Gunther Andersson

Publications (17)53.31 Total impact

• Article: Role of zinc oxide thickness on the photovoltaic performance of laminated organic bulk-heterojunction solar cells

  Anirudh Sharma, Mihail Ionescu, Gunther Andersson, David Lewis
  Solar Energy Materials and Solar Cells 08/2013; · 4.54 Impact Factor
• Article: Surface structure of a "non-amphiphilic" protic ionic liquid.

  Deborah Wakeham, Petru Niga, Christiaan Ridings, Gunther Andersson, Andrew Nelson, Gregory G Warr, Steven Baldelli, Mark W Rutland, Rob Atkin
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  ABSTRACT: The nanostructure of the ethanolammonium nitrate (EtAN)-air surface has been investigated using X-ray reflectometry (XRR), vibrational sum frequency spectroscopy (VSFS) and neutral impact collision ion scattering spectroscopy (NICISS). The XRR data decays more rapidly than expected for a perfectly sharp interface, indicating a diffuse electron (scattering length) density profile. Modelling of the XRR data using three different fitting routines produced consistent interfacial profiles that suggest the formation of interfacial EtAN clusters. Consistent with this, VSFS reveals that the EtAN surface is predominantly covered by -CH(2)- moieties, with the -NH(3)(+) and -OH groups of the cation buried slightly deeper in the interface. The elemental profiles determined using NICISS also show enrichment of carbon relative to nitrogen and oxygen in the outermost surface layer, which is consistent with the surface cation orientation deduced from VSFS, and with the presence of EtAN aggregates at the liquid surface.
  Physical Chemistry Chemical Physics 01/2012; 14(15):5106-14. · 3.57 Impact Factor
• Source

  Available from: Vera Lockett

  Article: Significant changes of the charge distribution at the surface of an ionic liquid due to the presence of small amounts of water.

  Christiaan Ridings, Vera Lockett, Gunther Andersson
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  ABSTRACT: The influence of small amounts of water dissolved in 1-hexyl-3-methylimidazolium chloride ([C(6)mim][Cl]) on the composition of the surface of the ionic liquid is investigated with the depth profiling technique neutral impact collision ion scattering spectroscopy. The concentration depth profiles of the elements in the sample were determined at three different water concentrations and show that small amounts of water affect the charge distribution in the ionic liquid along the surface normal. At low water concentrations (2500 ppm) the cation shows a strong presence at the surface with the alkyl chains oriented towards the gas phase, followed by a layer of anions below the alkyl chains of the cation. At higher water content (6000 to 10,000 ppm) the chloride anion shows an increased concentration at the ionic liquid surface while the alkyl chains move towards the bulk showing that the surface charge becomes more negative with increasing water content. The effect is attributed to the influence of water on the hydrogen bonding network in the ionic liquid.
  Physical Chemistry Chemical Physics 12/2011; 13(48):21301-7. · 3.57 Impact Factor
• Article: Effect of indium and tin contamination on the efficiency and electronic properties of organic bulk hetero-junction solar cells

  Anirudh Sharma, Scott E. Watkins, David A. Lewis, Gunther Andersson
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  ABSTRACT: Organic photovoltaic devices using an electrode of indiumtin oxide (ITO) coated with a buffer layer of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) exposed to controlled humidity during fabrication showed a 65–75% decrease in efficiency and displayed S-shaped J–V curves, changes, which are attributed to different levels of indium and tin migration into the PEDOT:PSS film. A distinct shift in the secondary electron cut-off in the UV Photoelectron spectra (UPS) of ITO/PEDOT:PSS samples exposed to controlled humidity indicate an increase of the dipole at the ITO/PEDOT:PSS interface, which could explain the appearance of S-shaped J–V curves. Additionally, the electron density at low binding energies is reduced for the humidity exposed PEDOT:PSS suggesting a second mechanism for decreased device performance.
  Solar Energy Materials and Solar Cells 12/2011; 95(12):3251. · 4.54 Impact Factor
• Article: A layered structure at the surface of P3HT/PCBM blends.

