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  • 1.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Crystallization of P3HT Under Confinement: 2D vs 3D Nano-confinement2014Conference paper (Refereed)
    Abstract [en]

    Thin films of poly(3-hexylthiophene) (P3HT) are promising candidates for next generation of organic based electronic devices. Chain packing and crystallinity in such films have been shown to strongly affect their electronic and optical properties. Recently, confinement of thin semiconducting films have received a lot of interest, but there is still little known about the effect of nano-scale confinement and how its geometry affects crystallization in P3HT (REFS).

    Here, we present results on how the geometry of true nano-confinement (2D vs. 3D) influences crystallization and the final crystallinity in P3HT films. Thin P3HT films were either confined between two solid walls (2D), or in a three-dimensional cylinder (3D) resulting in free standing nanoscale cylinders. The films were characterized by 2D synchrotron grazing incidence X-ray diffraction (2D GIXD) and by atomic force microscopy (AFM).

    The results show a strong effect of the geometry of the confinement, and a different crystalline orientation between 2D and 3D confined films. Annealing time was also shown to strongly affect crystallinity, but in a different way compared to traditionally spun and annealed P3HT films. We discuss the effect of sample preparation, temperature and annealing time on crystallinity of P3HT in thin layers under confinement, and compare it to the crystallinity in non-confined thin films.

  • 2.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Electric Field Assisted Nano-patterning: A New Approach to Produce Ordered Arrays of High Aspect Ratio Nanostructures Inexpensively2014Conference paper (Refereed)
  • 3.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Formation of well defined 3D continuous networks of SWNTs into polystyrene and P3HT nanocomposites2012Conference paper (Other academic)
  • 4.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Formation of well defined percolated arrays of SWNTs into micropatterns of P3HT for solar cell applications2012Conference paper (Refereed)
  • 5.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lithographic Method2012Patent (Other (popular science, discussion, etc.))
  • 6.
    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 Film2014Other (Refereed)
  • 7.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Strong increase in crystallinity in thin P3HT films confined between two surfaces under applied pressure2012Conference paper (Other academic)
  • 8.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sun Seekers2014In: Pan European Networks: Science and Technology, ISSN 2049-2405, Vol. 11, p. 74-75Article in journal (Other (popular science, discussion, etc.))
  • 9.
    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.))
  • 10.
    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.

  • 11.
    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.

  • 12.
    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.

  • 13.
    Barbero, David R.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Stranks, Samuel D.
    Functional single-walled carbon nanotubes and nanoengineered networks for organic- and Perovskite-solar-cell applications2016In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 28, no 44, p. 9668-9685Article in journal (Refereed)
    Abstract [en]

    Carbon nanotubes have a variety of remarkable electronic and mechanical properties that, in principle, lend them to promising optoelectronic applications. However, the field has been plagued by heterogeneity in the distributions of synthesized tubes and uncontrolled bundling, both of which have prevented nanotubes from reaching their full potential. Here, a variety of recently demonstrated solution-processing avenues is presented, which may combat these challenges through manipulation of nanoscale structures. Recent advances in polymer-wrapping of single-walled carbon nanotubes (SWNTs) are shown, along with how the resulting nanostructures can selectively disperse tubes while also exploiting the favorable properties of the polymer, such as light-harvesting ability. New methods to controllably form nanoengineered SWNT networks with controlled nanotube placement are discussed. These nanoengineered networks decrease bundling, lower the percolation threshold, and enable a strong enhancement in charge conductivity compared to random networks, making them potentially attractive for optoelectronic applications. Finally, SWNT applications, to date, in organic and perovskite photovoltaics are reviewed, and insights as to how the aforementioned recent advancements can lead to improved device performance provided.

