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• 1.
PIPG Bioenergia-UNICAMP, Campinas, SP, Brazil.
Centro de Ciências e Tecnologias para a Sustentabilidade- UFSCa, Sorocaba, SP, Brazil. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. University of Campinas (UNICAMP), SP, Brazil . University of Campinas (UNICAMP), SP, Brazil . University of Campinas (UNICAMP), SP, Brazil . Delft University of Technology, Delft, The Netherlands. PIPG Bioenergia-UNICAMP, Campinas, SP, Brazil.
Ultra-Thin Films of Reduced Graphene Oxide (RGO) Nanoplatelets Functionalized with Different Organic Materials2016In: Journal of Bioprocessing & Biotechniques, ISSN 2155-9821, Vol. 6, no 3, article id 1000272Article in journal (Refereed)

This work aims the functionalization of reduced graphene oxide nanoplatelets with chitosan (G-chitosan) and also with poly(styrenesulfonic acid) (GPSS), thus forming stable, dispersed aqueous solutions. G-chitosan and GPSS solutions allowed the layer-by-layer (LbL) film formation with glucose oxidase (GOx), establishing multilayered nanostructures with elevated control in thickness and morphology. The graphene nanoplatelets were characterized by UV-vis and FTIR spectroscopies, resulting in good adherence and linear deposition of the graphene nanoplatelets with GOx in the LbL structures.Cyclic voltammetry shows an enlargement in the current intensity with increasing number of deposited LbL layers, possibly owing to the formation of conducting paths by the graphene nanoplatelets in the tailored multilayer nanomaterial formed

• 2.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design. Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design. Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design. Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design. Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design. Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
Contacting paper-based supercapacitors to printed electronics on paper substrates2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 476-480Article in journal (Refereed)

Hybrid printed electronics, in which printed structures and silicon-based components co-exist will likely be among the first commercial solutions. In this case the paper substrate acts much in the same way as circuit boards, containing conductive tracks and acting as a carrier for the electrical components. It is important to consider the contacting of the components to be able to produce low resistance electrical contacts to the conductive tracks. Supercapacitors are able to deliver a large amount of current in a short time and are a good option for short term energy storage and if the printed product is to be used only one, or a few times, it can be the only power source needed. When manufacturing printed electronics, the overall resistance of the printed tracks as well as the contact resistance of the mounted components will add up to the total resistance of the system. A high resistance will cause a voltage drop from the power source to the component. This will waste power that goes to Joule heating and also the voltage and current available to components may be too low to drive them. If the intention is to use a power supply such as batteries or solar cells this becomes a limitation. In this article have been tested several conductive adhesives used to contact paper based supercapacitors to ink jet printed silver tracks on paper. The best adhesive gives about 0.3 Ω per contact, a factor 17 better compared to the worst which gave 5 Ω. The peak power that is possible to take out from a printed system with a flexible battery and super capacitors is about 10 times higher than compared with the same system with only the battery.

• 3.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Low-Cost, Environmentally Friendly Electric Double-Layer Capacitors: Concept, Materials and Production2017Doctoral thesis, comprehensive summary (Other academic)

Today’s society is currently performing an exit from fossilfuel energy sources. The change to sustainable alternativesrequires inexpensive and environmentally friendly energy storagedevices. However, most current devices contain expensive,rare or toxic materials. These materials must be replaced bylow-cost, abundant, nontoxic components.In this thesis, I suggest the production of paper-based electricdouble-layer capacitors (EDLCs) to meet the demand oflow-cost energy storage devices that provide high power density.To fulfill the requirements of sustainable and environmentallyfriendly devices, production of EDLCs that consist of paper,graphite and saltwater is proposed. Paper can be used as aseparator between the electrodes and as a substrate for theelectrodes. Graphite is suited for use as an active material in theelectrodes, and saltwater can be employed as an electrolyte.Westudied and developed different methods for the productionof nanographite and graphene from graphite. Composites containingthese materials and similar advanced carbon materialshave been tested as electrode materials in EDLCs. I suggest theuse of cellulose nanofibers (CNFs) or microfibrillated cellulose(MFC) as a binder in the electrodes. In addition to improvedmechanical stability, the nanocellulose improved the stabilityof graphite dispersions and the electrical performance of theelectrodes. The influence of the cellulose quality on the electricalproperties of the electrodes and EDLCs was investigated.The results showed that the finest nanocellulose quality is notthe best choice for EDLC electrodes; MFC is recommended forthis application instead. The results also demonstrated thatthe capacitance of EDLCs can be increased if the electrodemasses are adjusted according to the size of the electrolyte ions.Moreover, we investigated the issue of high contact resistancesat the interface between porous carbon electrodes and metalcurrent collectors. To reduce the contact resistance, graphitefoil can be used as a current collector instead of metal foils.Using the suggested low-cost materials, production methodsand conceptual improvements, it is possible to reduce the material costs by more than 90% in comparison with commercialunits. This confirms that paper-based EDLCs are apromising alternative to conventional EDLCs. Our findings andadditional research can be expected to substantially supportthe design and commercialization of sustainable EDLCs andother green energy technologies.

• 4.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Paper-based supercapacitors2013In: Young Researchers’ Abstracts 2013, 2013Conference paper (Refereed)

Supercapacitors are high performance energy storage devices that offer many advantages like high power densities, fast charge/discharge times and long lifetimes. Due to high purchase prices the use of supercapacitors is limited. Thus we introduced the concept of low cost paper-based supercapacitors. Paper serves as a carrier for the active electrode material, as ion conductor and as separator in the supercapacitor. Different carbon materials, like graphene, graphite and activated carbon are used as active material for the electrodes. We are developing a process to produce large quantities of inexpensive graphene by mechanical exfoliation of graphite. Both coated and filled electrode papers were prepared and tested in supercapacitors. Besides graphene we coated several graphene/graphite composites on paper. By adding small amounts of gold nanoparticles or nanofibrillated cellulose (NFC) the supercapacitors performance can be improved to a great extent. Specific capacitances of up to 100 F/g for coated paper electrodes and sheet-resistances as low as 0.5 Ω/sq could be obtained. Another advantage of this concept is that papermaking technologies can be used to prepare conducting electrodes, thin separators and manufacture the device itself. The paper industry has the ability to facilitate a large scale production of inexpensive supercapacitors.