  Natalya Schmerl, Gunther Andersson
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  ABSTRACT: In an organic photovoltaic device, a layer consisting of two organic compounds, one functioning as an electron acceptor and the other as an electron donor, is sandwiched between two electrodes. Sufficient concentration of the electron acceptor is required at the interface to the low work function electrode as well as sufficient concentration of the electron donor at the interface to the high work function electrode. Frequently used compounds are poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM). It is reported in the literature that blends of these materials show a gradient throughout the polymer layer within devices due to phase separation. The direction of the gradient is dependent on the surface energy of the substrates onto which the polymer solutions are spincoated. This is assumed to be detrimental in the usual device structure of photovoltaic devices. In this report the surface of the blend was studied with a combination of a depth profiling technique sensitive for elemental composition and two electron spectroscopy techniques differing in their surface sensitivity. After spin coating, a thin layer of PCBM with a thickness of approximately a single monolayer was found just below the blend surface. The implication for organic photovoltaic devices is discussed.
  Physical Chemistry Chemical Physics 09/2011; 13(33):14993-5002. · 3.57 Impact Factor
• Article: Effect of the aliphatic chain length on electrical double layer formation at the liquid/vacuum interface in the [C(n)mim][BF4] ionic liquid series.

  Christiaan Ridings, Vera Lockett, Gunther Andersson
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  ABSTRACT: Neutral impact collision ion scattering spectroscopy (NICISS) was used to determine the surface structure of three ionic liquids, 1-hexyl-3-methylimidazolium [C(6)mim], 1-octyl-3-methylimidazolium [C(8)mim], 1-decyl-3-methylimidazolium [C(10)mim] tetrafluoroborates [BF(4)]. Concentration depth profiles of the elements in an ionic liquid (IL) homologous series with a common anion were obtained. We show that separation between the oppositely charged ions is seen for all three ionic liquids, resulting in an electrical double layer formation. The surface charge shifts from more positive to more negative with increasing aliphatic chain length.
  Physical Chemistry Chemical Physics 08/2011; 13(38):17177-84. · 3.57 Impact Factor
• Article: Role of humidity on indium and tin migration in organic photovoltaic devices.

  Anirudh Sharma, Gunther Andersson, David A Lewis
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  ABSTRACT: The stability of a common interface used in organic photovoltaic cells, between the transparent electrode of Indium Tin Oxide (ITO) and a buffer layer of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) is strongly influenced by the presence of humidity during processing, leading to significant migration of indium and tin species into the PEDOT:PSS layer. The interface was studied using neutral impact collision ion scattering spectroscopy (NICISS) and X-ray photoelectron spectroscopy (XPS), to determine migration of indium and tin into the polymer layer. It was found that the migration starts almost instantly after spin coating of the aqueous PEDOT:PSS solution and it reaches a saturation level within twenty four hours. The indium and tin were found always uniformly distributed over the sampling depth of almost one-third of the thickness of the PEDOT:PSS layer. Exposure to humidity following annealing resulted in the highest concentration (1.8 × 10(-3) mol cm(-3)) of indium or tin species, corresponding to about one indium or tin moiety per 4.7 monomer units in the PEDOT:PSS. The maximum bulk concentration of indium is about two orders of magnitude higher after exposure to humid conditions compared to vacuum dried conditions. XPS measurements confirm the presence of both indium and tin in the PEDOT:PSS and the formation of salts with the metal ions as cations.
  Physical Chemistry Chemical Physics 03/2011; 13(10):4381-7. · 3.57 Impact Factor
• Article: Molecular scale characterization of the titania-dye-solvent interface in dye-sensitized solar cells.

  Philip Marquet, Gunther Andersson, Alan Snedden, Lars Kloo, Rob Atkin
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  ABSTRACT: Charge separation at the dye/titania interface in dye sensitized solar cells is strongly influenced by the thickness and homogeneity of the sensitizing dye layer, as this controls the potential drop across the interface, and the probability of an excited electron being transferred from the dye to the titania. In this study we use atomic force microscopy and the depth profiling method neutral impact collision ion scattering spectroscopy (NICISS) to investigate the thickness and homogeneity of N719 dye adsorbed to titania before and after rinsing with pure acetonitrile. Both experimental methods show that the dye layers are closed but inhomogeneous. Inhomogeneity is more pronounced for unrinsed samples.
  Langmuir 03/2010; 26(12):9612-6. · 4.19 Impact Factor
• Article: Electron Energy Loss spectroscopy of Liquid Glycerol

