| 1. |
- Dannetun, Per, et al.
(author)
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Evolution of Charge-Induced Gap States in Short Diphenylpolyenes as Studied by Photoelectron Spectroscopy
- 1994
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455 .- 0022-3654 .- 1541-5740. ; 98:11, s. 2853-2858
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Journal article (peer-reviewed)abstract
- The evolution of doping-induced electronic states within the otherwise forbidden energy gap has been studied as a function of the polyene length in a series of diphenylpolyenes. The chemical and electronic structures ha ve been studied using both X-ray and ultraviolet photoelectron spectroscopies. The results are interpreted with the help of quantum chemical calculations, performed using the semiempirical Austin Model 1 and valence effective Hamiltonian methods. The molecules studied area series of diphenylpolyenes, DPx, with x = 1-7 C=C double bonds in the pol yene part of the molecule. Since the frontier or bitals of the diphenylpolyenes are localized on the polyene chain portion of the molecule, there is a high degree of separation of the phenyl and polyene parts of the 11"-systems. Hence, many chemical and electronic properties of diphenylpolyenes are expected to be similar to those of short-chain trans-polyacetylene. For the longer molecules, n = 6 or 7, the present results indicate the presence of doubly charged, interacting soliton-antisoliton pairs, which appear as two new energy levels in the otherwise forbidden energy gap. In diphenyldecaheptaene to stilbene, i.e. 1 ≤ x ≤ 5, however, a singly charged state is formed at intermediate doping levels, after which the soliton-antisoliton pairs appear for the fully doubly charged systems. These results show that, remarkably, even for very short polyene segments, charges transferred are stored in the form of ( confined) solitons.
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| 2. |
- Dannetun, Per, et al.
(author)
-
New Results on Metal-Polymer Interfaces
- 1993
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In: Molecular Crystals and Liquid Crystals. - : Taylor & Francis. - 1542-1406 .- 1563-5287. ; 228:1, s. 43-48
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Journal article (peer-reviewed)abstract
- New results on studies of the early stages of formation of the aluminum-poly(p-phenylenevinylene) interface are presented.
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| 3. |
- Dannetun, Per, et al.
(author)
-
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
-
In: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 55:1, s. 212-217
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Journal article (peer-reviewed)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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| 4. |
- Dannetun, Per, et al.
(author)
-
Reactions of low work function metals Na, Al, and Ca on α,ω-€diphenyltetradecaheptaene. Implications for metal/polymer interfaces
- 1994
-
In: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 100:9, s. 6765-6771
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Journal article (peer-reviewed)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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| 5. |
- Dannetun, Per, et al.
(author)
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The evolution of charge-induced gap states in degenerate and non-degenerate conjugated molecules and polymers as studied by photoelectron spectroscopy
- 1994
-
In: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 67:1, s. 81-86
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Journal article (peer-reviewed)abstract
- We report the results of ultraviolet photoelectron spectroscopy (UPS) studies of the interaction between sodium and conjugated systems for a series of diphenylpolyees and diffrent oligomers of poly(p-phenylenevinylene) (PPV). The diphenylpolyenes include molecules containing two (i.e., stilbene) to 14 carbon atoms in the polyene part; stilbene itself can also be considered as a phenyl-capped monomer of PPV. Furthermore, a PPV oligomer with three phenylene units, as well as PPV itself, has been studied. The experimental results are interpreted with the help of quantum-chemical calculations using the Hartree-Fock semi-empirical Austin Model 1 (AM1) and valence-effective Hamiltonian (VEH) methods. An important result is that all the systems react strongly with sodium; at high doping levels two new doping-induced states are detected above the valence band edge of the pristine material. In the case of saturation-doped diphenylpolyenes (i.e., two sodiums per molecule), the new states can be discussed in terms of soliton-antisoliton pairs confined within the polyene part of the molecules; in contrast, the self-localized states induced in PPV and its oligomers have to be referred to as bipolarons.
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| 6. |
- Fredriksson, C., et al.
(author)
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Theoretical studies of the aluminum/poly(p-phenylene vinylene) interface
- 1993
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In: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 57:2, s. 4632-4637
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Journal article (peer-reviewed)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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| 7. |
- Fredriksson, C., et al.
(author)
-
Theoretical studies of the aluminum/trans-polyacetylene interface : Calculations of model systems and comparison to experiment
- 1993
-
In: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 57:2-3, s. 4590-4595
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Journal article (peer-reviewed)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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| 8. |
- Lazzaroni, R., et al.
