| 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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