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Zhang, H., Hedman, D., Feng, P., Han, G. & Akhtar, F. (2019). A high entropy B4(HfMo2TaTi)C and SiC ceramic composite. In: : . Paper presented at XVI ECerS CONFERENCE.
Open this publication in new window or tab >>A high entropy B4(HfMo2TaTi)C and SiC ceramic composite
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2019 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Refractory carbides HfC, Mo2C, TiC, TaC, B4C, and SiC were mixed with a molar ratio of 2:1:2:2:1:2 to fabricate multicomponent ceramic composite by pulsed current processing (PCP). From the starting materials that consist of face-centered cubic (FCC), hexagonal and rhombohedral crystal structures, the investigated carbide system is reported to form a single phase B4(HfMo2TaTi)C high-entropy ceramic (HEC) with SiC. The HEC phase contains uniform distribution of constitutional elements Hf, Mo, Ta, Ti, B and C, according to Energy dispersive X-ray spectroscopy (EDS) and wavelength dispersive X-ray spectroscopy (WDS) results.

The fabricated HEC phase displays a hexagonal crystal structure, with a high average lattice distortion of 8.26% (Figure 1). The HCP structure was observed by X-ray diffraction and selected area diffraction in transmission electron microscopy (TEM). Density-functional theory (DFT) optimization suggested that the hexagonal crystal structure has alternating layers of metal atoms and carbon/boron atoms, i.e. metal atoms of Hf, Mo, Ta and Ti were distributed on the (0001) plane in the hexagonal lattice, while the carbon/boron atoms formed hexagonal 2D grids on the (0002) plane in the hexagonal unit cell. Despite of the vast differences in the crystal structures and lattice parameters among the utilized carbides, the formation of the unique hexagonal lattice structure of B4HfMo2TaTi)C can be a result of independent diffusion of the metal and nonmetal atoms. The sintered HEC ceramic composite exhibits excellent oxidation resistance at mediate temperature, 900 ºC for 50h, and elevated temperature, 2000 ºC for 20 s. Nanoindentation test shows that the HEC phase has a high hardness of 35 GPa. The remarkable improvement compared to the theoretical hardness value estimated based on the rule of mixtures (23 GPa) was contributed by the severe lattice distortion in the hexagonal structure.

National Category
Materials Engineering
Identifiers
urn:nbn:se:ltu:diva-74894 (URN)
Conference
XVI ECerS CONFERENCE
Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2019-06-24
Zhang, H., Hedman, D., Feng, P., Han, G. & Akhtar, F. (2019). A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite. Dalton Transactions, 48(16), 5161-5167
Open this publication in new window or tab >>A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite
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2019 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, no 16, p. 5161-5167Article in journal (Refereed) Published
Abstract [en]

A multicomponent composite of refractory carbides, B4C, HfC, Mo2C, TaC, TiC and SiC, of rhombohedral, face-centered cubic (FCC) and hexagonal crystal structures is reported to form a single phase B4(HfMo2TaTi)C ceramic with SiC. The independent diffusion of the metal and nonmetal atoms led to a unique hexagonal lattice structure of the B4(HfMo2TaTi)C ceramic with alternating layers of metal atoms and C/B atoms. In addition, the classical differences in the crystal structures and lattice parameters among the utilized carbides were overcome. Electron microscopy, X-ray diffraction and calculations using density functional theory (DFT) confirmed the formation of a single phase B4(HfMo2TaTi)C ceramic with a hexagonal close-packed (HCP) crystal structure. The DFT based crystal structure prediction suggests that the metal atoms of Hf, Mo, Ta and Ti are distributed on the (0001) plane in the HCP lattice, while the carbon/boron atoms form hexagonal 2D grids on the (0002) plane in the HCP unit cell. The nanoindentation of the high-entropy phase showed hardness values of 35 GPa compared to the theoretical hardness value estimated based on the rule of mixtures (23 GPa). The higher hardness was contributed by the solid solution strengthening effect in the multicomponent hexagonal structure. The addition of SiC as the secondary phase in the sintered material tailored the microstructure of the composite and offered oxidation resistance to the high-entropy ceramic composite at high temperatures.