(author)
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Chemical and electronic aspects of metal/conjugated polymer interfaces : Implications for electronic devices
- 1995
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In: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 71:1-3, s. 2159-2162
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Journal article (peer-reviewed)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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| 9. |
- Lazzaroni, R., et al.
(author)
-
Electronic Structure of Metal/Polymer Interfaces : aluminum on Conjugated Polymers
- 1991
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In: Metallized Plastics 2. - Boston, MA : Springer. - 9781489907370 - 9781489907356 ; , s. 199-212
-
Book chapter (other academic/artistic)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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| 10. |
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| 11. |
- Lögdlund, Michael, et al.
(author)
-
A photoelectron spectroscopy study of the charge-induced π-electronic structural changes in α.ω.-diphenyltetradecaheptaene, a model molecule for polyacetylene
- 1993
-
In: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 57:2, s. 4722-4727
-
Journal article (peer-reviewed)abstract
- The π€-electronic structural changes in diphenylpolyene, α.ω.-diphenyltetradecaheptaene, or DP7, have been studied upon gradually doping with sodium Xu using X-ray and Ultraviolet Photoelectron Spectroscopy, XPS and UPS. The spectra are interpreted with the help of the results from Austin Model 1 (AM1) and Valence Effective Hamiltonian (VEH) quantum chemical calculations. The results of the doping with sodium can be discussed in terms of two confined solitons on the polyene part of the molecule, which results in two new energy levels in the originally forbidden energy gap.
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| 12. |
- Lögdlund, Michael, et al.
(author)
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Experimental and Theoretical Studies of the Interaction of Metals with Polymer Surfaces : A Case Study of the Use of a Model Molecular System to Study the Nature of Charge Storage in Short Polyenes
- 1994
-
In: Frontiers of Polymers and Advanced Materials. - Boston, MA : Springer-Verlag New York. - 9781461360407 - 9781461524472 ; , s. 369-382
-
Book chapter (peer-reviewed)abstract
- The electronic and geometric changes in polyenes induced by doping with sodium have been studied using X-ray and Ultraviolet Photoeclectron Spectroscopy, and quantum chemical calculations. The molecular geometry changes induced by doping have been studied using the semiempirical Austin Model 1 method, the results of which has served as input parameters for Valence Effective Hamiltonian band structure calculations, which are compared with the experimental density-of-states data. The molecules studied are members of a series of diphenylpolyenes with 4, 5, 6 ir 7 C=C double bonds in the polyene part of the molecule, i.e., the series DPx, with x = 4, 5, 6 or 7. Since the frontier orbitals of the diphenylpolyenes are localized mostly on the polyene chain portion of the molecule, there is a high degree of separations in energy of the phenyl and polyene parts of the π-system. Hence, many chemical and electronic properties of diphenylpolyenes are similar to those of (at least short chain) trans-polyacerylene. The present doping results indicate the charge is stored in short polyenes in the form of two confined solitons per molecule.
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| 13. |
- Lögdlund, Michael, et al.
(author)
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Soliton pair charge storage in doped polyene molecules : Evidence from photoelectron spectroscopy studies
- 1993
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 70:7, s. 970-973
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Journal article (peer-reviewed)abstract
- The π-electronic structural changes in a polyene molecule containing seven double bonds, α,ω-diphenyltetradecaheptaene (DP7), have been studied upon gradually doping with sodium, using x-ray and ultraviolet photoelectron spectroscopies. The spectra are interpreted with the help of detailed quantum chemical calculations. Analysis of the evolution of the XPS and UPS spectra as a function of doping with sodium indicates that the extra charges are stored in the form of two charged solitons on the polyene part of the molecules, which results in two new energy levels in the originally forbidden energy gap.
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| 14. |
- Lögdlund, Michael, et al.
(author)
-
The electronic structure of α,ω-diphenyltetradecaheptaene, a model molecule for polyacetylene, as studied by photoelectron spectroscopy
- 1992
-
In: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 51:1, s. 187-195
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Journal article (peer-reviewed)abstract
- The advantages of using model systems for spectroscopic studies of conjugated polymers and interface formation, as well as for charge-induced electronic and geometric structural changes, are discussed. The electronic structure of a diphenylpolyene, α,ω-diphenyltetradecaheptaene, or DP7, is an example of a model molecular system studied using X-ray and Ultraviolet Photoelectron Spectroscopy, XPS, and UPS. The spectra are interpreted with the help of the results from MNDO, VEH and INDO/S-CI quantum chemical calculations. The frontier orbitals of DP7 are localized mostly on the polyene chain portion of the molecule, resulting in a high degree of separation of the phenyl and polyene parts of the π-system. The INDO calculations show two regions of shake-up features corresponding to a benzene-like part and a polyene-like part. The most important individual shake-up transitions, which contribute to the two observed shake-up spectral features, involve one-electron redistributions separable into contributions from the polyene chain and from the phenyl groups. The analysis indicates the extent to which many chemical and electronic properties of DP7 are expected to be similar to those of (at least short chain) trans-polyacetylene.
