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  • 1.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fractal analysis of scanning probe microscopy images1996In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 355, no 1-3, p. 221-228Article in journal (Refereed)
    Abstract [en]

    The accuracy and precision of several algorithms, including newly developed, for calculating the fractal dimension from scanning probe microscopy images of material surfaces are investigated. The algorithms are based on the area-perimeter method, a variance method or versions of the structure function method. The latter two methods show good correspondence to computer simulated images, with known fractal dimensions, and have successfully been applied also on real images. The results show that these two methods give reliable fractal dimensions and are well suited to describe surface roughness quantitatively.

  • 2.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Scanning probe microscopy: Applications1994Licentiate thesis, comprehensive summary (Other academic)
  • 3.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Studies of plasma-facing materials and macromolecules using scanning probe microscopy1995Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main topic of this thesis is experimental analysis of material surfaces using scanning probe microscopies. These microscopes are used for characterization through high-resolution topographical imaging, but also for controlled modification of surfaces and molecules. The surface characterization includes evaluation and development of fractal methods for surface roughness determination. The term modification is used for manipulating the structures on a microscale by scraping them with a tiny tip. The major application of this technique in the present work is the analysis of effects induced by plasma-surface interactions. Such studies are fundamental in the understanding of erosion and deposition processes on the first wall in controlled fusion devices. In this work, scanning probe microscopes were for the first time used for studying such plasma-facing materials. Both the surface structure and composition have to be known in order to evaluate new wall-materials for fusion reactors. The materials studied here are graphites, SiC/Al coatings, graphite-silicon mixtures and various silicon carbide based composites. They were all exposed to plasmas, either to lowenergy deuterium plasmas and ions in laboratory experiments, or to the plasma in a socalled tokamak. The results show the usefulness of these high-resolution microscopes in the study of plasma-surface interaction. Several other surface sensitive techniques were also applied, at the home laboratories of our collaborators, the most important ones being Rutherford backscattering spectroscopy and nuclear reaction analysis. The scanning probe microscopy in combination with the ion-beam analysis made it possible to trace fine structural features on the surfaces and to measure the surface roughness. The main results are: (i) the detection of the initial stages of bubble/blister formation on CSi mixtures, SiC/AI coatings and graphites; (ii) the morphological changes and the physical properties of the silicon carbide composites; (iii) the distinction of radiation damages on different phases of multicomponent composites; (iv) the estimation of layer thickness with scanning probe microscopy; (v) the determination of the structure of codeposited layers formed during exposure in a tokamak; (vi) the uptake of deuterium by the materials. The atomic force microscope has also been used to study the human protein spectrin, and we managed to image free spectrins with molecular resolution in an almost natural environment. The elongated spectrin macromolecule was found to be 100 rim long and 5 nm broad. Indications of a substructure were observed. The force between the sensor tip and the molecules was crucial, both for sample movement, manipulation and image resolution. Therefore, the instrument was rebuilt to operate with so called tapping-mode in liquid. Preliminary results with this method on spectrin are presented.

  • 4.
    Almqvist, Nils
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bhatia, R
    Neuroscience Research Institute, University of California, Santa Barbara.
    Primbs, G
    Neuroscience Research Institute, University of California, Santa Barbara.
    Desai, N
    NutraSweet Company, Chicago.
    Banerjee, S
    Department of Chemical Engineering, University of California, Santa Barbara.
    Lal, R
    Neuroscience Research Institute, University of California, Santa Barbara.
    Elasticity and adhesion force mapping reveals real-time clustering of growth factor receptors and associated changes in local cellular rheological properties2004In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 86, no 3, p. 1753-1762Article in journal (Refereed)
    Abstract [en]

    Cell surface macromolecules such as receptors and ion channels serve as the interface link between the cytoplasm and the extracellular region. Their density, distribution, and clustering are key spatial features influencing effective and proper physical and biochemical cellular responses to many regulatory signals. In this study, the effect of plasma-membrane receptor clustering on local cell mechanics was obtained from maps of interaction forces between antibody-conjugated atomic force microscope tips and a specific receptor, a vascular endothelial growth factor (VEGF) receptor. The technique allows simultaneous measurement of the real-time motion of specific macromolecules and their effect on local rheological properties like elasticity. The clustering was stimulated by online additions of VEGF, or antibody against VEGF receptors. VEGF receptors are found to concentrate toward the cell boundaries and cluster rapidly after the online additions commence. Elasticity of regions under the clusters is found to change remarkably, with order-of-magnitude stiffness reductions and fluidity increases. The local stiffness reductions are nearly proportional to. receptor density and, being concentrated near the cell edges, provide a mechanism for cell growth and angiogenesis.

  • 5.
    Almqvist, Nils
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Delamo, Y
    Neuroscience Research Institute, University of California.
    Smith, BL
    Thomson, NH
    Laboratoire d'Océanographie Biologique (LOB).
    Bartholdson, A
    Department of Physics and Astronomy, University of Leeds.
    Lal, R
    Marine Science Institute, University of California.
    Brzezinski, M
    Neuroscience Research Institute, University of California.
    Hansma, PK
    Luleå tekniska universitet.
    Micromechanical and structural properties of a pennate diatom investigated by atomic force microscopy2001In: Journal of Microscopy, ISSN 0022-2720, E-ISSN 1365-2818, Vol. 202, no 3, p. 518-532Article in journal (Refereed)
    Abstract [en]

    The mechanisms behind natural nanofabrication of highly structured silicas are increasingly being investigated. We have explored the use of a standard Nanoscope III Multimode atomic force microscope (AFM) to study the silica shell of diatoms. The delicate structures of the shell surface of the diatom Navicula pelliculosa (Breb.) Hilse were imaged and the shell's micromechanical properties were measured semi-quantitatively with a resolution down to approximately 10 nm. The technique to measure elasticity and hardness with the AFM was demonstrated to be useable even on these hard glass-like surfaces, Different experimental configurations and evaluation methods were tested, They gave a consistent result of the shell micromechanical properties, The first results showed that the diatom shell's overall hardness and elasticity was similar to that of known silicas. However, regions with different mechanical proper ties were distinguished. The elastic modulus varied from 7 to 20 GPa, from 20 to 100 GPa and from 30 to hundreds of GPa depending on the location. In general, the hardness measurements showed similar spatial differences, The hardness values ranged from 1 to 12 GPa but one specific part of the shell was even harder. Hence, certain localized regions of the shell were significantly harder or more elastic. These regions coincide with known characteristic features and mechanisms appearing at the different stages of the shell's growth. These results show that this method serves as a complementary tool in the study of silica biomineralization, and can detect eventual crystalline phases.

  • 6.
    Almqvist, Nils
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fredriksson, Sverker
    Backman, Lars
    Imaging human erythrocyte spectrin with atomic force microscopy1994In: Micron, ISSN 0968-4328, E-ISSN 1878-4291, Vol. 25, no 3, p. 227-232Article in journal (Refereed)
    Abstract [en]

    Isolated spectrin covalently attached to a surface in a liquid environment as well as dried on mica has been studied with a contact-mode atomic force microscope. Both pyramidal and conical-type cantilever tip facets were used in the AFM. Our images show structures and give dimensions that correlate well with previous structural studies using transmission electron microscopy.

