| 1. |
- Segervald, Jonas, et al.
(författare)
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Plasmonic metasurface assisted by thermally imprinted polymer nano‐well array for surface enhanced Raman scattering
- 2022
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Ingår i: Nano Select. - : John Wiley & Sons. - 2688-4011. ; 3:9, s. 1344-1353
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Tidskriftsartikel (refereegranskat)abstract
- Plasmonic nanometasurfaces/nanostructures possess strong electromagnetic field enhancement caused by resonant oscillations of free electrons, and has been extensively applied in biosensing, nanophotonic and photocatalysis. However, fabrication of uniform nanostructured metasurfaces by conventional methods is complicated and costly, which mitigates a wide-spread use of this technique in ubiquitous applications. Here, we present a facile and scalable method to fabricate an active nanotrench plasmonic gold substrate. The surface comprises sub-10 nm plasmonic nanogaps and their formation is assisted by a pre-fabrication of nano-imprinted polymer nano-well arrays. The plasmonic metasurface is optimized to maximize the density of the nano-trenches by tuning the substrate material, imprinting procedure and film deposition. We show that the surface Raman enhancement due to plasmonic resonances correlates well with trench density and reach a meritorious enhancement factor of EF > 105 over large surfaces.We further show that the electric field strength at the nanotrench features are well explained by finite element method simulations using COMSOL Multiphysics. The plasmonic substrate is transparent in the visible spectrum and conductive. In combination with a scalable bottom-up fabrication the plasmonic metasurface opens up for a wider use of the sensitive and reliable SERS substrate in applications such as portable sensing devices and for future internet of things.
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| 2. |
- Enevold, Jenny, 1981-
(författare)
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Structure and morphology control of organic semiconductors for functional optoelectronic applications
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The functionality and application of organic semiconductors are largely dependent on their constituent structure and morphology. This thesis presents a number of functional and novel approaches for the control and tuning of structural and morphological features of a variety of organic semiconductor materials, and also demonstrates that these approaches can be utilized for improved device operation of field-effect transistors, organic solar cells and light-emitting electrochemical cells.The fullerene family is a particular group of closed-cage organic semiconductors, which can be photochemically coupled into larger dimeric or polymeric structures through the excitation of the fullerene molecules by light emission. In Paper I, we perform a detailed experimental and analytical investigation, which demonstrates that this photochemical monomer-to-dimer transformation requires that both constituent fullerene molecules are photoexcited. The direct consequence is that the initial probability for the photochemical transformation is dependent on the square of the light-emission intensity.The photochemical coupling of fullerene molecules commonly results in a distinctly lowered solubility in common hydrophobic solvents, which can be utilized for the direct patterning of fullerene films by resist-free lithography. In Paper II, we utilize this patterning opportunity for the fabrication of one-dimensional fullerene nano-stripes using two-beam laser interference lithography. A desired high contrast between the patterned and non-patterned fullerene regions is facilitated by the non-linear response of the photochemical transformation process, as predicted by the findings in Paper I. The patterned fullerene nano-stripes were utilized as the active material in field-effect transistors, which featured high electron mobility and large on-off ratio.This patterning was in Paper III extended into easy tunable two-dimensional fullerene structures by the design and development of an exposure setup, essentially comprising a laser and a spatial light modulator featuring >8 millions of independently controlled mirrors. With this approach, we could fabricate well-defined fullerene microdots over a several square-millimeter sized area, which was utilized as an internal out-coupling layer in a light-emitting electrochemical cell with significantly enhanced light output.Paper IV reports on the development of a new “spray-sintering” method for the cost-efficient solution-based deposition of the active material in light-emitting electrochemical cells. This carefully designed approach effectively resolves the issue with phase separation between the hydrophobic organic semiconductor and the hydrophilic electrolyte that results in a sub-par LEC performance, and also allows for the direct fabrication of LEC devices onto complex surfaces, including a stainless-steel fork.Paper V finally reports on the design and synthesis of a soluble small molecule, featuring a donor-acceptor-donor configuration. It acts as the donor when combined with a soluble fullerene acceptor in the active material of organic solar cells, and such devices with optimized donor/acceptor nanomorphology feature a high open-circuit voltage of ~1.0 V during solar illumination.
