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Salaneck, William R
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Publications (10 of 142) Show all publications
Friedlein, R., Braun, S., de Jong, M. P., Osikowicz, W., Fahlman, M. & Salaneck, W. R. (2011). Ultra-fast charge transfer in organic electronic materials and at hybrid interfaces studied using the core-hole clock technique. JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, 183(1-3), 101-106.
Open this publication in new window or tab >>Ultra-fast charge transfer in organic electronic materials and at hybrid interfaces studied using the core-hole clock technique
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2011 (English)In: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, ISSN 0368-2048, Vol. 183, no 1-3, 101-106 p.Article in journal (Refereed) Published
Abstract [en]

The focus of this brief review is the use of resonant photoemission in its "core-hole clock" expression for the study of two important problems relevant for the field of organic electronics: the dynamical charge transfer across hybrid organic-inorganic interfaces, and the intermolecular charge transfer in the bulk of organic thin films. Following an outline of the technique, a discussion of its applicability and a short overview of experimental results obtained thus far, two examples are used to illustrate particular results relevant for the understanding of the charge transport in organic electronic devices. First, for Fe(II)-tetraphenylporphyrin molecules on semi-metallic molybdenum disulfide substrates, the electronic coupling to the substrate and the efficiency of charge transport across the interface different for the individual molecular electronic subsystems is discussed. And second, a discotic liquid crystalline material forming columnar assemblies is used to illustrate ultra-fast intermolecular charge transfer on the order of a few femtoseconds indicating an electronic coupling between the phthalocyanine units stronger than expected from the macroscopic charge transport characteristics of the material. (C) 2011 Published by Elsevier B.V.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2011
Keyword
Photoelectron Spectroscopy, Organic electronics, Core-hole-clock, Interfaces
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-67367 (URN)10.1016/j.elspec.2010.11.001 (DOI)000288831300014 ()
Available from: 2011-04-11 Created: 2011-04-11 Last updated: 2011-04-11
Braun, S., Liu, X., Salaneck, W. R. & Fahlman, M. (2010). Fermi level equilibrium at donor-acceptor interfaces in multi-layered thin film stack of TTF and TCNQ. Organic electronics, 11(2), 212-217.
Open this publication in new window or tab >>Fermi level equilibrium at donor-acceptor interfaces in multi-layered thin film stack of TTF and TCNQ
2010 (English)In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 11, no 2, 212-217 p.Article in journal (Refereed) Published
Abstract [en]

Organic hetero-junctions in multi-layered thin film stacks comprising alternate layers of the molecular donor-tetrathiafulvalene (TTF) and the acceptor - tetracyanoquinodimethane (TCNQ), have been studied by ultraviolet photoelectron spectroscopy ( UPS). We show that the energy level alignment at the organic-organic interfaces in the stacks depends only upon the relative energy structure of the donor and acceptor molecules, in particular, the molecular integer charge transfer (ICT) states. The observed interfacial dipoles, across the multi-layered organic stacks, correspond to the difference in energy between the positive and the negative charge transfer states of the molecules constituting the interface. Consequently, Fermi level across the multi-layer system is pinned to those states, since the energetic conditions for the charge transfer across the interface are fulfilled. Hence the energy level alignment at donor - acceptor interfaces studied can be rationalized on the basis of integer charge transfer model (ICT-model). Moreover, we present the photoelectron spectra where 0.85 eV shift of the highest occupied molecular orbital (HOMO) of TTF during formation of TCNQ over-layer is directly observed. These studies contribute to the understanding of the nature of the offset between the frontier electronic levels of the donor and acceptor components which is of high importance in the engineering of efficient organic solar cells.

