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  • 1.
    Medeiros, Paulo V. C.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk kemi. Linköpings universitet, Tekniska högskolan.
    Electronic properties of complex interfaces and nanostructures2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis investigates the structural and electronic properties of graphene, polyaromatic hydrocarbon (PAH) molecules, and other carbon-based materials, when interacting with metallic surfaces, as well as under the influence of different types of perturbations. Density functional theory, incorporating van der Waals interactions, has been employed.

    PAH molecules can, with gradual accuracy, be considered as approximations to an infinite graphene layer. A method to estimate the contributions to the binding energies and net charge transfers from different types of carbon atoms and CH groups in graphene- and PAH-metal systems has been generalized. In this extended method, the number and the nature of the functional groups is determined using a first-principles approach, rather than intuitively or through empirical considerations. Relationships between charge transfers, interface dipole moments and work functions in such systems are explored.

    Although the electronic structure of physisorbed graphene keeps most of the features of freestanding graphene, the use of large supercells in calculations makes it difficult to resolve the changes introduced in the band structures of such materials. In this thesis, this was the initial motivation for the development of a method to perform the Brillouin zone unfolding of band structures. This method, as initially developed, is shown to be of general use for any periodic structure, and is even further generalized – through the introduction of the unfolding density operator – to tackle the unfolding of the eigenvalues of any arbitrary operator, with  both scalar as well as spinor eigenstates.

    A combined experimental and theoretical investigation of the self-assembly of a binary mixture of 4,9-diaminoperylene-quinone-3,10-diimine (DPDI) and 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) molecules on Ag(111) is presented. The DFT calculations performed here allow for the investigation of the interplay between molecule-molecule and molecule-surface interactions in the network.

    Besides the main results mentioned above, this thesis also incorporates a study of silicon-metal nanostructures, as well as an investigation of the use of hybrid graphene-graphane structures as prototypes for atomically precise design in nanoelectronics.

    Delarbeid
    1. Benzene, coronene, and circumcoronene adsorbed on gold, and a gold cluster adsorbed on graphene: Structural and electronic properties
    Åpne denne publikasjonen i ny fane eller vindu >>Benzene, coronene, and circumcoronene adsorbed on gold, and a gold cluster adsorbed on graphene: Structural and electronic properties
    2012 (engelsk)Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, nr 20, s. 205423-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Density functional theory (DFT) calculations were performed in order to investigate the stability and the electronic structure of graphene-gold interfaces. Two configurations were studied: a gold cluster interacting with graphene and different polycyclic aromatic hydrocarbon (PAH) molecules, namely, C6H6 (benzene), C24H12 (coronene), and C54H18 (circumcoronene) adsorbed on an Au(111) surface. Nonlocal interactions were accounted for by using the semiempirical DFT-D2 method of Grimme. A limited set of calculations were also performed by using the first-principles van der Waals density functional method (vdW-DF). Adsorption distances around 3 angstrom and electronic charge transfer values of about (3-13) x 10(-3)e(-) per carbon atom were predicted for all systems. No major changes resulting from the adsorption of the gold cluster were detected in the graphenes density of states. The DFT-D2 results involving the adsorption of the PAH molecules on gold show an estimated binding energy of 73 meV per carbon atom, as well as an electronic charge loss of 0.10 x 10(-2) e(-), also per carbon atom, for an extended graphene sheet adsorbed on a gold surface. The modeling of the adsorption of C6H6 molecule on a gold surface suggests that the vdW-DF method provides more accurate results for the binding energies of such systems, in comparison to pure DFT calculations, which do not take the nonlocal interactions into account, as well as to simulations employing the DFT-D2 method.