• 5.
Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
Supercapacitors with graphene coated paper electrodes2012Conference paper (Refereed)
• 6.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Characterization of nanographite and graphene produced in a high-pressure homogenizer2014In: Graphene Week 2014, 2014Conference paper (Refereed)

Supercapacitor electrodes are often made of porous carbon materials such as activated carbon, but also graphene was frequently used as active electrode material. Graphene can be produced by mechanical exfoliation, chemical exfoliation, chemical vapor deposition or other elaborate methods. These techniques are relatively expensive and produce small quantities only. Recently we presented a method to produce nanographite and graphene by mechanical exfoliation of graphite in a high-pressure homogenizer. In our contribution “Large-scale production of graphene” by Nicklas Blomquist we suggest to optimize the geometry of the shear zone and increase the feeding pressure to obtain a higher yield.

In this study we evaluated the influence of these process optimizations on the structural and electrical properties of the nanographite-graphene mixture. The produced dispersions were characterized in terms of particle size and shape by using a particle size analyzer, a transmission electron microscope (TEM) and an atomic force microscope (AFM). In order to analyze the performance of the produced material as electrodes for supercapacitors, electrodes were produced by vacuum filtration. The electrodes were studied by sheet-resistance and capacitance measurements. Furthermore, the structure of the electrode surface and the cross section of the electrode were visualized by using a scanning electron microscope (SEM).

Comparisons with previously produced nanographite-graphene dispersions showed an increase in yield of the exfoliated nanomaterials. The optimized shear zone increased the production of nanosized particles and flakes and enhanced the material quality.

• 7.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Inexpensive production of graphene by mechanical treatment of graphite2014In: Graphene Study 2014, 2014Conference paper (Other academic)
• 8.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Electrode Mass Balancing as an Inexpensive and Simple Method to Increase the Capacitance of Electric Double-Layer Capacitors2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 9, p. 1-12, article id e0163146Article in journal (Refereed)

Symmetric electric double-layer capacitors (EDLCs) have equal masses of the same active material in both electrodes. However, having equal electrode masses may prevent the EDLC to have the largest possible specific capacitance if the sizes of the hydrated anions and cations in the electrolyte differ because the electrodes and the electrolyte may not be completely utilized. Here we demonstrate how this issue can be resolved by mass balancing. If the electrode masses are adjusted according to the size of the ions, one can easily increase an EDLC's specific capacitance. To that end, we performed galvanostatic cycling to measure the capacitances of symmetric EDLCs with different electrode mass ratios using four aqueous electrolytes-Na2SO4, H2SO4, NaOH, and KOH (all with a concentration of 1 M)-and compared these to the theoretical optimal electrode mass ratio that we calculated using the sizes of the hydrated ions. Both the theoretical and experimental values revealed lower-than-1 optimal electrode ratios for all electrolytes except KOH. The largest increase in capacitance was obtained for EDLCs with NaOH as electrolyte. Specifically, we demonstrate an increase of the specific capacitance by 8.6% by adjusting the electrode mass ratio from 1 to 0.86. Our findings demonstrate that electrode mass balancing is a simple and inexpensive method to increase the capacitance of EDLCs. Furthermore, our results imply that one can reduce the amount of unused material in EDLCs and thus decrease their weight, volume and cost.

• 9.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Enhanced electrical and mechanical properties of nanographite electrodes for supercapacitors by addition of nanobrillated cellulose2014Conference paper (Refereed)

Graphene and other porous carbon materials are widely used as electrodes in supercapacitors. In order to form mechanically stable electrodes, binders can be added to the conducting electrode material. However, most binders degrade the electrical performance of the electrodes. Here we show that by using nanobrillated cellulose (NFC) as binder the electrical properties, such as sheet-resistance, were enhanced. NFC is a good ion conductor and improves the access of ions to the electrodes. Thus electrodes made of a mixture of nanographite and NFC achieved larger capacitances in supercapacitors than electrodes with nanographite only. The lowest sheet-resistance and the highest capacitance were measured at NFC contents of 10{15% in ratio to the total amount of active material. Furthermore, NFC formed a network that improved the mechanical stability of the electrodes signicantly. Beside the mechanical stability, NFC stabilized the aqueous nanographite dispersion that was used to prepare the electrodes. NFC avoids the restacking of the delaminated graphene akes by forming a ber network between the graphene layers.

• 10.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Influence of Electrode Mass Ratio on Capacitance of Supercapacitors2015In: Abstract Book, ISEECap 2015, 2015, p. 132-Conference paper (Refereed)
• 11.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. STT Emtec AB, Sundsvall.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Metal-free supercapacitor with aqueous electrolyte and low-cost carbon materials2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 39836Article in journal (Refereed)

Electric double-layer capacitors (EDLCs) or supercapacitors (SCs) are fast energy storage devices with high pulse efficiency and superior cyclability, which makes them useful in various applications including electronics, vehicles and grids. Aqueous SCs are considered to be more environmentally friendly than those based on organic electrolytes. Because of the corrosive nature of the aqueous environment, however, expensive electrochemically stable materials are needed for the current collectors and electrodes in aqueous SCs. This results in high costs for a given energy-storage capacity. To address this, we developed a novel low-cost aqueous SC using graphite foil as the current collector and a mix of graphene, nanographite, simple water-purification carbons and nanocellulose as electrodes. The electrodes were coated directly onto the graphite foil by using casting frames and the SCs were assembled in a pouch cell design. With this approach, we achieved a material cost reduction of greater than 90% while maintaining approximately one-half of the specific capacitance of a commercial unit, thus demonstrating that the proposed SC can be an environmentally friendly, low-cost alternative to conventional SCs.

• 12. Bäckström, Joakim
Optical properties of YBa$_2$Cu$_3$O$_7 - \delta$ and PrBa$_2$Cu$_3$O$_7 - \delta$ films: High-energy correlations and metallicity2004In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 70, no 17Article in journal (Refereed)

We have investigated the temperature dependence of the dielectric functions of a high-Tc superconducting YBa2Cu3O7-- (Y-123) and a nonsuperconducting PrBa2Cu3O7-- (Pr-123) thin film using spectral ellipsometry. We evaluate the data by means of thermal-difference and sum-rule analysis techniques. We find that a spectral-weight transfer into the bands between 4 and 5 eV takes place before Y-123 becomes superconducting. We identify an anomaly around 1 eV that can be explained by a sudden plasma-frequency drop of the order of an meV around Tc. The absence of any sudden effects in the dielectric properties of Pr-123 suggests that both observations are intimately related to the superconducting state. Our findings point out that high-energy degrees of freedom must be considered for the understanding of high-temperature superconductivity.

• 13. Bäckström, Joakim
Raman scattering in YBa2Cu4O8 and PrBa2Cu4O8 - indications of pseudogap effects in non-superconducting PrBa2Cu4O82000In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 341, p. 2251-2252Article in journal (Refereed)

By analysis of the temperature evolution of Raman spectra, we connect an observed supression in low-energy electronic density of states to an anomalous sharpening of the Ba-phonon mode in superconducting YBa2Cu4O8 (Y-124) at around T=150 K. We link the supression of electronic excitations to an opening of a pseudogap. Similar effects observed for the Ba-phonon mode at roughly the same temperature in non-superconducting PrBa2Cu4O8 (Pr-124) suggests that a pseduogap opens up around 150 K also in this material.

