| 1. |
- Dannetun, Per, et al.
(författare)
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Proceedings of the International Conference on Science and Technology of Synthetic Metals The chemical and electronic structure of the interface between aluminum and conjugated polymers or molecules
- 1993
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Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 55:1, s. 212-217
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between aluminum and α-ω-diphenyltetradecaheptaenee (DP7), α-sexithienyl (6T), and poly(p-phenylenevinylene) (PPV), respectively have been studied using both X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS). The UPS valence band spectra, are interpreted with the help of quantum chemical calculations based upon Modified Neglect of Diatomic Overlap (MNDO), Valence Effective Hamitonian (VEH) and ab initio Hartree-Fock methods. DP7 is a model molecule for polyacetylene, while 6T is a model molecule (an oligomer) of polythiophene. The results indicate that aluminum reacts strongly with the surfaces of all of the materials studied. The π-electronic structure of each material was strongly modified. Furthermore, aluminum reacts preferentially with the polyene partof DP7, with the vinylene part of PPV, and with the α-carbons of the thiophene nits of 6T.
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| 2. |
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| 3. |
- Dannetun, Per, et al.
(författare)
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The chemical and electronic structure of the interface between aluminum and polythiophene semiconductors
- 1993
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 99:1, s. 664-672
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the chemical nature and the electronic structure of the interface between a low work function metal,aluminum, and a conjugated polymersemiconductor, polythiophene. We have studied the initial stages of the interface formation by depositing the metal onto the surface of a polymer film. Charge transfer processes between the metal and the polymer are analyzed using core‐level x‐ray photoelectron spectroscopy (XPS); the evolution upon metallization of the valence electronic levels directly related to the polymerelectronic structure is followed with ultraviolet photoelectron spectroscopy (UPS). With these techniques, we investigate the deposition of aluminum on two polythiophene systems (i) the alkyl‐substituted poly‐3‐octylthiophene and (ii) the α‐sexithiophene oligomer. The experimental data are compared to the results of a recent quantum chemical study on model systems consisting of thiophene oligomers (up to sexithiophene) interacting with a few Al atoms. The interaction of polythiophene with Al atoms is found to modify dramatically the structure of the conjugated backbone, as strong carbon–aluminum bonds are formed in the α positions of the thiophene rings. A large charge transfer takes place from the Al atoms to the polymer chain, and the upper π levels of the polymer are strongly affected. The metallization is contrasted to the doping of conjugated polymers with alkali metals
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| 4. |
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| 5. |
- Crispin, Xavier, et al.
(författare)
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Characterization of the interface dipole at organic/metal interfaces
- 2002
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 124:27, s. 8131-8141
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Tidskriftsartikel (refereegranskat)abstract
- In organics-based (opto)electronic devices, the interface dipoles formed at the organic/metal interfaces play a key role in determining the barrier for charge (hole or electron) injection between the metal electrodes and the active organic layers. The origin of this dipole is rationalized here from the results of a joint experimental and theoretical study based on the interaction between acrylonitrile, a p-conjugated molecule, and transition metal surfaces (Cu, Ni, and Fe). The adsorption of acrylonitrile on these surfaces is investigated experimentally by photoelectron spectroscopies, while quantum mechanical methods based on density functional theory are used to study the systems theoretically. It appears that the interface dipole formed at an organic/metal interface can be divided into two contributions: (i) the first corresponds to the "chemical" dipole induced by a partial charge transfer between the organic layers and the metal upon chemisorption of the organic molecules on the metal surface, and (ii) the second relates to the change in metal surface dipole because of the modification of the metal electron density tail that is induced by the presence of the adsorbed organic molecules. Our analysis shows that the charge injection barrier in devices can be tuned by modulating various parameters: the chemical potential of the bare metal (given by its work function), the metal surface dipole, and the ionization potential and electron affinity of the organic layer.
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| 6. |
- Crispin, Xavier, et al.
