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  • 1.
    Annamalai, Alagappan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sandström, Robin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Muehlbacher, Inge
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Double donor Sb5+doped hematite (Fe3+) photoanodes for surface-enhanced PEC water splitting2018In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 256Article in journal (Other academic)
  • 2.
    Annamalai, Alagappan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sandström, Robin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mühlbacher, Inge
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Influence of Sb5+ as a Double Donor on Hematite (Fe3+) Photoanodes for Surface-Enhanced Photoelectrochemical Water Oxidation2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 19, p. 16467-16473Article in journal (Refereed)
    Abstract [en]

    To exploit the full potential of hematite (α-Fe2O3) as an efficient photoanode for water oxidation, the redox processes occurring at the Fe2O3/electrolyte interface need to be studied in greater detail. Ex situ doping is an excellent technique to introduce dopants onto the photoanode surface and to modify the photoanode/electrolyte interface. In this context, we selected antimony (Sb5+) as the ex situ dopant because it is an effective electron donor and reduces recombination effects and concurrently utilize the possibility to tuning the surface charge and wettability. In the presence of Sb5+ states in Sb-doped Fe2O3 photoanodes, as confirmed by X-ray photoelectron spectroscopy, we observed a 10-fold increase in carrier concentration (1.1 × 1020 vs 1.3 × 1019 cm–3) and decreased photoanode/electrolyte charge transfer resistance (∼990 vs ∼3700 Ω). Furthermore, a broad range of surface characterization techniques such as Fourier-transform infrared spectroscopy, ζ-potential, and contact angle measurements reveal that changes in the surface hydroxyl groups following the ex situ doping also have an effect on the water splitting capability. Theoretical calculations suggest that Sb5+ can activate multiple Fe3+ ions simultaneously, in addition to increasing the surface charge and enhancing the electron/hole transport properties. To a greater extent, the Sb5+- surface-doped determines the interfacial properties of electrochemical charge transfer, leading to an efficient water oxidation mechanism.

  • 3.
    Barbero, David
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    SWNT networks art cover2014Other (Other (popular science, discussion, etc.))
  • 4.
    Barbero, David
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Carbon nanotube networks: nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading2014In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 26, no 19, p. 3164-Article in journal (Refereed)
    Abstract [en]

    Arrays of nano-engineered carbon nanotube networks embedded in nanoscale polymer structures enable highly efficient charge transport as demonstrated by D. R. Barbero and co-workers on page 3111. An increase in charge transport by several orders of magnitude is recorded at low nanotube loading compared to traditional random networks in either insulating (polystyrene) or semiconducting (polythiophene) polymers. These novel networks are expected to enhance the performance of next generation hybrid and carbon based photovoltaic devices.

  • 5.
    Barbero, David
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading2014In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 26, no 19, p. 3111-3117Article in journal (Refereed)
    Abstract [en]

    We demonstrate a simple and controllable method to form periodic arrays of highly conductive nano-engineered single wall carbon nanotube networks from solution. These networks increase the conductivity of a polymer composite by as much as eight orders of magnitude compared to a traditional random network. These nano-engineered networks are demonstrated in both polystyrene and polythiophene polymers.

  • 6.
    Barbero, David R.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ultralow Percolation Threshold in Nanoconfined Domains2017In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 11, no 10, p. 9906-9913Article in journal (Refereed)
    Abstract [en]

    Self-assembled percolated networks play an important role in many advanced electronic materials and devices. In nanocarbon composites, decreasing the percolation threshold phi(c) is of paramount importance to reduce nanotube bundling, minimize material resources and costs, and enhance charge transport. Here we demonstrate that three-dimensional nanoconfinement in single-wall carbon nanotube/polymer nanocomposites produces a strong reduction in phi(c) reaching the lowest value ever reported in this system of phi(c) approximate to 1.8 X 10(-5) wt % and 4-5 orders of magnitude lower than the theoretical statistical percolation threshold oh phi(stat) Moreover, a change in network resistivity and electrical conduction was observed with increased confinement, and a simple resistive model is used to accurately estimate the difference in is in the confined networks. These results are explained in terms of networks' size, confinement, and tube orientation as determined by atomic force microscopy, electrical conductivity measurements, and polarized Raman spectroscopy. Our findings provide important insight into nanoscale percolated networks and should find application in electronic nanocomposites and devices.

