| 1. |
- Badel, Xavier, et al.
(författare)
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Formation of ordered pore arrays at the nanoscale by electrochemical etching of n-type silicon
- 2004
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Ingår i: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 36:1/3, s. 245-254
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical etching has been studied to structure n-type silicon substrates at the nanoscale. In this work, well-ordered pore arrays with diameters in the range of 150-500 nm and depths up to 50 mum have been fabricated. The pores were successfully formed by anodic etching in (100)oriented n-type silicon wafers of low-resistivity, typically 1 Omegacm, using aqueous hydrofluoric acid solutions. The lithographic step was performed in a thermally grown oxide using a stepper and dry oxide etching technique. Two types of oxide openings and pitch sizes were tested. The smallest oxide opening realised at this stage was 0.5 mum for a pitch of 1 mum. Stable pore formation was obtained and the smallest pore size obtained was about 200 nm with an aspect ratio close to 100.
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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- Crispin, Annica, et al.
(författare)
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Influence of dopant on the electronic structure of spiro-oligophenyl-based disordered organic semiconductors
- 2002
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 116:18, s. 8159-8167
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the dopant on the electronic structure of spiro-oligophenyl-based disordered organic semiconductors was studied by means of photoelectron spectroscopy. With lithium atoms as dopants, two charges were stored on the same spiro branch in the form of bipolarons, for spiro-quarterphenyl and spiro-sexiphenyl. For doping with the sodium atoms, the size of the counter ions made it less energetically desirable to store two charges onto a single branch, and the charged species were polarons independent of the level of doping which was confirmed by optical absorption data.
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| 7. |
- Crispin, Xavier, et al.
(författare)
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Conductivity, Morphology, Interfacial Chemistry, and Stability of Poly(3,4- ethylene dioxythiophene)–Poly(styrene sulfonate) : A Photoelectron Spectroscopy Study
- 2003
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Ingår i: Journal of Polymer Science Part B. - : John Wiley & Sons. - 0887-6266 .- 1099-0488. ; 41:21, s. 2561-2583
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Forskningsöversikt (refereegranskat)abstract
- X-ray photoelectron spectroscopy (XPS) has been used to characterize poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDT/PSS), one of the most common electrically conducting organic polymers. A correlation has been established between the composition, morphology, and polymerization mechanism, on the one hand, and the electric conductivity of PEDT/PSS, on the other hand. XPS has been used to identify interfacial reactions occurring at the polymer-on-ITO and polymer-on-glass interfaces, as well as chemical changes within the polymer blend induced by electrical stress and exposure to ultraviolet light.
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| 8. |
- de Jong, Michel P, et al.
(författare)
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The electronic structure of n- and p-doped phenyl-capped 3,4-ethylenedioxythiophene trimer
- 2003
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 118:14, s. 6495-6502
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Tidskriftsartikel (refereegranskat)abstract
- A study was conducted on the effects of chemical doping on the chemical and electronic structure of condensed molecular solid films of the ethylenedioxythiophene (EDOT) trimer using ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS). Phenyl-capped EDOT oligomers were potential candidates for molecular electronics applications and serve as model molecules for PEDOT. By combining UPS, XPS, and NEXAFS, a clear picture of the doping induced changes in the electronic structure of phenyl-capped EDOT-trimer was obtained.
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| 9. |
- Fahlman, Mats, et al.
(författare)
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Iron-polyaniline interfaces : Implications for corrosion protection
- 2003
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Ingår i: American Chemical Society Symposium Series (ACS). - 0097-6156 .- 1947-5918. ; 843, s. 76-89
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Tidskriftsartikel (refereegranskat)abstract
- The early stages of interface formation between iron and a three-ring model molecule (trimer) of emeraldine base form of polyaniline (EB) were investigated using theoretical (DFT) and experimental (XPS) methods: Iron atoms were sputter-deposited in ultra high vacuum onto thin oligomer films, with X-ray photoelectron spectroscopy (XPS) core level spectra taken after each deposition. Similar studies were carried out for Fe sputter-deposited on EB polymer films as well. Based on the chemical shifts of the core level peaks and the theoretical results, iron was determined to donate charge (e(-)) into the trimer and EB films. The reverse case where thin films of trimer and EB were deposited on iron also was studied. The C(1s) core level shake up spectra show that the pi-electronic structure is modified for trimer and EB coatings on iron as compared to coatings on gold. (C) 2003 American Chemical Society.