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| 3. |
- Lindh, E. Mattias, 1986-
(författare)
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On the operation of light-emitting electrochemical cells
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We are in the midst of a technological revolution that permeates nearly all human activities; artificial light is one of the most visible contributors in this societal change. If more efficient, green, and versatile light sources can be developed, they might improve the life of millions of people around the world while causing minimal damage to our climate and environment. The unique operational mechanism of the light-emitting electrochemical cell (LEC) makes it an ideal fit for some unconventional and emerging uses of light, in for example medicine and security.By exploiting this operational mechanism, in which mobile ions enable electrochemical doping of a luminescent polymer, we have designed and fabricated new bilayer LEC architectures. The bilayer LEC features patterned light emission that is easily adjustable during fabrication, and that can be configured to suit new applications of light. Given the light-emitting nature of the LEC, it is somewhat surprising that the optical understanding of its operation is rather limited. To fill this knowledge gap, we investigate how the optical properties of the luminescent polymer respond to electrochemical doping. We find that the complex-refractive index spectrum in the active layer of an LEC, as a direct result of the doping, varies in both space and time. The thin-film structure of an LEC implies that computational predictions of its luminous output need to consider internal reflections and interference. Finally, we implement a doping dependent optical thin-film simulation model. It enables us to precisely replicate the experimental luminance and angle-dependent emission spectrum for a range of LECs with different thicknesses. Using the model we can also identify and quantify many of the different optical loss mechanisms in LECs, which has not previously been done. The insights that we have collected on the path towards our present model will be useful for computational determination of device parameters that are otherwise difficult to acquire.The improved understanding of the optical operation of LECs is important for the maturation of the technology, as it facilitates formulation of relevant and accurate research questions. Hopefully, our results will accelerate the development of the field, so that useful products based on this technology can become available in the not too distant future.
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| 4. |
- Lundberg, Petter, 1988-
(författare)
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Light for a brighter morrow : paving the way for sustainable light-emitting devices
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We live in an artificially lit world, where light enhances our productivity and improves our quality of life. Today our appetite for light is stronger than ever, and emerging light-emitting technologies do not just replace the classical incandescent light bulb, they also open up for a new world of applications. The problem is that our environment does not cope with the increased energy demand during fabrication and usage, and the insufficient recycling that currently follows this rapid technological development. We must therefore adapt, and from here on out consider the entire environmental footprint and the necessity of our devices. Organic electronics has the potential to become sustainable. It allows for cheap and energy-efficient fabrication methods, using abundant materials, mainly carbon. Such sophisticated conductive plastics can be made thin and flexible, and they are thereby very versatile. It is in this context that we find the light-emitting electrochemical cell (LEC)—a strong contender for affordable and sustainable light. The LEC has a simple device design that is fit for solution based fabrication and new useful applications in, for example, medicine. The simple LEC design is enabled by its operational mechanism, where mobile ions aid electronic charge injection and improves electric conductivity by electrochemical doping. However, this dynamic nature complicates the attainment of devices that are efficient, bright, and retain a long lifetime. Herein, we face these challenges with sustainability as the beacon. We find that careful design of the active material, and selection of its constituents, can lead to LECs that are both efficient and bright. Importantly we show that this is attainable with entirely organic active materials, via thermally activated delayed fluorescence; thereby moving away from unsustainable phosphorescent emitters that contain problematic rare metals. With large-scale manufacturing in mind, we introduce a tool that identifies environmentally benign and functional solvents. Furthermore we design and validate a realistic optical model that unveils the common optical loss mechanisms in LECs. The insights gained guide the optical design of highly efficient LECs in the transition towards an upscaled production.I hope that the progress made will contribute to a road map for the design of sustainable light-emitting devices. It is then our responsibility, as a society, to make use of them where needed.
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| 5. |
- Persson, Per-Axel, et al.
(författare)
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The physical properties of high-pressure polymerized C60
- 1997
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Ingår i: Journal of Physics and Chemistry of Solids, volume 58, issue 11. - : Elsevier B.V.. ; 58:11, s. 1881-1885
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Konferensbidrag (refereegranskat)abstract
- We have studied the structural, thermophysical, and spectroscopic properties of polymeric C60 obtained by high pressure treatment at pressures and temperatures near 1 GPa and 600 K. We present here a brief overview of our results for the structural and thermophysical properties and a more detailed report on recent results obtained by Raman spectroscopy on both thin films, polycrystalline, and single crystal material. The results presented include a comparison between Raman results for photopolymerized and pressure polymerized thin films and a preliminary estimate of the binding energy of polymeric C60.