  • 7.
    Almqvist, Nils
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fredriksson, Sverker
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rubel, Marek
    Royal Institute of Technology, Physics Department, S-10405 Stockholm, Sweden.
    Emmoth, Birger
    Royal Institute of Technology, Physics Department, S-10405 Stockholm, Sweden.
    SFM and STM topographic studies of carbon-based surfaces exposed to deuterium plasma1994In: Book of abstracts: Microprobe Symposium, Vadstena, April 25-26, 1994, 1994Conference paper (Refereed)
  • 8.
    Almqvist, Nils
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Quist, Arjan P
    Mälardalen University, Department of Chemical Engineering, Box 325 SE-63105 Eskilstuna, Sweden.
    Lal, Ratnesh
    University of California, Neuroscience Research Institute, Santa Barbara, CA 93106, USA.
    Elastic properties of living cells studied by multimodal atomic force microscopy2000In: Abstract book Nordic-Baltic SPM Workshop, 2000: abstract #1, 2000Conference paper (Refereed)
  • 9.
    Almqvist, Nils
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rubel, M.
    Franconi, E.
    Surface characterization of SiC composites exposed to deuterium ions, using atomic force microscopy1995In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 201, no 1-2, p. 277-285Article in journal (Refereed)
    Abstract [en]

    We study the influence of deuterium plasma on the surface structure of SiC based composites. The substrates are silicon carbides doped with titanium diboride, aluminium nitride or graphite. A number of surface sensitive techniques are used to characterize the substrates, before and after exposure to low-energy deuterium ions, the main method being atomic force microscopy. The microscope reveals distinct morphological changes on the irradiated samples. The density and surface area of the samples probably influence the content of deuterium in the surfaces. However, this study shows that the amount of graphite aggregated on the surfaces is of crucial importance for the uptake of deuterium.

  • 10.
    Almqvist, Nils
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rubel, M.
    Physics Department - Frescati, Royal Institute of Technology, Association EURATOM-NFR.
    Fredriksson, Sverker
    Emmoth, B.
    Physics Department - Frescati, Royal Institute of Technology, Association EURATOM-NFR.
    Wienhold, P.
    Institute of Plasma Physics, Forschungszentrum Jülich, Association EURATOM-KFA.
    Ilyinsky, L.
    Institute of Electrical Engineering, St. Petersburg.
    AFM and STM characterization of surfaces exposed to high flux deuterium plasma1995In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 220-222, no 1-3, p. 917-921Article in journal (Refereed)
    Abstract [en]

    This paper reports the results of scanning tunneling (STM) and atomic force microscopy (AFM) studies of D+ irradiated graphite and graphite-silicon mixtures. The microscopes were used for studying surface topography and for measuring the surface roughness. The substrates were exposed at various temperatures (60 and 700°C) to different doses of deuterium ions in simulators of plasma - surface interactions and in the TEXTOR tokamak. Also nuclear reaction analysis (NRA) and Rutherford backscattering spectroscopy were applied for the qualitative and quantitative determination of surface composition. The initial stages of radiation damage, nanometer-sized bubbles/blisters, were found in plasma-eroded surfaces. These structures only appeared in the graphite phase on the multicomponent material. The microroughness of the surfaces was measured. We also used the AFM for probing the thickness of the plasma-modified layers. The results correlate with the presence of deuterium measured by NRA depth-profiling. Moreover, the AFM reveals the co-deposited layers formed on surfaces facing the tokamak plasma. The appearance of these layers is clearly correlated to the amount of co-deposited atoms.

  • 11.
    Almqvist, Nils
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rubel, M.
    Nannetti, C.A.
    Franconi, E.
    Fredriksson, Sverker
    Emmoth, B.
    Scanning probe microscopy and thermo-mechanical characterization of silicon carbide composites1995In: Fourth Euro-Ceramics: the proceedings of the Fourth European Ceramic Society Conference / [ed] S. Meriani; V. Sergo, Gruppo Ed. Faenza Ed. , 1995, Vol. 3, p. 361-368Conference paper (Refereed)
    Abstract [en]

    series of SiC-based composites was obtained by sintering. Since such materials are considered for fusion applications, their thermal shock resistance and behaviour under deuterium irradiation are of primary interest. Extensive bulk and surface characterisation of pure and doped (AlN, TiB2, graphite) silicon carbides treated by a deuterium plasma was carried out. The change in surface structure following irradiation is addressed, and major factors influencing deuterium retention are discussed.

  • 12.
    Almqvist, Nils
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rubel, M.
    Royal Institute of Technology, Physics Department-Frescati, Association EURATOM-NFR.
    Wienhold, P.
    Institute of Plasma Physics, Forschungszentrum Jülich, Association EURATOM-KFA.
    Fredriksson, Sverker
    Roughness determination of plasma-modified surface layers with atomic force microscopy1995In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 270, no 1-2, p. 426-430Article in journal (Refereed)
    Abstract [en]

    Graphite surfaces exposed to the deuterium plasma in the TEXTOR tokamak were characterized in detail by means of scanning probe microscopy, ion beam analysis and colorimetry methods. The aim is to study the composition and structure of thin layer deposits formed on surfaces subjected to the tokamak plasma. The surface roughness was measured and parametrized in terms of fractal dimension and scaling constant. Several different methods for the fractal analysis of plasma-exposed surfaces have been critically evaluated. The main emphasis of this paper is on the correlation between surface roughness (fractal parameters), the amount of deposited atoms and the layer thickness.

  • 13.
    Almqvist, Nils
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Thomson, Neil H.
    Smith, Bettye L.
    Stucky, Galen D.
    Morse, Daniel E.
    Hansma, Paul K.
    Methods for fabricating and characterizing a new generation of biomimetic materials1999In: Materials science & engineering. C, biomimetic materials, sensors and systems, ISSN 0928-4931, E-ISSN 1873-0191, Vol. 7, no 1, p. 37-43Article in journal (Refereed)
    Abstract [en]

    Bringing together current ideas in the fields of biomineralization and composite laminate materials, we have attempted to fabricate model materials that mimic abalone nacre through the rapid assembly of inorganic tablets, such as talc. Several physical methods were tested to aid the orientation of the talc tablets in fluid suspensions with a low percentage, 10% by dry weight, of organic binding material. The orientation of talc tablets in the synthesized composites was characterized by X-ray diffraction and scanning electron microscopy. The modulus of rupture of the materials was measured in a three-point bending test. We demonstrate that the alignment of tablets increases by the use of physical methods and from chemical surface treatment. Important factors to consider in making materials that mimic abalone nacre are discussed. Important factors to consider in making materials that mimic abalone nacre are discussed.

