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  • 1.
    Karlsson, Linda
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Transmission Electron Microscopy of 2D Materials: Structure and Surface Properties2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    During recent years, new types of materials have been discovered with unique properties. One family of such materials are two-dimensional materials, which include graphene and MXene. These materials are stronger, more flexible, and have higher conductivity than other materials. As such they are highly interesting for new applications, e.g. specialized in vivo drug delivery systems, hydrogen storage, or as replacements of common materials in e.g. batteries, bulletproof clothing, and sensors. The list of potential applications is long for these new materials.

    As these materials are almost entirely made up of surfaces, their properties are strongly influenced by interaction between their surfaces, as well as with molecules or adatoms attached to the surfaces (surface groups). This interaction can change the materials and their properties, and it is therefore imperative to understand the underlying mechanisms. Surface groups on two-dimensional materials can be studied by Transmission Electron Microscopy (TEM), where high energy electrons are transmitted through a sample and the resulting image is recorded. However, the high energy needed to get enough resolution to observe single atoms damages the sample and limits the type of materials which can be analyzed. Lowering the electron energy decreases the damage, but the image resolution at such conditions is severely limited by inherent imperfections (aberrations) in the TEM. During the last years, new TEM models have been developed which employ a low acceleration voltage together with aberration correction, enabling imaging at the atomic scale without damaging the samples. These aberration-corrected TEMs are important tools in understanding the structure and chemistry of two-dimensional materials.

    In this thesis the two-dimensional materials graphene and Ti3C2Tx MXene have been investigated by low-voltage, aberration-corrected (scanning) TEM. High temperature annealing of graphene covered by residues from the synthesis is studied, as well as the structure and surface groups on single and double Ti3C2Tx MXene. These results are important contributions to the understanding of this class of materials and how their properties can be controlled.

    List of papers
    1. Residue reduction and intersurface interaction on single graphene sheets
    Open this publication in new window or tab >>Residue reduction and intersurface interaction on single graphene sheets
    Show others...
    2016 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 100, p. 345-350Article in journal (Refereed) Published
    Abstract [en]

    Large regions of pristine graphene are essential to applications which rely on the ideal graphene properties. Common methods for transferring chemical vapour deposition grown graphene to suitable substrates leaves metal oxide particles and poly(methyl methacrylate) (PMMA) residues on opposing surfaces, which degrade the properties. A common method to reduce the residues include annealing in vacuum or in argon, however, residues remain on the graphene sheet. The present investigation reports on the metal oxide particle ripening and PMMA decomposition on a single graphene sheet during in-situ annealing up to 1300 degrees C in a transmission electron microscope. It is shown that the PMMA residues are increasingly reduced at elevated temperatures although the reduction is strongly correlated to the metal oxide particle coverage on the opposing graphene surface. This is shown to occur as a consequence of an electrostatic interaction between the residues and that this prevents the establishment of large clean areas. (C) 2016 Elsevier Ltd. All rights reserved.

    Place, publisher, year, edition, pages
    Pergamon Press, 2016
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-126123 (URN)10.1016/j.carbon.2016.01.007 (DOI)000369961400040 ()
    Note

    Funding Agencies|Swedish Research Council [621-2012-4359, 622-2008-405, 642-2013-8020]; Olle Engkvist foundation; Knut and Alice Wallenbergs Foundation; European Research Council [258509]; IBS Korea [IBS-RO11-D1]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00971]

    Available from: 2016-03-15 Created: 2016-03-15 Last updated: 2017-11-30Bibliographically approved
    2. Atomically Resolved Structural and Chemical Investigation of Single MXene Sheets
    Open this publication in new window or tab >>Atomically Resolved Structural and Chemical Investigation of Single MXene Sheets
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    2015 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 15, no 8, p. 4955-4960Article in journal (Refereed) Published
    Abstract [en]

    The properties of two-dimensional (2D) materials depend strongly on the chemical and electrochemical activity of their surfaces. MXene, one of the most recent additions to 2D materials, shows great promise as an energy storage material. In the present investigation, the chemical and structural properties of individual Ti3C2 MXene sheets with associated surface groups are investigated at the atomic level by aberration corrected STEM-EELS. The MXene sheets are shown to exhibit a nonuniform coverage of O-based surface groups which locally affect the chemistry. Additionally, native point defects which are proposed to affect the local surface chemistry, such as oxidized titanium adatoms (TiOx), are identified and found to be mobile.