• 14.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
In-situ TEM Probing of Nanomaterials2009Doctoral thesis, comprehensive summary (Other academic)

Nanomaterials because of their small size, may have special properties unlikely to be seen in ordinary types of materials. Nanomaterials like nanotubes,nanowires and nanoparticles are best studied at the nanoscale, vital but also problematic. In this thesis we use a transmission electron microscope (TEM)combined with a scanning tunneling microscope probe. This system allows TEM images to be captured and recorded into a movie together with recordedelectrical data for real time analysis. Using this method we found that the electrical conductivity of molybdenumbased nanowires Mo6S3I6 can be improved by current induced transformation. This might be a general method of improving nanowires which is of high valueif the wires are to be used in electrical circuits or ﬁeld emission devices. The bending modulus for these nanowires were also determined, by an electromechanical resonance method, to 4.9 GPa. The sintering phase of silver nanoparticles, used in electrical conductive ink for printing electrical circuits, were studied by the in-situ TEM probing method. We observed that percolation path ways are formed and that the dispersive agent of the particles can be pyrolysed into a net of carbon with characteristics similar to graphite. We also developed a method for decorating nanowires and nanotubes with gold nanoparticles. Nanowire particle composites are often used in assembling more complex devices (electronic circuits) or for linking to organic molecules (biosensor applications) and existing particle decoration methods are either difficult or with low yield. By in situ TEM probing we found that carbon nanocages can be grown onto these gold nanoparticles. The size of the gold nanoparticles is controllable an thus the size of the nanocages. These nanocages may be used in medicine- or hydrogen storage-applications.

• 15.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
Nanowire Transformation and Annealing by Joule Heating2010In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 21, no 16, p. 165704-165704Article in journal (Refereed)

Joule heating of bundles of Mo6S3I6 nanowires, in real time, was studied using in situ TEM probing. TEM imaging, electron diffraction, and conductivity measurements showed a complete transformation of Mo6S3I6 into Mo via thermal decomposition. The resulting Mo nanowires had a conductivity that was 2-3 orders higher than the starting material. The conductivity increased even further, up to 1.8 x 10(6) S m(-1), when the Mo nanowires went through annealing phases. These results suggest that Joule heating might be a general way to transform or anneal nanowires, pointing to applications such as metal nanowire fabrication, novel memory elements based on material transformation, or in situ improvement of field emitters.

• 16.
KTH.
Cone motion viscosity and optical second harmonic generation of ferroelectric liquid crystalline dendrimers2001In: Liquid crystals (Print), ISSN 0267-8292, E-ISSN 1366-5855, Vol. 28, no 6, p. 861-868Article in journal (Refereed)

We report second harmonic generation in a ferroelectric liquid crystalline trimer and ferroelectric liquid crystalline dendrimers of first, second and third generation. Thin cells were filled with the compounds by capillary forces at elevated temperature, and cooled from the surface stabilized ferroelectric state to below the glass transition temperature, while kept in an electric field. The cone motion viscosity and the threshold electric field for unwinding of the helix axis of the chiral tilted smectic mesophases were studied separately at elevated temperature, and these data were used to optimize the preparation of the films. The measured response time was between 0.3 and 3ms, which corresponds to a cone motion viscosity between 0.5 and 50 Pa s. Second harmonic generation was studied both at elevated temperature with an electric field and at room temperature with and without electric field. The first generation dendrimer exhibited a strong increase in the second order non-linear optical response with time at room temperature. The d23-coefficient of this dendrimer was approximately four times larger than for the other macromolecules and was 0.045 pm/V. The relatively large d-coe cient of the first generation dendrimer is ascribed to crystallization, which improved the orientation of the molecular dipoles.

• 17. Kall, M.
Resonance Raman scattering as a probe of oxygen dynamics in YBa2Cu3Ox1998In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 59, p. 1988-1990Article in journal (Refereed)

We report on the metastable photo-bleaching of the 2.15 eV yellow Raman resonance in oxygen deficient YBa2Cu3Ox (x = 6.35-6.87), extending investigations by Wake ct al. (Phys. Rev. Lett., 1991,67, 3728) for x approximate to 7. Polarization, x dependence and phonon spectra indicate that the resonance is localized at oxygen vacancies in long CuO-chains. The resonance is thermally reactivated from the metastable bleached state with a relaxation time tau similar to exp[Delta/k(B)T] with Delta approximate to 1 eV. The resulting temperature dependent equilibrium resonance intensity essentially miners the oxygen superstructure disordering around T* approximate to 100 degrees C observed in the same crystals by hard X-ray diffraction, thus offering a new effective probe of chain-oxygen dynamics in YBa2Cu3Ox. (C) 1998 Elsevier Science Ltd. All rights reserved.

• 18.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom . Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
Investigation of charge collection in a CdTe-Timepix detector2013In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 8, no May, p. Art. no. C05003-Article in journal (Refereed)

Energy calibration of CdTe detectors is usually done using known reference sources disregarding the exact amount of charge that is collected in the pixels. However, to compare detector and detector model the quantity of charge collected is needed. We characterize the charge collection in a CdTe detector comparing test pulses, measured data and an improved TCAD simulation model [1]. The 1 mm thick detector is bump-bonded to a TIMEPIX chip and operating in Time-over-Threshold (ToT) mode. The resistivity in the simulation was adjusted to match the detector properties setting a deep intrinsic donor level [2]. This way it is possible to adjust properties like trap concentration, electron/hole lifetime and mobility in the simulation characterizing the detector close to measured data cite [3].

• 19.
Chinese Academy of Sciences, Beijing, China.
Chinese Academy of Sciences, Beijing, China. Chinese Academy of Sciences, Beijing, China. Chinese Academy of Sciences, Beijing, China. Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. Chinese Academy of Sciences, Beijing, China.
Study of n-type doping in germanium by temperature based PF+ implantation2020In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 31, p. 161-166Article in journal (Refereed)

Incorporation of P in germanium was studied by using PF+ molecular implantation in a range from room temperature to 400 °C. The presence of F acted as a barrier for P in-diffusion and resulted in higher activation of P at room temperature. In addition, it is found that when the implantation is performed at 400 °C, the residual defects are stable and the diffusion of P can be blocked during activation annealing. Therefore, the final junction depth could be well controlled by the implantation process itself. This method is meaningful for the shallow junction formation in sub 14-nm Ge-based FinFETs or high-performance photodetectors.