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| 10. |
- Friedlein, Rainer, et al.
(författare)
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Electronic structure of conjugated polymers and interfaces in polymer-based electronics
- 2003
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Ingår i: Synthetic Metals (Proceedings of the International Conference on Science and Technology of Synthetic Metals). - 0379-6779. ; 135:1-3, s. 275-277
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Konferensbidrag (refereegranskat)abstract
- The electronic structure of conjugated polymers and interfaces in polymer-based electronics were analyzed. Fine structure were observed in the region of the first resonance with pi-final state symmetry, between 284.1 eV and 285.8 eV. The electronic transitions from the non-dispersed C(1s) level to specific parts of the unoccupied band structure were generated. It was found that for a dispersing valence band, in the presence of a core-hole, a given photon energy corresponded to an excitation into a state with a distinct wave vectors.
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| 11. |
- Friedlein, Rainer, et al.
(författare)
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Electronic structure of highly ordered films of self-assembled graphitic nanocolumns
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:19, s. 195414-
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Tidskriftsartikel (refereegranskat)abstract
- Highly ordered, several nanometers thick films of alkylated large planar, polycyclic aromatic hydrocarbon (PAH) molecules have been grown on semi-metallic molybdenum disulfide substrates. The films are characterized by a two-dimensional lateral arrangement of columns standing at the surface on a macroscopic scale. The self-assembly of such insulated columns of face-to-face disks with surface-induced vertical alignment has been achieved directly from solution processing. Angle-resolved photoelectron spectra revealed a highly anisotropic quasi-one-dimensional electronic structure with an extended π-electronic wave function. An intermolecular dispersion of the highest occupied band of at least 0.15 eV along the stacking direction has been measured. A partial breakdown of the concept of quasimomentum due to the finite size of the nano-objects perpendicular to the stacks is observed.
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| 12. |
- Friedlein, Rainer, et al.
(författare)
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High intercalation levels in lithium perylene stoichiometric compounds
- 2002
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 354:5-6, s. 389-394
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Tidskriftsartikel (refereegranskat)abstract
- Both amorphous and polycrystalline films of the aromatic hydrocarbon perylene are found to accept as high as one lithium per 3.3±0.1 carbon atoms. Phases composed of stoichiometric compounds with two, four and six lithium atoms per molecule are observed. The intercalation involves a substantial charge transfer from the lithium atoms to the molecules. Moreover, a high binding energy of the dopant-induced valence band electronic states is observed by photoelectron spectroscopy. Those observations suggest a high energy storage capacity for small- and medium-size aromatic hydrocarbons and their potential use in batteries. © 2002 Elsevier Science B.V. All rights reserved.
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| 13. |
- Friedlein, Rainer, et al.
(författare)
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Molecular parameters controlling the energy storage capability of lithium polyaromatic hydrocarbon intercalation compounds
- 2004
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 129:1, s. 29-33
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Tidskriftsartikel (refereegranskat)abstract
- One route for improving the performance of Li-based batteries is to optimize the carbon-based electrode. In order to find the best carbon-based materials, the specific roles of the molecular and solid-state contributions have to be understood. Here, the molecular contributions are analyzed. A semi-quantitative method is proposed to compare the charge storage capability of polyaromatic hydrocarbon molecules (PAHs). For planar PAHs, the ability to store electrical energy is found to be to a large extend determined by a single parameter, that is the electronic hardness (half the electronic gap) Multiplied the number of carbon atom in the molecule. A compilation of results for oligophenyls, oligoacenes and medium-size planar systems suggests trends in the dependence of the energy storage capability on the size and shape of the molecules. (C) 2003 Elsevier B.V. All rights reserved.
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| 14. |
- Friedlein, Rainer, et al.