  • 7.
    Barbero, David
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Skrypnychuk, Vasyl
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Victor
    Hilke, Michael
    Mannsfeld, Stefan
    Toney, Mike
    Improved Crystallinity and Increased Vertical Charge Transport in a P3HT Film Deposited on Single Layer  Graphene2014Conference paper (Refereed)
  • 8.
    Barzegar, Hamid Reza
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Department of Physics, University of California, Berkeley, California 94720, United States ‡ Department of Physics, Umeå University, SE-901 87 Umeå, Sweden § Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States ∥ Kavli Energy NanoSciences Institute at the University of California, Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zettl, Alex
    Department of Physics, University of California, Berkeley, California 94720, United States.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Self-assembled PCBM nanosheets: a facile route to electronic layer-on-Layer heterostructures2018In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 2, p. 1442-1447Article in journal (Refereed)
    Abstract [en]

    We report on the self-assembly of semicrystalline [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanosheets at the interface between a hydrophobic solvent and water, and utilize this opportunity for the realization of electronically active organic/organic molecular heterostructures. The self-assembled PCBM nanosheets can feature a lateral size of >1 cm2 and be transferred from the water surface to both hydrophobic and hydrophilic surfaces using facile transfer techniques. We employ a transferred single PCBM nanosheet as the active material in a field-effect transistor (FET) and verify semiconductor function by a measured electron mobility of 1.2 × 10–2 cm2 V–1 s–1 and an on–off ratio of ∼1 × 104. We further fabricate a planar organic/organic heterostructure with the p-type organic semiconductor poly(3-hexylthiophene-2,5-diyl) as the bottom layer and the n-type PCBM nanosheet as the top layer and demonstrate ambipolar FET operation with an electron mobility of 8.7 × 10–4 cm2 V–1 s–1 and a hole mobility of 3.1 × 10–4 cm2V–1 s–1.

  • 9.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Carbon nanotubes and graphene polymer composites for opto-electronic applications2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Carbon nanotubes are carbon based structures with outstanding electronical and mechanical properties. They are used in a wide range of applications, usually embedded in polymer in the form of composites, in order to affect the electronic behavior of the matrix material. However, as the nanotubes properties are directly dependent on their intrinsic structure, it is necessary to select specific nanotubes depending on the application, which can be a complicated and inefficient process. This makes it attractive to be able to reduce the amount of material used in the composites.

    In this thesis, focus is placed on the electrical properties of the composites. A simple patterning method is presented which allows the use of extremely low amounts of nanotubes in order to increase the electrical conductivity of diverse polymers such as polystyrene (PS) or poly(3-hexylthiophene) (P3HT). This method is called nanoimprint lithography and uses a flexible mold in order to pattern composite films, leading to the creation of conducting nanotube networks, resulting in vertically conducting samples (from the bottom of the film to the top of the imprinted patterns).

    In parallel, X-ray diffraction measurements have been conducted on thin P3HT polymer films. These were prepared on either silicon substrate or on graphene, and the influence of the processing conditions as well as of the substrate on the crystallinity of the polymer have been investigated. The knowledge of the crystalline structure of P3HT is of great importance as it influences its electronic properties. Establishing a link between the processing conditions and the resulting crystallinity is therefore vital in order to be able to make opto-electronic devices such as transistor or photovoltaic cells.

