| 1. |
- Forsberg, Viviane, 1981-, et al.
(författare)
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Photodetector of multilayer exfoliated MoS2 deposited on polyimide films
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We fabricated a photodetector based on multilayer molybdenum disulfide (MoS2) by micromechanical cleavage of a molybdenite crystal using a polyimide film. We deposited 40 nm of gold by vacuum sputtering and copper tape was used for the contacts. Without any surface treatment, we achieved high responsivity at different incident optical power. The calculated responsivity was 23 mA/W of incident optical power in the range between 400 and 800 nm. For the responsivity measurement it was estimated that MoS2 have a bandgap of 1.6 eV, which lies between monolayer and multilayer films. The thickness of the MoS2 thin film was determined by Raman spectroscopy evaluating the difference between the in plane and out of plane Raman modes. The measurement of IV curves indicated Ohmic contacts in respect to the Au regardless of the incident optical power. Our device fabrication was much simpler than previous reported devices and can be used to test the light absorption and luminescence capabilities of exfoliated MoS2.
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| 2. |
- Alecrim, Viviane, et al.
(författare)
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Exfoliated Layered Materials for Digital Fabrication
- 2015
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Ingår i: NIP & Digital Fabrication Conference. ; , s. 192-194
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Konferensbidrag (refereegranskat)abstract
- We introduced an exfoliation method of MoS2 in a 3% solution of sodium dodecyl surfactant at high concentration (i.e. 2 g/L). The bulk MoS2 was thinned by mechanical exfoliation between sand papers and the resulting powder was used to prepare dispersions by liquid exfoliation through probe sonication. The resulting dispersion consisted of very thin MoS2 nanosheets in surfactant solution with average lateral size around 126 nm. This may be interesting for applications in inkjet printed electronics.
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| 3. |
- Andersson, Kerstin I, et al.
(författare)
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Lignin removal from wastewater by adsorption
- 2009
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Ingår i: Proceedings - 2009 International Mechanical Pulping Conference, IMPC 2009. ; , s. 280-285
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Konferensbidrag (refereegranskat)abstract
- Lignin contributes to residual COD in wastewater after biological treatment. Available methods for removal of recalcitrant material like lignin, e.g. chemical oxidation and coagulation, are associated with heavy operational expenses. Stringent discharge requirements demand new cost-effective methods for removal of recalcitrant COD. Adsorption is an important mechanism for lignin removal in biological wastewater treatment. A study of lignin, using activated carbon as a model adsorbent, was performed to learn more about the adsorption behaviour of lignin. At the adsorbent dose 4 g/L and an initial lignin concentration of 0.5 g/L, 77% of the lignin was removed after six hours. The adsorption kinetics was found to follow the pseudo second-order rate expression and no temperature dependency could be observed in the temperature range studied.
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| 4. |
- Besharati, Farshid, et al.
(författare)
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The EVI Distributed Shared Memory System
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- With the data handled by companies and research institutes getting larger and larger every day, there is a clear need for faster computing. At the same time, we have reached the limit of power consumption and more power efficient computing is also called for, both in the datacenter and in the supercomputer room. For that, there is a great push, both in industry and academia, towards increasing the amount of computing power per watt consumed. With this shift towards a different computing paradigm, many older ideas are looked upon in a new light. One of these is the distributed shared memory (DSM) systems. It is becoming harder and harder to achieve higher performance and better power efficiency at the same form factor as we have always had. Furthermore, while we have seen a stop in the constant increase of processor speeds, there is a constant increase in network communication speeds. Software implemented DSM is again a viable solution for high performance computing, without the need for sacrificing ease of programming for performance gains. The goal of this course was to develop such a system, and learn in the process. We chose to work with the Adapteva Parallella boards and design a DSM system there. Over one semester we designed and developed that system.
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| 5. |
- Forsberg, Viviane, 1981-, et al.
(författare)
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Exfoliated MoS2 in Water without Additives
- 2016
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 11:4
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Tidskriftsartikel (refereegranskat)abstract
- Many solution processing methods of exfoliation of layered materials have been studied during the last few years; most of them are based on organic solvents or rely on surfactants andother funtionalization agents. Pure water should be an ideal solvent, however, it is generallybelieved, based on solubility theories that stable dispersions of water could not be achievedand systematic studies are lacking. Here we describe the use of water as a solvent and thestabilization process involved therein. We introduce an exfoliation method of molybdenumdisulfide (MoS2) in pure water at high concentration (i.e., 0.14±0.01 g L−1). This was achieved by thinning the bulk MoS2by mechanical exfoliation between sand papers and dis-persing it by liquid exfoliation through probe sonication in water. We observed thin MoS2nanosheets in water characterized by TEM, AFM and SEM images. The dimensions of thenanosheets were around 200 nm, the same range obtained in organic solvents. Electropho-retic mobility measurements indicated that electrical charges may be responsible for the sta-bilization of the dispersions. A probability decay equation was proposed to compare thestability of these dispersions with the ones reported in the literature. Water can be used as asolvent to disperse nanosheets and although the stability of the dispersions may not be ashigh as in organic solvents, the present method could be employed for a number of applications where the dispersions can be produced on site and organic solvents are not desirable.
