Željko Šljivančanin

Extended atomic hydrogen dimer configurations on the graphite(0001) surface

We present density functional theory calculations and scanning tunneling microscopy experiments investigating the structures and kinetics of extended hydrogen dimer configurations on the graphite (0001) surface. We identify several hydrogen dimer structures where surface mediated interactions between the two hydrogen atoms lead to increased binding energy even at interatom separations as large as 7 A. By modeling the formation of dimers as sequential adsorption of hydrogen atoms, we find that these dimer configurations exhibit decreased barriers to sticking for the second H atom, compared to the sticking barrier of an H atom on the clean surface. According to our calculations, the activation energies for desorption of a single H atom from any of the experimentally observed extended dimers are higher than the barriers for diffusion to the paradimer configuration. Consequently, molecular hydrogen formation out of the extended dimer structures takes place via diffusion over the paradimer configuration.

Adsorption of O2 and NO on Pd nanocrystals supported on Al2O3/NiAl(110): overlayer and edge structures

Abstract Adsorbate-induced overlayers on nanosized metal clusters have been studied with atomic resolution for the first time. Using scanning tunneling microscopy on supported palladium nanocrystals it was found that oxygen forms a p(2×2) overlayer phase and nitric oxide a c(4×2) overlayer phase. Adsorption of oxygen has a prominent effect on the cluster edges. On the basis of density functional theory calculations the effect is assigned to an oxygen-induced edge reconstruction.

Structure and stability of small H clusters on graphene

The structure and stability of small hydrogen clusters adsorbed on graphene is studied by means of Density Functional Theory (DFT) calculations. Clusters containing up to six H atoms are investigated systematically -- the clusters having either all H atoms on one side of the graphene sheet (\textit{cis}-clusters) or having the H atoms on both sides in an alternating manner (\textit{trans}-cluster). The most stable cis-clusters found have H atoms in ortho- and para-positions with respect to each other (two Hs on neighboring or diagonally opposite carbon positions within one carbon hexagon) while the most stable trans-clusters found have H atoms in ortho-trans-positions with respect to each other (two Hs on neighboring carbon positions, but on opposite sides of the graphene). Very stable trans-clusters with 13-22 H atoms were identified by optimizing the number of H atoms in ortho-trans-positions and thereby the number of closed, H-covered carbon hexagons. For the cis-clusters, the associative H

Electronic properties of the partially hydrogenated armchair carbon nanotubes

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Electronic and optical properties of reduced graphene oxide

desorption was investigated. Generally, the desorption with the lowest activation energy proceeds via para-cis-dimer states, i.e.\ involving somewhere in the H clusters two H atoms that are positioned on opposite sites within one carbon hexagon. H

Ab initio study of structural and electronic properties of partially reduced graphene oxide

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Translational energy and state resolved observations of D and D2 thermally desorbing from D clusters chemisorbed on graphite

desorption from clusters lacking such H pairs is calculated to occur via hydrogen diffusion causing the formation of para-cis-dimer states. Studying the diffusion events showed a strong dependence of the diffusion energy barriers on the reaction energies and a general odd-even dependence on the number of H atoms in the cis-clusters.

Analysis of energy gap opening in graphene oxide

By means of pseudopotential calculations based on density functional theory (DFT) we studied the effect of hydrogenation on electronic properties of armchair single-wall carbon nanotubes. The calculations demonstrate strong preference for formation of monoatomic H chains along the (5,5) nanotube axis with the H binding in an infinite H chain reaching the value of 2.58 eV per atom. Upon formation of chains of H adatoms, initially metallic (5,5) nanotubes change electronic structure to the semiconducting. The opening of the band gap of ∼0.6 eV is accompanied with antiferromagnetic coupling of ferromagnetically ordered magnetic moments on C atoms in vicinity of the H chain. These electronic properties are strikingly similar to those previously observed in narrow graphene nanoribbons with zigzag edges.

Adsorption sites of individual metal atoms on ultrathin MgO(100) films

Controlled reduction of graphene oxide is an alternative and promising method to tune the electronic and optically active energy gap of this two-dimensional material in the energy range of the visible light spectrum. By means of ab initio calculations, based on hybrid density functional theory, that combine the Hartree–Fock method with the generalized gradient approximation (GGA), we investigated the electronic, optical, and radiative recombination properties of partially reduced graphene oxide, modelled as small islands of pristine graphene formed in an infinite sheet of graphene oxide. We predict that tuning of optically active gaps, in the wide range from ∼6.5 eV to ∼0.25 eV, followed by the electron radiative transition times in the range from ns to μs, can be effected by controlling the level of oxidization.

Oxygen dissociation at close-packed Pt terraces, Pt steps, and Ag-covered Pt steps studied with density functional theory

Controlled reduction of graphene oxide (GO) is a promising method to tune the electronic band gap of this two-dimensional material in the energy range of the visible light spectrum. By means of ab initio calculations, based on density functional theory at the generalized gradient approximation level, we investigated electronic properties of partially reduced graphene oxide, modelled as periodic array of small islands of pristine graphene embedded in an infinite sheet of GO. The calculations demonstrated that, by varying the size of the graphene islands from two to eight carbon atoms, it was possible to tune the electronic band gap in a range from 4.38 to 1.31 eV, which is of great importance to the utilization of graphene-based materials in photonic devices.