  • 10.
    Boulanger, Nicolas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nano-engineered Nanotube Networks for Enhanced Vertical Charge Transport at Ultralow Nanotube Loading in a P3HT Nanocomposite Film2014Conference paper (Refereed)
    Abstract [en]

    Due to their exceptional charge transport properties, single wall carbon nanotubes (SWNTs) are expected to enhance the performance of organic based photovoltaic (PV) solar cells through an ultrafast charge transfer process when placed in contact with a semiconducting organic interface such as poly-3-hexylthiophene (P3HT)1.

     

    However, in order to produce efficient charge transport through the active layer, a percolated network of interconnected tubes must be formed. Typical methods (e.g. spin-coating, drop-casting) do not form an efficient pathway for charges, and they often result in randomly organized networks and nanotube aggregates which have been shown to lower conductivity2,3.

     

    Here, we present a new concept where nanoscale nano-engineered SWNT networks are formed in a composite film made of >90% semi-conducting nanotubes in a P3HT matrix.4 These nanoscale networks result in several orders of magnitude increase in charge transport through the composite layer made of P3HT, and compared to an identical composite film simply spun or drop-cast. These nano-networks also result in a strong effective decrease of the percolation threshold, thereby offering the possibility to use much lower amounts of nanotubes in devices. We discuss these results and the mechanisms of charge transport enhancement.

    1. Stranks, S. D. ; Weisspfennig, C.; Parkinson, P.; Johnston, M. B. ; Herz, L. M. ; Nicholas, R. J.  Nano Lett. 2011, 11(1), 66–72.
    2. Nirmalraj, P. N. ; Lyons, P. E. ; Coleman, J. N. ; Boland, J. J. Nano Lett. 2009, 9(11), 3890–3895.
    3. Kymakis, E.; Amaratunga, G. A. J.  J. Appl. Phys. 2006, 99 (8), 084302.
    4. Barbero, D. R. ; Boulanger, N.; Ramstedt; M., Yu, J. , Advanced Materials 2014, 21, 3111.
  • 11.
    Boulanger, Nicolas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nanostructured networks of single wall carbon nanotubes for highly transparent, conductive, and anti-reflective flexible electrodes2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 2, article id 021116Article in journal (Refereed)
    Abstract [en]

    Highly transparent, anti-reflective, flexible, and conductive electrodes are produced by nanopatterning of a polymer composite made of single wall carbon nanotubes (SWNTs). The formation of nanostructures creates interconnected nanotubes and vertically aligned SWNT networks which greatly improves charge transport compared to a traditionally mixed composite. These electrodes moreover possess high transparency (98% at 550 nm) and good anti-reflective properties. The use of low nanotube loadings provides an economical solution to make conductive and highly transparent flexible electrodes. The process used is simple and can be easily scaled to large areas by roll to roll processes.

  • 12.
    Boulanger, Nicolas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barbero, David R.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ordered and Highly Conductive Carbon Nanotube Nano-Networks in a emiconducting Polymer Film by Solution Processing2015In: Advanced Electronic Materials, ISSN 2199-160X, Vol. 1, no 5, article id 1400030Article in journal (Refereed)
  • 13.
    Boulanger, Nicolas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    SWNT nano-engineered networks strongly increase charge transport in P3HT2014In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 6, no 20, p. 11633-11636Article in journal (Refereed)
    Abstract [en]

    We demonstrate the formation of arrays of 3D nano- sized networks of interconnected single-wall carbon nanotubes (SWNT) with well defined dimensions in a poly-3- hexylthiophene (P3HT) thin film. These novel nanotube nano-networks produce efficient ohmic charge transport, even at very low nanotube loadings and low voltages. An increase in conductivity between one and two orders of magnitude is observed compared to a random network. The formation of these nano-engineered networks is compatible with large area imprinting and roll to roll processes, which makes it highly desirable for opto-electronic and energy conversion applications using carbon nanotubes.