Place, publisher, year, edition, pages
Amsterdam, Netherlands: , 2010
Keyword
Integer charge transfer model, ICT-model, Organic-organic interfaces, Organic donor, Organic acceptor, TTF, TCNQ, Fermi level pinning, Organic solar cells, Hetero-junctions, Interfaces, Organic electronics, Photoelectron spectroscopy, UPS
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-54253 (URN)10.1016/j.orgel.2009.10.018 (DOI)000274583200007 ()
Note

Original Publication: Slawomir Braun, Xianjie Liu, William R Salaneck and Mats Fahlman, Fermi level equilibrium at donor-acceptor interfaces in multi-layered thin film stack of TTF and TCNQ, 2010, ORGANIC ELECTRONICS, (11), 2, 212-217. http://dx.doi.org/10.1016/j.orgel.2009.10.018 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/

Available from: 2010-03-05 Created: 2010-03-05 Last updated: 2017-12-12Bibliographically approved
Yim, K.-H., Doherty, W. J., Salaneck, W. R., Murphy, C. E., Friend, R. H. & Kim, J.-S. (2010). Phase-Separated Thin Film Structures for Efficient Polymer Blend Light-Emitting Diodes. NANO LETTERS, 10(2), 385-392.
Open this publication in new window or tab >>Phase-Separated Thin Film Structures for Efficient Polymer Blend Light-Emitting Diodes
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2010 (English)In: NANO LETTERS, ISSN 1530-6984, Vol. 10, no 2, 385-392 p.Article in journal (Refereed) Published
Abstract [en]

We report laterally and vertically phase-separated thin film structures in conjugated polymer blends created by polymer molecular weight variation. We find that micrometer-scale lateral phase separation is critical in achieving high initial device efficiency of light-emitting diodes, whereas improved balance of charge carrier mobilities and film thickness uniformity are important in maintaining high efficiency at high voltages. The optoelectronic properties of these blend thin films and devices are strongly influenced by the polymer chain order/disorder and the interface state formed at polymer/polymer heterojunctions.

Keyword
Organic semiconductors, conjugated polymer blends, polymer light-emitting diodes, phase separation, thin film morphology
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-54060 (URN)10.1021/nl9025105 (DOI)000274338800005 ()
Available from: 2010-02-22 Created: 2010-02-22 Last updated: 2010-02-22
Salaneck, W. R. (2009). Classical ultraviolet photoelectron spectroscopy of polymers. JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, 174(1-3), 3-9.
Open this publication in new window or tab >>Classical ultraviolet photoelectron spectroscopy of polymers
2009 (English)In: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, ISSN 0368-2048, Vol. 174, no 1-3, 3-9 p.Article in journal (Refereed) Published
Abstract [en]

Although X-ray photoelectron spectroscopy of polymers was well established by Clark and coworkers in the 1970s, ultraviolet photoelectron spectroscopy of polymer films, was developed later. Previous to the 1970s, the first attempts to use ultraviolet light on polymer films took the form of appearance potential (valence band edge) measurements. Only some years later could the full valence band region of thin polymer films, including insulating polymers, semiconducting polymers and electrically conducting polymers. The development of what might be termed "classical ultraviolet photoelectron spectroscopy" of polymer films may be loosely based upon a variety of issues, including adapting thin polymer film technology to ultra high vacuum studies, the widespread use of helium resonance lamps for studies of solid surfaces, the combined advent of practical and sufficient theoretical-computational methods. The advent of, and the use of, easily available synchrotron radiation for multi-photon spectroscopies, nominally in the area of the near UV, is not included in the term "classical". At the same time, electrically conducting polymers were discovered, leading to applications of the corresponding semiconducting polymers, which added technologically driven emphasis to this development of ultraviolet photoelectron spectroscopy for polymer materials. This paper traces a limited number of highlights in the evolution of ultraviolet photoelectron spectroscopy of polymers, from the 1970s through to 2008. Also, since this issue is dedicated to Prof. Kazuhiko Seki, who has been a friend and competitor for over two decades, the author relies on some of Prof. Sekis earlier research, unpublished, on who-did-what-first. Prof. Sekis own contributions to the field, however, are discussed in other articles in this issue. (C) 2009 Elsevier B.V. All rights reserved.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-51771 (URN)10.1016/j.elspec.2009.03.024 (DOI)
Available from: 2009-11-18 Created: 2009-11-17 Last updated: 2009-11-18
Braun, S., Salaneck, W. R. & Fahlman, M. (2009). Energy-Level Alignment at Organic/Metal and Organic/Organic Interfaces. ADVANCED MATERIALS, 21(14-15), 1450-1472.
Open this publication in new window or tab >>Energy-Level Alignment at Organic/Metal and Organic/Organic Interfaces
2009 (English)In: ADVANCED MATERIALS, ISSN 0935-9648, Vol. 21, no 14-15, 1450-1472 p.Article, review/survey (Refereed) Published
Abstract [en]