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| 6. |
- Forsberg, Viviane, 1981-, et al.
(författare)
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Printability of functional inkjet inks onto commercial inkjet substrates and a taylor made pigmented coated paper
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Printed electronics are of increasing interest. The substrates used have primarily been plastics although the interest for cellulose-based substrates is increasing due to the environmental aspect as well as cost. The requirements of substrates for electronically active inks differs from graphical inks and therefore we have investigated a custom-made pigment based coated paper and compared it to commercial photo-papers and a coated PE film.Our goal with the study of different substrates was to select the most suitable substrate to print water based 2D materials inkjet inks for flexible electronics.The discovery of graphene, a layered material achieved from the exfoliation of graphite, has resulted in the study of other materials with similar properties to cover areas where graphene could not be used due to the absence of a bandgap in the material. For example in thin film transistors (TFT) a semiconductor layer is essential to enable turn on and off the device. This semiconductor layer can be achieved using various materials but particular interest have been dedicated to abundant and cheap 2D materials such as the transition metal dichalcogenide (TMD) molybdenum disulfide (MoS2). To date, most of the dispersions based on TMDs use organic solvents or water solutions of surfactants. Previously we focus on the study of environmental friendly inks produced by liquid phase exfoliation (LPE) of MoS2 in water using cellulose stabilizers such as ethyl cellulose (EC), cellulose nanofibrils (CNF) and nanofibrilcellulose (NFC). We have study various aspects of the ink fabrication includi ng pH range, the source of MoS2, nanosheets thickness, particle size distribution, ink stabilizers, ink concentration, viscosity and surface tension. These inks have very low concentration requiring a number of printing passes to cover the substrate. Therefore the substrate selection is crucial as a large amount of solvent is to be absorb by the substrate. Our goal was to use such an ink to print electrodes of MoS2 into a paper substrate after substrate selection.Commercial photo papers, a commercial coated PE film and a tailor made multilayer pigment coated paper substrate were used for the substrate selection analysis. We print the substrates using a DIMATIX inkjet printer with a 10 pL printing head using the distillated water waveform supplied by the printer manufacturer. The voltage used was 23V and 4 nozzles were used for the print outs. The inkjet ink used was the organic PEDOT:PSS. We printed lines ranging from 1 pixel to 20 pixels with 1, 2 and 3 printing passes. The printing quality was evaluated through measurements of the waviness of the printed lines measured after imaging the printed samples with a SEM microscope. The line width measurement was done using the software from the SEM.We also evaluated the structure of the coatings using SEM and topography measurements. The ink penetration through the substrates was evaluated using Raman Spectroscopy. For the pigmented coated sample we measured 4% of ink penetration through the substrate for the 1pxl printed line printed once onto the paper. Cross-section SEM images of the printed lines were made to visualize the ink penetration into the substrate.Regarding the electrical conductivity of the printed samples, the differences in resistivity varying the width of the printed lines and the number of printed passes were evaluated. The resistivity of the printed electrodes was evaluated using the 2-points probe method. Before the resistivity measurements, the printed substrates were heated at 50°C and 100°C for 30 minutes in an oven.We choose the PEDOT:PSS ink because it is a low price ink compared to metal nanoparticles inks for printed electronics. The print outs had low resistivity at a few printing passes with no need for sintering at high temperatures. The MoS2 ink has a very high resistance at a few printing passes due to lower coverage of the substrate therefore for this ink these measurements were not possible to be made. The main pigment composition of the paper coatings of the substrates was evaluated using FT-IR and EDX, these data plus the coating structure evaluated by SEM was related to the print quality.The best in test papers were used to print MoS2 electrodes. After the printing tests, another step for the optimization of the MoS2 ink properties shall be carried out in future studies for better print quality. We also evaluated the surface energy of the substrates through contact angle measurements to match the surface tension of the PEDOT:PSS ink and later the MoS2 ink. Although the pigmented coated printing substrate did not show better results than the commercial photo papers and PE foil in terms of line quality, it shows the lowest resistivity and sufficient results for low cost recyclable electronics, which do not require high conductivity. Nevertheless, the substrate was very thin and it could even be used in magazines as traditional lightweight coated papers (LWC) are used but with the additional of a printed electronic feature.
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| 7. |
- Zhang, Renyun, et al.