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| 6. |
- Sundqvist, Bertil, et al.
(författare)
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Structural and physical properties of pressure polymerized C60
- 1998
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Ingår i: Carbon, vol. 36 issue 5-6. - : Elsevier B.V.. ; 36:5-6, s. 657-660
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Konferensbidrag (refereegranskat)abstract
- We discuss the structural and dynamic properties of C60 polymerized under low-P, low-T conditions, and suggest that the disordered mixed orthorhombic-tetragonal-rhombohedral phases produced under these conditions arise from nucleation of molecular chains in random directions because of the quasi-free molecular rotation under standard reaction conditions in the fcc phase of C60. Polymerization in He gives results qualitatively different from those obtained in other media.
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| 7. |
- Wågberg, Thomas, et al.
(författare)
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2D polymerization and doping of fullerenes under pressure
- 2000
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Ingår i: High Pressure Research vol. 18. - : Gordon & Breach. ; 18:1-6, s. 139-143
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Konferensbidrag (refereegranskat)abstract
- Tetragonal polymeric C60 has been studied by Raman spectroscopy and other methods. Attempts have been made to transform samples from the tetragonal to the orthorhom-bic phase and vice versa. The results suggest that the transformation is direct with no intermediate stage with free molecules. Tetragonal C60 has also been intercalated by potassium metal.
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| 8. |
- Wågberg, Thomas, et al.
(författare)
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Spectroscopic study of phase transformations between orthorhombic and tetragonal C60 polymers
- 2006
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Ingår i: The European Physical Journal B: Condensed Matter and Complex Systems. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 49:1, s. 59-65
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed study of transformations between the orthorhombic and tetragonal polymeric states of C60. The transformations are characterised by Raman spectroscopy and X-ray diffraction. We show that the transformation from the orthorhombic (O) phase to the tetragonal (T) phase is very fast and our results indicate that the transformation goes via an intermediate dimer (D) state in a two-stage process, O↦D and, D↦T transformations, where the second process is slower than the first. On the other hand, the transformation from the tetragonal to the orthorhombic phase is significantly slower, indicating a high-energy threshold to break the polymer bonds at the temperatures used. The results also support earlier suggestions that the tetragonal phase contains disordered dimers that can be viewed as lattice defects in the formation of higher polymers.
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| 9. |
- Flygare, Mattias, 1978-
(författare)
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The influence of crystallinity on the properties of carbon nanotubes
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbon nanotubes have been advertised as a material with quite extraordinary properties, both mechanically and electrically. The truth is that carbon nanotubes is not one material, but several different. Depending on the method used to produce them, and consequently the quality of the atomic structure within their walls, their physical properties can also differ drastically. In this doctoral thesis a method was developed for quantifying the degree of order within the tubes' walls, namely their crystallinity, by using transmission electron microscopy. The method enables the characterization of the inherent properties of the tubes such as electrical conductivity and bending stiffness, alongside the determination of crystallinity, making it possible to quantify the influence of tube crystallinity on these critical properties. Furthermore, a model for electrical conduction in the outermost wall of multi-walled carbon nanotubes is suggested, enabling the determination of intrinsic quantities like the sheet resistance of individual crystallite grains within the walls and the boundaries in-between them. The studies reveal a profound shift in both mechanical and electrical behavior at a critical crystallite size, with large differences connected to production method, and even between individual tubes from the same production batch. These findings successfully explain previously seen differences and highlight the need for well-defined characterization techniques with protocols and classification systems, in order to successfully exploit the promising properties of carbon nanotubes in the future.
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| 10. |
- Eriksson, Axl, et al.
(författare)
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Synthesis of Well-Ordered Functionalized Silicon Microwires Using Displacement Talbot Lithography for Photocatalysis
- 2024
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 9:18, s. 20623-20628
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Tidskriftsartikel (refereegranskat)abstract
- Metal-assisted chemical etching (MACE) is a cheap and scalable method that is commonly used to obtain silicon nano- or microwires but lacks spatial control. Herein, we present a synthesis method for producing vertical and highly periodic silicon microwires, using displacement Talbot lithography before wet etching with MACE. The functionalized periodic silicon microwires show 65% higher PEC performance and 2.3 mA/cm2 higher net photocurrent at 0 V compared to functionalized, randomly distributed microwires obtained by conventional MACE at the same potentials.
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