| 1. |
- Gedde, Ulf W, et al.
(författare)
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Mass and charge transport in polyethylene – Structure, morphology and properties
- 2023
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 266
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Forskningsöversikt (refereegranskat)abstract
- Polyethylene is a model for semicrystalline polymers that provides the option to vary crystallinity within wide ranges and then to establish relationships between structure and mass and charge transport properties. Three different topics are covered: diffusion of n-hexane in polyethylene, extensive penetrant uptake kinetics, swelling and the design of a novel sensor, and finally electrical conduction in polyethylene, a field important to modern distribution of electric power (HVDC). This feature article presents past and ongoing studies at KTH Royal Institute of Technology using a variety of experimental methods and computer-aided simulation and modelling.
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| 2. |
- Moyassari, Ali, et al.
(författare)
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First-principle simulations of electronic structure in semicrystalline polyethylene
- 2017
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 146:20
-
Tidskriftsartikel (refereegranskat)abstract
- In order to increase our fundamental knowledge about high-voltage cable insulation materials, realistic polyethylene (PE) structures, generated with a novel molecular modeling strategy, have been analyzed using first principle electronic structure simulations. The PE structures were constructed by first generating atomistic PE configurations with an off-lattice Monte Carlo method and then equilibrating the structures at the desired temperature and pressure using molecular dynamics simulations. Semicrystalline, fully crystalline and fully amorphous PE, in some cases including crosslinks and short-chain branches, were analyzed. The modeled PE had a structure in agreement with established experimental data. Linear-scaling density functional theory (LS-DFT) was used to examine the electronic structure (e.g., spatial distribution of molecular orbitals, bandgaps and mobility edges) on all the materials, whereas conventional DFT was used to validate the LS-DFT results on small systems. When hybrid functionals were used, the simulated bandgaps were close to the experimental values. The localization of valence and conduction band states was demonstrated. The localized states in the conduction band were primarily found in the free volume (result of gauche conformations) present in the amorphous regions. For branched and crosslinked structures, the localized electronic states closest to the valence band edge were positioned at branches and crosslinks, respectively. At 0 K, the activation energy for transport was lower for holes than for electrons. However, at room temperature, the effective activation energy was very low (similar to 0.1 eV) for both holes and electrons, which indicates that the mobility will be relatively high even belowthe mobility edges and suggests that charge carriers can be hot carriers above the mobility edges in the presence of a high electrical field.
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| 3. |
- Nilsson, Fritjof, et al.
(författare)
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Simulating the effective electric conductivity of polymer composites with high aspect ratio fillers
- 2016
-
Ingår i: Composites Science And Technology. - : Elsevier. - 0266-3538 .- 1879-1050. ; 132, s. 16-23
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Tidskriftsartikel (refereegranskat)abstract
- Three simulation models have been developed for predicting the electrical conductivity and the electrical percolation threshold of field-grading polymer composites intended for high voltage applications. The three models are based on finite element modelling (FEM), percolation threshold modelling (PTM) and electrical networks modelling (ENM). A Monte Carlo algorithm was used to construct the geometries, with either soft-core (overlapping) or hard-core/soft-shell (non-overlapping) fibres. Conductivity measurements on carbon-fibre/PMMA composites with well-defined fibre aspect ratios were used for experimental validation. The average fibre orientations were calculated from scanning electron micrographs. The soft-core PTM model with experimental fibre orientations and without adjustable parameters gave accurate (R-2 = 0.984) predictions of the electrical percolation threshold as a function of aspect ratio. The corresponding soft-core ENM model, with close-contact conductivity calculated with FEM, resulted in good conductivity predictions for the longest fibres, still without the use of any adjustable parameters. The hard-core/soft-shell versions of the models, using the shell thickness as an adjustable parameter, gave similar but slightly poorer results.
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| 4. |
- Unge, Mikael, et al.