• 20.
Durham University, United Kingdom.
Durham University, United Kingdom. Durham University, United Kingdom. Durham University, United Kingdom. Durham University, United Kingdom. University of São Paulo-USP, Brazil; Durham University, United Kingdom. Durham University, United Kingdom. Durham University, United Kingdom.
Computing with carbon nanotubes: Optimization of threshold logic gates using disordered nanotube/polymer composites2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 13, article id 134903Article in journal (Refereed)

This paper explores the use of single-walled carbon nanotube (SWCNT)/poly(butyl methacrylate) composites as a material for use in unconventional computing. The mechanical and electrical properties of the materials are investigated. The resulting data reveal a correlation between the SWCNT concentration/viscosity/conductivity and the computational capability of the composite. The viscosity increases significantly with the addition of SWCNTs to the polymer, mechanically reinforcing the host material and changing the electrical properties of the composite. The electrical conduction is found to depend strongly on the nanotube concentration; Poole-Frenkel conduction appears to dominate the conductivity at very low concentrations (0.11% by weight). The viscosity and conductivity both show a threshold point around 1% SWCNT concentration; this value is shown to be related to the computational performance of the material. A simple optimization of threshold logic gates shows that satisfactory computation is only achieved above a SWCNT concentration of 1%. In addition, there is some evidence that further above this threshold the computational efficiency begins to decrease. (C) 2015 AIP Publishing LLC.

• 21. Neuber, G.
Generalized magneto-optical ellipsometry in ferromagnetic metals2004In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 455, p. 39-42Article in journal (Refereed)

We present spectral generalized magneto-optical ellipsometry as an optical tool to investigate magnetic and electronic properties of ferromagnetic materials. The advantage of the simultaneous observation of the dielectric and the magnetic responses within one measurement procedure is crucial for materials with coupled degrees of freedom near a phase transition or during annealing procedures to improve the film quality by removing grain boundaries. Moreover, we show the implementation of this technique within an UHV-cryostat for a temperature range between 4.2 and 800 K and fields up to 40 mT. Examplary measurements on iron and Permalloy demonstrate the comfortable application of this technique. (C) 2003 Elsevier B.V. All rights reserved.

• 22.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
Nonharmonic oscillations of nanosized cantilevers due to quantum-size effects2010In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 81, no 5, p. 054304-Article in journal (Refereed)

Using a one-dimensional jellium model and standard beam theory we calculate the spring constant of a vibrating nanowire cantilever. By using the asymptotic energy eigenvalues of the standing electron waves over the nanometer-sized cross-section area, the change in the grand canonical potential is calculated and hence the force and the spring constant. As the wire is bent more electron states fits in its cross section. This has an impact on the spring "constant" which oscillates slightly with the bending of the wire. In this way we obtain an amplitude-dependent resonans frequency that should be detectable.

• 23.
University of São Paulo, Brazil.
University of São Paulo, Brazil. University of São Paulo, Brazil. University of São Paulo, Brazil. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. São Carlos Institute of Physics, University of São Paulo, USP, P.O. Box 369, São Carlos, SP, Brazil . University of São Paulo, Brazil. University of São Paulo, Brazil. University of São Paulo, Brazil.
Experimental evidence for the mode of action based on electrostatic and hydrophobic forces to explain interaction between chitosans and phospholipid Langmuir monolayers2016In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 145, p. 201-207Article in journal (Refereed)

The interaction between chitosans and Langmuir monolayers mimicking cell membranes has been explained with an empirical scheme based on electrostatic and hydrophobic forces, but so far this has been tested only for dimyristoyl phosphatidic acid (DMPA). In this paper, we show that the mode of action in such a scheme is also valid for dipalmitoyl phosphatidyl choline (DPPC) and dipalmitoyl phosphatidyl glycerol (DPPG), whose monolayers were expanded and their compressibility modulus decreased by interacting with chitosans. In general, the effects were stronger for the negatively charged DPPG in comparison to DPPC, and for the low molecular weight chitosan (LMWChi) which was better able to penetrate into the hydrophobic chains than the high molecular weight chitosan (Chi). Penetration into the hydrophobic chains was confirmed with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and sum frequency generation (SFG) spectroscopy. A slight reduction in conformational order of the lipid chains induced by the chitosans was quantitatively estimated by measuring the ratio between the intensities of the methyl (r+) and methylene (d+) peaks in the SFG spectra for DPPG. The ratio decreased from 35.6 for the closely packed DPPG monolayer to 7.0 and 6.6 for monolayers containing Chi and LMWChi, respectively. Since in both cases there was a significant phospholipid monolayer expansion, the incorporation of chitosans led to chitosan-rich and lipid-rich condensed domains, which mantained conformational order for their hydrophobic tails. The stronger effects from LMWChi are ascribed to an easier access to the hydrophobic tails, as corroborated by measuring aggregation in solution with dynamic light scattering, where the hydrodynamic radius for LMWChi was close to half of that for Chi. Taken together, the results presented here confirm that the same mode of action applies to different phospholipids that are important constituents of mammalian (DPPC) and bacterial (DPPG) cell membranes.

• 24.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
Monte Carlo simulation of electron transport in semiconducting zigzag carbon nanotubes2013Doctoral thesis, comprehensive summary (Other academic)

Since the advent of nanoscale material based electronic devices, there has been a considerable interest in exploring carbon nanotubes from fundamental science and technological perspectives. In carbon nanotubes, the atoms form a cylindrical structure with a diameter of the order 1nm. The length of the nanotubes can extend up to several hundred micrometers. Carbon nanotubes exhibit a variety of intriguing electronic properties such as semiconducting and metallic behaviour, due to the quantum confinement of the electrons in the circumferential direction. Much of the study dedicated to describe the behaviour of carbon nanotube-based devices assumes for simplicity the nanotube to be a ballistic material. However, in reality the phonon scattering mechanism exists also in nanotubes, of course, and can generally not be neglected, except in very short nanotubes. In this work, we focus attention on exploring the steady-state electron transport properties of semiconducting single-walled carbon nanotubes, including both phonon scattering and defect (vacancy) scattering, using the semi-classical bulk single electron Monte Carlo method.

The electron energy dispersion relations are obtained by applying the zone folding technique to the dispersion relations of graphene, which are calculated using the tight-binding description. The vibrational modes in the carbon nanotubes are studied using a fourth nearest-neighbour force constant model. Both the electron-phonon and the electron-defect interactions are formulated within the tight-binding framework, and their corresponding scattering rates are computed and analyzed. In particular, the dependence of the phonon scattering rate and the defect scattering rate on the diameter of the nanotube, on temperature and on electron energy is studied. It is shown that the differences observed in the scattering rate between different nanotubes mainly stem from the differences in their band structure.