In this Review, we summarize recent work on modeling of organic/metal and organic/organic interfaces. Some of the models discussed have a semiempirical approach, that is, experimentally derived values are used in combination with theory, and others rely completely of calculations. The models are categorized according to the types of interfaces they apply to, and the strength of the interaction at the interface has been used as the main factor. We explain the basics of the models, their use, and give examples on how the models correlate with experimental results. We stress that given the complexity of organic/metal and organic/organic interface formation, it is crucial to know the exact way in which the interface was formed before choosing the model that is applicable, as none of the models presented covers the whole range of interface interaction strengths (weak physisorption to strong chemisorption).

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-18404 (URN)10.1002/adma.200802893 (DOI)
Available from: 2009-05-25 Created: 2009-05-25 Last updated: 2010-09-06
Zhan, Y., de Jong, M., Li, F., Dediu, A., Fahlman, M. & Salaneck, W. R. (2008). Energy level alignment and chemical interaction at Alq3/Co interfaces for organic spintronic devices. , 78(4).
Open this publication in new window or tab >>Energy level alignment and chemical interaction at Alq3/Co interfaces for organic spintronic devices
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2008 (English)Article in journal (Refereed) Published
Abstract [en]

The electronic structure of the interface between tris(8-hydroxyquinoline) aluminum (Alq3) and cobalt was investigated by means of photoelectron spectroscopy. As demonstrated recently, this interface is characterized by efficient spin injection in organic spintronic devices. A strong interface dipole that reduces the effective work function of cobalt by about 1.5 eV was observed. This leads to a large barrier for hole injection into the highest occupied molecular-orbital (HOMO) level of 2.1 eV, in agreement with a previously proposed model based on electron transport in Co-Alq3 -La0.7 Sr0.3 MnO3 spin valves. Further experimental results indicate that chemical interaction occurs between the Alq3 molecules and the cobalt atoms, while the latter penetrate the Alq3 layer upon vapor deposition of Co atoms. The data presented lead to significant progress in understanding the electronic structure of the Co-on- Alq3 interface and represent a significant step toward the definition of the interface parameters for the efficient spin injection in Alq3 based spin valves. © 2008 The American Physical Society.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-44378 (URN)10.1103/PhysRevB.78.045208 (DOI)76426 (Local ID)76426 (Archive number)76426 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2011-01-10
de Jong, M. P., Osikowicz, W., Sorensen, S., Sergeyev, S., Geerts, Y. & Salaneck, W. R. (2008). Femtosecond charge transfer in assemblies of discotic liquid crystals. The Journal of Physical Chemistry C, 112(40), 15784-15790.
Open this publication in new window or tab >>Femtosecond charge transfer in assemblies of discotic liquid crystals
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2008 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 40, 15784-15790 p.Article in journal (Refereed) Published
Abstract [en]