  • 14.
    Boulanger, Nicolas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Victor
    Hilke, Michael
    Toney, Michael F.
    Barbero, David R.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Graphene induced electrical percolation enables more efficient charge transport at a hybrid organic semiconductor/graphene interface2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 6, p. 4422-4428Article in journal (Refereed)
    Abstract [en]

    Self-assembly of semiconducting polymer chains during crystallization from a liquid or melt dictates to a large degree the electronic properties of the resulting solid film. However, it is still unclear how charge transport pathways are created during crystallization. Here, we performed complementary in situ electrical measurements and synchrotron grazing incidence X-ray diffraction (GIXD), during slow cooling from the melt of highly regio-regular poly(3-hexylthiophene) (P3HT) films deposited on both graphene and on silicon. Two different charge transport mechanisms were identified, and were correlated to the difference in crystallites' orientations and overall amount of crystallites in the films on each surface as molecular self-assembly proceeded. On silicon, a weak charge transport was enabled as soon as the first edge-on lamellae formed, and further increased with the higher amount of crystallites (predominantly edge-on and randomly oriented lamellae) during cooling. On graphene however, the current remained low until a minimum amount of crystallites was reached, at which point interconnection of conducting units (face-on, randomly oriented lamellae and tie-chains) formed percolated conducting pathways across the film. This lead to a sudden rapid increase in current by approximate to 10 fold, and strongly enhanced charge transport, despite a much lower amount of crystallites than on silicon.

  • 15.
    Boulanger, Nicolas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Nano-Engineered Materials and Organic Electronics Laboratory.
    Yu, Victor
    Hilke, Michael
    Toney, Michael F.
    Barbero, David R.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Nano-Engineered Materials and Organic Electronics Laboratory.
    In situ probing of the crystallization kinetics of rr-P3HT on single layer graphene as a function of temperature2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 12, p. 8496-8503Article in journal (Refereed)
    Abstract [en]

    We studied the molecular packing and crystallization of a highly regio-regular semiconducting polymer poly(3-hexylthiophene) (P3HT) on both single layer graphene and silicon as a function of temperature, during cooling from the melt. The onset of crystallization, crystallites' size, orientation, and kinetics of formation were measured in situ by synchrotron grazing incidence X-ray diffraction (GIXD) during cooling and revealed a very different crystallization process on each surface. A favored crystalline orientation with out of plane pi-pi stacking formed at a temperature of 200 degrees C on graphene, whereas the first crystallites formed with an edge-on orientation at 185 degrees C on silicon. The crystallization of face-on lamellae revealed two surprising effects during cooling: (a) a constant low value of the pi-pi spacing below 60 degrees C; and (b) a reduction by half in the coherence length of face-on lamellae from 100 to 30 degrees C, which corresponded with the weakening of the 2nd or 3rd order of the in-plane (k00) diffraction peak. The final ratio of face-on to edge-on orientations was 40% on graphene, and 2% on silicon, revealing the very different crystallization mechanisms. These results provide a better understanding of how surfaces with different chemistries and intermolecular interactions with the polythiophene polymer chains lead to different crystallization processes and crystallites orientations for specific electronic applications.

  • 16.
    Ekspong, Joakim
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Surface activation of graphene nanoribbons for oxygen reduction reaction by nitrogen doping and defect engineering: An ab initio study2018In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 137, p. 349-357Article in journal (Refereed)
    Abstract [en]

    Introducing heteroatoms and creating structural defects on graphene is a common and rather successful strategy to transform its inert basal plane into an efficient metal-free electrocatalyst for oxygen reduction reaction (ORR). However, the intricate atomic configuration of defective graphenes difficult their optimization as ORR electrocatalysts, where not only a large density of active sites is desirable, but also excellent electrical conductivity is required. Therefore, we used density functional theory to investigate the current-voltage characteristics and the catalytic active sites towards ORR of nitrogen-doped and defective graphene by using 8 zig-zag graphene nanoribbons as model systems. Detailed ORR catalytic activity maps are created for ten different systems showing the distribution of catalytic hot spots generated by each defect. Subsequently, the use of both current-voltage characteristics and catalytic activity maps allow to exclude inefficient systems that exhibit either low electrical conductivity or have adsorption energies far from optimal. Our study highlights the importance of considering not only the interaction energy of reaction intermediates to design electrocatalysts, but also the electrical conductivity of such configurations. We believe that this work is important for future experimental studies by providing insights on the use of graphene as a catalyst towards the ORR reaction. 