    sted, utgiver, år, opplag, sider
    American Physical Society, 2012
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-78270 (URN)10.1103/PhysRevB.85.205423 (DOI)000304081900010 ()
    Merknad
    Funding Agencies|Swedish Foundation for International Cooperation in Research and Higher Education (STINT)|YR2009-7017|Swedish Research Council (VR)||Tilgjengelig fra: 2012-06-08 Laget: 2012-06-08 Sist oppdatert: 2017-12-07
    2. Optical and Magnetic Excitations of Metal-Encapsulating Si Cages: A Systematic Study by Time-Dependent Density Functional Theory
    Åpne denne publikasjonen i ny fane eller vindu >>Optical and Magnetic Excitations of Metal-Encapsulating Si Cages: A Systematic Study by Time-Dependent Density Functional Theory
    Vise andre…
    2014 (engelsk)Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 21, s. 11377-11384Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    A systematic study of the optical and magnetic excitations of 12 MSi12 and four MSi10 transition metal encapsulating Si cages has been carried out by employing real time time-dependent density functional theory. Criteria for the choice of transition metals (M) are clusters stability, synthesizability, and diversity. It was found that both the optical absorption and the spin-susceptibility spectra are mainly determined by, in decreasing order of importance, (1) the cage shape, (2) the group in the Periodic Table to which M belongs, and (3) the period of M in the Periodic Table. Cages with similar structures and metal species that are close to each other in the Periodic Table possess spectra sharing many similarities; for example, the optical absorption spectra of the MSi12 (M = V, Nb, Ta, Cr, Mo, and W), which are highly symmetric and belong to groups 4 and 5 of the Periodic Table, all share a very distinctive peak at around 4 eV. In all cases, although some of the observed transitions are located at the Si skeleton of the cages, the transition metal species is always significant for the optical absorption and the spin-susceptibility spectra. Our results provide fingerprint data for identification of gas-phase MSi12 and MSi10 by optical absorption spectroscopy.

    sted, utgiver, år, opplag, sider
    American Chemical Society (ACS), 2014
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-108167 (URN)10.1021/jp4096562 (DOI)000336771700025 ()
    Tilgjengelig fra: 2014-06-26 Laget: 2014-06-26 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    3. Effects of extrinsic and intrinsic perturbations on the electronic structure of graphene: Retaining an effective primitive cell band structure by band unfolding
    Åpne denne publikasjonen i ny fane eller vindu >>Effects of extrinsic and intrinsic perturbations on the electronic structure of graphene: Retaining an effective primitive cell band structure by band unfolding
    2014 (engelsk)Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 4, s. 041407-1-041407-4Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We use a band unfolding technique to recover an effective primitive cell picture of the band structure of graphene under the influence of different types of perturbations. This involves intrinsic perturbations, such as structural defects, and external ones, comprising nitrogen substitutions and the inclusion of graphene in adsorbed systems. In such cases, the band unfolding provides a reliable and efficient tool for quantitatively analyzing the effect of doping and defects on the electronic structure of graphene. We envision that this approach will become a standard method in the computational analysis of graphene's electronic structure in related systems.

    sted, utgiver, år, opplag, sider
    American Physical Society, 2014
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-103755 (URN)10.1103/PhysRevB.89.041407 (DOI)000332243600001 ()
    Tilgjengelig fra: 2014-01-26 Laget: 2014-01-26 Sist oppdatert: 2017-12-06bibliografisk kontrollert
    4. Hybrid platforms of graphane-graphene 2D structures: prototypes for atomically precise nanoelectronics
    Åpne denne publikasjonen i ny fane eller vindu >>Hybrid platforms of graphane-graphene 2D structures: prototypes for atomically precise nanoelectronics
    Vise andre…
    2014 (engelsk)Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 43, s. 23558-23563Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    First-principles calculations demonstrate that line/ribbon defects, resulting from a controlled dehydrogenation in graphane, lead to the formation of low-dimensional electron-rich tracks in a monolayer. The present simulations point out that hybrid graphane-graphene nanostructures exhibit important elements, greatly required for the fabrication of efficient electronic circuits at the atomic level.

    sted, utgiver, år, opplag, sider
    Royal Society of Chemistry, 2014
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-112661 (URN)10.1039/c4cp03698k (DOI)000343974100007 ()25285905 (PubMedID)
    Merknad

    Funding Agencies|Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq); Fundacao de Amparo a Pesquisa do Estado da Bahia ( FAPESB).; Swedish Research Council (VR)