(författare)
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Cellulose-Based Fully Green Triboelectric Nanogenerators with Output Power Density of 300 W m−2
- 2020
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 32:38
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Tidskriftsartikel (refereegranskat)abstract
- Triboelectric nanogenerators (TENGs) have attracted increasing attention because of their excellent energy conversion efficiency, the diverse choice of materials, and their broad applications in energy harvesting devices and self-powered sensors. New materials have been explored, including green materials, but their performances have not yet reached the level of that for fluoropolymers. Here, a high-performance, fully green TENG (FG-TENG) using cellulose-based tribolayers is reported. It is shown that the FG-TENG has an output power density of above 300 W m−2, which is a new record for green-material-based TENGs. The high performance of the FG-TENG is due to the high positive charge density of the regenerated cellulose. The FG-TENG is stable after more than 30 000 cycles of operations in humidity of 30%–84%. This work demonstrates that high-performance TENGs can be made using natural green materials for a broad range of applications.
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| 8. |
- Zhang, Renyun, et al.
(författare)
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Energy Harvesting Using Wastepaper-Based Triboelectric Nanogenerators
- 2023
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Ingår i: Advanced Engineering Materials. - : Wiley. - 1438-1656 .- 1527-2648. ; 25:11
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Tidskriftsartikel (refereegranskat)abstract
- Inks and toners used for printing contain materials, such as polyester, with strong triboelectric properties to enhance the binding effects, making wastepaper, such as magazines and newspapers, good candidates for triboelectric materials. Herein, high-output power triboelectric nanogenerators (TENGs) that utilize wastepaper as triboelectric layers (wastepaper-based triboelectric nanogenerators (WP–TENGs)) are reported. Journal paper and office copy paper wastes are investigated. The results show that the maximum power densities of the WP–TENGs reach 43.5 W m−2, which is approximately 250 times the previously reported output of the TENG with a recycled triboelectric layer made from wastepaper. The maximum open circuit voltage (V OC) and short circuit current (I SC) are 774 V and 3.92 mA (784 mA m−2), respectively. These findings can be applied to extend the life cycle of printed papers for energy harvesting, and they can later be applied for materials recycling to enhance the sustainable development of our society.
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| 9. |
- Zhang, Renyun, et al.
(författare)
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Soap-film coating : High-speed deposition of multilayer nanofilms
- 2013
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Ingår i: Scientific Reports. - Nature Publishing Group : Springer Science and Business Media LLC. - 2045-2322. ; 3, s. Art. no. 1477-
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Tidskriftsartikel (refereegranskat)abstract
- The coating of thin films is applied in numerous fields and many methods are employed for the deposition of these films. Some coating techniques may deposit films at high speed; for example, ordinary printing paper is coated with micrometre-thick layers of clay at a speed of tens of meters per second. However, to coat nanometre thin films at high speed, vacuum techniques are typically required, which increases the complexity of the process. Here, we report a simple wet chemical method for the high-speed coating of films with thicknesses at the nanometre level. This soap-film coating technique is based on forcing a substrate through a soap film that contains nanomaterials. Molecules and nanomaterials can be deposited at a thickness ranging from less than a monolayer to several layers at speeds up to meters per second. We believe that the soap-film coating method is potentially important for industrial-scale nanotechnology.
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| 10. |
- Zhang, Renyun, et al.
(författare)
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Triboelectric nanogenerators with ultrahigh current density enhanced by hydrogen bonding between nylon and graphene oxide
- 2023
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Ingår i: Nano Energy. - 2211-2855 .- 2211-3282. ; 115
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Tidskriftsartikel (refereegranskat)abstract
- The triboelectric properties of the tribolayers are essential factors affecting the current density of triboelectric nanogenerators (TENGs). To enhance the current density, composites have been developed to tune their triboelectric properties. Previous studies have reported enhanced TENG performance with composite materials, primarily based on their composition, while chemical interactions between the components have been less analyzed. In this study, we report a novel approach to improve the current density of a TENG by introducing dipole-dipole interactions between a nylon filter membrane and graphene oxide (GO) through hydrogen bonds. The Raman spectroscopy confirmed the occurrence of the interactions resulting from hydrogen bonding. The enhancing mechanisms of hydrogen bonds were further analyzed by Kelvin probe force microscope (KPFM) measurement, which demonstrated that hydrogen bonding could influence the surface potential of the coated GO, leading to increased output of the nylon/GO@NFM TENG (NGN-TENG). Our results show that an ultrahigh current density of 1757 mA·m−2 was obtained with a 2 × 2 cm2 NGN-TENG. Additionally, we demonstrated the feasibility of using the NGN-TENG as a motion sensor to sense finger motions. These findings suggest that the introduction of hydrogen bonds in TENG composites can provide a promising route for improving their performance.
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