  • 14.
    Barbero, David
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Skrypnychuck, Vasyl
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Stella, Antonio
    Confinement effects in thin semiconducting organic films2013Conference paper (Refereed)
    Abstract [en]

    Understanding and controlling crystallite formation and orientation in thin semiconducting polymer films is paramount to building more efficient organic electronic devices for renewable energies. Indeed, chain packing and crystallization in such films determines to a large extent their electronic and optical properties [1-6]. Surprinsingly, little work has been done on the influence of confinement in semiconducting films. In this talk, we present results on the effect of confinement under applied pressure in one of the highest performing and most widely used organic semiconductor: regio-regular poly-3-hexylthiophene (rr-P3HT) thin films. We studied films with thickness ranging from ≈15-100 nm, and processed in various conditions of annealing and nano-confinement. Using X-ray diffraction techniques, atomic force microscopy (AFM) and UV vis spectroscopy we show that crystalline orientation, crystal density, kinetics and optical absorbance are affected by confinement. We expect these findings to help better understand the role of confinement on crytallization in semiconducting films, and to have strong implications for organic electronic applications and photovoltaics.

  • 15.
    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)
  • 16.
    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.
  • 17.
    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.

  • 18.
    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)
  • 19.
    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.

  • 20.
    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.

  • 21.
    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.

  • 22.
    Hakobyan, Shoghik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Barbero, David R.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Preparation of Antifouling Polymer Brushes Functionalized with Gallium Salicylidene Acylhydrazide ComplexesManuscript (preprint) (Other academic)
  • 23.
    Hakobyan, Shoghik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rzhepishevska, Olena
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Barbero, David R.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Functionalization of zwitterionic polymer brushes, do they remain antifouling?2018In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 50, no 11, p. 1001-1006Article in journal (Refereed)
    Abstract [en]

    Polymer brushes are surface coatings that can be tailored in many ways to suit specific demands including reduction of protein and bacterial fouling of biomaterials. Previously, we reported that antifouling poly (2-(methacryloxy)ethyl)dimethyl-3-sulphopropyl ammonium hydroxide) brushes dramatically reduced formation of bacterial biofilm. We hypothesized that: (1) this brush could be efficiently functionalized with a small molecule (2-oxo-2-[N-(2,4,6-trihydroxybenzylidene)-hydrazino]-acetamide, ME0163, hydrazone) and that (2) the antifouling property would remain also after functionalization. Diblock co-polymer brushes of 2-(methacryloxy)ethyl)dimethyl-3-sulphopropyl ammonium hydroxide and poly (glycidyl methacrylate) were formed by surface-initiated atom transfer radical polymerization (SI-ATRP), and the ME0163 hydrazone was covalently bound to the surface via a ring-opening reaction. Functionalization of the surfaces was followed by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and UV-Vis spectroscopy. The influence of temperature, reaction time, and reagent concentrations on the immobilization process was investigated. Surfaces with high degree of functionalization could be made in this way. However, the functionalization rendered the surface more hydrophobic, and the antifouling property of the brush was lost, thus, disproving the second of our starting hypotheses but corroborating the first.

  • 24. Kan, Zhipeng
    et al.
    Colella, Letizia
    Canesi, Eleonora V.
    Vorobiev, Alexei
    Skrypnychuk, Vasyl
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Terraneo, Giancarlo
    Barbero, David R.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bertarelli, Chiara
    MacKenzie, Roderick C. I.
    Keivanidis, Panagiotis E.
    Charge transport control via polymer polymorph modulation in ternary organic photovoltaic composites2016In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 4, no 4, p. 1195-1201Article in journal (Refereed)
    Abstract [en]

    The control on the charge transport properties of ternary organic photovoltaic P3HT : PCBM : QBT devices is enabled by modulating the distribution of P3HT polymorphs in the device photoactive layers. Negligible amounts of QBT induce striking modifications in the P3HT lamellar stacking direction, forming both densely packed and non-densely packed P3HT chains. The former reduce the charge carrier recombination rate, enabling an increased fill factor and short-circuit device photocurrent.

  • 25.
    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.