A bulk single electron Monte Carlo simulator was developed to study the electron transport in semiconducting zigzag carbon nanotubes. As a first step, we included only electron-phonon scattering, neglecting all other possible scattering mechanisms. With this scattering mechanism, the steady-state drift velocity and the mobility for the nanotubes (8,0), (10,0), (11,0), (13,0) and (25,0) were calculated as functions of the electric-field strength and lattice temperature, and the results are presented and analysed here. The dependence of the mobility on the lattice temperature can be clearly seen at low electric-field strengths. At such electric-field strengths, the scattering is almost entirely due to acoustic phonons, whereas at high electric-field strengths optical phonon emission processes dominate. It is shown that the saturation of the steady-state drift velocity at high electric-field strengths is due to the emission of high-energy optical phonons. The results indicate the presence of Negative differential resistance for some of the nanotubes considered in this work. The discrepancy found in the literature concerning the physical reason for the appearance of negative differential resistance is clarified, and a new explanation is proposed. It is also observed that the backward scattering is dominant over the forward scattering at high electric-field strengths.

We then included also defect scattering, actually electron-vacancy scattering, for the nanotubes (10,0) and (13,0). The steady-state drift velocities for these nanotubes are calculated as functions of the density of vacancies, electric-field strength and the lattice temperature, using three different vacancy concentrations. The results indicate the presence of Negative differential resistance at very low concentration of defects, and how this feature may depend on the concentration of defects. The dependence of the steady-state drift velocity on the concentration of defect and the lattice temperature is discussed. The electron distribution functions for different temperatures and electric field strengths are also calculated and investigated for all the semiconducting nanotubes considered here. In particular, a steep barrier found in the electron distribution function is attributed to the emission of high energy optical phonons.

• 25.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Tight-binding calculations of electron scattering rates in semiconducting zigzag carbon nanotubes2011Licentiate thesis, comprehensive summary (Other academic)

The technological interest in a material depends very much on its electrical, magnetic, optical and/or mechanical properties. In carbon nanotubes the atoms form a cylindrical structure with a diameter of the order 1 nm, but the nanotubes can be up to several hundred micrometers in length. This makes carbon nanotubes a remarkable model for one-dimensional systems. A lot of efforts have been dedicated to manufacturing carbon nanotubes, which is expected to be the material for the next generation of devices. Despite all the attention that carbon nanotubes have received from the scientific community, only rather limited progress has been made in the theoretical understanding of their physical properties. In this work, we attempt to provide an understanding of the electron-phonon and electron-defect interactions in semiconducting zigzag carbon nanotubes using a tight-binding approach. The electronic energy dispersion relations are calculated by applying the zone-folding technique to the dispersion relations of graphene. A fourth-nearest-neighbour force constant model has been applied to study the vibrational modes in the carbon nanotubes. Both the electron-phonon interaction and the electron-defect interaction are formulated within the tight-binding approximation, and analyzed in terms of their quantum mechanical scattering rates. Apart from the scattering rates, their components in terms of phonon absorption, phonon emission, backscattering and forward scattering have been determined and analyzed. The scattering rates for (5,0), (7,0), (10,0), (13,0) and (25,0) carbon nanotubes at room temperature and at 10K are presented and discussed. The phonon scattering rate is dependent on the lattice temperature in the interval 0-0.17 eV. We find that backscattering and phonon emission are dominant over forward scattering and phonon absorption in most of the energy interval. However, forward scattering and phonon absorption can be comparable to backscattering and phonon emission in limited energy intervals. The phonon modes associated with each peak in the electron-phonon scattering rates have been identified, and the similarities in the phonon scattering rates between different nanotubes are discussed. The dependence of the defect scattering rate on the tube diameter is similar to that of the phonon scattering rate. Both the phonon and the defect scattering rates show strong dependence on the tube diameter (i.e., the scattering rate decreases as a function of the index of the nanotube). It is observed that the backscattering and forward scattering for electrons interacting with defects occur with same frequency at all energies, in sharp contrast to the situation for phonon scattering. It is demonstrated that the differences in the scattering rate between different tubes are mainly due to the differences in their band structures.

• 26.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Electron-phonon and electron-defect scattering rates in semiconducting zigzag carbon nanotubes2010In: Proceedings - 2010 8th International Vacuum Electron Sources Conference and Nanocarbon, IVESC 2010 and NANOcarbon 2010, IEEE conference proceedings, 2010, p. 282-283Conference paper (Refereed)

The electron transport properties of single walled carbon nanotubes are of fundamental importance for the development of carbon based nanotechnology. Carbon nanotubes can display both chemical and structural defects, which affect electronic states near the Fermi level. This is further complicated by the fact that the concentration of defects depends upon the method of synthesis. In this work, we have investigated both electron-phonon and electron-defect scattering in semiconducting zigzag carbon nanotubes by calculating and analyzing the quantum-mechanical scattering rates for these processes. One objective of this work is to give a theoretical limit for the concentration of defects at which electron-defect scattering rates would be comparable to the electron-phonon scattering rates.

• 27.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Electron-Phonon and electron-defect Scattering Rates in Semiconducting Zig-Zag Carbon Nanotubes2012In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 9, no 1, p. 22-25Article in journal (Refereed)

Electron-phonon and electron-defect scattering rates have been calculated within a tight-binding approach for semiconducting zigzag carbon nanotubes. The scattering rates for (5,0), (7,0), (10,0), (13,0) and (25,0) nanotubes have been investigated. The electron-phonon scattering rate shows both diameter and temperature dependence, and the dependence of the electron-defect scattering rate on nanotube diameter is similar to that of the electron-phonon scattering rate. Backscattering and forward scattering for electrons interacting with defects occur with equal probability at all energies. The importance of electron-defect scattering relative to electron-phonon scattering depends very much on the energy of the electron.

• 28.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Electron-phonon scattering rates in semiconducting zigzag carbon nanotubes2011In: Journal of Computational and Theoretical Nanoscience, ISSN 1546-1955, Vol. 8, no 9, p. 1694-1702Article in journal (Refereed)

The energy dependence of the scattering rate for electrons interacting with phonons in semiconducting zig-zag carbon nanotubes has been investigated using a tight-binding method. Apart from the scattering rates, their components in terms of phonon emission, phonon absorption, backscattering and forward scattering have been determined. Results for (7, 0), (10, 0), (13, 0) and (25, 0) nanotubes at both room temperature and at 10K are presented and discussed. It is demonstrated that backscattering of the electron generally is more likely than forward scattering, and that phonon absorption can be comparable to, or even more important than, phonon emission in limited energy intervals. Furthermore, the phonons responsible for the main features in the scattering rates have been identified, and the similarities in the scattering rates between different nanotubes are clarified.

