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A Theoretical Study: The Connection between Stability of Single-Walled Carbon Nanotubes and Observed Products
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. (Tillämpad fysik)ORCID iD: 0000-0003-1542-6170
2017 (English)Licentiate thesis, comprehensive summary (Other academic)Alternative title
En Teoretisk Studie: Sambandet mellan Stabiliteten for Enkelväggiga Kolnanorör och Observerade Produkter (Swedish)
Abstract [en]

Over the past 20 years’ researchers have tried to utilize the remarkable properties of single-walled carbon nanotubes (SWCNTs) to create new high-tech materials and devices, such as strong light-weight composites, efficient electrical wires and super-fast transistors. But the mass production of these materials and devices are still hampered by the poor uniformity of the as produced SWCNTs. SWCNTs are hollow cylindrical tubes of carbon where the atomic structure of the tube wall consists of just a single atomic layer of carbon atoms arranged in a hexagonal grid. For a SWCNT the orientation of the hexagonal grid making up the tube wall is what determines its properties, this orientation is known as the chirality of a SWCNT. As an example, SWCNTs of certain chiralities will be electrically conductive while others having different chiralities will be semiconducting.

Today’s large scale methods for producing SWCNTs, commonly known as growth of SWCNTs, gives products with a large spread of different SWCNT chiralities. A mixture of chiralities will give products with a mixture of different properties and this is one of the major problems holding back the use of SWCNTs in future materials and devices. The ultimate goal is to achieve growth of SWCNTs where the resulting product is uniform meaning that all of the SWCNTs have the same chirality, a process termed chirality-specific growth. To active chirality-specific growth of SWCNTs requires us to obtain a better fundamental understanding about how SWCNTs grow, both from an experimental and a theoretic point of view.

This thesis focuses on theoretical studies of SWCNT properties and how they relate to the growth process, giving us vital new information about how SWCNTs grow and taking us ever closer to achieving the ultimate goal of chirality-specific growth. First an introduction to the field is given and the current state of the art experiments, focusing on chirality-specific growth of SWCNTs are presented. A brief review of the current theoretical works and computer simulations related to growth of SWCNTs is also presented. The new results presented in this thesis are obtained using first principle density functional theory calculations. The first study shows a correlation between the stability of SWCNT fragments and the observed products from experiments. Calculations confirm that in 84\% of the investigated cases the chirality of experimental products matches the chirality of the most stable SWNT fragments (within 0.2 eV). Further theoretical calculations also reveal a previously unknown link between the stability of SWCNT fragments and their length. The calculations show that at specific SWCNT fragment lengths the most stable chirality changes, thus introducing the concept of a switching length for SWCNTs. How these new results link to the existing theoretical understanding of SWNT growth are discussed at the end of the thesis.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2017.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keyword [en]
Single-walled carbon nanotubes, density functional theory, catalytic chemical vapor deposition, chirality-specific growth, stability, length, diameter, edge, chirality
National Category
Condensed Matter Physics Atom and Molecular Physics and Optics
Research subject
Applied Physics
Identifiers
URN: urn:nbn:se:ltu:diva-62321ISBN: 978-91-7583-837-3 (print)ISBN: 978-91-7583-838-0 (electronic)OAI: oai:DiVA.org:ltu-62321DiVA: diva2:1078955
Presentation
2017-05-03, E632, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2017-03-09 Created: 2017-03-07 Last updated: 2017-03-09Bibliographically approved
List of papers
1. On the Stability and Abundance of Single Walled Carbon Nanotubes
Open this publication in new window or tab >>On the Stability and Abundance of Single Walled Carbon Nanotubes
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2015 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, 16850Article in journal (Refereed) Published
Abstract [en]

Many nanotechnological applications, using single-walled carbon nanotubes (SWNTs), are only possible with a uniform product. Thus, direct control over the product during chemical vapor deposition (CVD) growth of SWNT is desirable, and much effort has been made towards the ultimate goal of chirality-controlled growth of SWNTs. We have used density functional theory (DFT) to compute the stability of SWNT fragments of all chiralities in the series representing the targeted products for such applications, which we compare to the chiralities of the actual CVD products from all properly analyzed experiments. From this comparison we find that in 84% of the cases the experimental product represents chiralities among the most stable SWNT fragments (within 0.2 eV) from the computations. Our analysis shows that the diameter of the SWNT product is governed by the well-known relation to size of the catalytic nanoparticles, and the specific chirality is normally determined by the product’s relative stability, suggesting thermodynamic control at the early stage of product formation. Based on our findings, we discuss the effect of other experimental parameters on the chirality of the product. Furthermore, we highlight the possibility to produce any tube chirality in the context of recent published work on seeded-controlled growth.

National Category
Other Physics Topics
Research subject
Tillämpad fysik
Identifiers
urn:nbn:se:ltu:diva-8424 (URN)10.1038/srep16850 (DOI)6ef8fdc5-e0fd-40e1-8ac0-14060031f749 (Local ID)6ef8fdc5-e0fd-40e1-8ac0-14060031f749 (Archive number)6ef8fdc5-e0fd-40e1-8ac0-14060031f749 (OAI)
Note
Validerad; 2015; Nivå 2; 20151119 (danhed)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-03-07Bibliographically approved
2. Length dependent stability of single-walled carbon nanotubes and how it affects their growth
Open this publication in new window or tab >>Length dependent stability of single-walled carbon nanotubes and how it affects their growth
2017 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 116, 443-447 p.Article in journal (Refereed) Published
Abstract [en]

Using density-functional theory the stability of armchair and zigzag single-walled carbon nanotubes and graphene nanoribbons was investigated. We found that the stability of armchair and zigzag nanotubes has different linear dependence with regard to their length, with switches in the most stable chirality occurring at specific lengths for each nanotube series. We explain these dependencies by competing edge and curvature effects. We have found that within each series armchair nanotubes are the most stable at short lengths, while zigzag nanotubes are the most stable at long lengths. These results shed new insights into why (near) armchair nanotubes are the dominant product from catalytic chemical vapor deposition growth, if templating is not used. Paradoxically, the stability of armchair nanotubes at short lengths favors their growth although zigzag nanotubes are more stable at long lengths, resulting in the production of the least stable nanotubes.

Keyword
Single-walled carbon nanotubes; Density functional theory; Stability; Selective growth; Chirality
National Category
Other Physics Topics
Research subject
Applied Physics
Identifiers
urn:nbn:se:ltu:diva-61856 (URN)10.1016/j.carbon.2017.02.007 (DOI)2-s2.0-85012164107 (ScopusID)
Note

Validerad; 2017; Nivå 2; 2017-02-15 (andbra)

Available from: 2017-02-07 Created: 2017-02-07 Last updated: 2017-03-07Bibliographically approved

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