(författare)
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Chemisorption of acrylonitrile on the Cu(100) surface: A local density functional study
- 1999
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 111:7, s. 3237-3251
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of chemically grafting polyacrylonitrile onto transition metal electrodes via electropolymerization leads to promising applications in the fields of corrosion protection or metal surface functionalization. The initial step of the electrografting mechanism is the adsorption of the acrylonitrile monomer on the metal surface from solution. Here, we investigate theoretically this adsorption process on the copper (100) surface; Density Functional Theory is used in the Local Spin Density approximation to describe the electronic and structural properties of acrylonitrile adsorbed on copper clusters. The chemisorption of acrylonitrile on the copper surface is confirmed experimentally via X-Ray Photoelectron Spectroscopy. The thermodynamic characteristics of the adsorption process are also studied via statistical mechanics. Finally, determining the influence of the copper cluster size on the adsorption of acrylonitrile allows to extrapolate the properties of the acrylonitrile/Cu(100) surface from those of acrylonitrile/copper clusters. (C) 1999 American Institute of Physics. [S0021-9606(99)70231-X].
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| 7. |
- Crispin, X, 1968-, et al.
(författare)
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Controlling the electrografting of polymers onto transition metal surfaces through solvent vs monomer adsorption
- 1999
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 121:1, s. 176-187
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Tidskriftsartikel (refereegranskat)abstract
- Electropolymerization of methacrylic monomers opens the possibility of chemically grafting a wide range of polymers onto transition metal surfaces. In this work, the electropolymerization of polyacrylonitrile and polyethyl acrylate is studied in different solvents; we experimentally confirm that the choice of solvent is a critical parameter for obtaining electrografted polymers. A density-functional theory-based study modeling the interaction of solvent (acetonitrile, dimethylformamide, and pyridine) or monomer (acrylonitrile and ethyl acrylate) molecules with the Ni(100) metal surface provides the means to classify the organic molecules with respect to their ability to interact with the surface. The surface binding-energy difference between monomer and solvent is introduced in a Frumkin-type isotherm. This allows us to rationalize the experimental observations in terms of a competitive adsorption at the metal surface between the monomer and the solvent. The first step in the electrografting mechanism thus appears to be the chemisorption of the monomer at the electrode surface before cathodic polarization is applied; the chemisorbed monomer is therefore the first species reduced, giving rise to an adsorbed reactive intermediate, which is thus able to start the polymerization of a grafted chain.
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| 8. |
- Crispin, Xavier, 1972-, et al.
(författare)
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Electronic delocalization in discotic liquid crystals : A joint experimental and theoretical study
- 2004
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 126:38, s. 11889-11899
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Tidskriftsartikel (refereegranskat)abstract
- Discotic liquid crystals emerge as very attractive materials for organic-based (opto)electronics as they allow efficient charge and energy transport along self-organized molecular columns. Here, angle-resolved photoelectron spectroscopy (ARUPS) is used to investigate the electronic structure and supramolecular organization of the discotic molecule, hexakis(hexylthio)diquinoxalino[2,3-a:2′,3′-c]phenazine, deposited on graphite. The ARUPS data reveal significant changes in the electronic properties when going from disordered to columnar phases, the main feature being a decrease in ionization potential by 1.8 eV following the appearance of new electronic states at low binding energy. This evolution is rationalized by quantum-chemical calculations performed on model stacks containing from two to six molecules, which illustrate the formation of a quasi-band structure with Bloch-like orbitals delocalized over several molecules in the column. The ARUPS data also point to an energy dispersion of the upper π-bands in the columns by some 1.1 eV, therefore highlighting the strongly delocalized nature of the π-electrons along the discotic stacks.
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| 9. |
- Crispin, Xavier, et al.
(författare)
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Understanding the initial stages of polymer grafting on metals : A photoelectron spectroscopy study of acrylonitrile adsorption on transition metal surfaces
- 2001
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 121:1-3, s. 57-74
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Tidskriftsartikel (refereegranskat)abstract
- X-ray and UV photoelectron spectroscopies show that acrylonitrile is chemisorbed on iron, nickel and copper polycrystalline surfaces via the carbon and nitrogen atoms. Depending on the conditions used, different adsorption geometries are found. The molecules can either be adsorbed flat on the surface and chemically bound by a (2pp)-(3d/4s) overlap via both the C=C double bond and the C=N nitrile group or they can be adsorbed perpendicular to the surface via a covalent interaction between the nitrogen lone pair and the 3d-4s levels of the metals. Analysis of the XPS data obtained on molecular mono-layers chemisorbed on metal surfaces emphasizes the importance of initial-state effects (charge transfer upon chemisorption, contribution of the metal surface dipole) and final-state effects (metal screening and polarization effect within the mono-layer). The correlation between the XPS and UPS data illustrates the importance of the metal surface dipole in understanding the workfunction changes upon molecular adsorption on metal surfaces. © 2001 Elsevier Science B.V. All rights reserved.