• 29.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
High-field electron transport in semiconducting zigzag carbon nanotubes2012In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 23, no 26, p. 265703-265709Article in journal (Refereed)

Electron transport in semiconducting zigzag carbon nanotubes is studied by solving the Boltzmann transport equation using the single-particle Monte Carlo technique. The electronic band structure is based on a standard nearest-neighbour tight-binding parameterisation, and the phonon spectrum is calculated using a fourth nearest-neighbour force constant model. The electron-phonon scattering probabilities are calculated within a tight-binding formalism. The steady-state drift velocities for the semiconducting zigzag nanotubes (8,0), (10,0), (11,0), (13,0), and (25,0) are computed as functions of electric field strength and temperature, and the results are analysed here. The results show the presence of negative differential resistance at high electric fields for some of the nanotubes. The drift velocity and the low field mobility reach a maximum value of and, respectively, for a (25,0) nanotube.

• 30. Uesaka, Tetsu
GENERAL FORMULA FOR HYGROEXPANSION OF PAPER1994In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 29, no 9, p. 2373-2377Article in journal (Refereed)
• 31.
Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design. Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
Fluid-Structure Interactions in Random Fibre Networks2012Conference paper (Refereed)
• 32.
Durham university, UK.
Durham university, UK. Durham university, UK. Durham university, UK. Durham university, UK. Durham university, UK. Durham university, UK. Durham university, UK. Durham university, UK. Durham university, UK.
Exploring the alignment of carbon nanotubes dispersed in a liquid crystal matrix using coplanar electrodes2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 12, article id 125303Article in journal (Refereed)

We report on the use of a liquid crystalline host medium to align single-walled carbon nanotubes in an electric field using an in-plane electrode configuration. Electron microscopy reveals that the nanotubes orient in the field with a resulting increase in the DC conductivity in the field direction. Current versus voltage measurements on the composite show a nonlinear behavior, which was modelled by using single-carrier space-charge injection. The possibility of manipulating the conductivity pathways in the same sample by applying the electrical field in different (in-plane) directions has also been demonstrated. Raman spectroscopy indicates that there is an interaction between the nanotubes and the host liquid crystal molecules that goes beyond that of simple physical mixing.

• 33.
Universidade de São Paulo, Brazil . Universidade Federal de Santa Catarina, Brazil . Universidade Federal de Santa Catarina, Brazil . University of Windsor, Canada . UNESP Univ Estadual Paulista, Brazil.
Exploring copper nanostructures as highly uniform and reproducible substrates for plasmon-enhanced fluorescence2015In: The Analyst, ISSN 0003-2654, E-ISSN 1364-5528, Vol. 140, no 2, p. 476-482Article in journal (Refereed)

The unique properties of metallic nanostructures of coinage metals that can sustain localized surface plasmon resonances (LSPR) put them at the centre of plasmon-enhanced phenomena. The theory of plasmonic phenomena based on LSPR is well-established. However, the fabrication of plasmonic substrates, reproducibly, is still challenging for applications in surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF). In this work we describe well-ordered copper nanostructures (CuNSs), produced by electrodeposition and nanosphere lithography, as active substrates for SEF. After a detailed spectroscopic and microscopic characterization, CuNSs are successfully applied as SEF-active substrates using a well-known perylene derivative as a target molecule. The signal reproducibility from CuNS substrates was established by comparing the results against those obtained from a simply roughened Cu substrate. Under optimal conditions, signal variability is around 4%.

• 34.
University of São Paulo, Brazil.
UNESP, Brazil. UNESP, Brazil. University of São Paulo, Brazil. University of São Paulo, Brazil. UNESP, Brazil. University of São Paulo, Brazil.
Vibrational spectroscopy for probing molecular-level interactions in organic films mimicking biointerfaces2014In: Advances in Colloid and Interface Science, ISSN 0001-8686, E-ISSN 1873-3727, Vol. 207, no Special Issue: Helmuth Möhwald Honorary Issue, p. 199-215Article in journal (Refereed)

Investigation into nanostructured organic films has served many purposes, including the design of functionalized surfaces that may be applied in biomedical devices and tissue engineering and for studying physiological processes depending on the interaction with cell membranes. Of particular relevance are Langmuir monolayers, Langmuir-Blodgett (LB) and layer-by-layer (LbL) films used to simulate biological interfaces. In this review, we shall focus on the use of vibrational spectroscopy methods to probe molecular-level interactions at biomimetic interfaces, with special emphasis on three surface-specific techniques, namely sum frequency generation (SFG), polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and surface-enhanced Raman scattering (SERS). The two types of systems selected for exemplifying the potential of the methods are the cell membrane models and the functionalized surfaces with biomolecules. Examples will be given on how SFG and PM-IRRAS can be combined to determine the effects from biomolecules on cell membrane models, which include determination of the orientation and preservation of secondary structure. Crucial information for the action of biomolecules on model membranes has also been obtained with PM-IRRAS, as is the case of chitosan removing proteins from the membrane. SERS will be shown as promising for enabling detection limits down to the single-molecule level. The strengths and limitations of these methods will also be discussed, in addition to the prospects for the near future.

• 35.
University of São Paulo, Brazil.
Jagiellonian University, Poland. University of São Paulo, Brazil. University of São Paulo, Brazil. University of São Paulo, Brazil. University of São Paulo, Brazil. Jagiellonian University, Poland.
Semifluorinated thiols in Langmuir monolayers: A study by nonlinear and linear vibrational spectroscopies2015In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 460, p. 290-302Article in journal (Refereed)

A series of semifluorinated thiols of the general formula CmF2m+1CnH2nSH (abbr. FmHnSH) have been synthesized and characterized in Langmuir monolayers with surface pressure-area isotherms, complemented with polarization-modulated reflection absorption spectroscopy (PM-IRRAS) and sum-frequency generation (SFG) techniques. A comparative analysis was performed for compounds having the same length of fluorinated segment (F-10) and variable length of the hydrogenated part (H-6, H-10, H-12), and having identical hydrogenated segment (H-12) connected to a fluorinated moiety of different lengths (F-6, F-8, F10). For the sake of comparison, an alkanethiol (H18SH) was also examined, and F10H10COOH and F10H10OH molecules were used for helping the assignment of SFG spectra of CH stretches. SFG was applied to investigate the hydrocarbon chain and the terminal CF3 group, while PM-IRRAS was used to probe CF2 groups. The number of gauche defects in the hydrocarbon chain increased with the increasing length of the molecule, either by elongation of the hydrogenated or perflu-orinated part. SFG measurements recorded at three polarization combinations (ppp, ssp, sps) enabled us to estimate the tilt angle of the terminal CF3 group in semifluorinated thiol molecules as ranging from 35 to 45, which is consistent with nearly vertical fluorinated segments. Upon increasing the surface pressure, the fluorinated segment gets slightly more upright, but the hydrocarbon chain tilt increases while keeping the same average number of gauche defects. The extent of disorder in the hydrogenated segment may be controlled by varying the size of the fluorinated segment, and this could be exploited for designing functionalized surfaces with insertion of other molecules in the defect region.