  • 17.
    Iakunkov, Artem
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sun, Jinhua
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rebrikova, Anastasia
    Korobov, Mikhail
    Klechikov, Alexey
    Umeå University, Faculty of Science and Technology, Department of Physics. Department of Physics and Astronomy, Uppsala University, Uppsala, 751 20, Sweden.
    Vorobiev, Alexei
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Aleksandr V.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Swelling of graphene oxide membranes in alcohols: effects of molecule size and air ageing.2019In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, p. 11331-11337Article in journal (Refereed)
    Abstract [en]

    Swelling of Hummers graphene oxide (HGO) membranes in a set of progressively longer liquid alcohols (methanol to 1-nonanol) was studied using synchrotron radiation XRD after air ageing over prolonged periods of time. Both precursor graphite oxides and freshly prepared HGO membranes were found to swell in the whole set of nine liquid alcohols with an increase of interlayer spacing from ∼7 Å (solvent free) up to ∼26 Å (in 1-nonanol). A pronounced effect of ageing on swelling in alcohols was found for HGO membranes stored in air. The HGO membranes aged for 0.5–1.5 years show progressively slower swelling kinetics, a non-monotonic decrease of saturated swelling in some alcohols and complete disappearance of swelling for alcohol molecules larger than hexanol. Moreover, the HGO membranes stored under ambient conditions for 5 years showed a nearly complete absence of swelling in all alcohols but preserved swelling in water. In contrast, precursor graphite oxide powder showed unmodified swelling in alcohols even after 4 years of ageing. Since the swelling defines the size of permeation channels, the ageing effect is one of the important parameters which could explain the strong variation in reported filtration/separation properties of GO membranes. The time and conditions of air storage require standardization for better reproducibility of results related to performance of GO membranes in various applications. The ageing of GO membranes can be considered not only as a hindrance/degradation for certain applications, but also as a method to tune the swelling properties of HGO membranes for better selectivity in sorption of solvents and for achieving better selective permeability.

  • 18.
    Ruhal, Rohit
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Antti, Henrik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rzhepishevska, Olena
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barbero, David R.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wai, Sun Nyunt
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    A multivariate approach to correlate bacterial surface properties to biofilm formation by lipopolysaccharide mutants of Pseudomonas aeruginosa2015In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 127, no 0, p. 182-191Article in journal (Refereed)
    Abstract [en]

    Abstract Bacterial biofilms are involved in various medical infections and for this reason it is of great importance to better understand the process of biofilm formation in order to eradicate or mitigate it. It is a very complex process and a large range of variables have been suggested to influence biofilm formation. However, their internal importance is still not well understood. In the present study, a range of surface properties of Pseudomonas aeruginosa lipopolysaccharide mutants were studied in relation to biofilm formation measured in different kinds of multi-well plates and growth conditions in order to better understand the complexity of biofilm formation. Multivariate analysis was used to simultaneously evaluate the role of a range of physiochemical parameters under different conditions. Our results suggest the presence of serum inhibited biofilm formation due to changes in twitching motility. From the multivariate analysis it was observed that the most important parameters, positively correlated to biofilm formation on two types of plates, were high hydrophobicity, near neutral zeta potential and motility. Negative correlation was observed with cell aggregation, as well as formation of outer membrane vesicles and exopolysaccharides. This work shows that the complexity of biofilm formation can be better understood using a multivariate approach that can interpret and rank the importance of different factors being present simultaneously under several different environmental conditions, enabling a better understanding of this complex process.