  • 14.
    Antzutkin, Oleg
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Norlin, N.
    Hellberg, M.
    Eriksson, P.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Leapman, R.D.
    Tycko, R.
    Petkova, A.T.
    Toth, I.
    Howes, A.P.
    Dupree, R.
    Binding of Aluminium(III)-Citrate Complexes, [Al3(H-1Cit)3(OH)]-4 and [Al3(H-1Cit)3(OH)4]-7, to Alzheimer's A-beta(1-40) Peptides: In situ Atomic Force, Electron Microscopy and Solid State 13C and 27Al NMR Studies2005In: Sixth Keele Meeting on Aluminium: Aluminium Lithosphere to Biosphere (and Back), Centro de Estudos do Ambiente e Mar, Universidade de Aveiro , 2005, p. 16-Conference paper (Other academic)
    Abstract [en]

    It is believed that Alzheimer's disease (AD) amyloid-β-peptide (Aβ) deposits contribute directly to the disease's progressive neurodegeneration. Aggregation cascade for Aβ peptides, its relevance to neurotoxicity in the course of AD, various factors modulating Aβ aggregation kinetics and experimental methods useful for these studies were recently discussed [1]. Al(III), Zn(II), Cu(II) and Fe(III) ions are often colocalized at the center of the core of Alzheimer's amyloid plaques [2] and are suggested to promote aggregation of physiological concentrations of Aβ [3]. It has also been suggested that Al can block calcium permeable putative Aβ-peptide channels in bilayer membranes [4]. Therefore studies of complexation of metal ions with Aβ-oligomers and fibrils are important in the search for the causes of and potential treatments for AD.We studied effects of highly soluble and biologically relevant aluminium(III)-citrate compounds, [Al3(H-1Cit)3(OH)]-4 and [Al3(H-1Cit)3(OH)4]-7, on the fibrillogenesis of Aβ(1-40). All resonances in 156.37 MHz 27Al and 90.52 MHz 13C MAS NMR spectra of powder Al(III)-citrate complexes were assigned. 27Al MAS NMR of dialysed samples of Aβ(1-40) co-incubated with the Al(III)-citrate complexes at different concentrations in TRIS buffer solutions, pH 7.4, shows that Al(III)-citrates bind to Aβ(1-40) as [Al3(H-1Cit)3(OH)]-4 and either accelerate ([Al3(H-1Cit)3(OH)]-4 complex) or retard ([Al3(H-1Cit)3(OH)4]-7 compound) aggregation of Aβ(1-40) as revealed by AFM. [1] ON Antzutkin, Magn. Reson. Chem. 42 (2004) 231; [2] MA Lovell et al., J. Neurol. Sci. 158 (1998) 47; Ch Exley et al., Al and Alzheimer's disease, Ch Exley (Ed)1998) 47; Ch Exley , Ch Exley (Ed) Elsevier Science, 2001, 421; [3] PW Mantyh et al., J. Neurochem. 61 (1993) 1171; [4] N Arispe et al, PNAS 90 (1993) 567.

  • 15.
    De Melo, C.
    et al.
    Université de Lorraine, CNRS, IJL, Nancy, France; Department of Materials Science and Engineering, Saarland University, Saarbrücken, Germany.
    Jullien, M.
    Université de Lorraine, CNRS, IJL, Nancy, France.
    Ghanbaja, J.
    Université de Lorraine, CNRS, IJL, Nancy, France.
    Montaigne, F.
    Université de Lorraine, CNRS, IJL, Nancy, France.
    Pierson, J.-F.
    Université de Lorraine, CNRS, IJL, Nancy, France.
    Soldera, F.
    Department of Materials Science and Engineering, Saarland University, Saarbrücken, Germany.
    Rigoni, Federica
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mücklich, F.
    Department of Materials Science and Engineering, Saarland University, Saarbrücken, Germany.
    Horwat, D.
    Université de Lorraine, CNRS, IJL, Nancy, France.
    Local Structure and Point-Defect-Dependent Area-Selective Atomic Layer Deposition Approach for Facile Synthesis of p-Cu2O/n-ZnO Segmented Nanojunctions2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 43, p. 37671-37678Article in journal (Refereed)
    Abstract [en]

    Area-selective atomic layer deposition (AS-ALD) has attracted much attention in recent years due to the possibility of achieving accurate patterns in nanoscale features, which render this technique compatible with the continuous downscaling in nanoelectronic devices. The growth selectivity is achieved by starting from different materials and results (ideally) in localized growth of a single material. We propose here a new concept, more subtle and general, in which a property of the substrate is modulated to achieve localized growth of different materials. This concept is demonstrated by selective growth of high-quality metallic Cu and semiconducting Cu2O thin films, achieved by changing the type of majority point defects in the ZnO underneath film exposed to the reactive species using a patterned bilayer structure composed of highly conductive and highly resistive areas, as confirmed by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The selective growth of these materials in a patterned ZnO/Al-doped ZnO substrate allows the fabrication of p-Cu2O/n-ZnO nanojunctions showing a nonlinear rectifying behavior typical of a p-n junction, as confirmed by conductive atomic force microscopy (C-AFM). This process expands the spectra of materials that can be grown in a selective manner by ALD and opens up the possibility of fabricating different architectures, taking advantage of the area-selective deposition. This offers a variety of opportunities in the field of transparent electronics, catalysis, and photovoltaics.

  • 16.
    de Melo, Claudia
    et al.
    Université de Lorraine, CNRS, IJL, F-54000 Nancy, France;Department of Materials Science and Engineering, Saarland University, D-66123 Saarbrücken, Germany.
    Jullien, Maud
    Université de Lorraine, CNRS, IJL, F-54000 Nancy, France.
    Battie, Yann
    LCP-A2MC, Institut Jean Barriol, Université de Lorraine, 1 Blvd. Arago, 57070 Metz, France.
    En Naciri, Aotmane
    LCP-A2MC, Institut Jean Barriol, Université de Lorraine, 1 Blvd. Arago, 57070 Metz, France.
    Ghanbaja, Jaafar
    Université de Lorraine, CNRS, IJL, F-54000 Nancy, France.
    Montaigne, François
    Université de Lorraine, CNRS, IJL, F-54000 Nancy, France.
    Pierson, Jean-François
    Université de Lorraine, CNRS, IJL, F-54000 Nancy, France.
    Rigoni, Federica
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Migot, Sylvie
    Department of Materials Science and Engineering, Saarland University, D-66123 Saarbrücken, Germany.
    Mücklich, Frank
    Department of Materials Science and Engineering, Saarland University, D-66123 Saarbrücken, Germany.
    Horwat, David
    Université de Lorraine, CNRS, IJL, F-54000 Nancy, France.
    Tunable Localized Surface Plasmon Resonance and Broadband Visible Photoresponse of Cu Nanoparticles/ZnO Surfaces2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 47, p. 40958-40965Article in journal (Refereed)
    Abstract [en]

    Plasmonic Cu nanoparticles (NP) were successfully deposited on ZnO substrates by atomic layer deposition (ALD) owing to the Volmer–Weber island growth mode. An evolution from Cu NP to continuous Cu films was observed with an increasing number of ALD cycles. Real and imaginary parts of the NP dielectric functions, determined by spectroscopic ellipsometry using an effective medium approach, evidence a localized surface plasmon resonance that can be tuned between the visible and near-infrared ranges by controlling the interparticle spacing and size of the NP. The resulting Cu NP/ZnO device shows an enhanced photoresponse under white light illumination with good responsivity values, fast response times, and stability under dark/light cycles. The significant photocurrent detected for this device is related to the hot-electron generation at the NP surface and injection into the conduction band of ZnO. The possibility of tuning the plasmon resonance together with the photoresponsivity of the device is promising in many applications related to photodetection, photonics, and photovoltaics.