(författare)
-
Coarse-Grained Model for Prediction of Hole Mobility in Polyethylene
- 2023
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 19:21, s. 7882-7894
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Tidskriftsartikel (refereegranskat)abstract
- Electrical conductivity measurements of polyethylene indicate that the semicrystalline structure and morphology influence the conductivity. To include this effect in atomistic charge transport simulations, models that explicitly or implicitly take morphology into account are required. In the literature, charge transport simulations of amorphous polyethylene have been successfully performed using short oligomers to represent the polymer. However, a more realistic representation of the polymer structure is desired, requiring the development of fast and efficient charge transport algorithms that can handle large molecular systems through coarse-graining. Here, such a model for charge transport simulations in polyethylene is presented. Quantum chemistry calculations were used to define six segmentation rules on how to divide a polymer chain into shorter segments representing localized molecular orbitals. Applying the rules to amorphous systems yields distributions of segments with mode and median segment lengths relatively close to the persistence length of polyethylene. In an initial test, the segments of an amorphous polyethylene were used as hopping sites in kinetic Monte Carlo (KMC) simulations, which yielded simulated hole mobilities that were within the experimental range. The activation energy of the simulated system was lower compared to the experimental values reported in the literature. A conclusion may be that the experimental result can only be explained by a model containing chemical defects that generate deep traps.
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| 5. |
- Unge, Mikael, et al.
(författare)
-
Coarse-Grained Model for Prediction of Hole Mobility in Polyethylene
- 2023
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 19:21, s. 7882-7894
-
Tidskriftsartikel (refereegranskat)abstract
- Electrical conductivity measurements of polyethylene indicate that the semicrystalline structure and morphology influence the conductivity. To include this effect in atomistic charge transport simulations, models that explicitly or implicitly take morphology into account are required. In the literature, charge transport simulations of amorphous polyethylene have been successfully performed using short oligomers to represent the polymer. However, a more realistic representation of the polymer structure is desired, requiring the development of fast and efficient charge transport algorithms that can handle large molecular systems through coarse-graining. Here, such a model for charge transport simulations in polyethylene is presented. Quantum chemistry calculations were used to define six segmentation rules on how to divide a polymer chain into shorter segments representing localized molecular orbitals. Applying the rules to amorphous systems yields distributions of segments with mode and median segment lengths relatively close to the persistence length of polyethylene. In an initial test, the segments of an amorphous polyethylene were used as hopping sites in kinetic Monte Carlo (KMC) simulations, which yielded simulated hole mobilities that were within the experimental range. The activation energy of the simulated system was lower compared to the experimental values reported in the literature. A conclusion may be that the experimental result can only be explained by a model containing chemical defects that generate deep traps.
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| 6. |
- Unge, Mikael, et al.
(författare)
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Hole mobility in amorphous polyethylene - Impact of intra-chain electronic coupling
- 2023
-
Ingår i: 2023 IEEE Conference on Electrical Insulation and Dielectric Phenomena, CEIDP 2023. - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350335620
-
Konferensbidrag (refereegranskat)abstract
- Experimental results indicate that electrical conductivity in polyethylene depend on the morphology. In order to simulate mobility in polyethylene the morphology need to be included implicitly or explicitly. To include the morphology explicitly in atomic scale simulation of mobility the charge transport along the chain need to described. Marcus theory can be used to describe the hopping process. Here a ghost atom model was used to calculate electronic coupling both along and between chains. A factor 10 difference was seen between intra-chain electronic coupling obtained here compared to previous results. However, the charge transport in amorphous polyethylene was primarily limited by the inter-chain electronic coupling.
