| 1. |
- Bhatt, Pramod, et al.
(författare)
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Ferromagnetism above room temperature in nickel-tetracyanoethylene thin films
- 2009
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 19:36, s. 6610-6615
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Tidskriftsartikel (refereegranskat)abstract
- Room temperature ferromagnetic ordering is reported in Ni-tetracyanoethylene (TCNE) thin films fabricated on Au substrates using physical vapor deposition (PVD) under ultra high vacuum conditions. This technique enables the preparation of very clean films without having any kind of contamination from oxygen-containing species, solvents or precursor molecules. Film stoichiometry was obtained from X-ray photoelectron spectroscopy (XPS) measurements. XPS derived stoichiometry points to a similar to 1 : 2 ratio between Ni and TCNE resulting in Ni(TCNE)(x), x approximate to 2. No evidence of pure Ni metal in the in situ grown films was present in the XPS or the ultraviolet photoelectron spectroscopy (UPS) measurements within the detection limits of the techniques.
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| 2. |
- Carlegrim, Elin, et al.
(författare)
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Air-stable organic-based semiconducting room temperature thin film magnet for spintronics applications
- 2008
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Ingår i: Applied Physics Letters. - : Institutionen för teknik och naturvetenskap. - 0003-6951 .- 1077-3118. ; 92:16, s. 163308-
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we report on a preparation method of vanadium tetracyanoethylene, V(TCNE)x, an organic-based semiconducting room temperature thin film magnet. Previously, this compound has been reported to be extremely air sensitive but this preparation method leads to V(TCNE)x, which can retain its magnetic ordering at least several weeks in air. The electronic structure has been studied by photoelectron spectroscopy and the magnetic properties by superconducting quantum interference device. The properties mentioned above, in combination with complete spin polarization, makes this air-stable V(TCNE)x a very promising material for spintronic devices.
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| 3. |
- Carlegrim, Elin, et al.
(författare)
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Near-edge x-ray absorption studies of Na-doped tetracyanoethylene films : A model system for the V(TCNE)x room-temperature molecular magnet
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : Institutionen för teknik och naturvetenskap. - 1098-0121 .- 1550-235X. ; 77:5, s. 054420-1-054420-8
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Tidskriftsartikel (refereegranskat)abstract
- V(TCNE)(x), with TCNE=tetracyanoethylene and x similar to 2, is an organic-based molecular magnet with potential to be used in spintronic devices. With the aim of shedding light on the unoccupied frontier electronic structure of V(TCNE)(x) we have studied pristine TCNE and sodium-intercalated TCNE by near edge x-ray absorption fine structure (NEXAFS) spectroscopy as well as with theoretical calculations. Sodium-intercalated TCNE was used as a model system of the more complex V(TCNE)(x) and both experimental and theoretical results of the model compound have been used to interpret the NEXAFS spectra of V(TCNE)(x). By comparing the experimental and theoretical C K-edge of pristine TCNE, the contributions from the various carbon species (cyano and vinyl) could be disentangled. Upon fully sodium intercalation, TCNE is n doped with one electron per molecule and the features in the C and N K-edge spectra of pristine TCNE undergo strong modification caused by partially filling the TCNE lowest unoccupied molecular orbital (LUMO). When comparing the C and N K-edge NEXAFS spectra of fully sodium-doped TCNE with V(TCNE)(x), the spectra are similar except for broadening of the features which originates from structural disorder of the V(TCNE)(x) films. The combined results from the model system and V(TCNE)(x) suggest that the lowest unoccupied molecular orbital with density on the nitrogen atoms in V(TCNE)(x) has no significant hybridization with vanadium and is similar to the so-called singly occupied molecular orbital of the TCNE anion. This suggests that the LUMO of V(TCNE)(x) is TCNE- or vanadiumlike, in contrast to the frontier occupied electronic structure where the highest occupied molecular orbital is a hybridization between V(3d) and cyano carbons. The completely different nature of the unoccupied and occupied frontier electronic structure of the material will most likely affect both charge injection and transport properties of a spintronic device featuring V(TCNE)(x).
