Resistance simulations for junctions of SW and MW carbon nanotubes with various metal substrates

Abstract This theoretical study focuses on junctions between the carbon nanotubes (CNTs) and contacting metallic elements of a nanocircuit. Numerical simulations on the conductance and resistance of these contacts have been performed using the multiple scattering theory and the effective media cluster approach. Two models for CNT-metal contacts have been considered in this paper: a) first principles "liquid metal" model and b) semi-empirical model of "effective bonds" based on Landauer notions on ballistic conductivity. Within the latter, which is a more adequate description of chirality effects, we have simulated both single-wall (SW) and multi-wall (MW) CNTs with different morphology. Results of calculations on resistance for different CNT-Me contacts look quantitatively realistic (from several to hundreds kOhm, depending on chirality, diameter and thickness of MW CNT). The inter-wall transparency coefficient for MW CNT has been also simulated, as an indicator of possible 'radial current' losses

Theoretical Simulations on Electric Properties of CNT-Me and GNR-Me Interconnects Using Effective Media Approach

Abstract To overcome disadvantages of nowadays microtechnology, a further miniaturization of electronic devices, high integration level as well as increase of both operation frequencies and power density is required, including the use of adequate materials and innovative chip interconnects. Due to their unique physical properties, especially due to a ballistic (without losses) mechanism of conductivity, carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) attract a permanently growing technological interest, for example, as promising candidates for nanointerconnects in a high-speed electronics

Atomic and electronic structure of both perfect and nanostructured Ni(111) surfaces: First-principles calculations

article i nfo In this study, we perform first principles simulations on both atomically smooth and nanostructured Ni(111) slabs. The latter contains periodically distributed nickel nanoclusters atop a thin metal film gradually growing from adatoms and serving as a promising catalyst. Applying the generalized gradient approximation within the formalism of the density functional theory we compare the atomic and electronic structures of Ni bulk, as well as both perfect and nanostructured (111) surfaces obtained using two different ab initio approaches: (i) the linear combination of atomic orbitals and (ii) the projector augmented plane waves. The most essential inter-atomic forces between the Ni adatoms upon the substrate have been found to be formed via: (i) attractive pair-wise interactions, (ii) repulsive triple-wise interactions within a triangle and (iii) attractive triple-wise interactions within a line between the nearest adatoms. The attractive interactions surmount the repulsive forces, hence resulting in the formation of stable clusters from Ni adatoms. The magnetic moment and the effective charge (within both Mulliken and Bader approaches) of the outer atoms in Ni nanoparticles increase as compared to those for the smooth Ni(111) surface. The calculated electronic charge redistribution in the Ni nanoclusters features them as possible adsorption centers with increasing catalytic activity, e.g., for further synthesis of carbon nanotubes

Simulations on the mechanism of CNT bundle growth upon smooth and nanostructured Ni as well as θ-Al2O3 catalysts

Abstract In the current study, we have performed ab initio DFT calculations on the gradually growing 2D periodic models of capped single-wall carbon nanotubes (SW CNTs) upon their perpendicular junctions with the Ni(111) substrate, in order to understand the peculiarities of the initial stage of their growth on either smooth or nanostructured catalytic particles. Appearance of the adsorbed carbon atoms upon the substrate follows from the dissociation of CVD hydrocarbon molecules, e.g., CH4: (CH4)ads → (CH)ads+3Hads and (CH)ads → Cads+Hads. (Since the effective growth of CNTs upon Ni nanoparticles occur inside the nanopores of amorphous alumina, we have also simulated analogous surface reactions upon the θ-Al2O3(010) slabs). Association of the adsorbed carbon atoms upon the catalyst surface precedes further swelling of the (Cn)ads islands after appearance of pentagonal defects within a honeycomb sheet which are more probable upon the catalyst surface containing either defects or nanoclusters (as in the case of the nanostructured substrate). The gradual growth of the capped CNTs is considerably more effective upon the nanostructured Ni(111) substrate compared to a smooth nickel substrate (cf. values of CNT adhesion energy per boundary C atom for chiralities of either armchair-type, 4.04 vs. 2.51 eV, or zigzag-type, 4.61 vs. 2.14 eV, respectively). The electronic charge transfer from the Ni catalyst towards the CNTs has been calculated for both chiralities (> 1 e per C atom), i.e., quite strong chemical bonds are formed within the CNT/Ni(111) interconnects