    Keywords
    MXene, Ti3C2Tx, Aberration corrected STEM, Surface Chemistry, Surface
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-120927 (URN)10.1021/acs.nanolett.5b00737 (DOI)000359613700017 ()26177010 (PubMedID)
    Available from: 2015-08-31 Created: 2015-08-31 Last updated: 2017-12-04Bibliographically approved
  • 2.
    Karlsson, Linda
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Department of Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States.
    Barsoum, Michel W.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Department of Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States.
    Persson, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Atomically Resolved Structural and Chemical Investigation of Single MXene Sheets2015In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 15, no 8, p. 4955-4960Article in journal (Refereed)
    Abstract [en]

    The properties of two-dimensional (2D) materials depend strongly on the chemical and electrochemical activity of their surfaces. MXene, one of the most recent additions to 2D materials, shows great promise as an energy storage material. In the present investigation, the chemical and structural properties of individual Ti3C2 MXene sheets with associated surface groups are investigated at the atomic level by aberration corrected STEM-EELS. The MXene sheets are shown to exhibit a nonuniform coverage of O-based surface groups which locally affect the chemistry. Additionally, native point defects which are proposed to affect the local surface chemistry, such as oxidized titanium adatoms (TiOx), are identified and found to be mobile.

  • 3.
    Karlsson, Linda
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Mockuté, Aurelija
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Ingason, Arni Sigurdur
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Ta, Huy Q.
    Sungkyunkwan University, South Korea; Sungkyunkwan University, South Korea.
    Rummeli, Mark H.
    Soochow University, Peoples R China; Soochow University, Peoples R China; IFW Dresden, Germany; Polish Academic Science, Poland.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Graphene on graphene formation from PMMA residues during annealing2017In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 137, p. 191-194Article in journal (Refereed)
    Abstract [en]

    PMMA is a common support material for transferring graphene between substrates. However, PMMA residues typically remain on the graphene sheet after the transfer process. A high temperature annealing process is commonly applied to reduce the amount of PMMA residues. It is also known that high temperature annealing of PMMA causes the PMMA to graphitize, which has been used as a method to synthesize graphene on metal substrates. In this letter we show the development of additional graphene layers during high temperature annealing, which occurs on a single, clean, graphene sheet. The additional graphene is nucleated from the decomposition products of PMMA residues. (C) 2017 Elsevier Ltd. All rights reserved.

  • 4.
    Karlsson, Linda
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Mockuté, Aurelija
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Sigurdur Ingason, Arni
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Ta, Huy Q.
    Polish Academic Science, Poland; Sungkyunkwan University, South Korea; Soochow University, Peoples R China; Soochow University, Peoples R China.
    Rummeli, Mark H.
    Polish Academic Science, Poland; Soochow University, Peoples R China; Soochow University, Peoples R China; IFW Dresden, Germany.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Per O. Å.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Residue reduction and intersurface interaction on single graphene sheets2016In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 100, p. 345-350Article in journal (Refereed)
    Abstract [en]

    Large regions of pristine graphene are essential to applications which rely on the ideal graphene properties. Common methods for transferring chemical vapour deposition grown graphene to suitable substrates leaves metal oxide particles and poly(methyl methacrylate) (PMMA) residues on opposing surfaces, which degrade the properties. A common method to reduce the residues include annealing in vacuum or in argon, however, residues remain on the graphene sheet. The present investigation reports on the metal oxide particle ripening and PMMA decomposition on a single graphene sheet during in-situ annealing up to 1300 degrees C in a transmission electron microscope. It is shown that the PMMA residues are increasingly reduced at elevated temperatures although the reduction is strongly correlated to the metal oxide particle coverage on the opposing graphene surface. This is shown to occur as a consequence of an electrostatic interaction between the residues and that this prevents the establishment of large clean areas. (C) 2016 Elsevier Ltd. All rights reserved.

  • 5.
    Mendoza, Arturo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Optics . Linköping University, The Institute of Technology. Cinvestav-IPN, Unidad Querétaro, Mexico.
    Arreola-Jardón, Gerardo
    Cinvestav-IPN, Unidad Querétaro, Mexico.
    Karlsson, Linda
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Persson, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Jiménez-Sandoval, Sergio
    Cinvestav-IPN, Unidad Querétaro, Mexico.
    Optical properties of CuCdTeO thin films sputtered from CdTe-CuO composite targets2014In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 571, p. 706-711Article in journal (Refereed)
    Abstract [en]

    The effective complex dielectric function (ε) of Cu and O containing CdTe thin films is reported in the spectral range of 0.05 to 6 eV. The films were fabricated by rf sputtering from targets comprised by a mixture of CdTe and CuO powders with nominal Cu and O concentrations in the range of 2–10 at.%. Low concentration levels improved the crystalline quality of the films. Spectroscopic ellipsometry and transmittance measurements were used to determine ε. The critical point energies E1, E11, and E2 of CdTe are red-shifted with the incorporation of Cu and O. Also, an absorption band is developed in the infrared range which is associated with a mixture of CdTe and low resistivity phases Cu2 − xTe according to an effective medium analysis. The elemental distribution of the films was mapped by energy dispersive X-ray spectroscopy using scanning transmission electron microscopy.

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