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| 7. |
- Berling Holm, Katarina
(författare)
-
The Chorda Tympani Nerve : Role in Taste Impairment in Middle Ear Disease and after Ear Surgery
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The chorda tympani nerve, also known as the taste nerve, runs uncovered through the middle ear cavity, a localization that exposes the nerve to pathological processes and surgical trauma in the middle ear. People operated on for otosclerosis tend to complain more about postoperative taste disturbances than those operated on for chronic otitis media. It has been suggested that this difference may be explained by gradual deterioration of chorda tympani nerve function caused by chronic otitis media infection and that further impairment caused by surgery is less noticeable in these patients.This thesis aimed to evaluate the function of the chorda tympani nerve, the effects of middle ear disease on taste and complications resulting from ear surgery for chronic otitis media or otosclerosis. This information will help to improve the ear surgeon’s ability to predict the prognosis of iatrogenic taste disturbances in patients with middle ear disease and after ear surgery.Taste was assessed using electrogustometry and the filter paper disc method before and after surgery for chronic otitis media or otosclerosis. Patients also completed questionnaires about symptoms and quality of life. The status of the chorda tympani nerve upon surgical opening of the ear and grading of the trauma to the nerve during the surgery were recorded. The ultrastructure of the chorda tympani nerve from healthy ears and from ears with chronic otitis media was examined. Electrogustometry and the filter paper disc method were evaluated.The results of electrogustometry and the filter paper disc method were highly reproducible, although their correlation was moderate. Patients with chronic otitis media, patients with a more traumatized nerve, female patients and younger patients were more likely to report postoperative taste disturbances. Most of the patients recovered their taste after 1 year. The quality of life study showed only minor changes after surgery. Electron microscopic observations of nerves from ears with chronic otitis media showed signs of structural degeneration, although signs of regeneration, such as sprouting were also observed. This results may explain the recovery of taste postoperatively and indicate that the nerve should be carefully handled during surgery.
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| 8. |
- Christmansson, Marita, et al.
(författare)
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A case study of a principally new way of materials kitting—an evaluation of time consumption and physical workload
- 2002
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Ingår i: International Journal of Industrial Ergonomics. - : Elsevier. - 0169-8141 .- 1872-8219. ; 30:1, s. 49-65
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a materials kitting case study, using an alternative method for materials kitting: the traditional picker-to-material principle was replaced with a material-to-picker approach. The study was made in a materials supply workshop of an automobile plant shortly after this kitting process had been introduced. The materials kitting was video recorded and the material pickers’ physical exposure was assessed using ambulatory equipment to make an integrated registration of muscular activity, work postures and movements. The material pickers assessed work situations perceived as physically stressful. The materials kitting showed improved productivity as compared with other kitting methods. The study indicated that the work situation offered pickers low levels of physical exposure. The picking work was rather light but involved great repetitiveness in arm movements. The material pickers experienced the work as repetitive and having some physically stressful work situations. The integrated analyses showed: (1) that exposure in picking operations was similar to, but could be distinguished from, other work activities and (2) that picking from one type of storage package, Euro pallets, resulted in higher exposure than picking from plastic containers. More studies are needed on the implications of exposure levels in materials picking.
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| 9. |
- Kubyshkina, Elena, et al.
(författare)
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Ab-initio Modeling of Interfacial Region in Nanocomposite Dielectrics
- 2015
-
Ingår i: 2015 Electrical Insulation Conference (EIC). - : IEEE. - 9781479973545 ; , s. 618-620
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Konferensbidrag (refereegranskat)abstract
- The interfacial region between a base matrix and nanoparticles in nanocomposite dielectrics is often referred to as the main cause of good performance of nanocomposites as insulating materials. In the present work we compare electronic structure of the interfacial region in the polyethylene magnesium oxide nanocomposite with the electronic structures of its bulk constituents. The calculations were performed with density functional theory, the LDA and AM05 functionals were used. Hydroxylated, silanol-terminated (-SiOH) MgO surfaces and an interface (a surface with grafted through Si alkane chains) were studied. Investigation has shown the presence of surface states in untreated (hydroxylated) MgO (111) surface, while for both silanized surfaces these states are removed. It results in 1.7 eV higher band gap energy compared to the untreated case. Untreated regions present in treated nanoparticle are proposed to behave as traps for electrons.