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| 4. |
- Carlegrim, Elin, et al.
(författare)
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The unoccupied electronic structure of the semi-conducting room temperature molecular magnet V(TCNE)2
- 2008
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Ingår i: Chemical Physics Letters. - : Institutionen för teknik och naturvetenskap. - 0009-2614 .- 1873-4448. ; 452:1-3, s. 173-177
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Tidskriftsartikel (refereegranskat)abstract
- The unoccupied electronic structure of the organic-based magnet V(TCNE)x (TCNE = tetracyanoethylene, x~2) has been studied with near edge x-ray absorption fine structure (NEXAFS) and with photoelectron spectroscopy (PES). By studying V(TCNE)x upon sodium-doping, the electron-accepting state, i.e. the lowest unoccupied molecular orbital (LUMO) of V(TCNE)x was shown mainly to be localized on (TCNE)--units in contrast to the hole-accepting state, i.e. the highest occupied molecular orbital (HOMO), which previously was assigned primarily to be V(3d)-derived. This study also showed that there are trap states for electron transport located below the (TCNE)2- level, likely leading to decreased electron mobility.
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| 5. |
- de Jong, Michel P, et al.
(författare)
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Chemical bonding in V (TCNE)x (x~2) thin-film magnets grown in situ
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:6
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Golczak, Sebastian, et al.
(författare)
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Comparative XPS surface study of polyaniline thin films
- 2008
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Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738 .- 1872-7689. ; 179:39, s. 2234-2239
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Tidskriftsartikel (refereegranskat)abstract
- Polyaniline (PANI) films of different thickness have been deposited electrochemically at two different potentials of 0.8 and 1.2 V. Characterization of the surface composition of the material: oxidation states and structural changes have been performed using X-ray photoelectron spectroscopy (XPS). The main findings of this work show that the ratio of the imine to amine nitrogens for thicker films of PANI is close to unity, indicating that the surface layer of PANI is in the emeraldine form (base). On the other hand, the surface of thinner films of PANI contains similar to 14-20% imine nitrogen and similar to 60-70% amine nitrogen. This corresponds to an oxidation state close to that of protoemeraldine. Furthermore, XPS confirms a considerable amount of p-benzoquinone (BQ) as side product formed in all thin samples. The surface morphology examined by electron microscopy measurements shows that thin films have a uniform structure, whereas microporous structure with microchannels and microcaves inside, formed as a non-periodic network of microrods is characteristic for thicker PANI films.
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| 7. |
- Golczak, Sebastian, et al.
(författare)
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Degradation of microporous polyaniline film by UV-ozone treatment
- 2009
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Ingår i: POLYMER DEGRADATION AND STABILITY. - : Elsevier BV. - 0141-3910. ; 94:3, s. 350-354
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Tidskriftsartikel (refereegranskat)abstract
- Thin microporous polyaniline films in the emeraldine-base form (PANI-EB) have been prepared electrochemically at a potential of 0.8 V. The effect of ozone treatment on the structural changes of polyaniline thin films has been investigated using X-ray photoelectron spectroscopy, SEM and EPR. Surface analysis showed that oxidation occurs mainly at the carbon atoms, resulting in the formation of C=O and COOH species. The degradation reaction seems to be preferentially directed towards the quinoneimine units. At high extent of carbon oxidation, UV-ozone treatment may involve the direct oxidation of the nitrogen atoms to form -NOx species.
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| 8. |
- Jakobsson, Fredrik L. E., 1974-, et al.
(författare)
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Towards all-plastic flexible light emitting diodes
- 2006
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 433:1-3, s. 110-114
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Tidskriftsartikel (refereegranskat)abstract
- All-plastic light emitting diodes require the design and fabrication of low work function plastic electrodes. Here, we show that the work function of poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid (PEDOT-PSS) can be decreased from 4.8 eV to 3.9 eV by surface reaction with the strong electron-donor tetrakis(dimethylamino)ethylene (TDAE). The surface modification was characterized by photoelectron spectroscopy and optical spectroscopy. The low work function plastic electrode was used in a first prototype for all-plastic light emitting diodes.