    Tilgjengelig fra: 2014-12-05 Laget: 2014-12-05 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    5. Bonding, charge rearrangement and interface dipoles of benzene, graphene, and PAH molecules on Au(111) and Cu(111)
    Åpne denne publikasjonen i ny fane eller vindu >>Bonding, charge rearrangement and interface dipoles of benzene, graphene, and PAH molecules on Au(111) and Cu(111)
    2015 (engelsk)Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 81, s. 620-628Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We perform a theoretical study of the electronic properties of polyaromatic hydrocarbon (PAH) molecules, as well as benzene and graphene, adsorbed on copper and gold. The PAH molecules studied are coronene (C24H12), circumcoronene (C54H18) and circumcircumcoronene (C96H24), which we consider as gradual approximations to an infinite graphene layer. In order to understand how the size of the adsorbed PAH molecules influences the adsorbate-metal interactions, we generalize the approach used in our earlier study [Phys Rev B, 85 (2012), p. 205423] to decompose the binding energies and net charge transfers into separate contributions from specific groups of atoms, and we then show that the zigzag edges of the PAH molecules interact stronger with the metal surfaces than the armchair ones. We discuss the nature of binding in our model systems as well as the formation of interface dipoles. We show that for all model systems studied here, the charge rearrangement contribution to the interface dipoles can be expressed as the product of the charge involved in the formation of the dipole and the distance between well-defined centers of charge for electron accumulation and depletion. This distance is only marginally dependent on the specific PAH molecules, decreasing slowly with their size.

    sted, utgiver, år, opplag, sider
    Elsevier, 2015
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-113164 (URN)10.1016/j.carbon.2014.09.096 (DOI)000345682900066 ()
    Merknad

    Funding Agencies|Swedish Research Council (VR); Linkoping Linnaeus Initiative on Novel Functionalized Materials (VR); Swedish Foundation for Strategic Research (SSF) [RMA11-0029]; FunMat (Functional Nanoscale Materials) - a VINN Excellence Centre (Swedish Agency for Innovation Systems VINNOVA)

    Tilgjengelig fra: 2015-01-14 Laget: 2015-01-12 Sist oppdatert: 2017-12-05
    6. Unfolding spinor wave functions and expectation values of general operators: Introducing the unfolding-density operator
    Åpne denne publikasjonen i ny fane eller vindu >>Unfolding spinor wave functions and expectation values of general operators: Introducing the unfolding-density operator
    2015 (engelsk)Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, s. 041116(R)-041120(R)Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We show that the spectral weights W mK ⃗ (k ⃗ ) used for the unfolding of two-component spinor eigenstates ∣ ∣ ψ SC mK ⃗ ⟩=|α⟩|ψ SC mK ⃗ ,α⟩+|β⟩|ψ SC mK ⃗ ,β⟩ can be decomposed as the sum of the partial spectral weights W μ mK ⃗ (k ⃗ ) calculated for each component μ=α,β independently, effortlessly turning a possibly complicated problem involving two coupled quantities into two independent problems of easy solution. Furthermore, we define the unfolding-density operator ρ ˆ K ⃗ (k ⃗ ;ɛ) , which unfolds the primitive cell expectation values φ pc (k ⃗ ;ɛ) of any arbitrary operator φ ˆ according to φ pc (k ⃗ ;ɛ)=Tr(ρ ˆ K ⃗ (k ⃗ ;ɛ)φ ˆ ) . As a proof of concept, we apply the method to obtain the unfolded band structures, as well as the expectation values of the Pauli spin matrices, for prototypical physical systems described by two-component spinor eigenfunctions.

    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-114465 (URN)10.1103/PhysRevB.91.041116 (DOI)000348477200002 ()
    Merknad

    P. V. C. M, S. S., and J.B. acknowledge the Swedish Research Council (VR) for funding. S. S. T. acknowledges funding from the University of Basque Country UPV/EHU (GIC07-IT-756-13), the Departamento de Educacion del Gobierno Vasco and the Spanish Ministerio de Ciencia e Innovacion (FIS2010-19609-C02-01), the Tomsk State University Competitiveness Improvement Program, the Saint Petersburg State University (project 11.50.202.2015) and the Spanish Ministry of Economy and Competitiveness MINECO (FIS2013-48286-C2-1-P). Computer resources were allocated by the National Supercomputer Centre, Sweden, through SNAC and the MATTER consortium, as well as in the SKIF-Cyberia and CRYSTAL supercomputers at Tomsk State University.