  • 17.
    Dobryden, Illia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Weber, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Yang, Xiaofang
    Scanning probe microscopy study of magnetite particle force interactions in a solution2011Conference paper (Other academic)
  • 18.
    Dobryden, Illia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Potapova, Elisaveta
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Weber, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Application of AFM to probe micro- and nano-sized magnetite particle interaction in Ca2+ solution2014In: Proceedings of the International Summer School on Application of Scanning Probe Microscopy in Life Sciences, Soft Matter and Nanofabrication", Aalborg: River Publishers, 2014Conference paper (Other academic)
    Abstract [en]

    Natural magnetite is used for producing iron ore pellets, one of the raw materials in steel production. The quality of produced pellets depends on many factors, including the properties of the magnetite concentrate fed to pelletization. To be able to minimize the effect of the variations in feed properties on pellets quality, investigation of magnetite particle interaction with a focus on the surface properties is required. Atomic force microscopy (AFM), using the colloidal probe technique, is a suitable tool for measuring such particle-particle interaction in-situ. Natural particles are usually of micro-sizes (m-s) and have different sizes and shapes, which complicates an accurate investigation of particle interaction with AFM. To overcome such difficulties, synthetic nanoparticles are used instead. Process water chemistry is one of the factors affecting magnetite surface properties. Partial dissolution of calcite and apatite minerals, present in iron ore, results in high Ca2+ concentrations in the process water, which has been shown to have a major effect on the charge of the magnetite particles [1, 2]. The aim of this study was therefore to investigate forces and aggregation between magnetite particles, of micro- and nano-size (n-s), in Ca2+ solutions at various pH values. The spherical monodispersed magnetite nano-sized particles, with a diameter of approx. 10 nm, were synthesized by the precipitation technique [3]. Measurements were performed for m-s probe/m-s layer and m-s probe/n-s layer systems. Natural magnetite particles of 10-30 µm size were glued to NP-S cantilevers (Digital Instruments/Bruker, Santa Barbara, CA) with a measured spring constant of 0.12 N/m. Nano-sized particles were deposited on the glass slides by dip-coating. Roughness (Ra) of the n-s layers was measured with AFM and was about 10 nm for areas 1×1µm2, a representative high-resolution image is shown in Figure 1. Particle interaction was similar for m-s and n-s magnetite particles at pH 4 and 6. At pH 10, the interaction behavior was different due to probable surface modification of natural magnetite particles by ions from process water. The adhesion force for both interacting systems was measured, see ref. [4] for a detailed description of the results. To verify that ϛ-potential measurements could be used to predict the interaction between charged particles (in this case silica and magnetite) in solutions containing inorganic ions, force measurements between n-s magnetite layer and a SiO2 spherical probe (3.5 µm in diameter) were performed and correlated with the ϛ-potential results for these particles in the same solutions. Also, a DLVO simulation was performed to theoretically confirm the experimental interaction based on surface charge trends. An example of the simulated force curves is shown in Figure 2. The interaction between the probe and the magnetite surface was attractive at pH 4 and 6 but became repulsive at pH 8 and 10, which is in agreement with what could be expected from the ϛ-potential results for these particles.

  • 19.
    Dobryden, Illia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Potapova, Elisaveta
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Weber, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Force interactions between magnetite, silica, and bentonite studied with atomic force microscopy2015In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 42, no 4, p. 319-326Article in journal (Refereed)
    Abstract [en]

    Iron ore pellets consist of variety of mineral particles and are an important refined product used in steel manufacturing. Production of high-quality pellets requires good understanding of interactions between different constituents, such as magnetite, gangue residues, bentonite, and additives. Much research has been reported on magnetite, silica, and bentonite surface properties and their effect on pellet strength but more scant with a focus on a fundamental particle–particle interaction. To probe such particle interaction, atomic force microscopy (AFM) using colloidal probe technique has proven to be a suitable tool. In this work, the measurements were performed between magnetite–magnetite, bentonite–magnetite, silica–bentonite, and silica–magnetite particles in 1 mM CaCl2 solution at various pH values. The interaction character, i.e., repulsion or attraction, was determined by measuring and analyzing AFM force curves. The observed quantitative changes in interaction forces were in good agreement with the measured zeta-potentials for the particles at the same experimental conditions. Particle aggregation was studied by measuring the adhesion force. Absolute values of adhesion forces for different systems could not be compared due to the difference in particle size and contact geometry. Therefore, the relative change of adhesion force between pH 6 and 10 was used for comparison. The adhesion force decreased for the magnetite–magnetite and bentonite–silica systems and slightly increased for the magnetite–bentonite system at pH 10 as compared to pH 6, whereas a pronounced decrease in adhesion force was observed in the magnetite–silica system. Thus, the presence of silica particles on the magnetite surface could have a negative impact on the interaction between magnetite and bentonite in balling due to the reduction of the adhesion force.

  • 20.
    Dobryden, Illia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Chemistry, Division of Surface and Corrosion Science, KTH Royal Institute of Technology, Stockholm, SE-100 44, Sweden.
    Touati, Baligh
    Physics Condensed Matter Laboratory, Faculty of Science of Tunis, University of Tunis El-Manar.
    Gassoumi, Abdelaziz
    Physics Condensed Matter Laboratory, Faculty of Science of Tunis, University of Tunis El-Manar.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kamoun, Najoua
    Physics Condensed Matter Laboratory, Faculty of Science of Tunis, University of Tunis El-Manar.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Morphological and electrical characterization of Cu-doped PbS thin films with AFM2017In: Advanced Materials Letters, ISSN 0976-3961, E-ISSN 0976-397X, Vol. 8, no 11, p. 1029-1037Article in journal (Refereed)
    Abstract [en]

    Lead sulphide (PbS) is a direct band gap IV–VI intrinsic p-type semiconductor with good potential for application in solar cells, sensors, etc. Doping the films with Cu2+ ions may improve the electrical properties. Here, Cu-doped PbS films were deposited on conducting glass substrates. The morphology, topography and thickness of the doped PbS films were examined using atomic force microscopy (AFM) and high-resolution SEM. AFM analysis showed decreasing surface roughness and grain size with the increase of Cu2+ concentration from 0.5 to 2.0 at%. Local surface electrical measurements using conducting AFM and Kelvin probe force microscopy showed the possibility to probe semi-quantitatively the changes in surface potential, work function, and Fermi level upon doping of the films. The estimated apparent work function for the un-doped PbS grains in the film was slightly above 4.5 eV, while it decreased to a minimum value of 4.43-4.45 eV at 1–1.5 at% Cu-doping. Conducting AFM measurements showed that local resistance of the doped samples is lower than on pure PbS films. These results indicate Cu doping as an effective strategy to tune the electrical properties of PbS thin films toward the development of suitable optically active materials for application in photovoltaics.