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| 10. |
- Dannetun, Per, et al.
(författare)
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Interface formation between poly(2,5-diheptyl-p-phenylenevinylene) and calcium : implications for light-emitting diodes
- 1994
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Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 67:1-3, s. 133-136
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Tidskriftsartikel (refereegranskat)abstract
- The early stages of metal/polymer interface formation between calcium and poly(2,5-diheptyl-p-phenylenevinylene) (PDHPV) have been studied using both X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Charge transfer is observed from the metal atoms to the polymer; as a result the calcium atoms at the interface are ionic, and negative bipolarons appear as the charge-carrying species on the polymer chains. This n-type doping of PDHPV by calcium leads to the appearance of new electronic states in the polymer bandgap. The calcium atoms appear to diffuse into the near surface region of the polymer, rather than forming a well-defined overlayer on the organic films.
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| 11. |
- Dannetun, Per, et al.
(författare)
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Reactions of low work function metals Na, Al, and Ca on α,ω-€diphenyltetradecaheptaene. Implications for metal/polymer interfaces
- 1994
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 100:9, s. 6765-6771
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between different low work function metals aluminium,calcium and sodium, and α,ω‐diphenyltetradecaheptaene, a model molecule for certain conjugated polymers, have been investigated using both x‐ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The spectra are interpreted with the help of the results of quantum chemical calculations performed within the local spin density (LSD) approximation methodology. The metals are found to interact with the conjugated system in very different ways. Aluminium forms a covalent bond, which strongly modifies the π‐electronic structure of the conjugated molecule, while both the sodium and the calcium atoms act as doping agents, inducing new states in the otherwise forbidden bandgap. These new gap states can be viewed as a soliton–antisoliton pair for the Na/DP7 and a bipolaronic‐like defect for Ca/DP7.
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| 12. |
- Dannetun, P., et al.
(författare)
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The eletronic structure of emeraldine doped in situ from HCl in the gas phase as studied by photoelectron spectroscopy
- 1991
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Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 41:1-2, s. 645-648
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Tidskriftsartikel (refereegranskat)abstract
- The chemical and electronic structure of spin-coated films of polyaniline in the emeraldine state, treated in-situ with HCl in the gas phase, have been studied for the first time by means of X-ray Photoelectron Spectroscopy (XPS) and Ultra-violet Photoelectron Spectroscopy (UPS). Ultra thin films, of about several hundreds of Ångströms thickness, were spin-coated from a solution of chemically prepared emeraldine in NMP, onto substrates of aluminum or silicon. The salt forms were prepared both by (a) “wet†doping in 1M HCl and (b) the in-situ treatment of the films with HCl in the gas phase. With XPS three different types of chlorine have been observed, two ionic and one covalent. With UPS the valence band spectra of the doped and undoped state, are studied.
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| 13. |
- De Cupere, V., et al.
(författare)
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Effect of interfaces on the alignment of a discotic liquid-crystalline phthalocyanine
- 2006
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 22:18, s. 7798-7806
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the influence of the nature and number of solid interfaces on the alignment of the columns in a semiconducting discotic liquid crystal. The solid substrates have been characterized in terms of their roughness and surface energy. The alignment of the discotic liquid crystal columns on these substrates has been determined by optical microscopy under crossed polarizers and by tapping-mode atomic force microscopy. The nature of the substrates has negligible influence on the alignment. The key parameter is the confinement imposed to the film. These surprising observations are explained by the antagonist alignment role of gas and solid interfaces. © 2006 American Chemical Society.
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| 14. |
- Fredriksson, C., et al.