  Thomas Krebs, Gunther Andersson, Harald Morgner
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  ABSTRACT: The inelastic scattering of low energy electrons from liquid glycerol has been studied. For the first time, electron energy loss spectra of liquids are sufficiently well resolved to permit the identification of vibrations corresponding to individual bonds, namely the C–H and O–H stretching vibrations in glycerol. The angular distribution of the specular peak is very broad, indicating the absence of long-range order at the surface of the liquid. The measurement of the loss signals as a function of the primary electron energy suggests a hybrid mechanism of excitation. The excitation mechanism for the O–H vibration has a stronger impact character as compared to the C–H vibration. A negative ion resonance of glycerol is found at a primary energy of 8 eV. The signal intensities measured as a function of the specular angle of the electron beam appear to be influenced by the angular dependence of the dipole and impact scattering cross-section and a possible preferred orientation of the C–H and O–H groups at the surface of the liquid.
  Chemical Physics. 08/2007; 340:181-186.
• Source

  Available from: Thomas Krebs

  Article: Increased layer interdiffusion in polyelectrolyte films upon annealing in water and aqueous salt solutions.

  Thomas Krebs, Hazel L Tan, Gunther Andersson, Harald Morgner, P Gregory Van Patten
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  ABSTRACT: As-deposited films of multilayered polyelectrolytes are considered to be non-equilibrium structures. Due to the strong attraction between oppositely charged polyions, polyelectrolyte interdiffusion is thought to be suppressed during the adsorption process. Equilibration is promoted by a decrease of the electrostatic attraction between polyion pairs. We have used neutral impact collision ion scattering spectroscopy to investigate the influence of polyelectrolyte multilayer annealing in water and aqueous 1 M NaCl solutions at different temperatures (20 and 70 degrees C) on the increase in interpenetration of a single polyelectrolyte layer throughout the whole film. The multilayers were composed of poly(4-vinylpyridinium) and poly(4-styrenesulfonate). Contrast between neighboring layers was established by labelling the layer in question with the heavy atom ruthenium. It is found that both temperature and salt increase layer interpenetration, whereas salt has a stronger influence than temperature. From numerical simulations polyelectrolyte diffusion coefficients were evaluated for the different annealing conditions. The influence of temperature and salt on the equilibration of the film is interpreted in terms of increased screening of polyion charges and binding of small counterions to polyion monomeric units.
  Physical Chemistry Chemical Physics 01/2007; 8(46):5462-8. · 3.57 Impact Factor
• Article: Chemical potential of a nonionic surfactant in solution.

  Thomas Krebs, Gunther Andersson, Harald Morgner
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  ABSTRACT: The chemical potential of a surfactant in solution can be calculated from the Gibbs adsorption equation when the surface excess of the surfactant and the surface tension of the solution as a function of surfactant concentration are known. We have investigated a solution of the nonionic surfactant 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in the polar solvent 3-hydroxypropionitrile at concentrations below and above the critical micelle concentration (cmc). Neutral impact collision ion scattering spectroscopy was applied for the direct measurement of the surface excess of POPC as a function of concentration. The Gibbs adsorption equation was applied in conjunction with surface tension measurements to evaluate the chemical potential and the activity coefficients of POPC, respectively. We find that the solution shows ideal behavior up to the cmc and that the chemical potential remains constant at concentrations larger than the cmc.
  The Journal of Physical Chemistry B 12/2006; 110(47):24015-20. · 3.70 Impact Factor
• Source

  Available from: flinders.edu.au

  Article: Angle resolved ion scattering spectroscopy at surfaces of pure liquids: topography and orientation of molecules.

  Gunther Andersson
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  ABSTRACT: The topography of a liquid surface has not been the subject of experimental research because of a lack of experimental methods. The hereby outlined investigation shows how the topography of a liquid surface can be classified through the angular mode of neutral impact collision ion scattering spectroscopy. It further shows how concentration depth profiles with a high depth resolution are gained. These can be used as the basis to determine quantitatively the orientation of molecules. The substances investigated are the polar solvents formamide and benzyl alcohol.
  Physical Chemistry Chemical Physics 09/2005; 7(15):2942-7. · 3.57 Impact Factor
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  Available from: Thomas Krebs

  Article: Angle resolved ion scattering spectroscopy reveals the local topography around atoms in a liquid surface.