  • 19.
    Sandström, Robin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Annamalai, Alagappan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ekspong, Joakim
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mühlbacher, Inge
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Evaluation of Fluorine and Sulfonic Acid Co-functionalized Graphene Oxide Membranes in Hydrogen Proton Exchange Membrane Fuel Cell Conditions2019In: Sustainable Energy & Fuels, ISSN 2398-4902, Vol. 3, no 7, p. 1790-1798Article in journal (Refereed)
    Abstract [en]

    The use of graphene oxide (GO) based membranes consisting of self-assembled flakes with a lamellar structure represents an intriguing strategy to spatially separate reactants while facilitating proton transport in proton exchange membranes (PEM). Here we chemically modify GO to evaluate the role of fluorine and sulfonic acid groups on the performance of H2/O2 based PEM fuel cells. Mild fluorination is achieved by the presence of hydrogen fluoride during oxidation and subsequent sulfonation resulted in fluorine and SO3- co-functionalized GO. Membrane electrode assembly performance in low temperature and moderate humidity conditions suggested that both functional groups contribute to reduced H2 crossover compared to appropriate reference membranes. Moreover, fluorine groups promoted an enhanced hydrolytic stability while contributing to prevent structural degradation after constant potential experiments whereas sulfonic acid demonstrated a stabilizing effect by preserving proton conductivity.

  • 20.
    Skrypnychuk, Vasyl
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Victor
    Hilke, Michael
    Mannsfeld, Stefan C. B.
    Toney, Michael F.
    Barbero, David R.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Enhanced Vertical Charge Transport in a Semiconducting P3HT Thin Film on Single Layer Graphene2015In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 25, no 5, p. 664-670Article in journal (Refereed)
    Abstract [en]

    The crystallization and electrical characterization of the semiconducting polymer poly(3-hexylthiophene) (P3HT) on a single layer graphene sheet is reported. Grazing incidence X-ray diffraction revealed that P3HT crystallizes with a mixture of face-on and edge-on lamellar orientations on graphene compared to mainly edge-on on a silicon substrate. Moreover, whereas ultrathin (10 nm) P3HT films form well oriented face-on and edge-on lamellae, thicker (50 nm) films form a mosaic of lamellae oriented at different angles from the graphene substrate. This mosaic of crystallites with - stacking oriented homogeneously at various angles inside the film favors the creation of a continuous pathway of interconnected crystallites, and results in a strong enhancement in vertical charge transport and charge carrier mobility in the thicker P3HT film. These results provide a better understanding of polythiophene crystallization on graphene, and should help the design of more efficient graphene based organic devices by control of the crystallinity of the semiconducting film.

  • 21.
    Skrypnychuk, Vasyl
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Victor
    Hilke, Michael
    Toney, Michael
    Barbero, David R.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Reduced crystallinity and enhanced charge transport by melt annealing of an organic semiconductor on single layer graphene2016In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 4, no 19, p. 4143-4149Article in journal (Refereed)
    Abstract [en]

    We report on the effect of the annealing temperature on the crystallization and the electrical properties of the semiconducting polymer poly(3-hexylthiophene) (P3HT) on single layer graphene. Electrical characterization showed that heating the P3HT film above the melting point (Tm) resulted in a higher vertical charge carrier mobility. Grazing incidence X-ray diffraction (GIXD) revealed that the film was actually less crystalline overall, but that it consisted of a much higher number of face-on crystallites. We moreover show that annealing above Tm removes the existing seeds still present in the film at lower temperatures and enhances face-on formation. These results provide a better understanding of the influence of the annealing temperature on polythiophene crystallization on graphene, and it shows that the annealing at higher temperature induces a more favorable crystalline orientation which enhances charge transport, despite the reduction in the overall crystallinity. These results should help in the design of more efficient graphene based organic electronic devices by controlling the crystalline morphology of the semiconducting film.

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