(författare)
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Theoretical studies of the aluminum/poly(p-phenylene vinylene) interface
- 1993
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Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 57:2, s. 4632-4637
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Tidskriftsartikel (refereegranskat)abstract
- A molecular quantum chemical approach is used to study the aluminum on PPV (Poly(p-Phenylene Vinylene)) interface. We focus on modifications to the chemical and electronic structure of the polymer upon interaction with a submonolayer of aluminum. A model system, trans-stilbene, is taken to investigate the nature of the Al-PPV bonding. Energetically favorable conformations are then used as prototypes to study the evolution of the electronic structure as modified by the reaction with aluminum. Results at the ab initio Hartree-Fock level indicates that Al atoms react with the vinylene linkage rather than the phenyl groups at early stages of interface formation.
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| 15. |
- Fredriksson, C., et al.
(författare)
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Theoretical studies of the aluminum/trans-polyacetylene interface : Calculations of model systems and comparison to experiment
- 1993
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Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 57:2-3, s. 4590-4595
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between Al atoms and trans-polyacetylene has been studied quantum chemically at the ab initio Hartree-Fock level using oligomeric model systems. Investigations of the Al-polyacetylene bonding and modifications to the chemical and electronic structure of model systems for polyacetylene upon interaction with Al atoms are reported. The density-of-states is calculated for a polyene chain interacting with a pair of Al atoms. The results are discussed in relation to photoelectron spectra taken during Al deposition on an oligomeric model for polyacetylene (a diphenylpolyene with 7 C=C bonds in the polyene segment).
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| 16. |
- Lazzaroni, R., et al.
(författare)
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Chemical and electronic aspects of metal/conjugated polymer interfaces : Implications for electronic devices
- 1995
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Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 71:1-3, s. 2159-2162
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Tidskriftsartikel (refereegranskat)abstract
- The chemical nature and the electronic structure of metal/conjugated polymer interfaces are investigated in the context of polymer-based light-emitting diodes. We consider the interaction of low-workfunction metals (Al, Ca) with the surface of conjugated polymers or model oligomer molecules with a combined experimental and theoretical approach. The early stages of the interface formation are followed with X-ray and ultraviolet photoelectron spectroscopies and the experimental data are compared to the results of quantum chemical calculations. The reactions of Al and Ca with the organic surface are found to be fundamentally different: while the former forms new covalent bonds onto the polymer backbone, the latter tends to dope the conjugated system. Both types of reaction are expected to modify drastically the electronic properties of the polymer semiconductor.
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| 17. |
- Lazzaroni, R., et al.
(författare)
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Electronic Structure of Metal/Polymer Interfaces : aluminum on Conjugated Polymers
- 1991
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Ingår i: Metallized Plastics 2. - Boston, MA : Springer. - 9781489907370 - 9781489907356 ; , s. 199-212
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Aluminum has been deposited on two types of conjugated polymers, polyalkylthiophene and polyaniline. The polymers were in the undoped, neutral form which possesses semiconducting properties. The chemical structure of the metal/polymer interface has been investigated by X-ray and UV photoelectron spectroscopy. Core level spectra indicate that aluminum reacts with the sulfur atom of the polythiophene chain, strongly perturbing the π-electron system. In the case of polyaniline, the interaction with the metal depends on the oxidation state of the polymer. UPS data, combined with the results of band structure calculations, are interpreted in terms of the Al-induced modifications of the π-electron system.
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| 18. |
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| 19. |
- Lazzaroni, R., et al.
(författare)
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The Chemical and Electronic Structure of Metal/Conjugated Polymer Interfaces : A Joint Theoretical and Experimental Study
- 1993
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Ingår i: Intrinsically Conducting Polymers. - Dordrecht : Springer Netherlands. - 9780792324560 - 9789048143160 - 9789401719520 ; , s. 135-146
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Bokkapitel (refereegranskat)abstract
- We investigate the interface between aluminum and several prototypical conjugaced systems wich a combined experimental and theoretical approach. The experiments consist of following the evolution of the polymer surface during the early stages of aluminum deposition, with X-ray and Ultraviolet Photoe!ectron Spectroscopies (XPS, UPS). In parallel, we perform quantum chemical calculacions on mode! oligomer systems interacting with one to four Al atoms. Aluminum is found to internet strongly with the polymer chain. Al·carbon covalenc boods an: formed along the polymer backbone; the chain geomeuy is deeply modified and the π electron conjugation can be dramatically reduced.