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| 15. |
- Lögdlund, Michael, et al.
(author)
-
Theoretical and experimental studies of the interaction between sodium and oligothiophenes
- 1996
-
In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 53:24, s. 16327-16333
-
Journal article (peer-reviewed)abstract
- Quantum-chemical calculations and ultraviolet photoelectron spectroscopy (UPS) measurements have been performed in order to study the interaction between sodium and oligothiophenes, with a focus on the origin of experimentally observed relaxation energy effects in alkali-metal-doped conjugated molecules. Upon doping of a -sexithienylene (α-6T) with sodium atoms, (1) a broad feature appears in the valence band, in an energy region corresponding to the band gap in pristine α-6T, and (2) certain structural features in the valence band shift towards lower binding energies in the doped material. In particular, upon doping, a structural peak related to electronic levels mainly localized to the sulfur and b-carbon atoms destabilizes to an energy corresponding to that of the valence-band edge in pristine α-6T. The results of ab initio Hartree-Fock and local-spin-density calculations on α-trithienylene and bithiophene are consistent with the experimental data, and allow for an assignment of these destabilization effects in terms of initial-state relaxations. We stress that similar destabi-lization effects, reported for other alkali-metal-doped conjugated systems, had previously been proposed to be associated with final-state electronic screening, i.e., a dynamic artifact within the UPS measurements; this is in contradiction to the results of our ab initio theoretical studies. Our present results show that all structural features in the UPS data are contained in the results of sufficiently complete quantum chemical calculations.
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| 16. |
- Lögdlund, Michael, et al.
(author)
-
Theoretical study of the interaction between sodium and oligomers of poly(p-phenylenevinylene) and poly(p-phenylene)
- 1994
-
In: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 67:1-3, s. 141-145
-
Journal article (peer-reviewed)abstract
- The semi-empirical Austin Model 1 and the non-empirical pseudo-potential valence effective Hamiltonian (VEH) methods as well as the local spin density (LSD) approximation technique have been applied to the investigation of the doping-induced electronic and geometrical changes in some conjugated molecules related to poly(p-phenylene) and poly(p-phenylenevinylene) (PPV): biphenyl, stilbene and a phenyl-capped dimer of PPV. The theoretical results are compared with experimental valence band spectra, as recorded by ultraviolet photoelectron spectroscopy (UPS). The experimental UPS studies show that two ingap states are detected upon doping with alkali metals. The energy splitting between the two in-gap states increases as the molecule size decreases. The results of the LSD calculations agree very well with the experimental results, while the VEH method overestimates the energy splitting for the small molecules. The LSD modelling also indicates a destabilization of several high binding energy valence levels, due to the presence of counter-ions, in agreement with experiment.
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| 17. |
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| 18. |
- Xing, K. Z., et al.
(author)
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The electronic and geometric structures of neutral and potassium-doped poly[3-(4-octylphenyl)thiophene] studied by photoelectron spectroscopy
- 1996
-
In: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 76:1-3, s. 263-267
-
Journal article (peer-reviewed)abstract
- The electronic and geometric structures of poly [3-(4-octylphenyl)thiophene] have been studied by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS, respectively). Thermochromic effects, and new charge induced states generated by potassium doping, have been observed by direct UPS measurements. The experimental results are in very good agreement with the results of theoretical quantum chemical calculations performed with the Austin Model 1 semi-empirical model and the valence-effective Hamiltonian pseudo-potential model.
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| 19. |
- Xing, K. Z., et al.
(author)
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The electronic structure of neutral and alkali metal-doped poly[3-(4-octylphenyl)thiophene] studied by photoelectron spectroscopy
- 1996
-
In: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 80:1, s. 59-66
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Journal article (peer-reviewed)abstract
- The electronic structure of poly [3-(4-octylphenyl)thiophene] (POPT) has been studied by ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS), as well as by quantum chemical calculations. Both temperature-dependent effects on the electronic structure of the neutral system, as well as the generation of new electronic states induced by doping with alkaline metals, have been observed. The experimental results are in good agreement with the results of the quantum chemical calculations.
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