  • 26.
    Rzhepishevska, Olena
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hakobyan, Shoghik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ruhal, Rohit
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Gautrot, Julien
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    The surface charge of anti-bacterial coatings alters motility and biofilm architecture2013In: Journal of Biomaterials Science. Polymer Edition, ISSN 0920-5063, E-ISSN 1568-5624, Vol. 1, no 6, p. 589-602Article in journal (Refereed)
    Abstract [en]

    Bacterial biofilms affect many areas of human activity including food processing, transportation, public infrastructure, and most importantly healthcare. This study addresses the prevention of biofilms and shows that the surface charge of an abiotic substrate influences bacterial motility as well as the morphology and physiology of the biofilm. Grafting-from polymerisation was used to create polymer brush surfaces with different characteristics, and the development of Pseudomonas aeruginosa biofilms was followed using confocal microscopy. Interestingly, two types of biofilms developed on these surfaces: mushroom structures with high levels of cyclic diguanylate (c-di-GMP) were found on negatively charged poly (3-sulphopropylmethacrylate) (SPM) and zwitterionic poly (2-(methacryloyloxy)ethyl)dimethyl-3-sulphoproyl) ammonium hydroxide) (MEDSAH), while flat biofilms developed on glass, positively charged poly (2-(methacryloyloxy)-ethyl trimethyl ammonium chloride) (METAC), protein-repellent poly oligo(ethylene glycol methyl ether methacrylate) (POEGMA) and hydrophobic polymethylmethacrylate (PMMA). The results show that of all the surfaces studied, overall the negatively charged polymer brushes were most efficient in reducing bacterial adhesion and biofilm formation. However, the increased level of regulatory c-di-GMP in mushroom structures suggests that bacteria are capable of a quick physiological response when exposed to surfaces with varying physicochemical characteristics enabling some bacterial colonization also on negatively charged surfaces.

  • 27.
    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.

  • 28.
    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.

  • 29.
    Skrypnychuk, Vasyl
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wetzelaer, Gert-Jan A. H.
    Gordiichuk, Pavlo I.
    Mannsfeld, Stefan C. B.
    Herrmann, Andreas
    Toney, Michael F.
    Barbero, David R.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ultrahigh Mobility in an Organic Semiconductor by Vertical Chain Alignment2016In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 28, no 12, p. 2359-2366Article in journal (Refereed)
    Abstract [en]

    A method to produce highly efficient and long-range vertical charge transport is demonstrated in an undoped polythiophene thin film, with average mobilities above 3.1 cm(2) V-1 s(-1). These record high mobilities are achieved by controlled orientation of the polymer crystallites enabling the most efficient and fastest charge transport along the chain backbones and across multiple chains. The significant increase in mobility shown here may present a new route to producing faster and more efficient optoelectronic devices based on organic materials. [GRAPHICS] .

  • 30. Vorobiev, Alexei
    et al.
    Dennison, Andrew
    Chernyshov, Dmitry
    Skyrpnychuck, Vasyl
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Graphene oxide hydration and solvation: an in situ neutron reflectivity study2014In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 6, no 20, p. 12151-12156Article in journal (Refereed)
    Abstract [en]

    Graphene oxide membranes were recently suggested for applications in separation of ethanol from water using a vapor permeation method. Using isotope contrast, neutron reflectivity was applied to evaluate the amounts of solvents intercalated into a membrane from pure and binary vapors and to evaluate the selectivity of the membrane permeation. Particularly, the effect of D2O, ethanol and D2O–ethanol vapours on graphene oxide (GO) thin films (25 nm) was studied. The interlayer spacing of GO and the amount of intercalated solvents were evaluated simultaneously as a function of vapour exposure duration. The significant difference in neutron scattering length density between D2O and ethanol allows distinguishing insertion of each component of the binary mixture into the GO structure. The amount of intercalated solvent at saturation corresponds to 1.4 molecules per formula unit for pure D2O (1.4 monolayers) and 0.45 molecules per formula unit (one monolayer) for pure ethanol. This amount is in addition to H2O absorbed at ambient humidity. Exposure of the GO film to ethanol–D2O vapours results in intercalation of GO with both solvents even for high ethanol concentration. A mixed D2O–ethanol layer inserted into the GO structure is water enriched compared to the composition of vapours due to slower ethanol diffusion into GO interlayers

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