Place, publisher, year, edition, pages
Royal Society of Medicine Press, 2019
National Category
Materials Engineering Ceramics Composite Science and Engineering Other Physics Topics
Research subject
Engineering Materials; Applied Physics
Identifiers
urn:nbn:se:ltu:diva-72953 (URN)10.1039/C8DT04555K (DOI)000465328200037 ()30778490 (PubMedID)2-s2.0-85064521555 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-08-20 (johcin)

Available from: 2019-02-20 Created: 2019-02-20 Last updated: 2019-08-20Bibliographically approved
Zhang, H., Hedman, D., Feng, P., Han, G. & Akhtar, F. (2019). Correction: A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite. Dalton Transactions, 48(19), 6647-6647
Open this publication in new window or tab >>Correction: A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite
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2019 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, no 19, p. 6647-6647Article in journal (Refereed) Published
Abstract [en]

The authors regret that there is an error in writing the crystal structure in the article. The authors would like to address as follows:

The presented XRD and TEM results revealed a hexagonal crystal structure. The following analyses including the identification of the lattice parameters and the DFT calculation were based on a hexagonal lattice. Therefore, the HCP (hexagonal close-packed) structure mentioned in the article should be regarded as a hexagonal structure. The HCP term used in the introduction, where the article from Joshua Gild et al. was cited, should also be regarded as hexagonal AlB2 structure.

The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

Place, publisher, year, edition, pages
Royal Society of Medicine Press, 2019
National Category
Materials Engineering Ceramics Composite Science and Engineering Other Physics Topics
Research subject
Engineering Materials; Applied Physics
Identifiers
urn:nbn:se:ltu:diva-74978 (URN)10.1039/C9DT90099C (DOI)000472451000039 ()2-s2.0-85065896417 (Scopus ID)
Note

Coorection to: A high-entropy B 4 (HfMo 2 TaTi)C and SiC ceramic composite

(2019) Dalton Transactions, 48 (16), pp. 5161-5167.DOI:10.1039/c8dt04555k

Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2019-08-15Bibliographically approved
Hedman, D. (2017). A Theoretical Study: The Connection between Stability of Single-Walled Carbon Nanotubes and Observed Products. (Licentiate dissertation). Luleå: Luleå University of Technology
Open this publication in new window or tab >>A Theoretical Study: The Connection between Stability of Single-Walled Carbon Nanotubes and Observed Products
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Alternative title[sv]
En Teoretisk Studie: Sambandet mellan Stabiliteten for Enkelväggiga Kolnanorör och Observerade Produkter
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 produced SWCNTs. These 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, tubes with 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 chiralities. A mixture of chiralities will give products with a mixture of different properties. 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 where the resulting product is uniform, meaning that all of the SWCNTs have the same chirality, a process termed chirality-specific growth. To achieve chirality-specific growth of SWCNTs requires us to obtain a better fundamental understanding about how they grow, both from an experimental and a theoretical point of view.

This work focuses on theoretical studies of SWCNT properties and how they relate to the growth process, thereby giving us vital new information about how SWCNTs grow and taking us ever closer to achieving the ultimate goal of chirality-specific growth. In this thesis, 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 results presented in this thesis are obtained using first principle density functional theory. 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 SWCNT-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 SWCNT stability. How these new results link to the existing understanding of SWCNT growth is 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
Keywords
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:nbn:se:ltu:diva-62321 (URN)978-91-7583-837-3 (ISBN)978-91-7583-838-0 (ISBN)
Presentation
2017-05-03, E632, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2017-03-09 Created: 2017-03-07 Last updated: 2017-11-24Bibliographically approved
Hedman, D. & Larsson, A. (2017). Length dependent stability of single-walled carbon nanotubes and how it affects their growth. Carbon, 116, 443-447
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, p. 443-447Article 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.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
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)000397549300053 ()2-s2.0-85012164107 (Scopus ID)
Note

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

Available from: 2017-02-07 Created: 2017-02-07 Last updated: 2019-09-13Bibliographically approved
Hedman, D. (2017). Linking Stability of Single-Walled Carbon Nanotubes with Growth Products. In: : . Paper presented at European Advanced Materials Congress 2017, Stockholm, 22 - 24 August 2017.
Open this publication in new window or tab >>Linking Stability of Single-Walled Carbon Nanotubes with Growth Products
2017 (English)Conference paper, Oral presentation only (Other academic)
Abstract [en]