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| 10. |
- Kubyshkina, Elena, 1990-
(författare)
-
Ab initio modelling of interfaces in nanocomposites for high voltage insulation
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dielectric nanocomposite materials have been experimentally proven to have properties that are beneficial in applications for efficient energy transport. However, today there are still no empirical models or rules that can predict the performance of a certain combination of materials in the nanocomposite, and there are also no definitive explanations of their dielectric behavior. A deeper understanding of the phenomena behind these materials' response to an applied electric field can open new possibilities for improvement of the insulating properties of nanocomposites.The goal of this work is to locate the key processes that are responsible for dielectric performance. The methodology of the study is based on ab initio technology, that relies solely on the knowledge of chemical and structural composition of the material. In this work, the charge-related properties of nanocomposite interfaces are studied. The primary material of the study is chosen to be polyethylene-based composite with magnesium oxide nanoparticles.The impact of the nanoparticle crystal surface termination and its silane treatment on the electronic structure of the interface between MgO and polyethylene are investigated here. Moreover, the effects of presence of carboxyl defect and water molecule near the interface are considered in this work as well.Based on the calculated electronic structure data, a model for charge dynamics is proposed. The model explains mechanisms for conductivity and space charge reduction in nanocomposites, but also predicts an increase in thermal stress and susceptibility for chemical defects. It is suggested here that the suppression mechanisms for space charge and conductivity in nanocomposites are inherently unstable and can also accelerate material aging.
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| 11. |
- Kubyshkina, Elena, et al.
(författare)
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Communication : Band bending at the interface in polyethylene-MgO nanocomposite dielectric
- 2017
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 146:5
-
Tidskriftsartikel (refereegranskat)abstract
- Polymer nanocomposite dielectrics are promising materials for electrical insulation in high voltage applications. However, the physics behind their performance is not yet fully understood. We use density functional theory to investigate the electronic properties of the interfacial area in magnesium oxide-polyethylene nanocomposite. Our results demonstrate polyethylene conduction band matching with conduction bands of different surfaces of magnesium oxide. Such band bending results in long range potential wells of up to 2.6 eV deep. Furthermore, the fundamental influence of silicon treatment on magnesium oxide surface properties is assessed. We report a reduction of the surface-induced states at the silicon-treated interface. The simulations provide information used to propose a new model for charge trapping in nanocomposite dielectrics.
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| 12. |
- Kubyshkina, Elena, et al.
(författare)
-
Electronic properties of magnesium oxide-polyethylene interface
- 2016
-
Ingår i: Proceedings of the 2016 IEEE International Conference on Dielectrics, ICD 2016. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781509028023 ; , s. 788-791
-
Konferensbidrag (refereegranskat)abstract
- We use density functional theory to calculate band offsets for different configurations of magnesium oxide-polyethylene interface. Our study shows that band bending occurs at the contact between the polymer and the MgO particle. As a result, the surface of the MgO nanoparticle introduces deep traps up to 2 eV in the material. Also, the calculations indicate the possibility of a double layer formation within the nanoparticle.
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| 13. |
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| 14. |
- Kubyshkina, Elena, et al.
(författare)
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Impact of interfacial structure on the charge dynamics in nanocomposite dielectrics
- 2019
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 125:4
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that the chemistry at the interface between nanoparticle and polymer matrix influence charge dynamics in polymer nanocomposite. Applying density functional theory, we investigate the influence of crystal surface termination, silicon treatment, and water and carboxyl defect on the electronic properties of interfaces in MgO-polyethylene nanocomposite. The band offsets between the nanofiller and base matrix materials show a strong dependence on the chemical composition at the interface. Based on the calculated electronic structure, we propose a band alignment model for charge dynamics in nanocomposite dielectrics. The model not only provides a mechanism of reduction of space charge and conductivity but also predicts an increase in thermal stress and susceptibility to the chemical additives. It is suggested that the suppression mechanisms of space charge and conductivity in nanocomposites can be inherently unstable and promote material aging. The results of the study show a need for long-term performance tests of nanocomposite dielectrics.