The electronic coupling strength within columns of discotic liquid crystals is investigated using core-level resonant photoemission spectroscopy. Coexisting well-ordered and disordered regions are identified in thin films of tetra-alkoxy-substituted phthalocyanines with the aid of near edge X-ray absorption fine structure and photoelectron spectroscopies. These different regions are used to derive a lower limit for the intermolecular charge transfer bandwidth within the framework of the core-hole clock principle. We find average charge transfer times on the order of a few femtoseconds, that is, significantly faster than the C(ls) core-hole lifetime, which indicates a surprisingly strong electronic coupling between the phthalocyanine units as compared to what is expected from the charge transport characteristics of this material. © 2008 American Chemical Society.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-49943 (URN)10.1021/jp8037494 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Tsao, H., Pisula, W., Liu, Z., Osikowicz, W., Salaneck, W. R. & Mullen, K. (2008). From ambi- To unipolar behavior in discotic dye field-effect transistors. Advanced Materials, 20(14), 2715-2719.
Open this publication in new window or tab >>From ambi- To unipolar behavior in discotic dye field-effect transistors
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2008 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 20, no 14, 2715-2719 p.Article in journal (Refereed) Published
Abstract [en]

A study was conducted to demonstrate solution-processable ambipolar organic field-effect transistors based on a discotic dye. Such single component devices allow the study of the influence of supramolecular ordering on FET charge transport properties. These transistors exhibited ambipolarity even without any structural order. The absence of p-type behavior could not be explained by the increase of hole injection barrier or by interface trapping. It was rather observed that the change in morphology most probably lead to such a phenomenon. These findings further suggest that besides charge injection barriers and interface trapping, structural composition, that is, microscopic domain boundaries together with local defects in one-dimensional columnar systems, also trigger the loss of ambipolarity owing to lowering of the minority charge carrier mobility.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47099 (URN)10.1002/adma.200702992 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Lindell, L., Unge, M., Osikowicz, W., Stafström, S., Salaneck, W. R., Crispin, X. & de Jong, M. P. (2008). Integer charge transfer at the tetrakis(dimethylamino)ethylene/Au interface. Applied Physics Letters, 92(16), 163302-1-163302-3.
Open this publication in new window or tab >>Integer charge transfer at the tetrakis(dimethylamino)ethylene/Au interface
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2008 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 16, 163302-1-163302-3 p.Article in journal (Refereed) Published
Abstract [en]

In organic-based electronics, interfacial properties have a profound impact on device performance. The lineup of energy levels is usually dependent on interface dipoles, which may arise from charge transfer reactions. In many applications, metal-organic junctions are prepared under ambient conditions, where direct overlap of the organic system from the metal bands is prevented due to presence of oxides and/or hydrocarbons. We present direct experimental and theoretical evidence showing that the interface energetic for such systems is governed by exchange of an integer amount of electrons.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-20776 (URN)10.1063/1.2912818 (DOI)
Available from: 2009-09-18 Created: 2009-09-18 Last updated: 2017-12-13
de Jong, M. P., Tengstedt, C., Kanciurzewska, A., Carlegrim, E., Salaneck, W. R. & Fahlman, M. (2007). Chemical bonding in V (TCNE)x (x~2) thin-film magnets grown in situ. Physical Review B. Condensed Matter and Materials Physics, 75(6).
Open this publication in new window or tab >>Chemical bonding in V (TCNE)x (x~2) thin-film magnets grown in situ
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2007 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 6Article in journal (Refereed) Published
Abstract [en]

The molecule-based magnet V (TCNE)x, with TCNE=tetracyanoethylene, x˜2, shows an exceptionally high magnetic ordering temperature of about 400 K. With the aim to shed light on the origins of the robust magnetic ordering interactions, we have characterized the chemical bonding in V (TCNE)x thin films, prepared by an in situ chemical vapor deposition method, using photoelectron spectroscopy, x-ray absorption spectroscopy (XAS), and x-ray magnetic circular dichroism (XMCD). The XAS and XMCD results were interpreted by ligand field multiplet and charge transfer multiplet calculations, which show that the V-NC bonds are characterized by a large crystal field parameter 10Dq=2.3 eV and strong ligand to metal charge transfer effects, resulting in a hybrid V (3d) -CN ground state given by 60% 3 d3 and 40% 3 d4 L, where L is a hole on the cyano ligands. © 2007 The American Physical Society.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-49994 (URN)10.1103/PhysRevB.75.064407 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
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