    Tilgjengelig fra: 2015-02-20 Laget: 2015-02-20 Sist oppdatert: 2017-12-04
    7. Self-assembly of a DPDI+PTCDA mixed layer on Ag(111): Theory and experiments
    Åpne denne publikasjonen i ny fane eller vindu >>Self-assembly of a DPDI+PTCDA mixed layer on Ag(111): Theory and experiments
    Vise andre…
    (engelsk)Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We present a combined experimental and theoretical investigation of the self-assembly of a binary mixture of 4,9-diaminoperylene-quinone-3,10-diimine (DPDI) and 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) molecules on Ag(111). At a 1:1 ratio, the two molecules intermix to form a long-range ordered bimolecular network stabilized by intermolecular hydrogen bonding. We show, by means of low energy electron diffraction (LEED) measurements, that the self-assembled network is commensurate with the underlying silver surface. Scanning tunneling microscope (STM) measurements and density functional theory (DFT) calculations are combined to unravel the structural configuration of the system. Core-level binding energy shifts for the 1s levels of the O atoms, obtained from both X-ray photoelectron spectroscopy (XPS) measurements and DFT simulations, are reported and compared. Our DFT calculations allow the investigation of the interplay between molecule-molecule and molecule-surface interactions in the network. Our combined experimental-theoretical approach allows a precise characterization of the structural and electronic properties of the studied system.

    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-117846 (URN)
    Tilgjengelig fra: 2015-05-11 Laget: 2015-05-11 Sist oppdatert: 2015-05-11bibliografisk kontrollert
  • 2.
    Medeiros, Paulo V. C.
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Kostov Gueorguiev, Gueorgui
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Stafström, Sven
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Beräkningsfysik. Linköpings universitet, Tekniska högskolan.
    Benzene, coronene, and circumcoronene adsorbed on gold, and a gold cluster adsorbed on graphene: Structural and electronic properties2012Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, nr 20, s. 205423-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory (DFT) calculations were performed in order to investigate the stability and the electronic structure of graphene-gold interfaces. Two configurations were studied: a gold cluster interacting with graphene and different polycyclic aromatic hydrocarbon (PAH) molecules, namely, C6H6 (benzene), C24H12 (coronene), and C54H18 (circumcoronene) adsorbed on an Au(111) surface. Nonlocal interactions were accounted for by using the semiempirical DFT-D2 method of Grimme. A limited set of calculations were also performed by using the first-principles van der Waals density functional method (vdW-DF). Adsorption distances around 3 angstrom and electronic charge transfer values of about (3-13) x 10(-3)e(-) per carbon atom were predicted for all systems. No major changes resulting from the adsorption of the gold cluster were detected in the graphenes density of states. The DFT-D2 results involving the adsorption of the PAH molecules on gold show an estimated binding energy of 73 meV per carbon atom, as well as an electronic charge loss of 0.10 x 10(-2) e(-), also per carbon atom, for an extended graphene sheet adsorbed on a gold surface. The modeling of the adsorption of C6H6 molecule on a gold surface suggests that the vdW-DF method provides more accurate results for the binding energies of such systems, in comparison to pure DFT calculations, which do not take the nonlocal interactions into account, as well as to simulations employing the DFT-D2 method.