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| 9. |
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| 10. |
- Kanciurzewska, Anna, et al.
(författare)
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Study on Poly(3,4-ethylene dioxythiophene)-Poly(styrenesulfonate) as a plastic counter electrode in dye sensitized solar cells
- 2007
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Ingår i: Journal of Optoelectronics and Advanced Materials. - 1454-4164 .- 1841-7132. ; 9:4, s. 1052-1059
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Tidskriftsartikel (refereegranskat)abstract
- Dye sensitized solar cells with PEDOT-PSS coated directly on flexible polyester substrate as counter electrode have been fabricated. The behavior of such plastic counter electrode in the presence of I/I-3 redox electrolyte has been investigated with X-ray photoelectron spectroscopy. We have found that some of iodine species are "trapped" within the PEDOT-PSS layer. The presence of I-3, I-2 and PEDOT charge transfer complexes with iodine species may block the surface of the electrode. Furthermore, the PEDOT may be further oxidized (p-doped) during cell operation, which in turn may cause overoxidation and loss of conductivity in the PEDOT-PSS film. Additionally, the interactions between PEDOT and iodine species may be enlarged because of the partial loss of PSS protective counter ion. That has resulted in decrease of PEDOT-PSS catalytic activity for reduction of I-3 to I in the redox electrolyte and has caused worse cell performance than in case of DSSC with Pt counter electrode.
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| 11. |
- Saltó, Carmen, et al.
(författare)
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Control of neural stem cell adhesion and density by an electronic polymer surface switch.
- 2008
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Ingår i: Langmuir : the ACS journal of surfaces and colloids. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:24, s. 14133-8
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Tidskriftsartikel (refereegranskat)abstract
- Adhesion is an essential parameter for stem cells. It regulates the overall cell density along the carrying surface, which further dictates the differentiation scheme of stem cells toward a more matured and specified population as well as tissue. Electronic control of the seeding density of neural stem cells (c17.2) is here reported. Thin electrode films of poly(3,4-ethylenedioxythiophene) (PEDOT):Tosylate were manufactured along the floor of cell growth dishes. As the oxidation state of the conjugated polymer electrodes was controlled, the seeding density could be varied by a factor of 2. Along the oxidized PEDOT:Tosylate-electrodes, a relatively lower density of, and less tightly bonded, human serum albumin (HSA) was observed as compared to reduced electrodes. We found that this favors adhesion of the specific stem cells studied. Surface analysis experiments, such as photoelectron spectroscopy, and water contact angle measurements, were carried out to investigate the mechanisms responsible for the electronic control of the seeding density of the c17.2 neural stem cells. Further, our findings may provide an opening for electronic control of stem cell differentiation.
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| 12. |
- Tehrani, Payman, 1977-, et al.
(författare)
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The effect of pH on the elechtrochemical over-oxidation of PEDOT:PSS films
- 2007
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Ingår i: Solid State Ionics. - : ScienceDirect. - 0167-2738 .- 1872-7689. ; 177:39-40, s. 3521-3527
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Tidskriftsartikel (refereegranskat)abstract
- Chemical degradation of conjugated polymers is one cause of material failures in polymer-based (opto)electronic devices, but can also be used as a technique for subtractive patterning of polymer films. When a large anodic potential is applied to the conducting polymer blend poly(3,4-ethylenedioxythiophene)-poly(4styrenesulfonate), PEDOT:PSS, an over-oxidation reaction occurs, altering its electrical conductivity. Here, we have studied the effect of pH on the electrochemical over-oxidation process of PEDOT in PEDOT:PSS. High pH is associated with a decrease of over-oxidation potential and an increase of resistivity in the resulting film. Vibrational spectroscopy and photoelectron spectroscopy measurements on over-oxidized PEDOT:PSS films indicate that the decrease in conductivity results from cleavage of the conjugation pathway accompanied by the formation of sulfone, carbonyl and carboxylic groups in the polymer chain.
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| 13. |
- Tengstedt, Carl, 1974-, et al.