• 36.
Max-Planck-Institute.
Max-Planck-Institute. Max-Planck-Institute.
Surface dilational properties of mixed sodium dodecyl sulfate/dodecanol solutions2003In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 221, no 1-3, p. 185-195Article in journal (Refereed)

The surface dilatational properties of aqueous solutions of sodium dodecyl sulfate (SDS) and n-dodecanol areinvestigated in the frequency range 15/f5/500 Hz using the oscillating bubble method. The results demonstrate that apure dodecanol solution has an elastic surface without viscous effect whereas the surface of a SDS solution withoutadded dodecanol exhibits a strong viscoelastic behavior. Mixtures show graduated properties. The time behavior oftheir surface dilatational moduli demonstrates that dodecanol molecules drive the SDS molecules slowly out of thesurface. Therefore, the known one-component model describing the surface dilatational modulus can be used also forthese mixtures. A simple theoretical consideration explains this effect.

• 37.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Thermally reduced kaolin-graphene oxide nanocomposites for gas sensing2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, p. Art. no. 7676-Article in journal (Refereed)

Highly sensitive graphene-based gas sensors can be made using large-area single layer graphene, but the cost of large-area pure graphene is high, making the simpler reduced graphene oxide (rGO) an attractive alternative. To use rGO for gas sensing, however, require a high active surface area and slightly different approach is needed. Here, we report on a simple method to produce kaolin-graphene oxide (GO) nanocomposites and an application of this nanocomposite as a gas sensor. The nanocomposite was made by binding the GO flakes to kaolin with the help of 3-Aminopropyltriethoxysilane (APTES). The GO flakes in the nanocomposite were contacting neighboring GO flakes as observed by electron microscopy. After thermal annealing, the nanocomposite become conductive as showed by sheet resistance measurements. Based on the conductance changes of the nanocomposite films, electrical gas sensing devices were made for detecting NH3 and HNO3. These devices had a higher sensitivity than thermally annealed multilayer GO films. This kaolin-GO nanocomposite might be useful in applications that require a low-cost material with large conductive surface area including the demonstrated gas sensors.

• 38.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Soap-film coating: High-speed deposition of multilayer nanofilms2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, p. Art. no. 1477-Article in journal (Refereed)

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.

• 39.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Piezoelectric gated ZnO nanowire diode studied by in situ TEM probing2014In: Nano Energy, ISSN 2211-2855, Vol. 3, p. 10-15Article in journal (Refereed)

The piezoelectricity of ZnO nanowires has shown rising interests during the last few years and fields such as piezotronics and piezophotonics are emerging with a number of applications and devices. One such device is the piezoelectric gated ZnO nanowire diode, where the p–n junction is replaced by a dynamically created potential barrier created simply by bending the otherwise homogeneously doped nanowire. To further study this type of diode we used in situ transmission electron microscope (TEM) probing, where one electrode was fixed at the end of a ZnO nanowire and another moveable electrode was used both for bending and contacting the wire. Thereby we were able to further characterise this diode and found that the diode characteristics depended on whether the contact was made to the stretched (p-type) surface or to the compressed (n-type) surface of the wire. When the neutral line of the wire contacted, between the stretched and the compressed side, the I–V characteristics were independent on the current direction. The performance of the diodes upon different bending intensity showed a rectifying ratio up to the high value of 60:1. The diode ideality factor was found to be about 5. Moreover, the reverse breakdown voltages of the diode were measured and a local but permanent damage to the diode action was found when the voltage went over the reverse breakdown voltage.

• 40.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
Recent Progress on the Fabrication and Properties of Silver Nanowire-Based Transparent Electrodes2018In: Nanomaterials, ISSN 2079-4991, Vol. 8, no 8, article id 628Article in journal (Refereed)

Transparent electrodes (TEs) made of metallic nanowires, such as Ag, Au, Cu, and Ni, are attracting increasing attention for several reasons: (1) they can act as a substitute for tin oxide-based TEs such as indium-tin oxide (ITO) and fluorine-doped tin oxide (FTO); (2) various methods exist for fabricating such TEs such as filtration, spraying, and Meyer bar coating; (3) greater compatibility with different substrates can be achieved due to the variety of fabrication methods; and (4) extra functions in addition to serving as electrodes, such as catalytic abilities, can be obtained due to the metals of which the TEs are composed. There are a large number of applications for TEs, ranging from electronics and sensors to biomedical devices. This short review is a summary of recent progress, mainly over the past five years, on silver nanowire-based TEs. The focus of the review is on theory development, mechanical, chemical, and thermal stability as well as optical properties. The many applications of TEs are outside the scope of this review.

• 41.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
High-performance transparent and flexible electrodes made by flash-light sintering of gold nanoparticles2018In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 1, no 12, p. 7191-7198Article in journal (Refereed)

Metallic nanowire-based transparent electrodes (TEs) are potential alternatives to indium tin oxide (ITO). To achieve a high performance [sheet resistance (Rs) < 100 Ω/sq, transmittance (T%) > 90%], the nanowires must have a high length-to-diameter (L/D) ratio to minimize the number of wire-to-wire junctions. Attempts to produce TEs with gold nanowires have been made, and the results reveal difficulties in achieving the requirements. A successful strategy involves creating templated gold nanonetworks through multiple procedures. Here, we present a simple and efficient method that uses flash-light sintering of a gold nanonetwork film into gold TEs (Rs: 82.9 Ω/sq, T %: 91.79%) on a thin polycarbonate film (25 μm). The produced gold TEs have excellent mechanical, electrical, optical, and chemical stabilities. Mechanisms of the formation of gold nanonetworks and the effect of flash-light have been analyzed. Our findings provide a scalable process for producing transparent and flexible gold electrodes with a total processing time of less than 8 min without the use of heating, vacuum processing, and organic chemicals and without any material loss. This is possible because all the gold nanoparticles have been aggregated and filtrated on the filter membranes. The area density of gold is 0.094 g/m2 leading low material costs, which is very competitive with the price of commercial TEs.