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| 15. |
- Kubyshkina, Elena, et al.
(författare)
-
ZnO-polyethylene interface : Band alignment
- 2017
-
Ingår i: Proceedings of the International Symposium on Electrical Insulating Materials. - : Institute of Electrical Engineers of Japan. - 9784886860996 ; , s. 363-365
-
Konferensbidrag (refereegranskat)abstract
- Zinc oxide-polyethylene nanocomposites have a potential to be used for high voltage insulation. Here, we investigate electronic properties of zinc oxide-polyethylene interface using density functional theory. Interface states up to 1 eV below conduction band edge are found in polyethylene. Our results suggest that the energy bands of ZnO and polyethylene align to comply with vacuum level equality. We use our findings to establish mechanisms of band alignment at the interfaces between polyethylene and crystal materials.
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| 16. |
- Lindell, Linda, et al.
(författare)
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Integer charge transfer at the tetrakis(dimethylamino)ethylene/Au interface
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:16, s. 163302-1-163302-3
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 17. |
- Nilsson, Fritjof, et al.
(författare)
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Conductivity simulations of field-grading composites
- 2016
-
Ingår i: Journal of Physics D. - : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 49:33
-
Tidskriftsartikel (refereegranskat)abstract
- The electrical conductivity and the percolation threshold of field grading polymer composites intended for high voltage applications were examined with representative elementary volume simulation methods based on percolation threshold modeling (PTM) and electrical network modeling (ENM). Comparisons were made with experimental conductivity data for SiC-EPDM composites with spherical and angular particles, using different filler fractions and electrical field strengths. With a known conductivity of the filler particles (powder), the simulations could predict the percolation threshold and the composite conductivity as functions of the electrical field for a wide range of SiC-filler fractions. The effects of morphology, dispersion and filler shape were examined and the simulations were able to explain the experimental difficulty of reaching sufficient reproducibility when designing composites with filler fractions close to a percolation threshold. PTM of composites containing hard-core/soft-shell spheres revealed a y = (a + bx)((-1/c)) relationship (R-2 = 0.9997) between filler fraction and relative soft-shell thickness.
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| 18. |
- Stafström, Sven, et al.
(författare)
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Disorder Induced Electron Localization in Molecular Based Materials
- 2010
-
Ingår i: Oxford Handbook of Nanoscience and Technology. - : Oxford University Press. - 9780199533053 - 0199533059
-
Bokkapitel (refereegranskat)abstract
- This is an agenda-setting and high-profile book that presents an authoritative and cutting-edge analysis of nanoscience and technology. The Oxford Handbook of Nanoscience and Technology provides a comprehensive and accessible overview of the major achievements in different aspects of this field. The Handbook comprises 3 volumes, structured thematically, with 25 chapters each. Volume I presents fundamental issues of basic physics, chemistry, biochemistry, tribology etc. of nanomaterials. Volume II focuses on the progress made with host of nanomaterials including DNA and protein based nanostructures. Volume III highlights engineering and related developments, with a focus on frontal application areas. All chapters are written by noted international experts in the field. The book should be useful for final year undergraduates specializing in the field. It should prove indispensable to graduate students, and serious researchers from academic and industrial sectors working in the field of Nanoscience and Technology from different disciplines including Physics, Chemistry, Biochemistry, Biotechnology, Medicine, Materials Science, Metallurgy, Ceramics, Information Technology as well as Electrical, Electronic and Computational Engineering.
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| 19. |
- Tengstedt, Carl, et al.
