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Mechanical behaviour of carbon nanostructures
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Abstract

Carbon nanotubes (CNTs) have extraordinary mechanical and electrical properties. Together with their small dimensions and low density, they are attractive candidates for building blocks in future nanoelectromechanical systems and for many other applications. The extraordinary properties are however only attained by perfectly crystalline CNTs and quickly deteriorate when defects are introduced to the structure. The growth technique affects the crystallinity where in general CNTs grown by arc-discharge are close to perfectly crystalline, while CVD-grown CNTs have large defect densities. Mechanical deformation also affects these properties, even without introducing defects. When CNTs are bent they behave similarly to drinking straws, i.e. they buckle or ripple and their bending stiffness drops abruptly.

In this thesis, the mechanical behaviour of individual CNTs and vertically aligned carbon nanofibers (VACNFs) has been studied by performing force measurements inside electron microscopes. Cantilevered CNTs, and VACNFs, were bent using a force sensor, yielding force-deflection curves while their structure was imaged simultaneously.

We have found that CNTs grown by arc-discharge have a high enough crystallinity to possess a Young’s modulus close to the ideal value of 1 TPa. CVD-grown CNTs possess a Young’s modulus that is about one order of magnitude smaller, due to their large defect density. The VACNFs are yet another order of magnitude softer as a result of their cup-stacked internal structure.  We also found that a high defect density will increase the critical strain for the rippling onset and the relative post-rippling stiffness. Multi-walled CNTs with a small inner diameter are less prone to ripple and have a larger relative post-rippling stiffness. Our findings show large variations in the onset of rippling and the bending stiffness before and after rippling. These variations open up possibilities of tailoring the mechanical properties for specific applications.

Abstract [en]

Baksidetext

Carbon nanotubes (CNTs) have extraordinary mechanical and electrical properties. Together with their small dimensions and low density, they are attractive candidates for building blocks in nanoelectromechanical systems (NEMS), and many other applications.  In this thesis the mechanical behaviour of individual CNTs and vertically aligned carbon nanofibers has been studied by performing force measurements inside electron microscopes. We have found that the mechanical behaviour is very sensitive to the defect density and the internal structure of the CNTs. The extraordinary properties are only attained by defect free CNTs and quickly deteriorate if defects are introduced to the structure. Mechanical deformations also alter these properties. Single-walled CNTs behave similarly to drinking straws when bent, i.e. they buckle, while the inner tubes of multi-walled CNTs prevent buckling. Instead a more distributed rippling pattern is created for multi-walled CNTs. Both these deformation behaviours will cause an abrupt drop in the bending stiffness, which is detrimental for many applications. The findings in this work will have implications for the design of future NEMS.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2014.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2014:33
Keyword [en]
carbon nanotubes, CNT, multiwalled carbon nanotubes, MWCNT, rippling, buckling, mechanical properties, transmission electron microscopy, TEM, scanning electron microscopy, SEM, atomic force microscopy, AFM, Young’s modulus, in situ TEM, in situ SEM
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kau:diva-32041ISBN: 978-91-7063-566-3 (print)OAI: oai:DiVA.org:kau-32041DiVA: diva2:715795
Public defence
2014-06-13, 21A342, Karlstads universitet, Karlstad, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2010-4324
Note

Artikel 2 Image formation mechanisms tidigare som manuskript, nu publicerad: urn:nbn:se:kau:diva-16425 (MÅ 150924)

Available from: 2014-05-23 Created: 2014-05-06 Last updated: 2017-08-11Bibliographically approved
List of papers
1. Measurements of the critical strain for rippling in carbon nanotubes
Open this publication in new window or tab >>Measurements of the critical strain for rippling in carbon nanotubes
2011 (English)In: Applied Physics Letters, ISSN 0003-6951, Vol. 98, no 18, 3 pages- p.Article in journal (Refereed) Published
Abstract [en]

We report measurements of the bending stiffness in free standing carbon nanotubes, using atomic force microscopy inside a scanning electron microscope. Two regimes with different bending stiffness were observed, indicative of a rippling deformation at high curvatures. The observed critical strains for rippling were in the order of a few percent and comparable to previous modeling predictions. We have also found indications that the presence of defects can give a higher critical strain value and a concomitant reduction in Youngs modulus.