  • 21.
    Dobryden, Illia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Yang, Xiaofang
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Weber, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    An atomic force microscopy study of the interaction between magnetite particles: the effect of Ca2 + ions and pH2013In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 233, p. 116-122Article in journal (Refereed)
    Abstract [en]

    Force interactions between a microsize (m-s) magnetite probe and thin layers of synthesized magnetite particles as well as microsize (m-s) magnetite particles from magnetite concentrate were investigated using atomic force microscopy (AFM). Of special interest was the influence of Ca2 + ions and pH on the interaction between the probe and the two different magnetite particle surfaces. The probe and the magnetite surfaces were immersed in aqueous Ca2 + solutions (100, 10, and 1 mM) at various pH values (4, 6, and 10). The colloidal probe technique and a self-made computer program for automatic evaluation of adhesion forces were used. The analysis revealed an increase in adhesion force with increased calcium concentration at pH 6 for both the systems investigated. However, the adhesion behavior between the probe and the m-s and n-s magnetite particle surfaces is different at pH 10. The possible appearance of calcium carbonate precipitated onto the magnetite surfaces as well as the possible influence of already adsorbed silicate on magnetite particles from the concentrate is discussed. In addition to Ca, Cl and Na atoms, added to the working solutions, and the Fe and O detected signals, the SEM-EDS analysis also detected Si atoms on the surface of the m-s particles.

  • 22.
    Dobryden, Illia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Yang, Xiaofang
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Weber, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Interaction forces between surface modified magnetite particles in aqueous solution2011Conference paper (Other academic)
  • 23. Esser, H.G.
    et al.
    Karduck, P.
    Rubel, M.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Grobuch, L.
    Seggern, J. von
    Weshenfelder, F.
    Weinholdt, P.
    Comparison of different methods to characterize thin a-Si:H films1998In: Modern Developments and Applications in Microbeam Analysis, Wien: Encyclopedia of Global Archaeology/Springer Verlag, 1998, p. 163-170Chapter in book (Other academic)
  • 24.
    Furustig, Joel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Dobryden, Illia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The measurement of wear using AFM and wear interpretation using a contact mechanics coupled wear model2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 350-351, p. 74-81Article in journal (Refereed)
    Abstract [en]

    Detailed understanding of wear processes is required to improve the wear resistance and lifetime of machine components. Atomic force microscopy (AFM) is used to measure surface height profiles with high precision, before and after a wear experiment. The distribution and depth of wear on steel surfaces is then calculated using a relocation method. A numerical investigation of wear based on Archard's equation is conducted on the same measured surfaces. A good correlation was found between the model and experiment for wear larger than a hundred nm. The wear mechanisms considered in the numerical simulation was thus found to be the cause of the majority of the wear. On the scale of tens of nm the correlation was limited, but the measured wear was still analysed in detail.

  • 25.
    Ghamgosar, Pedram
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rigoni, Federica
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    You, Shujie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Dobryden, Iliya
    Division of Surface and Corrosion Science, KTH Royal Institute of Technolog.
    Gilzad Kohan, Mojtaba
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pellegrino, Anna Lucia
    Dipartimento Scienze Chimiche, Università degli Studi di Catania, INSTM UdR-Catania.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Malandrino, Graziella
    Dipartimento Scienze Chimiche, Università degli Studi di Catania, INSTM UdR-Catania.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    ZnO-Cu2O core-shell nanowires as stable and fast response photodetectors2018In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 51, p. 308-316Article in journal (Refereed)
    Abstract [en]

    In this work, we present all-oxide p-n junction core-shell nanowires (NWs) as fast and stable self-powered photodetectors. Hydrothermally grown n-type ZnO NWs were conformal covered by different thicknesses (up to 420 nm) of p-type copper oxide layers through metalorganic chemical vapor deposition (MOCVD). The ZnO NWs exhibit a single crystalline Wurtzite structure, preferentially grown along the [002] direction, and energy gap Eg=3.24 eV. Depending on the deposition temperature, the copper oxide shell exhibits either a crystalline cubic structure of pure Cu2O phase (MOCVD at 250 °C) or a cubic structure of Cu2O with the presence of CuO phase impurities (MOCVD at 300 °C), with energy gap of 2.48 eV. The electrical measurements indicate the formation of a p-n junction after the deposition of the copper oxide layer. The core-shell photodetectors present a photoresponsivity at 0 V bias voltage up to 7.7 µA/W and time response ≤0.09 s, the fastest ever reported for oxide photodetectors in the visible range, and among the fastest including photodetectors with response limited to the UV region. The bare ZnO NWs have slow photoresponsivity, without recovery after the end of photo-stimulation. The fast time response for the core-shell structures is due to the presence of the p-n junctions, which enables fast exciton separation and charge extraction. Additionally, the suitable electronic structure of the ZnO-Cu2O heterojunction enables self-powering of the device at 0 V bias voltage. These results represent a significant advancement in the development of low-cost, high efficiency and self-powered photodetectors, highlighting the need of fine tuning the morphology, composition and electronic properties of p-n junctions to maximize device performances.

  • 26. Hellberg, M.
    et al.
    Norling, N.
    Antzutkin, Oleg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Morphlogy and growth kinetics of Alzheimer's amyloid beta-peptides, Aβ(1-40) and the Arctic mutation Aβ(1-40)(E22G): in situ atomic force microscopy study2004In: Amyloid and amyloidosis: the proceedings of the Xth International Symposium on Amyloidosis / [ed] Martha Skinner; Gilles Grateau; Robert A. Kyle, Boca Raton, Fla: CRC Press, 2004, p. 408-410Conference paper (Refereed)
  • 27. Hellberg, Magnus
    et al.
    Norlin, Nils
    Olevik, David
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antzutkin, Oleg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    In situ scanning probe microscopy studies of morphology and growth kinetics in amyloid-peptide fibrillogenesis with custom designed tapping mode and pulsed force mode systems2004In: Proceedings of 5th Nordic-Baltic Scanning Probe Microscopy Workshop, 2004, p. 93-95Conference paper (Refereed)
    Abstract [en]

    We have used a commercial Nanoscope II atomic force microscope (AFM) with a custom designedtapping mode (TM) system to in situ monitor amyloid β-peptide aggregation related to Alzheimer’sdisease (AD). The custom tapping mode setup was successfully used to image the real timeaggregation behaviour of the arctic mutation amyloid β-peptide, Aβ(1-40), in vitro in aphysiologically relevant buffer and compare with the behaviour of the normal wild type of theAlzheimer’s amyloid peptide Aβ(1-40) at the same conditions. The investigation revealed distinctdifferences in fibrillogenesis behaviour for the two peptides. Our results demonstrate a previouslysuggested alternative fibrillogenesis pathway, of highly distinct aggregates with orderedmorphology as on-pathway. Moreover, additional investigations using a pulsed force mode (PFM)are under way.