(författare)
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Coulomb interactions in rubidium-doped tetracyanoethylene : a model system for organometallic magnets
- 2004
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:16, s. 165208-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of tetracyanoethylene (TCNE) has been studied both in its pristine state and upon stepwise rubidium intercalation, by UV and x-ray photoelectron spectroscopy as well as with theoretical calculations. The intercalated system may serve as a model for TCNE-based organometallic magnets, of which the electronic structure remains largely unknown. Rubidium is found to n-dope the TCNE molecules forming Rb+TCNE- with almost complete charge transfer. Calculations show a spin splitting of the former highest occupied molecular orbital level upon Rb doping. We see no evidence for the formation of doubly charged TCNE molecules. A gap opens up at the Fermi energy for Rb+TCNE- due to on-site Coulomb interactions. We estimate the on-site Coulomb interaction of amorphous TCNE doped with Rb to be ∼2 eV.
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| 20. |
- Unge, Mikael, et al.
(författare)
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Anderson localization in two-dimensional disordered systems
- 2003
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Ingår i: Synthetic Metals. - 0379-6779. ; 139:2, s. 239-244
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Tidskriftsartikel (refereegranskat)abstract
- Using the transfer matrix method we have calculated the localization length in a 2D (two dimension) rectangular lattice with both on-site and off-diagonal disorder. Using finite size scaling we show that systems with off-diagonal disorder are much more sensitive to disorder than the system with on-site disorder, e.g. at the same amount of disorder (W=w=2) the localization length for on-site disorder is 104 times longer than for off-diagonal disorder. We consider both isotropic and anisotropic systems, where the latter can be considered as a model for an organic crystal. In the anisotropic case the maximum localization length is at the band center, the isotropic system has a maximum away from the band center.
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| 21. |
- Unge, Mikael, et al.
(författare)
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Effect of long-range correlation on the metal-insulator transition in a disordered molecular crystal
- 2006
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:23
-
Tidskriftsartikel (refereegranskat)abstract
- Localization lengths of the electronic states in a disordered two-dimensional system, resembling highly anisotropic molecular crystals such as pentacene, have been calculated numerically using the transfer matrix method. The disorder is based on a model with small random fluctuations of induced molecular dipole moments which give rise to long-range correlated disorder in the on-site energies as well as a coupling between the on-site energies and the intermolecular interactions. Our calculations show that molecular crystals such as pentacene can exhibit states with very long localization lengths with a possibility to reach a truly metallic state. © 2006 The American Physical Society.
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| 22. |
- Unge, Mikael, et al.
(författare)
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Electron Localization in DNA
- 2003
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 3:10, s. 1417-1420
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Tidskriftsartikel (refereegranskat)abstract
- Electron localization lengths in different DNA sequences have been calculated numerically using the transfer matrix method. It is shown that electronic states associated with guanine can reach fairly long localization lengths in disordered guanine-cytosine double strands if both intra- and interstrand π−π interactions are considered. For DNA sequences containing all four bases, the electronic states become localized to very few base pairs. In particular, the human chromosome 22 and λ-DNA, both with approximately equal concentrations of the four bases, show insulating behavior.
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| 23. |
- Unge, Mikael
(författare)
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Electron mobility edge in amorphous polyethylene
- 2016
-
Ingår i: 2016 IEEE INTERNATIONAL CONFERENCE ON DIELECTRICS (ICD), VOLS 1-2. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781509028047 ; , s. 828-831
-
Konferensbidrag (refereegranskat)abstract
- The conduction mechanism in a material is to a large extent determined by the nature of the electronic states. Localized states give hopping conduction and delocalized states band transport. In amorphous materials there may be a transition from localized states at the band edges to delocalized states higher up in the band. Here we use linear scaling density functional theory and a percolation method to determine electron mobility in amorphous polyethylene. The electron mobility edge is determined to similar to 0.2 eV.
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| 24. |
- Unge, Mikael, et al.