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| 20. |
- Lazzaroni, R., et al.
(författare)
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The chemical and electronic structure of the interface between aluminum and conjugated polymers
- 1994
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 39:2, s. 235-244
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Tidskriftsartikel (refereegranskat)abstract
- The chemical and electronic structure of the interface between aluminum and several proto-typical conjugated systems is investigated with a combined experimental and theoretical approach. The experiments consists of following the evolution of the polymer surface during the early stages of aluminum deposition, with X-ray and Ultraviolet Photoelectron Spectroscopies (XPS, UPS). In parallel, quantum chemical calculations are performed on model oligomer systems interacting with isolated Al atoms. Aluminum is found to interact strongly with the polymer chain. New covalent Al-carbon bonds are formed along the polymer backbone; the chain geometry is deeply modified and the π electron conjugation can be dramatically reduced.
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| 21. |
- Lindell, Linda, 1976-, et al.
(författare)
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Characterization of the interface dipole at the paraphenylenediamine-nickel interface : A joint theoretical and experimental study
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:8, s. 84712-
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Tidskriftsartikel (refereegranskat)abstract
- In organic-based (opto)electronic devices, charge injection into conjugated materials is governed to a large extent by the metal-organic interface dipole. Controlling the injection of charges requires a better understanding of the fundamental origin of the interface dipole. In this context, photoelectron spectroscopies and density functional theory calculations are used to investigate the interaction between para-phenylenediamine (PPDA), an electron donor, and a polycrystalline nickel surface. The interface dipole formed upon chemisorption of one PPDA monolayer strongly modifies the work function of the nickel surface from 5.10 to 3.55 eV. The work function decrease of 1.55 eV is explained by the electron-donor character of PPDA and the modification of the electronic density at the metal surface. PPDA monolayers are composed of tilted molecules interacting via the nitrogen lone-pair and PPDA molecules chemisorbed parallel to the surface via their π-electron density. Annealing the monolayer leads to dehydrogenation of PPDA activated by the nickel surface, as found for other amines.
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| 22. |
- Lindell, Linda, et al.
(författare)
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Transparent, plastic, low-work-function poly(3,4-ethylenedioxythiophene) electrodes
- 2006
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 18:18, s. 4246-4252
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Tidskriftsartikel (refereegranskat)abstract
- Novel applications for flexible electronics, e.g., displays and solar cells, require fully flexible, transparent, stable, and low-work-function electrodes that can be manufactured via a low-cost process. Here, we demonstrate that surface chemistry constitutes a route to producing transparent low-work-function plastic electrodes. The work function of the conducting polymer poly(3,4-ethylenedioxythiophene)-tosylate, or PEDOT-Tos, is decreased by submonolayer surface redox reaction with a strong electron donor, tetrakis-(dimethylamino)ethylene (TDAE), allowing it to reach a work function of 3.8 eV. The interface formed between TDAE and PEDOT is investigated in a joint experimental and theoretical study using photoelectron spectroscopy and quantum chemical calculations. © 2006 American Chemical Society.
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| 23. |
- Osikowicz, Wojciech, et al.
(författare)
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A joint theoretical and experimental study on the electronic properties of phenyl-capped 3,4-ethylenedioxythiophene oligomers
- 2003
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 119:19, s. 10415-10420
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of a series of phenyl-capped EDOT oligomers was studied using ultraviolet photoelectron spectroscopy, in combination with quantum-chemical methods. The bulk IP of the neutral PEDOT polymer was estimated to be 4.2 eV. The frontier band structue was predicted from the evolution of the spectral features in the studied series of oligomers.
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| 24. |
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| 25. |
- Bubnova, Olga, et al.
(författare)
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Corrigendum: Semi-metallic polymers
- 2014
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Ingår i: Nature Materials. - : Springer Science and Business Media LLC. - 1476-1122 .- 1476-4660. ; 13, s. 662-662
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Tidskriftsartikel (refereegranskat)
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