  • 28.
    Jirlèn, Johan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lundström, Ingemar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Towards nanolithography with starch and α-amylase: Invited lecture2017In: Proceedings and Abstracts Book of European Advanced Materials Congress 2017, 2017Conference paper (Refereed)
    Abstract [en]

    Nanotechnology using enzyme technology to modify surfaces on the nanometer scale and nanostructuring surfaces is an evolving research field. One of the advantages with enzyme assisted nanolithography is the high substrate specificity. Scanning probe microscopy (SPM) in liquid or ambient conditions is highly suited for such nanolithography: we are in particular using atomic force microscopy (AFM) to develop negative nanolithography based on an enzyme and its substrate. The possibility of high accuracy positioning of the SPM probe tip is combined with the activity of an enzyme. There are very few related such studies by other groups [1-3]. In our approach, the enzyme is α-amylase and the substrate starch, whose hydrolysis into sugars by α-amylase is well studied on the macro-scale. The system α-amylase-starch is exploited as a model to demonstrate the proof of principle that the enzyme can be used with SPM methods to locally degrade starch and ultimately write nanopatterns on starch surfaces. Silicon surfaces are covered with smooth and thin layers of starch, whose roughness, morphology and nanomechanical properties are characterized by AFM methods. In the next step the degradation of these starch layers will be demonstrated with an AFM tip functionalized with amylase molecules, either on the apex of a “sharp” AFM tip (outer radius 5-50 nm) or on a micrometer-sized bead of silicon dioxide glued to an AFM cantilever. The α-amylase molecules may be either spontaneously adsorbed or covalently attached to the tip through established functionalization chemistry. Results will be presented related to the structure and quality of the starch layer and its degradation by amylase in solution as observed by AFM and FTIR-spectroscopy and to the activity of amylase immobilized on (silicon/silicon dioxide) surfaces. Preliminary results will be given on the local degradation of starch caused by AFM tips modified by α-amylase and/or by micro droplets of amylase solution released on the substrate by using the AFM tip in a dip-pen configuration. The ultimate goal is to achieve a situation like that illustrated in the drawing above, where a single (or few) α-amylase molecule(s) is attached on the AFM tip so to maintain its enzymatic activity and can be used to write nanopatterns in a layer of starch.

  • 29.
    Mannelquist, Anders
    et al.
    Luleå tekniska universitet.
    Almqvist, Nils
    Fredriksson, Sverker
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Influence of tip geometry on fractal analysis of atomic force microscopy images1998In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 66, no Supplement 1, p. S 891-S 895Article in journal (Refereed)
    Abstract [en]

    Fractal analysis of data from atomic force microscopy (AFM) is often necessary for studying surfaces with scale-invariant roughness. However, the fractal parameters are influenced by the finite-sized tip geometry of the AFM stylus. We make an extended study of such little-known effects. The so-called successive random algorithm is used to generate by computer ideal fractal surfaces with known fractal dimensions and varying height magnitudes. Tip-distorted AFM images are simulated from the ideal surfaces for the case of a strictly geometrical interaction between surface and tip. The AFM-induced error, taken as the difference in estimated parameters between ideal and distorted images, is shown to be largest for small scan sizes and high fractal dimensions. The dependence on AFM tip radius and surface height magnitude is analyzed by the structure function, variance and a Fourier method. The latter is shown to be unreliable for analyzing AFM images. We exemplify how the results can be applied to AFM images of real surfaces.

  • 30.
    Nordlund, Michael
    et al.
    Department of Chemistry - BMC, Uppsala University.
    Bhandary, Sumanta
    Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
    Sanyal, Biplab
    Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Grennberg, Helena
    Department of Chemistry - BMC, Uppsala University.
    Side-selective self-assembly of graphene and FLG on piezoelectric PVDF from suspension2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 7, article id 07LT01Article in journal (Refereed)
    Abstract [en]

    The deposition of few-layer graphene by self-assembly from suspension onto a piezoelectric polymer substrate is presented. The graphene self-assembles with negligible overlap between flakes, and with high selectivity for one of the faces of the substrate, an observation which is discussed and rationalized. A computational study on a model system further confirms the theory and supports the experimental results. The highest obtained degree of surface coverage was estimated to 77%

  • 31.
    Norlin, Nils
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hellberg, M.
    Luleå tekniska universitet.
    Filippov, Andrei
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sousa, A.A.
    National Institutes of Health, Bethesda.
    Gröbner, G.
    Umeå universitet.
    Leapman, R.D.
    National Institutes of Health, Bethesda.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antzutkin, Oleg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Aggregation and fibril morphology of the Arctic mutation of Alzheimer's Aβ peptide by CD, TEM, STEM and in situ AFM2012In: Journal of Structural Biology, ISSN 1047-8477, E-ISSN 1095-8657, Vol. 180, no 1, p. 174-189Article in journal (Refereed)
    Abstract [en]

    Morphology of aggregation intermediates, polymorphism of amyloid fibrils and aggregation kinetics of the "Arctic" mutant of the Alzheimer's amyloid β-peptide, Aβ (1-40)(E22G), in a physiologically relevant Tris buffer (pH 7.4) were thoroughly explored in comparison with the human wild type Alzheimer's amyloid peptide, wt-Aβ (1-40), using both in situ atomic force and electron microscopy, circular dichroism and thioflavin T fluorescence assays. For arc-Aβ (1-40) at the end of the 'lag'-period of fibrillization an abrupt appearance of ∼3 nm size 'spherical aggregates' with a homogeneous morphology, was identified. Then, the aggregation proceeds with a rapid growth of amyloid fibrils with a variety of morphologies, while the spherical aggregates eventually disappeared during in situ measurements. Arc-Aβ (1-40) was also shown to form fibrils at much lower concentrations than wt-Aβ (1-40): ≤2.5 μM and 12.5 μM, respectively. Moreover, at the same concentration, 50 μM, the aggregation process proceeds more rapidly for arc-Aβ (1-40): the first amyloid fibrils were observed after c.a. 72 h from the onset of incubation as compared to approximately 7 days for wt-Aβ (1-40). Amyloid fibrils of arc-Aβ (1-40) exhibit a large variety of polymorphs, at least five, both coiled and non-coiled distinct fibril structures were recognized by AFM, while at least four types of arc-Aβ (1-40) fibrils were identified by TEM and STEM and their mass-per-length statistics were collected suggesting supramolecular structures with two, four and six β-sheet laminae. Our results suggest a pathway of fibrillogenesis for full-length Alzheimer's peptides with small and structurally ordered transient spherical aggregates as on-pathway immediate precursors of amyloid fibrils.

  • 32.
    Rubel, M,
    et al.
    Alfvén Laboratory, Royal Institute of Technology, Association EURATOM -NFR.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wienhold, P.
    Institute of Plasma Physics, Forschungszentrum - Jülich, Association EURATOM.
    Wu, C.H.
    NET Team, Max-Planck-Institute for Plasma Physics.
    Behaviour of Si and Ti doped carbon composites under exposure to the deuterium plasma1998In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 258-263, no 1, p. 787-792Article in journal (Refereed)
    Abstract [en]

    Studies of the deuterium interaction with carbon-based substrates were performed for graphite doped either with SiC or with TiC (5% or 10% of Si or Ti) and carbon fibre composites doped with SiC (2.5; 8; 40% of carbide). Non-doped CFC and graphite were used as reference materials. The materials were exposed to the deuterium plasma in a tokamak or in simulators of plasma-surface interactions. The main emphasis was on the determination of the deuterium retention in the near surface region and in the bulk of the composites. Characterisation of the non-exposed and deuterium irradiated substrates was accomplished by means of RBS, NRA, EDS, laser profilometry and ultra-high resolution microscopies. The most important observations are connected with the penetration of the deposited deuterium into the bulk of composites - even a few millimetres beneath the surface. The rate of the process was found to be related to the structure of materials and, to a certain extent, to the content of dopants.