(författare)
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Surface-induced vertical alignment of self-assembled supramolecular columns of large polycyclic aromatic hydrocarbons and porphyrins
- 2004
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Ingår i: Synthetic metals. - : Elsevier BV. - 0379-6779 .- 1879-3290. ; 147:01-Mar, s. 79-83
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Tidskriftsartikel (refereegranskat)abstract
- Ordered films of polycyclic aromatic hydrocarbons (PAHs) and porphyrins with functional (e.g. thiophene) side-groups are good candidates for (opto-)electronic applications where fast charge separation and transport are required. Such highly ordered thin films of PAHs, including discotic hexa-peri-hexabenzocoronene (HBC) and C-132-C-16,C-4, as well as brominated functionalized porphyrin molecules have been grown from solutions on semi-metallic molybdenum disulfide substrates and characterized by angle-resolved valence band photoelectron spectroscopy. A vertical growth of self-assembled supramolecular columns perpendicular to the basal plane of the substrate along with their lateral ordering on the surface has been achieved. Annealing made it possible to increase the structural order in the HBC columns, with molecules positioned at a regular offset from the columnar axis. This permitted the formation of extended pi-electronic states with a bandwidth of at least 0.1-0.2 eV at room temperature. (C) 2004 Elsevier B.V. All rights reserved.
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| 15. |
- Friedlein, Rainer, et al.
(författare)
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The role of intermolecular polarization for the stability of lithium intercalation compounds of a- and ß-perylene
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:5, s. 2239-2245
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Tidskriftsartikel (refereegranskat)abstract
- The charge transfer in Li-intercalation compounds of the polyaromatic hydrocarbon perylene was examined. It was found that the valence and core-level photoelectron spectroscopies characterized the bonding configuration of the alkali metal atoms. The effect of intermolecular polarization on the ionization potential of Li atoms was compensated by a screening of the Madelung energy. The data collected illustrated that the large charge transfer in the a-perylene was due to the lower ionization potential of lithium atoms.
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| 16. |
- Jönsson, Stina, et al.
(författare)
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The effects of solvents on the morphology and sheet resistance in poly(3,4-ethylenedioxythiophene)–polystyrenesulfonic acid (PEDOT–PSS) films
- 2003
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Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 139:1, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Films of poly(3,4-ethylenedioxythiophene)–polystyrenesulfonic acid (PEDOT–PSS), prepared by coating the aqueous PEDOT–PSS dispersion and by coating a mixture of the PEDOT–PSS dispersion and different solvents, have been studied using four-point probe conductivity measurements, atomic force microscopy and photoelectron spectroscopy. The electrical conductivity of thin films of the second type (further on called PEDOT–PSS–solvents) was increased by a factor of about 600 as compared to films of the first type (further on called PEDOT–PSS–pristine). Morphological and physical changes occur in the polymer film due to the presence of the solvent mixture, the most striking being that the ratio of PEDOT-to-PSS in the surface region of the films is increased by a factor of ∼2–3. This increase of PEDOT at the surface indicates that the thickness of the insulating PSS ‘shell’ that surrounds the conducting PEDOT–PSS grains is reduced. The (partial) reduction of the excess PSS layer that surrounds the conducting PEDOT–PSS grains is proposed to lead to an increased and improved connectivity between such grains in the film and hence a higher conductivity. When PEDOT–PSS–solvents receives a post-coating heat treatment, the increased PEDOT-to-PSS ratio at the surface is maintained or even slightly improved, as is the increase in electrical conductivity, even though spectroscopy show that the solvent molecules are removed. This suggests that screening or doping by the solvents throughout the film are not likely to be the key mechanisms for the improved conductivity and supports our proposed mechanism of improved conductivity through improved connectivity between the conducting grains.
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| 17. |
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| 18. |
- Llopart Cudié, Xavier, et al.
