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  • 1.
    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.

  • 2.
    Mannelquist, Anders
    et al.
    Luleå tekniska universitet.
    Iwamoto, H
    University of Virginia School of Medicine.
    Szabo, G
    University of Virginia School of Medicine.
    Shao, Z
    University of Virginia School of Medicine.
    Near field optical microscopy in aqueous solution: implementation and characterization of a vibrating probe2002In: Journal of Microscopy, ISSN 0022-2720, E-ISSN 1365-2818, Vol. 205, no 1, p. 53-60Article in journal (Refereed)
    Abstract [en]

    Near field optical microscopy (NSOM) is one of the possible solutions to circumvent the diffraction limit, but the control of the optical probe in solution has been a technical challenge for practical applications. Most recently, it has been shown that the pipette used in the scanning ion conductance microscope can be modified to form a high resolution near field optical probe. When combined with a novel distance modulation mechanism, a robust near field microscope can be constructed for operation in aqueous solution. In this paper, we present technical details of this design and a further characterization of the NSOM system for imaging in solution. Fundamental limitations of this approach in comparison to other systems are also discussed. Based on the current technology, it is concluded that better than 50 nm resolution should be achievable with this technique for fluorescence, as well as fluorescence resonance energy transfer, imaging of biological specimens.

  • 3.
    Mouzon, Johanne
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Bhuiyan, Iftekhar Uddin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forsmo, Seija P.E.
    LKAB Research and Development.
    Hedlund, Jonas
    Cryo-SEM method for the observation of entrapped bubbles and degree of water filling in large wet powder compacts2011In: Journal of Microscopy, ISSN 0022-2720, E-ISSN 1365-2818, Vol. 242, no 2, p. 189-196Article in journal (Refereed)
    Abstract [en]

    There are generally two problems associated with cryogenic scanning electron microscopy (cryo-SEM) observations of large wet powder compacts. First, because water cannot be vitrified in such samples, formation of artefacts is unavoidable. Second, large frozen samples are difficult to fracture but also to machine into regular pieces which fit in standard holders, especially if made of hard materials like ceramics. In this article, we first describe a simple method for planning hard cryo-samples and a low-cost technique for cryo-fracture and transfer of large specimens. Subsequently, after applying the entire procedure to green pellets of iron ore produced by balling, we compare the influence of plunge- and unidirectional freezing on large entrapped bubbles throughout the samples as well as the degree of water filling at the outer surface of the pellets. By carefully investigating the presence of artefacts in large areas of the samples and by controlling the orientation of the sample during freezing and preparation, we demonstrate that unidirectional freezing enables the observation of large entrapped bubbles with minimum formation of artefacts, whereas plunge freezing is preferable for the characterization of the degree of water filling at the outer surface of wet powder compacts. The minimum formation of artefacts was due to the high packing density of the iron ore particles in the matrix

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