  • 33. Rubel, M.
    et al.
    Emmoth, B.
    Wienhold, P.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wu, C.H.
    Deuterium interaction with silicon-graphite materials exposed to the tokamak plasma1994In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 45, no 4, p. 429-434Article in journal (Refereed)
    Abstract [en]

    Silicon-containing composites are considered as plasma facing materials in controlled fusion devices. Comparative studies of deuterium interaction with carbon based substrates were performed for graphite-silicon mixtures (5-50 wt% of Si), carbon fibres and isotropic graphite. Both virgin and deuterium treated surfaces were characterized by means of several surface sensitive techniques. The substrates were exposed to the deuterium plasma in the TEXTOR tokamak, in a magnetron or in a hollow cathode. The uptake, retention and release of deuterium were investigated. Migration of deuterium from the plasma deposited layer to the bulk of the substrates was found for the graphite-silicon mixtures. The structure of the deuterium-containing deposits was studied using atomic force microscopy. The initial stage of bubble formation was observed on the surfaces exposed to the tokamak plasma

  • 34. Rubel, M.
    et al.
    Franconi, E.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Emmoth, B.
    Brossa, F.
    Behavior of SiC-Al coatings upon high dose irradiation with deuterium and helium ions1994In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 64, no 3, p. 205-211Article in journal (Refereed)
    Abstract [en]

    Al-SiC coatings obtained by vacuum plasma spraying co-deposition are considered as a new class of plasma-facing materials (PFMs) for fusion devices. The technical requirements for PFMs are stringent, since they have to withstand severe operation conditions, including bombardment by high fluxes of particles escaping the plasma. A number of Al-SiC coatings (containing 20 or 50wt.% SiC) deposited on Cu, stainless steel or graphite substrates were irradiated under laboratory conditions with high doses of deuterium or He ions. The surface properties of the materials were characterized before and after irradiation using several analytical techniques (Rutherford backscattering, nuclear reaction analysis, secondary ion mass spectrometry, Auger electron spectroscopy, energy-dispersive spectroscopy, microscopic methods and laser profilometry). Exposure to low-energy deuterium ions or deuterium plasma resulted in the implantation of 7-9 × 1016 D cm-2 in the near-surface layer. The initial steps of blister formation were also observed. Changes in the surface structure were noted following irradiation with 5He+ ions (1.7-2 MeV). Damage in the surface layer of the materials was dependent on the ion flux.

  • 35.
    Rubel, M.
    et al.
    Physics Department - Frescati, Royal Institute of Technology, Association EURATOM-NFR.
    Weinhold, P.
    Institute of Plasma Physics, Forschungszentrum Jülich, Association EURATOM-KFA.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Emmoth, B.
    Physics Department - Frescati, Royal Institute of Technology, Association EURATOM-NFR.
    Esser, H.G.
    Institute of Plasma Physics, Forschungszentrum Jülich, Association EURATOM-KFA.
    Könen, L.
    Institute of Plasma Physics, Forschungszentrum Jülich, Association EURATOM-KFA.
    Seggern, J. von
    Institute of Plasma Physics, Forschungszentrum Jülich, Association EURATOM-KFA.
    Winter, J.
    Institute of Plasma Physics, Forschungszentrum Jülich, Association EURATOM-KFA.
    Silicon fluxes in the scrape-off layer plasma during silicon-assisted operation of TEXTOR1995In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 220-222, p. 536-540Article in journal (Refereed)
    Abstract [en]

    Surface collector probes were applied at TEXTOR for the investigation of silicon fluxes in the scrape-off layer during the first silicon-assisted (silane puffing, siliconization) operation of a tokamak. Probe exposures were made in order to measure the evolution of Si fluxes and the influence of silicon on the behaviour of other impurity fluxes like boron, oxygen and metals. Studies were performed under different conditions: heating mode, plasma density and gas filling. Comparative exposures were made before introduction of Si into the machine as well as immediately and long time after the siliconization. The exposed graphite samples were examined by surface analysis techniques, including Auger electron and Rutherford backscattering spectroscopies, nuclear reaction analysis and ultra-high resolution microscopies. The most important findings are concerned with: (i) the relation between silicon to carbon and silicon to oxygen in the deposits; (ii) the change in radial profiles of Si, B and D fluxes during consecutive stages of the silicon-assisted operation, and the retention of deuterium in the Si containing codeposited layers. The influence of plasma density on the fluxes is considered and gettering of oxygen by silicon is also addressed. Comparison is also made to the results of VUV spectroscopy signals of silicon and oxygen impurities in the plasma.

  • 36.
    Schäffer, Tilman E
    et al.
    Department of Physics, University of California.
    Ionescu-Zanetti, Cristian
    Department of Physics, University of California.
    Proksch, Roger
    Department of Physics, University of California.
    Fritz, Monika
    Department of Physics, University of California.
    Walters, Deron A.
    Department of Physics, University of California.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zaremba, Charlotte M.
    Materials Research Laboratory, University of California.
    Belcher, Angela M.
    Marine Biotechnology Center, Department of Molecular Biology, University of California.
    Smith, Bettye L.
    Department of Physics, University of California.
    Stucky, Galen D.
    Department of Chemistry, University of California, Santa Barbara.
    Morse, Daniel E.
    Marine Biotechnology Center, Department of Molecular Biology, University of California.
    Hansma, Paul K.
    Department of Physics, University of California.
    Does abalone nacre form by heteroepitaxial nucleation or by growth through mineral bridges?1997In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 9, p. 1731-1740Article in journal (Refereed)
    Abstract [en]

    We present experimental support for a model of abalone nacre growth that is based on mineral bridges between successive aragonite tablets rather than on heteroepitaxial nucleation. Interlamellar sheets of organic polymers delineate the aragonite tablets but allow the tablets to grow mineral bridges through pores in the sheets. Atomic force microscope images of interlamellar organic sheets from flat pearls made by Haliotis rufescens (red abalone; marine gastropod mollusk) reveal a fibrous core and holes of 5-50 nm in diameter. Scanning ion conductance microscopy shows that these holes are actually pores through the interlamellar sheets. With the help of statistical analysis we can associate the pore-to-pore spacings in the interlamellar sheets with the observed offsets of successive nacre tablets. These results, supplemented by AFM, SEM, and TEM images, support and extend the model of biofabrication of gastropod nacre which is based on mineral bridges between the aragonite tablets.

  • 37.
    Sefer, Birhan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Materials Science and Metallurgical Engineering, Universitat Politècnica de Catalunya.
    Dobryden, Illia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Division of Surface and Corrosion Science, KTH Royal Institute of Technology.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Research and Technology Centre, GKN Aerospace Engine Systems.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chemical Milling of Cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo Alloys in Hydrofluoric-Nitric Acid Solutions2017In: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 73, no 4, p. 394-407Article in journal (Refereed)
    Abstract [en]

    The behavior of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo during chemical milling in hydrofluoric-nitric (HF-HNO3) acid solutions with 1:3 and 1:11 molar ratios was investigated using electrochemical and atomic force microscopy (AFM) techniques. Faster corrosion rate in 1:3 solutions was measured for Ti-6Al-4V than for Ti-6Al-2Sn-4Zr-2Mo, whereas in 1:11 solution Ti-6Al-2Sn-4Zr-2Mo exhibited higher corrosion rate. Scanning Kelvin probe force microscopy measurements revealed difference in the Volta potential between the α-laths and the β-layers in the Widmansttäten microstructure indicating operation of microgalvanic cells between the microconstituents when in contact with HF-HNO3 solution. The AFM topography measurements demonstrated faster corrosion of the α-laths compared to the β-layers, in both alloys. In 1:3 solutions, higher α/β height difference was measured in Ti-6Al-4V, whereas in 1:11 solution, the difference was higher in Ti-6Al-2Sn-4Zr-2Mo. The results revealed that the chemical milling behavior of the two investigated alloys is controlled by the microscopic corrosion behavior of the individual microconstituents.