  • 3.
    Medeiros, Paulo V. C.
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk kemi. Linköpings universitet, Tekniska högskolan.
    Müller, Kathrin
    Zernike Institute for Advanced Materials, University of Groningen, The Netherlands.
    Jung, Thomas A.
    Laboratory for Micro- and Nanotechnology, Paul-Scherrer-Institute, Switzerland.
    Gade, Lutz H.
    Anorganisch-Chemisches Institut, Universität Heidelberg, Germany.
    Stafström, Sven
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk kemi. Linköpings universitet, Tekniska högskolan.
    Björk, Jonas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk kemi. Linköpings universitet, Tekniska högskolan.
    Stöhr, Meike
    Zernike Institute for Advanced Materials, University of Groningen, The Netherlands.
    Self-assembly of a DPDI+PTCDA mixed layer on Ag(111): Theory and experimentsManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We present a combined experimental and theoretical investigation of the self-assembly of a binary mixture of 4,9-diaminoperylene-quinone-3,10-diimine (DPDI) and 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) molecules on Ag(111). At a 1:1 ratio, the two molecules intermix to form a long-range ordered bimolecular network stabilized by intermolecular hydrogen bonding. We show, by means of low energy electron diffraction (LEED) measurements, that the self-assembled network is commensurate with the underlying silver surface. Scanning tunneling microscope (STM) measurements and density functional theory (DFT) calculations are combined to unravel the structural configuration of the system. Core-level binding energy shifts for the 1s levels of the O atoms, obtained from both X-ray photoelectron spectroscopy (XPS) measurements and DFT simulations, are reported and compared. Our DFT calculations allow the investigation of the interplay between molecule-molecule and molecule-surface interactions in the network. Our combined experimental-theoretical approach allows a precise characterization of the structural and electronic properties of the studied system.

  • 4.
    Medeiros, Paulo V. C.
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Beräkningsfysik. Linköpings universitet, Tekniska högskolan.
    Stafström, Sven
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Beräkningsfysik. Linköpings universitet, Tekniska högskolan.
    Björk, Jonas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Beräkningsfysik. Linköpings universitet, Tekniska högskolan.
    Effects of extrinsic and intrinsic perturbations on the electronic structure of graphene: Retaining an effective primitive cell band structure by band unfolding2014Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 4, s. 041407-1-041407-4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We use a band unfolding technique to recover an effective primitive cell picture of the band structure of graphene under the influence of different types of perturbations. This involves intrinsic perturbations, such as structural defects, and external ones, comprising nitrogen substitutions and the inclusion of graphene in adsorbed systems. In such cases, the band unfolding provides a reliable and efficient tool for quantitatively analyzing the effect of doping and defects on the electronic structure of graphene. We envision that this approach will become a standard method in the computational analysis of graphene's electronic structure in related systems.

  • 5.
    Medeiros, Paulo Vinicius Da Costa
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk kemi. Linköpings universitet, Tekniska högskolan.
    Tsirpin, Stepan S.
    DIPC, San Sebastian 20018, Basque Country, Spain; Tomsk State Univ, Tomsk 634050, Russia; St Petersburg State Univ, St Petersburg 198504, Russia .
    Stafström, Sven
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk kemi. Linköpings universitet, Tekniska högskolan.
    Björk, Jonas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk kemi. Linköpings universitet, Tekniska högskolan.
    Unfolding spinor wave functions and expectation values of general operators: Introducing the unfolding-density operator2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, s. 041116(R)-041120(R)Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We show that the spectral weights W mK ⃗ (k ⃗ ) used for the unfolding of two-component spinor eigenstates ∣ ∣ ψ SC mK ⃗ ⟩=|α⟩|ψ SC mK ⃗ ,α⟩+|β⟩|ψ SC mK ⃗ ,β⟩ can be decomposed as the sum of the partial spectral weights W μ mK ⃗ (k ⃗ ) calculated for each component μ=α,β independently, effortlessly turning a possibly complicated problem involving two coupled quantities into two independent problems of easy solution. Furthermore, we define the unfolding-density operator ρ ˆ K ⃗ (k ⃗ ;ɛ) , which unfolds the primitive cell expectation values φ pc (k ⃗ ;ɛ) of any arbitrary operator φ ˆ according to φ pc (k ⃗ ;ɛ)=Tr(ρ ˆ K ⃗ (k ⃗ ;ɛ)φ ˆ ) . As a proof of concept, we apply the method to obtain the unfolded band structures, as well as the expectation values of the Pauli spin matrices, for prototypical physical systems described by two-component spinor eigenfunctions.