  Gunther Andersson, Thomas Krebs, Harald Morgner
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  ABSTRACT: Neutral impact collision ion scattering spectroscopy under normal incidence is known to yield the concentration depth profiles of all elements except hydrogen at the surface of liquids and other amorphous material. In the evaluation of the data one tactically has to assume that the top surface layer and the adjacent layers are laterally homogeneous. In the present paper we establish that the angular resolved mode of this spectroscopy is able to test with high accuracy whether the lateral homogeneity is valid and-if this is not the case-in which way the top layer is structured. In particular, it is possible to map out the local environment of selected atoms. We expect that this so far inaccessible information on the local topography at liquid surfaces will have an impact on the understanding of reactions at the gas/liquid interface.
  Physical Chemistry Chemical Physics 09/2005; 7(15):2948-54. · 3.57 Impact Factor
• Article: Internal structure of polyelectrolyte multilayers probed via neutral impact collision ion scattering spectroscopy.

  Hazel L Tan, Thomas Krebs, Gunther Andersson, David Neff, Michael Norton, Harald Morgner, P Gregory Van Patten
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  ABSTRACT: Layering in polyelectrolyte multilayer films has been studied by neutral impact collision ion scattering spectroscopy. The method affords a direct look at vertical ordering within these films at the nanometer scale. By labeling certain polyelectrolyte layers with heavy atom (Ru) probes, sufficient contrast has been obtained to visualize and quantify the distribution of these labeled polyelectrolytes throughout the film. The results indicate that the materials under investigation here produce linear film growth with very limited layer interpenetration. The interdigitation length between neighboring layers within the film is measured as 3.9 nm, which is approximately 1.4 times the thickness of an individual polycation/polyanion pair and is slightly less than the measured air/film roughness (4.7 nm). Detailed analysis shows that under the conditions used and at the depths probed in this study, the observed layer thickness is not significantly broadened by either instrumental or stochastic factors.
  Langmuir 04/2005; 21(6):2598-604. · 4.19 Impact Factor
• Source

  Available from: Thomas Krebs

  Article: Activity of surface active substances determined from their surface excess.

  Gunther Andersson, Thomas Krebs, Harald Morgner
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  ABSTRACT: Commonly, the surface excess is determined from surface tension measurements via the Gibbs equation. This equation relates the activity (chemical potential), the surface excess, and the surface tension. When knowing two out of the three quantities, the third one can be calculated. Unfortunately, in the case of surface active components the concentration is in most cases too low to determine the activity from a measurable change in the bulk properties and thus assumptions are made about the activity coefficients. However, if the surface excess is measured directly and the surface tension is known, the activity can be determined making use of the Gibbs equation. The surface excess is the quantity of a surfactant solution which changes most strongly with the concentration. Thus it is obvious that this procedure should be used to determine activity coefficients of surfactants. One of the few techniques for determining the surface excess directly is neutral impact collision ion scattering spectroscopy (NICISS). With NICISS concentration depth profiles can be measured in the surface near region with a depth resolution of a few angströms. The surface excess and the activities are investigated here for the system tetrabutylphosphonium bromide (Bu4PBr) dissolved in the polar solvent formamide.
  Physical Chemistry Chemical Physics 01/2005; 7(1):136-42. · 3.57 Impact Factor
• Article: Effect of indium and tin contamination on the efficiency and electronic properties of organic bulk hetero-junction solar cells

  Anirudh Sharma, Scott E. Watkins, David A. Lewis, Gunther Andersson
  Solar Energy Materials and Solar Cells. 95(12):3251-3255.
• Article: Energy-loss straggling of helium projectiles at low kinetic energies: Deconvolution of concentration depth profiles of inorganic salt solutes in aqueous solutions

  Gunther Andersson, Harald Morgner, Hartwig Pohl
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  ABSTRACT: Neutral impact collision ion scattering spectroscopy allows to determine concentration depth profiles. The method makes use of the energy loss of projectiles passing through matter to gain the depth information. The energy losses of the projectiles obey a statistical distribution, the energy-loss straggling. The energy-loss spectra are mainly given by the energy-loss straggling and the concentration depth profiles. Knowing the energy-loss straggling quantitatively makes it possible to deconvolute the energy-loss spectra. Here we use the Poisson distribution to describe the energy-loss straggling. The Poisson distribution and a previously developed method are used to deconvolute the energy-loss spectra of iodide of aqueous LiI solutions with concentrations between 5 and 7.2m. The iodide concentration depth profiles of these highly concentrated solutions are monotonous and do not show a local maximum near the surface.
  Phys. Rev. A. 78(3).