  • 38.
    Spencer, Andrew
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Dobryden, Illia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Surface characterization with functional parameters2011Conference paper (Other academic)
    Abstract [en]

    Typically engineering surfaces are characterized with traditional roughness parameters that perform some type of height averaging over the surface. Although these parameters describe the topography of the surface none of them necessarily describe the ability of the surface to carry out its function in a tribological contact. In this study an ICE cylinder liner has been investigated.The traditional Rk parameters (based on the Abbott curve) have been calculated as well as functional ‘flow factors’which modify the Reynolds equation to incorporate the effects of surface topography.To calculate flow factors the homogenization technique has been implemented and a full 3D contact mechanics model has been incorporated so that surface functionality in mixed lubrication can be studied. Furthermore, the cylinder liner surface has been measured with both white light interferometery and an AFM so that the effect of measuring technique on roughness and functional parameters can be investigated.

  • 39.
    Spencer, Andrew
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Dobryden, Illia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The influence of AFM and VSI techniques on the accurate calculation of tribological surface roughness parameters2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 57, p. 242-250Article in journal (Refereed)
    Abstract [en]

    Vertical Scanning Interferometry (VSI) may induce optical artefacts in surface topography measurements. The influence of these optical artefacts on the calculation of Rk surface roughness parameters, contact stiffness and flow factors were studied. Two surface measurement techniques were used: Atomic Force Microscopy (AFM) and VSI. Calibration grids were used to make it easier to isolate the causes of these artefacts, while a real engineering surface was used to compare these two techniques in an industrially applied case. It was found that the optical artefacts have a large influence on all the roughness parameters, contact stiffness and flow factors calculated on the calibration grids. However, for the engineering surface the differences between AFM and VSI measurements were much smaller.

  • 40.
    Thomson, Neil. H.
    et al.
    Physics Department. University of California Santa Barbara, Santa Barbara.
    Smith, Bettye L.
    Physics Department. University of California Santa Barbara, Santa Barbara.
    Almqvist, Nils
    Schmitt, Lutz
    Department of Chemistry, Stanford University.
    Kashlev, Mikhail
    National Cancer Institute. Frederick Cancer Research and Development Center, Frederick, Maryland.
    Kool, Eric T.
    Department of Chemistry, University of Rochester.
    Hansma, Paul K.
    Physics Department. University of California Santa Barbara, Santa Barbara.
    Orientation of single, active Escherichia coli RNA polymerase molecules for study with Atomic Force Microscopy1997In: Proceedings of SCANNING 97:: Monterey, California, USA. Scanning, 19: 135–184, John Wiley & Sons Ltd , 1997, p. 139-140Conference paper (Refereed)
  • 41. Thomson, Neil H.
    et al.
    Smith, Bettye L.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Schmitt, Lutz
    Kashlev, Mikhail
    Kool, Eric T.
    Hansma, Paul K.
    Oriented, active Escherichia coli RNA polymerase: an atomic force microscope study1999In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 76, no 2, p. 1024-1033Article in journal (Refereed)
    Abstract [en]

    RNA polymerase (RNAP) molecules to be imaged under aqueous buffer using tapping-mode atomic force microscopy (AFM). Recombinant RNAP molecules containing histidine tags (hisRNAP) on the C-terminus were specifically immobilized on ultraflat gold via a mixed monolayer of two different Ω-functionalized alkanethiols. One alkanethiol was terminated in an ethylene-glycol (EG) group, which resists protein adsorption, and the other was terminated in an N-nitrilotriacetic acid (NTA) group, which binds the histidine tag through two coordination sites with a nickel ion. AFM images showed that these two alkanethiols phase-segregate. Specific binding of the hisRNAP molecules was followed in situ by injecting proteins directly into the AFM fluid cell. The activity of the hisRNAP bound to the NTA groups was confirmed with a 42-base circular single-stranded DNA template (rolling circle), which the RNAP uses to produce huge RNA transcripts. These transcripts were imaged in air after the samples were rinsed and dried, since RNA also has low affinity for the EG-thiol and cannot be imaged under the buffers we used.

  • 42.
    Touati, Baligh
    et al.
    Physics Condensed Matter Laboratory, Faculty of Science of Tunis, University of Tunis El -Manar.
    Dobryden, Illia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Salem, Yassine Ben
    Physics Condensed Matter Laboratory, Faculty of Science of Tunis, University of Tunis El -Manar.
    Gassoumi, Abdelaziz
    Physics Condensed Matter Laboratory, Faculty of Science of Tunis, University of Tunis El -Manar.
    Natile, Marta Maria
    CNR-IENI, Dipartimento di Scienze Chimiche, Università di Padova.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kamoun, Najoua
    Physics Condensed Matter Laboratory, Faculty of Science of Tunis, University of Tunis El -Manar.
    Morphological and electrical characterization of Cu-doped PbS thin films2016Conference paper (Refereed)
    Abstract [en]

    Lead sulphide (PbS) thin films represent a direct band gap IV–VI p-type semiconductor material (Eg= 0.41 eV) and have a good potential application in solar cells, infrared detector devices, sensors, etc[1]. The electrical properties of PbS film can be tuned via doping with Cu2+ and Cd2+[2, 3]. These ions have good ability to substitute Pb2+ locations in the PbS crystal lattice, and thus tune its energy band gap. Also, the structural properties of the film, such as the grain size, can depend on the dopant concentration and will affect the PbS band gap and conductivity. These features are important for instance, when PbS film are applied as photoactive materials in solar cells[4]. Here we present an investigation on doping PbS thin films by Cu. Cu-doped PbS films were deposited on ordinary glass and conducting glass substrates through chemical bath deposition. The samples deposited on the F:SnO2 conducting layers were used for a high-resolution SEM measurements and scanning spreading resistance microscopy (SSRM) characterization using scanning probe microscopy (SPM). The morphology and topography of the doped PbS films were examined using tapping mode AFM (NT-MDT Ntegra) and high-resolution SEM (Magellan 400 XHR-SEM). The crystalline shape was triangular and did not change much with the dopant concentration increase from 0.5% to 2%. Films in the range 120 to 380 nm were considered. Good agreement was found between thickness measured through cross-section HR-SEM and Rutherford backscattering spectrometry (RBS). Also, the RBS investigation has shown that the film thickness tends to decrease for an increase of the dopant concentration. All the doped films seem having lower doping concentration, compared to the nominal one, as obtained from RBS analysis. XPS highlighted a Cu-enriched surface layer, possibly due to selective segregation of the doped films during their growth. Additionally, advanced electrical measurements using SSRM and Kelvin probe force microscopy (KPFM) are underway. The possibility of tuning both the electrical and optical properties of PbS thin films by doping represents a viable strategy for the development of suitable optically active materials for application in photovoltaics.

1 - 42 of 42
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