Place, publisher, year, edition, pages
American Institute of Physics, 2011
Keyword
Carbon nanotubes, mechanical properties, rippling, atomic force microscopy (AFM), scanning electron microscopy (SEM)
National Category
Materials Engineering Physical Sciences
Research subject
Materials Engineering; Physics
Identifiers
urn:nbn:se:kau:diva-10738 (URN)10.1063/1.3587613 (DOI)000290392300048 ()
Available from: 2012-02-08 Created: 2012-02-08 Last updated: 2017-12-06Bibliographically approved
2. Image formation mechanisms in scanning electron microscopy of carbon nanotubes,and retrieval of their intrinsic dimensions.
Open this publication in new window or tab >>Image formation mechanisms in scanning electron microscopy of carbon nanotubes,and retrieval of their intrinsic dimensions.
2013 (English)In: Ultramicroscopy, ISSN 0304-3991, Vol. 124, 35-39 p.Article in journal (Refereed) Published
Abstract [en]

We present a detailed analysis of the image formation mechanisms that are involved in the imaging of carbon nanotubes with scanning electron microscopy (SEM). We show how SEM images can be modelled by accounting for surface enhancement effects together with the absorption coefficient for secondary electrons, and the electron-probe shape. Images can then be deconvoluted, enabling retrieval of the intrinsic nanotube dimensions. Accurate estimates of their dimensions can thereby be obtained even for structures that are comparable to the electron-probe size (on the order of 2 nm). We also present a simple and robust model for obtaining the outer diameter of nanotubes without any detailed knowledge about the electron-probe shape.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Scanning electron microscopy; Carbon nanotubes; Imaging mechanisms; Deconvolution; Electron-probe shape
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-16425 (URN)10.1016/j.ultramic.2012.08.012 (DOI)000311823700006 ()23142742 (PubMedID)
Funder
Swedish Research Council, 2010-4324
Available from: 2014-02-21 Created: 2013-01-18 Last updated: 2015-09-24Bibliographically approved
3. Large variations in the onset of rippling in concentric nanotubes.
Open this publication in new window or tab >>Large variations in the onset of rippling in concentric nanotubes.
2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, 021910Article in journal (Refereed) Published
Abstract [en]

We present a detailed experimental study of the onset of rippling in highly crystalline carbon nanotubes. Modeling has shown that there should be a material constant, called the critical length, describing the dependence of the critical strain on the nanotube outer radius. Surprisingly, we have found very large variations, by a factor of three, in the critical length. We attribute this to a supporting effect from the inner walls in multiwalled concentric nanotubes. We provide an analytical expression for the maximum deflection prior to rippling, which is an important design consideration in nanoelectromechanical systems utilizing nanotubes.

Keyword
nanotubes, rippling, mechanical stiffness, TEM, AFM
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-30942 (URN)10.1063/1.4861605 (DOI)000330431000038 ()
Funder
Swedish Research Council, 2010-4324
Available from: 2014-01-20 Created: 2014-01-20 Last updated: 2017-12-06Bibliographically approved
4. Direct measurement of bending stiffness and estimation of Young’s modulus of vertically aligned carbon nanofibers
Open this publication in new window or tab >>Direct measurement of bending stiffness and estimation of Young’s modulus of vertically aligned carbon nanofibers
Show others...
2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 19Article in journal (Refereed) Published
Abstract [en]

We have measured the bending stiffness of as-grown vertically aligned carbon nanofibers using atomic force microscopy inside a scanning electron microscope. We show that the assumption of a uniform internal structure is inadequate in describing nanofibers mechanical properties and that a dual phase model is needed. We present a model in which different Young’s moduli are assigned to the inner graphitic core and the outer amorphous carbon shell and show that it provides a better fit to the measurements. We obtain values of 11±8 GPa and 63±14 GPa for the Young’s modulus of the inner core and the outer shell, respectively.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-13391 (URN)10.1063/1.4803853 (DOI)000319295200052 ()
Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2017-08-11Bibliographically approved
5. Mechanical beviour of carbon nanotubes in the rippled phase
Open this publication in new window or tab >>Mechanical beviour of carbon nanotubes in the rippled phase
(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-32067 (URN)
Funder
Swedish Research Council, 2010-4324
Available from: 2014-05-13 Created: 2014-05-13 Last updated: 2014-05-23Bibliographically approved

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