Many of the envisioned products and technologies using single-walled carbon nanotubes (SWCNTs) are only possible with a uniform product. Thus, control over the chirality during catalytical chemical vapor deposition (CCVD) growth of SWCNTs is necessary. Our highlighted works1,2 focuses on stabilities of SWCNTs and how that relates to growth, in order to reach the ultimate goal of chirality-specific growth. In ref.1 density functional theory (DFT) has been used to calculate the stability of SWCNT-fragments of all chiralities in the (n+m) = 8 to 18 series. The fragment stabilities are compare to the chiralities of actual CCVD products from all properly analysed experiments to date. The results show that in 84% of the cases the experimental products represent chiralities among the most stable SWCNT-fragments (within 0.2 eV) from the calculations. The analysed products from growth experiments show that diameters of SWCNTs are governed by the well-known relation to the size of the catalytic particle and that the specific chirality of SWCNT products are strongly dependent on the stability of the tubes within each series, suggesting thermodynamic control at the early stage of growth. Analysis of the relative energy show that for the lower series 8 to 10, zigzag SWCNTs are the most stable and for the higher series 11 to 18 the most stable chirality changes from zigzag to armchair. This switch in stability between armchair and zigzag chiralities is studied further in ref.2, where DFT was used to calculate the stability of armchair and zigzag SWCNTs and graphene nanoribbons (GNRs) of different lengths. The calculations show that the stability of armchair and zigzag tubes has different linear dependence with regard to their length, with switches in the most stable chirality occurring at specific lengths for each SWCNT-series. These dependencies are explained by competing edge and curvature energies. Within each series armchair nanotubes are the most stable at short lengths, while zigzag nanotubes are the most stable at long lengths, this sheds new light into why armchair and near-armchair tubes are the dominant product from CCVD 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 SWCNTs.

Keywords
Single-walled carbon nanotubes, Density functional theory, Chirality-specific growth, Stability
National Category
Condensed Matter Physics Atom and Molecular Physics and Optics Other Physics Topics
Research subject
Applied Physics
Identifiers
urn:nbn:se:ltu:diva-65325 (URN)
Conference
European Advanced Materials Congress 2017, Stockholm, 22 - 24 August 2017
Available from: 2017-08-25 Created: 2017-08-25 Last updated: 2017-11-24Bibliographically approved
Hedman, D. (2017). On the Stability of Single-Walled Carbon Nanotubes and how it relates to Growth. In: CCTN17: 12th International Symposium on Computational Challenges and Tools for Nanotubes. Paper presented at 12th International Symposium on Computational Challenges and Tools for Nanotubes, Belo Horizonte, Brazil, 25-30 June 2017.
Open this publication in new window or tab >>On the Stability of Single-Walled Carbon Nanotubes and how it relates to Growth
2017 (English)In: CCTN17: 12th International Symposium on Computational Challenges and Tools for Nanotubes, 2017Conference paper, Oral presentation only (Other academic)
Abstract [en]

Many envisioned products and technologies using single-walled carbon nanotubes (SWCNTs) are only possible with a uniform product. Thus, control over the chirality during catalytical chemical vapor deposition (CCVD) growth is necessary. Our highlighted works [1,2] focuses on stabilities of SWCNTs and how they relate to growth. In ref. [1] density functional theory (DFT) is used to calculate the stability of SWCNT-fragments of all chiralities in the 8-18 series. The fragment stabilities are compare with chiralities from actual CCVD products. The results show that 84% of the experimental products represent chiralities among the most stable SWCNT-fragments (within 0.2 eV) from the calculations. The analyzed products from growth experiments show that the chirality of SWCNT products are strongly dependent on the stability of the tubes within each series, suggesting thermodynamic control at the early stage of growth. Analysis of the relative energy show that for lower series 8-10, zigzag SWCNTs are the most stable and for higher series 11-18 the most stable chirality changes from zigzag to armchair. This switch in stability is studied further in ref. [2], where DFT is used to calculate the stability of armchair and zigzag SWCNTs and graphene nanoribbons of different lengths. The calculations show that the stability of armchair and zigzag tubes have different linear dependence with regards to their length, with switches in the most stable chirality occurring at specific lengths for each SWCNT-series. These dependencies are explained by competing edge and curvature energies. Within each series armchair nanotubes are most stable at short lengths, while zigzag nanotubes are most stable at long lengths. This sheds new light into why armchair and near-armchair tubes are dominant products from CCVD growth.

[1] D. Hedman, H.R Barzegar, A. Rosen, T. Wågberg, J.A Larsson, Sci. Rep., 2015, 5, 16850. [2] D. Hedman, J.A. Larsson, Carbon, 2017, 116, 443.

Keywords
Single-walled carbon nanotubes, Density functional theory, Chirality-specific growth, Stability
National Category
Condensed Matter Physics Atom and Molecular Physics and Optics Other Physics Topics
Research subject
Applied Physics
Identifiers
urn:nbn:se:ltu:diva-65029 (URN)
Conference
12th International Symposium on Computational Challenges and Tools for Nanotubes, Belo Horizonte, Brazil, 25-30 June 2017
Available from: 2017-08-13 Created: 2017-08-13 Last updated: 2019-09-13Bibliographically approved
Hedman, D., Barzegar, H. R., Rosén, A., Wågberg, T. & Larsson, A. (2015). On the Stability and Abundance of Single Walled Carbon Nanotubes (ed.). Paper presented at . Scientific Reports, 5, Article ID 16850.
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, article id 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)000364945200001 ()26581125 (PubMedID)2-s2.0-84947723240 (Scopus ID)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: 2019-06-14Bibliographically approved
Hedman, D., Barzegar, H. R., Rosén, A., Wågberg, T. & Larsson, A. (2015). The relation between stability and abundance of single walled carbon nanotubes (ed.). Paper presented at Towards Reality in Nanoscale Materials : 09/02/2015 - 11/02/2015. Paper presented at Towards Reality in Nanoscale Materials : 09/02/2015 - 11/02/2015.
Open this publication in new window or tab >>The relation between stability and abundance of single walled carbon nanotubes
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2015 (English)Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

