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Author

Sven Stafström

Other affiliations: University of Mons, AlliedSignal, Université de Namur  ...read more
Bio: Sven Stafström is an academic researcher from Linköping University. The author has contributed to research in topics: Polaron & X-ray photoelectron spectroscopy. The author has an hindex of 45, co-authored 223 publications receiving 8363 citations. Previous affiliations of Sven Stafström include University of Mons & AlliedSignal.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors present optical-absorption data together with band-structure calculations for the polaron lattice and bipolaron lattice for the highly conducting form of polyaniline, proton-doped polyemeraldine.
Abstract: We present optical-absorption data together with band-structure calculations for the polaron lattice and bipolaron lattice for the highly conducting form of polyaniline, proton-doped polyemeraldine. We show that the polaron-lattice band structure fully accounts for the observed optical transitions. These results are in marked contrast with the electronic structure of other doped conducting polymers, in that only one single broad polaron band appears deep in the gap together with a very narrow band nearly degenerate with the conduction-band edge.

770 citations

Journal ArticleDOI
26 Mar 1998-Nature
TL;DR: In this paper, the authors found that negative Poisson's ratio is rare in crystalline solids and showed that the existence of positive Poisson ratios up to the stability limit of 2 for cubic crystals in the orthogonal lateral direction.
Abstract: Poisson's ratio is, for specified directions, the ratio of a lateral contraction to the longitudinal extension during the stretching of a material Although a negative Poisson's ratio (that is, a lateral extension in response to stretching) is not forbidden by thermodynamics, this property is generally believed to be rare in crystalline solids1 In contrast to this belief, 69% of the cubic elemental metals have a negative Poisson's ratio when stretched along the [110] direction For these metals, we find that correlations exist between the work function and the extremal values of Poisson's ratio for this stretch direction, which we explain using a simple electron-gas model Moreover, these negative Poisson's ratios permit the existence, in the orthogonal lateral direction, of positive Poisson's ratios up to the stability limit of 2 for cubic crystals Such metals having negative Poisson's ratios may find application as electrodes that amplify the response of piezoelectric sensors

652 citations

Journal ArticleDOI
TL;DR: In this article, the buckled and curved basal planes were found to have a distorted graphitel-like microstructure, and the buckling is due to the incorporation of pentagons in the basal planes, giving rise to a fullerenelike micro-structure.
Abstract: ${\mathrm{CN}}_{x}$ films were found to have a distorted graphitelike microstructure consisting of buckled and curved basal planes using high-resolution electron microscopy. Nanoindentation showed an elastic recovery of 85%, and a hardness of $\ensuremath{\sim}60$ GPa. Based on detailed quantum chemical calculations and photoelectron spectroscopy, the observed structure is proposed to consist of a network of buckled ${\mathrm{sp}}^{2}$-hybridized ${\mathrm{CN}}_{x}$ planes, cross-linked by ${\mathrm{sp}}^{3}$-hybridized bonds. The buckling is shown to be due to the incorporation of pentagons in the basal planes, giving rise to a fullerenelike microstructure.

599 citations

Journal ArticleDOI
TL;DR: In this paper, a band unfolding technique was used to recover an effective primitive cell picture of the band structure of graphene under the influence of different types of perturbations, which involves intrinsic p...
Abstract: We use a band unfolding technique to recover an effective primitive cell picture of the band structure of graphene under the influence of different types of perturbations. This involves intrinsic p ...

434 citations

Journal ArticleDOI
06 Mar 1998-Science
TL;DR: Rare crystal phases that expand in one or more dimensions when hydrostatically compressed are identified and shown to have negative Poisson's ratios, which may be used to fabricate porous solids that either expand in all directions when hydroStatically compressed with a penetrating fluid or behave as if they are incompressible.
Abstract: Rare crystal phases that expand in one or more dimensions when hydrostatically compressed are identified and shown to have negative Poisson's ratios. Some of these crystals (i) decrease volume and expand in two dimensions when stretched in a particular direction and (ii) increase surface area when hydrostatically compressed. Possible mechanisms for achieving such negative linear and area compressibilities are described for single crystals and composites, and sensor applications are proposed. Materials with these properties may be used to fabricate porous solids that either expand in all directions when hydrostatically compressed with a penetrating fluid or behave as if they are incompressible.