(författare)
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Medipix2, a 64k pixel readout chip with 55 μm square elements working in single photon counting mode
- 2002
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Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 49, s. 2279-2283
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Tidskriftsartikel (refereegranskat)abstract
- The Medipix2 chip is a pixel detector readout chip consisting of 256×256 identical elements, each working in single photon counting mode for positive or negative input charge signals. Each pixel cell contains around 500 transistors and occupies a total surface area of 55 μm×55 μm. A 20 μm width octagonal opening connects the detector and the preamplifier input via bump-bonding. The preamplifier feedback provides compensation for detector leakage current on a pixel by pixel basis. Two identical pulse height discriminators are used to create a pulse if the preamplifier output falls within a defined energy window. These digital pulses are then counted with a 13-bit pseudo-random counter. The counter logic, based in a shift register, also behaves as the input/output register for the pixel. Each cell also has an 8-bit configuration register which allows masking, test-enabling and 3-bit individual threshold adjust for each discriminator. The chip can be configured in serial mode and read out either serially or in parallel. The chip is designed and manufactured in a 6-metal 0.25 μm CMOS technology. Preliminary measurements show very good agreement with simulations.
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| 19. |
- Marciniak Braun, Slawomir, et al.
(författare)
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Light Induced Damage in Poly(3,4-ethylenedioxythiophene) and its Derivatives Studied by Photoelectron Spectroscopy
- 2004
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Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 141:1-2, s. 67-73
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Tidskriftsartikel (refereegranskat)abstract
- Poly(3,4-ethylenedioxythiophene), usually known as PEDOT, and derivatives have attracted significant interest because of their high electrical conductivity. This electric property, however, deteriorates upon exposure to solar radiation. X-ray photoelectron spectroscopy (XPS) has been used to study the UV-light-induced chemical changes in doped PEDOT, as well as in both neutral and doped forms of its alkylated derivative—PEDOT-C14H29. Analysis of the XPS data indicates an oxidation of the sulfur in the thiophene ring. Apparently, photo-oxidation leads to the formation of sulfon groups, SO2, resulting in a disruption of π-conjugation in PEDOT, which there by diminishes the conductivity of the organic layer. This hypothesis is supported by the results of a study of model molecules for pristine and the oxidized PEDOT unit: 3,4 ethylenedioxythiophene (EDOT) and 3,4 ethylenedioxythiophene and S-dioxide (EDOT-SO2), respectively.
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| 20. |
- Osikowicz, Wojciech, et al.
(författare)
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Transparent low-work-function indium tin oxide electrode obtained by molecular scale interface engineering
- 2004
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 85:9, s. 1616-1618
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Tidskriftsartikel (refereegranskat)abstract
- Transparent low-work-function indium tin oxide (ITO) electrode was obtained by using molecular scale interface engineering. The modified ITO surface may be used as electron injecting electrode in polymer light-emitting devices. ITO surfaces, exposed to TDAE molecules, were found to be stable upon exposure to air, and to mild annealing. Photoelectron spectroscopy measurements show that the low-work-function of the modified electrode remains upon exposure to air in gentle annealing.
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| 21. |
- Zotti, G., et al.
(författare)
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Electrochemical and XPS studies toward the role of monomeric and polymeric sulfonate counterions in the synthesis, composition, and properties of poly(3,4-ethylenedioxythiophene)
- 2003
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 36:9, s. 3337-3344
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemically prepared poly(3,4-ethylenedioxythiophene) (PEDT) poly(styrenesulfonate) (PSS), produced from acidic (PSSH) and basic (PSSNa) PSS, was characterized by cyclic voltammetry CV, UV-vis spectroscopy, in situ conductivity, and XPS spectroscopy and was compared with electrochemically prepared PEDT/tosylate and chemically prepared PEDT/PSS. CV analysis shows that the polymer synthesis is strongly affected by the nucleophilic character of the counteranion. Although CV and UV-vis spectroscopy show that the structure and degree of polymerization (oligomeric, ca. 10 EDT units) of the PEDT backbone is the same for all polymers, XPS is able to explain the different conductivity values for these materials (ranging from 1 S cm-1 for PEDT/PSSNa to 400-450 S cm-1 for PEDT/tosylate) based on doping level and composition. In particular, critical results are observed to be the ratios between sulfonate and thiophene units in the polymers: the higher the PEDT concentration, the higher the conductivity. XPS also explains by solvent-induced nanometer-scale segregation between PEDT/PSS and excess PSS particles the often reported conductivity enhancement of chemically prepared PEDT/PSS upon treatment with polar solvents.
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