| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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