330 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors report highly efficient polymer solar cells based on a bulk heterojunction of polymer poly(3-hexylthiophene) and methanofullerene.
Abstract: Converting solar energy into electricity provides a much-needed solution to the energy crisis the world is facing today. Polymer solar cells have shown potential to harness solar energy in a cost-effective way. Significant efforts are underway to improve their efficiency to the level of practical applications. Here, we report highly efficient polymer solar cells based on a bulk heterojunction of polymer poly(3-hexylthiophene) and methanofullerene. Controlling the active layer growth rate results in an increased hole mobility and balanced charge transport. Together with increased absorption in the active layer, this results in much-improved device performance, particularly in external quantum efficiency. The power-conversion efficiency of 4.4% achieved here is the highest published so far for polymer-based solar cells. The solution process involved ensures that the fabrication cost remains low and the processing is simple. The high efficiency achieved in this work brings these devices one step closer to commercialization.

5,431 citations

Journal ArticleDOI
TL;DR: In this paper, the authors describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of diamond-like carbon.
Abstract: Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

5,400 citations

Journal ArticleDOI
TL;DR: Electronic Coupling in Oligoacene Derivatives: Factors Influencing Charge Mobility, and the Energy-Splitting-in-Dimer Method 3.1.
Abstract: 2.2. Materials 929 2.3. Factors Influencing Charge Mobility 931 2.3.1. Molecular Packing 931 2.3.2. Disorder 932 2.3.3. Temperature 933 2.3.4. Electric Field 934 2.3.5. Impurities 934 2.3.6. Pressure 934 2.3.7. Charge-Carrier Density 934 2.3.8. Size/molecular Weight 935 3. The Charge-Transport Parameters 935 3.1. Electronic Coupling 936 3.1.1. The Energy-Splitting-in-Dimer Method 936 3.1.2. The Orthogonality Issue 937 3.1.3. Impact of the Site Energy 937 3.1.4. Electronic Coupling in Oligoacene Derivatives 938

3,635 citations

Journal ArticleDOI
01 Jan 1992-Nature
TL;DR: In this paper, a flexible polyethylene terephthalate (PET) based light-emitting diodes (LEDs) were constructed from conjugated polymers, using poly(ethylene-terephthalates) as the substrate, soluble poly-aniline as the hole-injecting electrode, substituted poly(1,4-phenylene-vinylene) as electroluminescent layer and calcium as the electron-injection top contract.
Abstract: THE recent fabrication of light-emitting diodes (LEDs) from conjugated polymers1,2demonstrates the technological potential of this class of electronic materials. A variety of colours are possible, because the wavelength of luminescence emission can be chemically tuned during synthesis1–4. In addition, the mechanical properties of polymers suggest that light-emitting structures can be made that are more flexible than their inorganic counterparts, provided appropriate materials can be found for the substrate and electrodes. Here we report the fabrication of a fully flexible LED using poly(ethylene terephthalate) as the substrate, soluble poly-aniline as the hole-injecting electrode, a substituted poly(1,4-phenylene-vinylene) as the electroluminescent layer and calcium as the electron-injecting top contract. The structure is mechanically robust and may be sharply bent without failure. The LED is easily visible under room lighting and has an external quantum efficiency of about 1%. With a turn-on voltage for light emission of 2–3 V, the 'plastic' LED demonstrates that this unique combination of optical, electrical and mechanical properties can be used to make novel structures that are compatible with conventional devices.

2,513 citations

Journal ArticleDOI
TL;DR: School of Chemistry, Bio21 Institute, University of Melbourne, 30 Flemington Road, Victoria 3010, Australia; School of Materials Science and Engineering, Nanyang Technological University, Nastyang Avenue, Republic of Singapore 639798; Institute of Materials Research and Engineering (IMRE) and the Agency for Science, Technology and Research (A*STAR), 3 Research Link, Singapore 117602.
Abstract: A review was presented to demonstrate a historical description of the synthesis of light-emitting conjugated polymers for applications in electroluminescent devices. Electroluminescence (EL) was first reported in poly(para-phenylene vinylene) (PPV) in 1990 and researchers continued to make significant efforts to develop conjugated materials as the active units in light-emitting devices (LED) to be used in display applications. Conjugated oligomers were used as luminescent materials and as models for conjugated polymers in the review. Oligomers were used to demonstrate a structure and property relationship to determine a key polymer property or to demonstrate a technique that was to be applied to polymers. The review focused on demonstrating the way polymer structures were made and the way their properties were controlled by intelligent and rational and synthetic design.

2,378 citations