Ab initio simulations on charged interstitial oxygen migration in corundum

We have performed this work within the framework of the EUROfusion Consortium receiving funding from the European grant agreement 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Authors thank R. Vila, A.I. Popov, A. Luchshik and R.A. Evarestov for fruitful discussions. To carry out large-scale calculations, we have used the HPC supercomputer at Stuttgart University (Germany)We have calculated possible migration trajectories for single-charged interstitial Oi− anion using large-scale hybrid density functional theory within linear combination of atomic orbitals approach to defective α-Al2O3 crystals. The most energetically favorable configuration for charged Oi− anion is formation of pseudo-dumbbell (split interstitial) with a regular Oreg ion. For charged interstitial oxygen migration, the energy barrier turns out to be ∼0.8–1.0 eV. This is considerably smaller than that for a neutral interstitial atoms (1.3 eV), in agreement with experimental data.EUROfusion Consortium receiving funding from the European grant agreement 633053; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

First Principle Evaluation of Photocatalytic Suitability for TiO2-Based Nanotubes

Water splitting under the influence of solar light on semiconducting electrodes Immersed in aqueous electrolyte is a potentially clean and renewable source for hydrogen fuel production. Its efficiency depends on relative position of the band gap edges (the visible light interval between infrared and ultraviolet (UV) ranges of electromagnetic spectrum corresponds to gap widths 1.5–2.8 eV) accompanied by a proper band alignment relative to both reduction (H+/H2) and oxidation (O2/H2O) potentials (−4.44 eV and −5.67 eV on energy scale for vacuum, respectively) which must be positioned inside the band gap. Its width for TiO2 anatase-structured bulk is experimentally found to be 3.2 eV, which corresponds to photocatalytic activity under UV light possessing only ~1% efficiency of sunlight energy conversion. Noticeable growth of this efficiency can be achieved by by adjusting the band gap edges for titania bulk through nanoscale transformation of its morphology to anatase-type nanotubes (NTs) (formed by folding of (001) or (101) nanothin TiO2 sheets consisting of 9 or 6 atomic layers and possessing either (n,0) or (−n,n) chiralities, respectively) accompanied by partial substitution of pristine atoms by CO, FeTi, NO and SO single dopants as well as NO+SO codopants. In the latter case, the band gap can be reduced down to 2.2 eV while the efficiency is achieved up to ~15%. The energy differences between the edges of band gap (VB and CB), the highest occupied and lowest unoccupied impurity levels inside the band gap (HOIL and LUIL, respectively) induced in doped NTs, while preserving the proper disposition of these levels relatively to the redox potentials, so that εVB<εHOIL<εO2/H2O<εH+/H2<εLUIL<εCB, thus reducing the photon energy required for dissociation of H2O molecule. In this chapter, we analyze applicability of large-scale first principle calculations on the doped single-wall titania NTs of different morphologies with the aim of establishment of their suitability for photocatalytic water splitting

First principles modeling of 3d-metal doped three-layer fluorite-structured TiO2 (4,4) nanotube to be used for photocatalytic hydrogen production

This study has been supported by the EC ERA.Net RUS Plus project No. 237 WATERSPLIT, Russian Basic Research Foundation No. 16-53-76019, and additionally by the IMIS2 Program (Latvia). The authors are also indebted to R. A. Evarestov and O. Lisovski for stimulating discussions as well as to A. Chesnokov for technical assistance.We have estimated theoretically the photocatalytic suitability of thinnest single-wall fluorite-structured titania (4,4) nanotube (NT) possessing three layers each (O-Ti-O) and doped by Sc, V, Cr, Mn, Fe, Co, Ni, Cu and Zn atoms substituted for host Ti atoms. For this goal, we have performed large-scale ab initio calculations on TiO2 NTs with three-layer morphology doped by 3d transition metals, using (i) the method of linear combination of atom-centered Gaussian-type orbitals (LCAO) based on the hybrid density functional theory (DFT) incorporating the Hartree-Fock (HF) exchange contribution (DFT+HF) and (ii) the method of linearized augmented cylindrical waves (LACW) with the muffin-tin approximation based on the local density functional approach (LDA). We have compared the ground state electronic structure, particularly the one-electron densities of states (DOSs) from the LCAO and LACW calculations for periodic arrangements of the 3d-metal dopant atoms. The results show clear evidence for a potential photocatalytic application for water splitting in the case of the Sc-doped titania nanotubes only. These NTs show both a reduced band gap of 2.0 eV relative to the pristine NT and an absence of defect-induced levels between the redox potentials of hydrogen and oxygen, so that electron-hole recombination becomes unlikely. Other 3d dopants with higher atomic number, although their band gap also covers the favorable green to orange region of the solar spectrum, are unsuitable because their defect-induced levels are positioned between the redox potential of oxygen and hydrogen, which can be expected to lead to rapid electron-hole recombination.--//--Dmitry Bocharov, Sergei Piskunov, Yuri F. Zhukovskii, Eckhard Spohr, Pavel N. D'yachkov, First principles modeling of 3d-metal doped three-layer fluorite-structured TiO2 (4,4) nanotube to be used for photocatalytic hydrogen production, Vacuum, Volume 146, 2017, Pages 562-569, ISSN 0042-207X, https://doi.org/10.1016/j.vacuum.2017.05.002.EC ERA.Net RUS Plus project No. 237 WATERSPLIT; Russian Basic Research Foundation No. 16-53-76019; IMIS2 Program (Latvia); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017 TeamingPhase2 under grant agreement No. 739508, project CAMART2