The ability to utilize the remarkable electrical and mechanical properties of single walled carbon nanotubes (SWNTs) can be hugely beneficial for technological applications. The limiting factors for these technological applications is that many of them rely on specific electrical/mechanical properties of the SWNT. The mechanical and electrical properties of a SWNT depends on its chiral indecencies n and m, which means that in order to get a desired electrical/mechanical property one needs to synthesize SWNTs with specific chiral indecencies.Huge effort has been put on trying to synthesize SWNTs with specific chiral indecencies or to post-purify them after synthesis. Although post-purification methods can result in a relatively high yield of SWNTs with specific chiralities, such methods are expensive, time consuming and may damage the SWNTs. A more efficient method would be to selectively grow/synthesize SWNTs with the desired properties. Chemical vapor deposition (CVD) has become a favored technique for trying to achieve selective SWNT growth since the process involves several controllable growth parameters.In our work we have investigated the relation between the relative stability of different SWNTs and compared that to the experimentally observed statistical abundance of the same SWNTs. The relative energy of the SWNTs was calculated using density functional theory with the VASP-code. We have chosen to include all the SWNTs in the (n+m) = 8,9,10,11,12,13,14,15,16,17 and 18-series in our calculations, this equals 80 SWNTs in total. The SWNT models used in our calculations are six layered hydrogen terminated SWNT fragments where each layer contains 2(n+m) carbon atoms.Our calculations show a remarkable connection between the relative stability of the SWNTs and their statistical abundance in experiments. The most stable SWNT in each series correlates with the most abundant SWNT in that series, as found in the experimental results gathered from the literature.

Keywords
Carbon nanotubes, Selective growth, Chirality, Density functional theory, Raman spectroscopy, Photoluminescence, Natural sciences - Physics, Naturvetenskap - Fysik
National Category
Other Physics Topics
Research subject
Tillämpad fysik
Identifiers
urn:nbn:se:ltu:diva-29568 (URN)313ce9f9-bfc3-4577-8725-0f5637db3f36 (Local ID)313ce9f9-bfc3-4577-8725-0f5637db3f36 (Archive number)313ce9f9-bfc3-4577-8725-0f5637db3f36 (OAI)
Conference
Towards Reality in Nanoscale Materials : 09/02/2015 - 11/02/2015
Note
Godkänd; 2015; 20150219 (danhed)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
Hedman, D. & Fjellström, M. (2013). Modeling the interactions between magnetic particles (ed.). Paper presented at .
Open this publication in new window or tab >>Modeling the interactions between magnetic particles
2013 (English)Report (Other academic)
Abstract [en]

The aim of the work presented here is to describe the appearance of force curves from atomic force microscopy measurements between two interacting magnetic particles. A model treating particles as points is first presented. This model is found to accurately describe interactions involving spherical particles, but is not equally successful in describing interactions between particles of cylindrical and conical geometries at short surface separations. Effects from particle geometries are introduced in the dimensional model through dimensional analysis. A characteristic length describing the vertical extent of the particles is defined. An example calculation of the characteristic length for a spherical particle of known radius is presented. The same computational method is then applied to several experimental force curves from atomic force microscopy measurements. The calculated characteristic lengths are of comparable size to the known vertical extent of the particles. Reconstruction of the experimental force curves using the calculated characteristic lengths in the dimensional model gives good agreement between theory and experiment.

Publisher
p. 25
Keywords
Magnetic dipole, Magnetic interaction, Microsized particles, Magnetite, Atomic force microscopy, Natural sciences - Physics, Naturvetenskap - Fysik
National Category
Other Physics Topics
Research subject
Tillämpad fysik
Identifiers
urn:nbn:se:ltu:diva-22908 (URN)4c6a7509-7c59-42a7-b9f3-f3c41711fe8f (Local ID)4c6a7509-7c59-42a7-b9f3-f3c41711fe8f (Archive number)4c6a7509-7c59-42a7-b9f3-f3c41711fe8f (OAI)
Note
Godkänd; 2013; 20140505 (danhed)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1542-6170

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