• 42.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
A facile one-step method for synthesising a parallelogram-shaped single-crystalline ZnO nanosheet2014In: Materials Science and Engineering: B, ISSN 0921-5107, Vol. 184, p. 1-6Article in journal (Refereed)

ZnO nanosheets are found to be useful in many fields such as sensors and electronics. Non-uniform- shaped ZnO nanosheets are synthesised using several methods; moreover, uniformly shaped ones are less studied. Here, we report on a simple one-step method to synthesise parallelogram-shaped single- crystalline ZnO nanosheets. By controlling the reaction of Zn(NO3 )2 and hexamethylenetetramine (HMT) in ethanol, average 30 nm-thick nanosheets with a high aspect ratio of 1:100 were obtained. The par- allelogram angles were between 97◦ and 99◦. Transmission electron microscopy (TEM) diffraction and X-ray diffraction (XRD) showed that the nanosheets were wurtzite-structured single-crystalline ZnO. Moreover, a growth mechanism of these parallelogram nanosheets is suggested based on the experi- mental results. These results suggest a new simple solution process to synthesise uniformly shaped ZnO nanosheets allowing large-scale production to be employed.

• 43.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Graphite-carbon nanotube flexible electrodes for dye-sensitized solar cells2014Conference paper (Refereed)

Dye-sensitized solar cell (DSSC) is a low cost and efficient way to transform solar radiation to electricity. Indium tin oxide (ITO) and fluorine doped tin oxide (FTO) coated glass are two kinds of transparent electrodes that are mostly used to fabricate DSSCs. However, these two kinds electrodes lack flexibility, limiting their development. [1] Flexible electrodes are desired in DSSC because of they are lightweight, low cost and ro田l-to-roll compatible. There are attempts to replace both [1] or one [2] of the two electrodes in DSSC. However, the efficiencies are relatively low. Here we reported a simple method to fabricate graphite-carbon nanotube (G-CNT) composited flexible electrode for using as counter electrode in DSSC. The electrodes are simple fabricated by reverse filtration and flash sintering, leading to highly flexible (360 °C) and conductive (sheet resistance, 100 Ohm/sq) electrodes that can be used as both catalyzer and current collector. The energy conversion efficiency of such electrode based DSSC can reach 2.02% with fill factor of 0.56 (Figure 1).

Figure 1. Photograph of the G-CNT composited flexible electrode, and the J-V characterization of the fabricated DSSC.

References:

[1]    W. Wang, Q. Zhang, H. Li, G. W. Wu, D. C. Zou, D. P. Yu, Adv. Funct. Mater. 2012, 22, 2775-2782.

[2]    B. Wang, L. L. Kerr, Sol. Energy Mater. Sol. Cells. 2011, 95, 2531-2535.

• 44.
Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design. Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
Simple Fabrication of Gold Nanobelts and Patterns2012In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 7, no 1, p. Art. no. e30469-Article in journal (Refereed)

Gold nanobelts are of interest in several areas; however, there are only few methods available to produce these belts. We report here on a simple evaporation induced self-assembly (EISA) method to produce porous gold nanobelts with dimensions that scale across nanometer (thickness ~80 nm) and micrometer (width ~20 μm), to decimeter (length ~0.15 m). The gold nanobelts are well packed on the beaker wall and can be easily made to float on the surface of the solution for depositing onto other substrates. Microscopy showed that gold nanobelts had a different structure on the two sides of the belt; the density of gold nanowires on one side was greater than on the other side. Electrical measurements showed that these nanobelts were sensitive to compressive or tensile forces, indicating a potential use as a strain sensor. The patterned nanobelts were further used as a template to grow ZnO nanowires for potential use in applications such as piezo-electronics. © 2012 Zhang et al.

• 45.
Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design. Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
Size and concentration controlled growth of porous gold nanofilm2012In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 209, no 3, p. 519-523Article in journal (Refereed)

At an air/water interface, diffusion-limited aggregation (DLA) of gold nanoparticles can form porous gold thin films. This porous film roughly consists of a network of irregular nanowires. For this air–water system, external parameters like temperature are well studied, while the influence of internal parameters, e.g., the size and concentration of the nanoparticles, have not been studied in detail. Here, we report on the growth of porous gold nanofilms for different nanoparticle sizes and concentrations to get a relationship between the morphology of the films and the internal parameters. The gold nanoparticles were synthesized by reducing HAuCl4 using sodium citrate. Transmission electron microscopy (TEM) characterization

showed a linear relation between the formed gold nanowires and the concentration of HAuCl4 if the concentration of sodium citrate is unchanged. A linear dependency was also found between the wire diameter and the gold nanoparticle concen- tration, and between the wire diameter and volume fraction of the nanoparticles. The electrical resistance of the films was measured, showing a linear relation between resistance and the inverse of the cross-sectional area of the nanowires. This study shows the relation between the morphology and resistance of the grown porous films and the controllable internal parameters that will be useful in further exploration of this thin-film growth method.

• 46.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Nanogenerator made of ZnO nanosheet networks2017In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 32, no 5, article id 054002Article in journal (Refereed)

The piezoelectricity of nanomaterials attracts a great deal of attention due to its broad application, including the harvesting of ambient mechanical energy to power small electronics devices. We report here a simple method to fabricate piezoelectric nanogenerators consisting of networks of ZnO nanosheets grown on aluminum (Al) foils, where the Al acts as both a substrate for growth and as an electrode contacting the ZnO network. A second, top electrode was tapped, rolled, or rubbed against the ZnO to generate piezoelectricity. This second electrode was either a copper foil or fluorine doped tin oxide (FTO) glass. A piezo voltage of up to 0.924 V was detected during rolling and 6 μA was the highest current observed when rubbing the ZnO film with a FTO glass. Due to its simplicity, this nanogenerator fabrication method has the potential to be scaled up for the industrial production of piezoelectric energy harvesting devices.

• 47.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
Magnetic Nanoparticles in Biomedical Applications2011In: OMICS: Biomedical Perspectives and Applications / [ed] Debmalya Barh, Kenneth Blum, Margaret A. Madigan, CRC Press, 2011, 1Chapter in book (Refereed)
• 48.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Porous Gold Films: A Short Review on Recent Progress2014In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 7, p. 3834-3854Article, review/survey (Refereed)

Porous gold films have attracted increasing interest over the last ten years due to the unique properties of high specific surface area and electrical conductivity combined with chemical stability and ability to alter the surface chemistry. Several methods have been developed to synthesize porous gold films such as de-alloying, templating, electrochemical, and self-assembling. These porous gold films are used in diverse fields, for example, as electrochemical and Raman sensors or for chemical catalysis. Here, we provide a short review on the progress of porous gold films over the past ten years, including the synthesis and applications of such films.

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