  • 6.
    Mota, F. de B.
    et al.
    University of Federal Bahia, Salvador, Brazil .
    Rivelino, R.
    University of Federal Bahia, Salvador, Brazil .
    Medeiros, Paulo Vinicius Da Costa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Beräkningsfysik. Linköpings universitet, Tekniska högskolan.
    Mascarenhas, A. J. S.
    University of Federal Bahia, Salvador, Brazil .
    de Castilho, C. M. C.
    University of Federal Bahia, Salvador, Brazil .
    Hybrid platforms of graphane-graphene 2D structures: prototypes for atomically precise nanoelectronics2014Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 43, s. 23558-23563Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    First-principles calculations demonstrate that line/ribbon defects, resulting from a controlled dehydrogenation in graphane, lead to the formation of low-dimensional electron-rich tracks in a monolayer. The present simulations point out that hybrid graphane-graphene nanostructures exhibit important elements, greatly required for the fabrication of efficient electronic circuits at the atomic level.

  • 7.
    Oliveira, Micael J. T.
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan. University of Coimbra, Portugal.
    Medeiros, Paulo V. C.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Beräkningsfysik. Linköpings universitet, Tekniska högskolan.
    Sousa, Jose R. F.
    University of Coimbra, Portugal .
    Nogueira, Fernando
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan. University of Coimbra, Portugal.
    Gueorguiev, Gueorgui Kostov
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Optical and Magnetic Excitations of Metal-Encapsulating Si Cages: A Systematic Study by Time-Dependent Density Functional Theory2014Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 21, s. 11377-11384Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A systematic study of the optical and magnetic excitations of 12 MSi12 and four MSi10 transition metal encapsulating Si cages has been carried out by employing real time time-dependent density functional theory. Criteria for the choice of transition metals (M) are clusters stability, synthesizability, and diversity. It was found that both the optical absorption and the spin-susceptibility spectra are mainly determined by, in decreasing order of importance, (1) the cage shape, (2) the group in the Periodic Table to which M belongs, and (3) the period of M in the Periodic Table. Cages with similar structures and metal species that are close to each other in the Periodic Table possess spectra sharing many similarities; for example, the optical absorption spectra of the MSi12 (M = V, Nb, Ta, Cr, Mo, and W), which are highly symmetric and belong to groups 4 and 5 of the Periodic Table, all share a very distinctive peak at around 4 eV. In all cases, although some of the observed transitions are located at the Si skeleton of the cages, the transition metal species is always significant for the optical absorption and the spin-susceptibility spectra. Our results provide fingerprint data for identification of gas-phase MSi12 and MSi10 by optical absorption spectroscopy.

  • 8.
    Vinicius Da Costa Medeiros, Paulo
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Beräkningsfysik. Linköpings universitet, Tekniska högskolan.
    Kostov Gueorguiev, Gueorgui
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Stafström, Sven
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Beräkningsfysik. Linköpings universitet, Tekniska högskolan.
    Bonding, charge rearrangement and interface dipoles of benzene, graphene, and PAH molecules on Au(111) and Cu(111)2015Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 81, s. 620-628Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We perform a theoretical study of the electronic properties of polyaromatic hydrocarbon (PAH) molecules, as well as benzene and graphene, adsorbed on copper and gold. The PAH molecules studied are coronene (C24H12), circumcoronene (C54H18) and circumcircumcoronene (C96H24), which we consider as gradual approximations to an infinite graphene layer. In order to understand how the size of the adsorbed PAH molecules influences the adsorbate-metal interactions, we generalize the approach used in our earlier study [Phys Rev B, 85 (2012), p. 205423] to decompose the binding energies and net charge transfers into separate contributions from specific groups of atoms, and we then show that the zigzag edges of the PAH molecules interact stronger with the metal surfaces than the armchair ones. We discuss the nature of binding in our model systems as well as the formation of interface dipoles. We show that for all model systems studied here, the charge rearrangement contribution to the interface dipoles can be expressed as the product of the charge involved in the formation of the dipole and the distance between well-defined centers of charge for electron accumulation and depletion. This distance is only marginally dependent on the specific PAH molecules, decreasing slowly with their size.

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