(författare)
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Electron traps in polyethylene due to water
- 2022
-
Ingår i: ICD 2022 - IEEE 2022 4th International Conference on Dielectrics. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 210-213
-
Konferensbidrag (refereegranskat)abstract
- Electron traps in polyethylene (PE) origin from water has been calculated using density functional theory. Atomistic structure has been simulated using molecular dynamics (MD) and used to calculate the electronic structure. Densities comparable with experimentally determined values are obtained. Both single water molecules and cluster of water molecules are considered. For a single water molecule both electron and hole states are within the bands from PE. The electron state is close to the conduction band minima (CBM) and may coincide with the CBM depending on the local atomic density. The absence of electron traps due to water is contradictory to previous simulation results but can be explained by atomic density and relaxation of conduction states of PE. Systems with 10 water molecules relaxed to two pentamers in the MD simulations. Calculation of trap levels of the pentamers result in trap levels in the order of 0.1-0.3 eV.
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| 25. |
- Unge, Mikael, et al.
(författare)
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Electronic conductivity of polymer electrolytes : electronic charge transport properties of LiTFSI-doped PEO
- 2020
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 22:15, s. 7680-7684
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of poly(ethyleneoxide) with and without a common electrolyte lithium bis(trifluoromethane)sulfonimide salt is calculated from first principles. Introducing the salt into the polymer electrolyte significantly reduces the band gap, down to 0.6 eV. Thus, this will have a significant impact on the leakage currents in polymer electrolytes used in all-solid-state batteries.
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| 26. |
- Unge, Mikael, 1977-
(författare)
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Electronic properties of organic molecular materials
- 2004
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the context of molecular based electronics, different molecular systems have been studied. In molecular crystals of pentacene, the conduction process has been reported to occur in a single layer in field-effect transistor applications. The electron localization length and its sensitivity to disorder of such two-dimensional disordered systems have been calculated. The electron localization in DNA has also been investigated. Our results show that DNA containing an approximately equal amount of the four basis is insulating. For instance, the human chromosome 22 is an insulator even though it has long-range correlation, which elsewhere has been suggested to give delocalized states.The on-site Coulomb interaction has been calculated for rubidium-doped tetracyanoethylene (TCNE). If the electronic state is localized to a small region, e.g., a single molecule, the on-site Coulomb interaction becomes important. The interaction is a measure of the work needed to add an extra electron to the system. When the electronic state is localized to a single molecule/site it becomes large. The result has been used to interpret the outcome of ultraviolet photoelectron spectroscopy (UPS) measurements.
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| 27. |
- Unge, Mikael, et al.
(författare)
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High field ion mobility in dielectric polymers : A molecular dynamics study of water in poly(dimethylsiloxane)
- 2017
-
Ingår i: Proceedings of the International Symposium on Electrical Insulating Materials. - : Institute of Electrical Engineers of Japan. - 9784886860996 ; , s. 467-469
-
Konferensbidrag (refereegranskat)abstract
- Detailed understanding of charge transport phenomena in dielectrics is important in order to understand the influence of chemical composition on the dielectric properties. Material simulation methods such as density functional theory (DFT) and molecular dynamics (MD) can be used to calculate basic properties of the material. Here we focus on mobility of ions at high fields by applying MD simulations. In a recent study of ionic mobility in polyethylene, it was shown that ion mobility starts to deviate from the Einstein relation at high fields, resulting in a linear increase of the mobility [1]. We argue that this is due to conformational change of the surrounding polymers through elastic scattering which facilitates and thus accelerates the charged molecule. Here we investigate this effect of water in poly(dimethylsiloxane) (PDMS).
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| 28. |
- Unge, Mikael
(författare)
-
Identification of structural criteria for valence state localization in linear alkanes
- 2018
-
Ingår i: 2018 IEEE 2nd International Conference on Dielectrics, ICD 2018. - : Institute of Electrical and Electronics Engineers Inc.. - 9781538663899
-
Konferensbidrag (refereegranskat)abstract
- Electronic charge transport in polyethylene is via a hopping mechanism. Theoretically hopping transport in polymers can be studied using kinetic Monte Carlo and Marcus Theory. An essential input to the charge transport simulation is to describe how the electronic states localize. Holes in polyethylene localized along the polymer backbone. In the amorphous phase the electronic states are localized to segments of the polymers. No structural criteria is available that determine how electronic states will distribute along the polymer backbone. Here we have applied quantum chemistry to study conformations of linear alkanes in order to identify structural criteria for valence states localization. Two subsequent gauche formations is identified as one localization criterion.
