting magnetic one. The electronic structure calculations demonstrate a possibility to control the spin properties of low-dimensional π-conjugated carbon and <I>h</I>-BN fragments by direct exchange with MnO-derived LSMO(001) surface for spin-related applications.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Yamada, Yoichi,Kuklin, Artem V.,Sato, Sho,Esaka, Fumitaka,Sumi, Naoto,Zhang, Chunyang,Sasaki, Masahiro,Kwon, Eunsung,Kasama, Yukihiko,Avramov, Pavel V.,Sakai, Seiji Elsevier 2018 Carbon Vol.133 No.-
<P><B>Abstract</B></P> <P>We report the scanning tunneling microscope (STM) observation of the Li<SUP>+</SUP> ion endohedral C<SUB>60</SUB> on Cu(111), prepared by means of evaporation of a high-purity Li<SUP>+</SUP>@C<SUB>60</SUB>[PF<SUB>6</SUB> <SUP>−</SUP>] salt. The electronic state of Li<SUP>+</SUP>@C<SUB>60</SUB> in the Li<SUP>+</SUP>@C<SUB>60</SUB>[PF<SUB>6</SUB> <SUP>−</SUP>] salt was also determined using photoemission and X-ray absorption spectroscopy, along with the density functional theory (DFT) calculations. In the salt, Li and PF<SUB>6</SUB> had nearly single positive and negative charge, respectively; thus the C<SUB>60</SUB> cage was practically neutral. The salt decomposed under ultra-high vacuum while heating at 400 °C. This allowed the selective deposition of Li<SUP>+</SUP>@C<SUB>60</SUB> on Cu(111). Although secondary-ion mass spectroscopy of the deposited Li<SUP>+</SUP>@C<SUB>60</SUB> film showed a decrease in the Li-content during evaporation, Li<SUP>+</SUP>@C<SUB>60</SUB> was successfully identified using STM. The DFT calculations of Li<SUP>+</SUP>@C<SUB>60</SUB> on Cu(111) suggested that the Li<SUP>+</SUP> ion was singly charged and the location of the Li<SUP>+</SUP> ion was displaced in an upward direction, which altered the local density of states in an upper section of C<SUB>60</SUB>, especially for LUMO+2. The calculated results were mostly in agreement with the bias-dependent STM and dI/dV images. However, an inconsistency was observed between the calculation and experiments in case of empty state imaging where tip-induced displacement of the Li<SUP>+</SUP> ion may occur.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Baek, Woohyeon,Gromilov, Sergey A.,Kuklin, Artem V.,Kovaleva, Evgenia A.,Fedorov, Alexandr S.,Sukhikh, Alexander S.,Hanfland, Michael,Pomogaev, Vladimir A.,Melchakova, Iuliia A.,Avramov, Paul V.,Yusen American Chemical Society 2019 NANO LETTERS Vol.19 No.3
<P>For the first time, lonsdaleite-rich impact diamonds from one of the largest Popigai impact crater (Northern Siberia) with a high concentration of structural defects are investigated under hydrostatic compression up to 25 GPa. It is found that, depending on the nature of a sample, the bulk modulus for lonsdaleite experimentally obtained by X-ray diffraction in diamond-anvil cells is systematically lower and equal to 93.3-100.5% of the average values of the bulk moduli of a diamond matrix. Density functional theory calculations reveal possible coexistence of a number of diamond/lonsdaleite and twin diamond biphases. Among the different mutual configurations, separate inclusions of one lonsdaleite (001) plane per four diamond (111) demonstrate the lowest energy per carbon atom, suggesting a favorable formation of single-layer lonsdaleite (001) fragments inserted in the diamond matrix. Calculated formation energies and experimental diamond (311) and lonsdaleite (331) powder X-ray diffraction patterns indicate that all biphases could be formed under high-temperature, high-pressure conditions. Following the equation of states, the bulk modulus of the diamond (111)/lonsdaleite (001) biphase is the largest one among all bulk moduli, including pristine diamond and lonsdaleite.</P> [FIG OMISSION]</BR>
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>
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>
Effects of catalysts on structural and adsorptive properties of iron oxide-silica nanocomposites
Cătălin Ianăși,Paula Ianăși (b. Svera),Adina Negrea,Mihaela Ciopec,Oleksandr I. Ivankov,Alexander I. Kuklin,László Almásy,Ana-Maria Putz 한국화학공학회 2021 Korean Journal of Chemical Engineering Vol.38 No.2
Iron oxide-silica nanocomposites were prepared by sol-gel method using ammonia (NH3), acetic acid (CH3COOH) and hydrochloric acid (HCl) catalysts to generate different pH values for the reaction conditions. As starting precursors, for the silica, respectively, for the iron oxide, tetraethylorthosilicate (TEOS) and iron-III-acetylacetonate were used. The physico-chemical characterization of the materials revealed that the sample obtained with HCl catalyst displays the largest surface area (300m2/g), the most compact network structure, highest surface roughness, biggest crystallite size (14 nm), magnetization (7 emu/g) and superparamagnetic behavior. These materials were tested for adsorption of Cr6+ and Zn2+ from aqueous solution. Sample M-HCl presented the highest surface area and was further used for adsorption of metal ions. Kinetic, thermodynamic and equilibrium adsorption measurements studies were made for Cr6+ and Zn2+. To establish the material behavior from a thermodynamic point of view, temperature and contact time of adsorption process, activation energy, free energy, of standard enthalpy and entropy were calculated. The kinetic behavior was modelled by pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models and the adsorption characteristics were determined by modelling the experimental data with Langmuir, Freundlich and Sips isotherms.