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Transmission Electron Microscopy of 2D Materials: Structure and Surface Properties
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0002-7500-9777
2016 (English)Doctoral 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.

Place, publisher, year, edition, pages
Linköping University Electronic Press, 2016. , 86 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1745
Keyword [en]
Transmission Electron Microscopy, Two-dimensional materials, Graphene, MXene, Ti3C2Tx, Low-voltage TEM, Aberration-corrected TEM, monchromated TEM, Scanning transmission electron microscopy, Electron energy loss spectroscopy
National Category
Condensed Matter Physics Nano Technology
URN: urn:nbn:se:liu:diva-127526DOI: 10.3384/diss.diva-127526ISBN: 978-91-7685-832-5 (Print)OAI: diva2:926538
Public defence
2016-06-15, Planck, Fysikhuset, Campus Valla, Linköping, 09:15 (English)
Swedish Research Council, 621-2012-4359Swedish Research Council, 622-2008-405Swedish Research Council, 642-2013-8020Swedish Research Council, 621-2009-5294
Available from: 2016-05-23 Created: 2016-05-02 Last updated: 2016-05-23Bibliographically approved
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
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2016 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 100, 345-350 p.Article 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
urn:nbn:se:liu:diva-126123 (URN)10.1016/j.carbon.2016.01.007 (DOI)000369961400040 ()

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: 2016-06-17Bibliographically 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, 4955-4960 p.Article 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.

MXene, Ti3C2Tx, Aberration corrected STEM, Surface Chemistry, Surface
National Category
Condensed Matter Physics
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: 2016-06-03Bibliographically approved

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