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| 29. |
- Unge, Mikael, 1977-
(författare)
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Molecular Electronics : A Theoretical Study of Electronic Structure of Bulk and Interfaces
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with theoretical studies of the electronic structure of molecules used in the context of molecular electronics. Both studies with model Hamiltonians and first principle calculations have been performed. The materials studied include molecular crystals of pentacene and DNA, which are used as active material in field-effect transistors and as tentative molecular wires, respectively. The molecular magnet compound TCNE and surface modification by means of chemisorption of TDAE on gold are also studied.Molecular crystals of pentacene are reported to have the highest field-effect mobility values for organic thin film field-effect transistors. The conduction process in field-effect transistors applications occurs in a single layer of the molecular crystal. Hence, in studies of transport properties molecular crystals of pentacene can be considered as a two dimensional system. An open question of these system is if the charge transport is bandlike or if as a result of disorder is a hopping process. We address this question in two of the included papers, paper I and paper II.The conducting properties of DNA are of interest for a broad scientific community. Biologist for understanding of oxidatively damaged DNA and physicist and the electronics community for use as a molecular wire. Some reports on the subject classifies DNA as a conductor while other report insulating behavior. The outcome of the investigations are heavily dependent on the type of DNA being studied, clearly there is a big difference between the natural and more or less random sequence in, e.g., λ-DNA and the highly ordered syntethic poly(G)-poly(C) DNA. It has been suggested that long-range correlation would yield delocalized states, i.e., bandlike transport, in natural DNA, especially in the human chromosome 22. In paper III we show that this is not the case. In general our results show that DNA containing an approximately equal amount of the four basis is an insulator in a static picture.An emerging research field is spintronics. In spintronic devices the spin of the charge carrier is as important as the charge. One can envision a device where spin alone is the carrier of information. In realizing spintronic devices, materials that are both magnetic and semiconducting are needed. Systems that exhibit both these properties are organic-based magnets. In paper IV the electronic structure of the molecular magnet compound TCNE is studied, both experimentally and theoretically.The injection of carriers from metal contacts to organic semiconductors is central to the performance of organic based devices. The interface between the metal contact and the organic material has been pointed out to be one of the device parameters that most significantly influences the device performance. This relates to the process of injection of charge carriers in to the organic material. In some contact and organic material combinations the energy barrier for charge injection can be very high. The barrier can be reduced by modify the interface dipole, this is achieved by a monolayer of adsorbed molecules at the interface. The molecule TDAE chemisorbed on gold is studied in paper V.
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| 30. |
- Unge, Mikael, et al.
(författare)
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TDAE chemisorbed on gold
- 2008
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Ingår i: Journal of Physics. - Bristol, United Kingdom : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 20:31
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Tidskriftsartikel (refereegranskat)abstract
- DFT calculations on tetrakis(dimethylamino)ethylene (TDAE) interacting with a gold surface have been performed. A monolayer of TDAE deposited on a gold surface creates an interface dipole, which decreases the barrier for electron injection from a gold contact into an (organic) electroactive material. This was studied by simulating the complex in two different ways, using a slab model and using a gold cluster surface. These approaches are shown to be complementary: the cluster results apply to the situation of isolated molecules and the slab results describe the case of interacting TDAE molecules on the gold surface. We found that there is a transfer of around one electronic charge per TDAE to the gold in the limit of non-interacting TDAE molecules. This charge transfer results in the formation of an interface dipole and a corresponding lowering of the work function of the surface. The lowering of the work function increases with increasing coverage and is as large as 2.4 eV for a monolayer of TDAE on gold. Due to depolarization effects, the charge transfer in this state is reduced to 0.56 times the electronic charge.
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| 31. |
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