(författare)
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Ultraviolet light-ozone treatment of poly(3,4-ethylenedioxy-thiophene)-based materials resulting in increased work functions
- 2006
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:4, s. 2085-2090
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Tidskriftsartikel (refereegranskat)abstract
- We describe a simple method to increase the work function of poly(3,4-ethylenedioxy-thiophene)-poly(perfluoroethylene sulfonic acid), PEDOT-PFESA, and poly(3,4-ethylenedioxy-thiophene)-poly(styrene sulfonic acid), PEDOT-PSS, by short exposure to ultraviolet light and ozone. The creation of carbonyl groups in the surface region forms a dipole layer shifting the vacuum level with a followed increase in work function. It has been shown that the work function of PEDOT-PFESA can be increased by as much as ∼ 0.4 eV to the absolute value of 6.3 eV and by at least ∼ 0.2 eV for PEDOT-PSS to the absolute value of 5.4 eV. The increase in work function has also proven to be time dependent with the largest increasing rate occurring for short exposure times. Upon ozone treatment, both PEDOT and PSS are oxidized whereas PFESA seems to be unaffected.
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| 14. |
- Tengstedt, Carl, et al.
(författare)
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UV-ozone treatment of PEDOT-based materials resulting in increased work functions
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We describe a simple method to increase the work function of PEDOT-PFESA and PEDOT-PSS by short exposure to UV and ozone in a "UVO-Cleaner®". The creation of carbonyl gmups in the surface region fotms a dipole layer shifting the vacuum level with a followed increase in work function. It has been shown that the work function of PEDOT-PFESA can be increased by as much as -0.4 eV to the absolute value of 6.3 eV and by at least -0.2 eV for PEDOT-PSS to the absolute value of 5.4 e V. The increase in work function has also proven to be time dependent with the largest increasing rate occuning for short exposure times. Upon ozone treatment, both PEDOT and PSS are oxidized whereas PFESA seems to be unaffected.
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| 15. |
- Tengstedt, Carl, et al.
(författare)
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V(TCNE)x : the electronic structure of an enigmatic, organic-based room temperature magnet revealed
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We have prepared and characterized thin films of V(TCNE)x in ultra-high vacuum using a novel film growth technique based on in-situ chemical vapor deposition of tetracyanoethylene, TCNE, and bis-benzene vanadium, V(C6H6)2. The in-situ preparation method enabled, for the first time, experimental analysis of the electronic structure. X-ray magnetic circular dichroism (XMCD) measurements recorded at the V L2,3-edge confirmed room temperature magnetic ordering. A combination of conventional photoelectron spectroscopy (PES) and resonant photoemission (RPE) measured at the x-ray absorption edges (V L3-edge, C K-edge, N K-edge) shows that the highest occupied electronic state is V(3d)-derived. Nearly complete quenching of the V(3d) orbital angular momentum is observed from the low value of the integrated XMCD signal, indicating a strong ligand field. The rearrangements of the TCNE" related valance electronic states observed in PED and near edge x-ray absorption fine structure (NEXAFS) spectra, in combination with the evidence of V(3d) and TCNE" π (π*) orbital overlap contained in RPE spectra, also point to strong, covalent type bonding.
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| 16. |
- Tengstedt, Carl, et al.
(författare)
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X-ray magnetic circular dichroism and resonant photomission of V(TCNE)x hybrid magnets
- 2006
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 96:5
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of V(TCNE)x were deposited in ultrahigh vacuum using a film growth technique based on in situ chemical vapor deposition of tetracyanoethylene, TCNE, and bis-benzene vanadium, V(C6H6)2. The in situ preparation method enabled, for the first time, experimental analysis of oxygen-free films. X-ray magnetic circular dichroism measurements recorded at the V L2,3 edge confirmed room temperature magnetic ordering. A combination of conventional photoelectron spectroscopy (PES) and resonant photoemission (RPE) measured at the V L3 edge shows that the highest occupied electronic state is V(3d) derived. The rearrangements of the TCNE- related valence electronic states observed in PES and the evidence of V(3d) and TCNE- p(p*) orbital overlap contained in RPE spectra, indicate that strong, covalent type bonding occurs between the vanadium and the TCNE molecules. © 2006 The American Physical Society.
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