Formation of linear Ni nanochains inside carbon nanotubes: Prediction from density functional theory

Abstract First principles calculations have been performed to investigate the ground state properties of monoperiodic single-walled carbon nanotubes (CNTs) containing nanochain of aligned Ni atoms inside. Using the PBE exchange-correlation functional ( E xc ) within the framework of density functional theory (DFT) we predict the clusterization of Ni filaments in ( n ,0) CNTs for n ⩾ 9 and for ( n , n ) CNTs for n ⩾ 6. The variations in formation energies obtained for equilibrium defective nanostructures allow us to predict the most stable Ni@CNT compositions. Finally, the electronic charge redistribution has been calculated in order to explore intermolecular properties leading to stronger Ni–Ni bond formation

Simulation of Young's moduli for hexagonal ZnO [0 0 0 1]-oriented nanowires: first principles and molecular mechanical calculations

The authors thank A Gulans, B Polyakov and S Vlassov for stimulating discussions. This study has been supported by the ERA.Net RUS Plus project No. 237 Watersplit. AB, RE and SL acknowledge the financial support by the Russian Foundation for Basic Research (Grant No. 17-03-00130-a) and the assistance of the Saint Petersburg State University Computer Center in the accomplishment of high-performance computations.Morphologically reproducible wurtzite-structured zinc oxide nanowires (ZnO NWs) can be synthesized by different methods. Since ZnO NWs have been found to possess piezoelectricity, a comprehensive study of their mechanical properties, e.g. deformations caused by external compression or stretching, is one of the actual tasks of this paper. We have calculated wurtzite-structured [0 0 0 1]-oriented ZnO NWs whose diameters have been varied within 1–5 nm and 1–20 nm ranges when using either ab initio (hybrid DFT-LCAO) or force-field (molecular mechanical) methods, respectively (the minimum diameter dNW of experimentally synthesized NWs has been estimated on average to be ~20 nm). When using both chosen calculation approaches, the values of Young's moduli determined for the mentioned ranges of NW diameters have been found to be qualitatively compatible (168–169 GPa for 5 nm NW thickness), whereas results of molecular mechanical simulations on YNW for 20 nm-thick NWs (160–162 GPa) have been qualitatively comparable with those experimentally measured along the [0 0 0 1] direction of NW loading. In all the cases, a gradual increase of the NW diameter has resulted in an asymptotic decrease of Young's modulus consequently approaching that (Yb) of wurtzite-structured ZnO bulk along its [0 0 0 1] axis. The novelty of this study is that we combine the computation methods of quantum chemistry and molecular mechanics, while the majority of previous studies with the same aim have focused on the application of different classical molecular dynamical methods.ERA.Net RUS Plus project No. 237 Watersplit; Russian Foundation for Basic Research (Grant No. 17-03-00130-a); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Real time polymer nanocomposites-based physical nanosensors: theory and modeling

Functionalized carbon nanotubes and graphene nanoribbons nanostructures, serving as the basis for the creation of physical pressure and temperature nanosensors, are considered as tools for ecological monitoring and medical applications. Fragments of nanocarbon inclusions with different morphologies, presenting a disordered system, are regarded as models for nanocomposite materials based on carbon nanoсluster suspension in dielectric polymer environments (e.g., epoxy resins). We have formulated the approach of conductivity calculations for carbon-based polymer nanocomposites using the effective media cluster approach, disordered systems theory and conductivity mechanisms analysis, and obtained the calibration dependences. Providing a proper description of electric responses in nanosensoring systems, we demonstrate the implementation of advanced simulation models suitable for real time control nanosystems. We also consider the prospects and prototypes of the proposed physical nanosensor models providing the comparisons with experimental calibration dependences