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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.

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: 2018-07-10Bibliographically approved
Alfieri, L., Bracale, A. & Larsson, A. (2017). New Power Quality Indices for the Assessment of Waveform Distortions from 0 to 150 kHz in Power Systems with Renewable Generation and Modern Non-Linear Loads. Energies, 10(10), Article ID 1633.
Open this publication in new window or tab >>New Power Quality Indices for the Assessment of Waveform Distortions from 0 to 150 kHz in Power Systems with Renewable Generation and Modern Non-Linear Loads
2017 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 10, article id 1633Article in journal (Refereed) Published
Abstract [en]

The widespread use of power electronics converters, e.g., to interface renewable generation systems with the grid or to supply some high-efficiency loads, has caused increased levels of waveform distortions in the modern distribution system. Voltage and current waveforms include spectral components from 0 kHz to 150 kHz, characterized by a non-uniform time-frequency behavior. This wide interval of frequencies is currently divided into "low-frequency" (from 0 kHz to 2 kHz) and "high-frequency" (from 2 kHz to 150 kHz). While the low-frequencies have been exhaustively investigated in the relevant literature and are covered by adequate standardization, studies for the high-frequencies have been addressed only in the last decade to fill current regulatory gaps. In this paper, new power quality (PQ) indices for the assessment of waveform distortions from 0 kHz to 150 kHz are proposed. Specifically, some currently available indices have been properly modified in order to extend their application also to wide-spectrum waveforms. In the particular case of waveform distortions due to renewable generation, numerical applications prove that the proposed indices are useful tools for the characterization of problems (e.g., overheating, equipment malfunctioning, losses due to skin effects, hysteresis losses or eddy current losses) in cases of both low-frequency and high-frequency distortions

Place, publisher, year, edition, pages
MDPI, 2017
Keywords
power quality indices; waveform distortions; high-frequency spectral components; fluorescent lamps; renewable generation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-66531 (URN)10.3390/en10101633 (DOI)000414578400188 ()2-s2.0-85044466671 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-11-09 (andbra)

Available from: 2017-11-09 Created: 2017-11-09 Last updated: 2018-06-14Bibliographically approved
Baran, J. D., Jarvis, S. P., Taylor, S., Thompson, D., Saywell, A., Mangham, B., . . . Larsson, A. (2015). A Case of Unusually Large Density of States Changes For Physisorption - TetraPhenyl-Porphyrins on Cu(111) (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 >>A Case of Unusually Large Density of States Changes For Physisorption - TetraPhenyl-Porphyrins on Cu(111)
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2015 (English)Conference paper, Oral presentation only (Other academic)
Abstract [en]

Conformational changes caused by surface adsorption can dramatically affect a molecule’s properties. The conformational flexibility of the porphyrin family of molecules has been exploited particularly well in a number of contexts, including prototypical molecular switches. Despite this level of study, however, the exact mechanisms underpinning conformational switching are often unclear. We show that the conformation of the tetra(4-bromophenyl) porphyrin (Br4TPP) on Cu(111) depends critically on the precise adsorption site of the molecule, and that, remarkably, large conformational changes are driven entirely by van der Waals (vdW) interactions between the molecule and the substrate surface. A combination of scanning probe microscopy, low temperature single molecule manipulation, dispersion-corrected density functional theory (DFT) and molecular dynamics (MD) simulations shows that van der Waals forces dominate the adsorption of TPP molecules, causing significant distortions of the molecular architecture so that the porphyrin can adopt one of two low energy conformations. In addition, scanning probe manipulation has been used to translate and switch the Br4TPP molecule between conformations via an intermediary, ‘hybrid’ structure. We have used the generalized gradient approximation (GGA) parameterization by Perdew—Burke—Ernzerhof (PBE), and the sparse-matter optBP86b-vdW20 (vdW-DFT) exchange and correlation functional to account for the missing dispersion forces. In order to check for the presence of chemical bonding we have analyzed the molecule-surface complexes using electron localization function (ELF) and Bader charges. We find that vdW-forces alone are capable of causing large shifts in the molecular density of states, despite the complete absence of chemical interactions.

National Category
Other Physics Topics
Research subject
Tillämpad fysik
Identifiers
urn:nbn:se:ltu:diva-38115 (URN)c669215a-709a-48fa-8f48-5a8dbaaf8657 (Local ID)c669215a-709a-48fa-8f48-5a8dbaaf8657 (Archive number)c669215a-709a-48fa-8f48-5a8dbaaf8657 (OAI)
Conference
Towards Reality in Nanoscale Materials : 09/02/2015 - 11/02/2015
Note
Godkänd; 2015; 20150219 (landar)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-11-25Bibliographically approved
Löfgren, R., Pawar, R., Öberg, S. & Larsson, A. (2015). Density functional theory calculations on the diamond nitrogen-vacancy center (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 >>Density functional theory calculations on the diamond nitrogen-vacancy center
2015 (English)Conference paper, Poster (with or without abstract) (Other academic)
National Category
Other Physics Topics
Research subject
Tillämpad fysik
Identifiers
urn:nbn:se:ltu:diva-31061 (URN)51b8208b-3e99-4c27-acd6-04b36de6c069 (Local ID)51b8208b-3e99-4c27-acd6-04b36de6c069 (Archive number)51b8208b-3e99-4c27-acd6-04b36de6c069 (OAI)
Conference
Towards Reality in Nanoscale Materials : 09/02/2015 - 11/02/2015
Note
Godkänd; 2015; Bibliografisk uppgift: Supercell and slab calculations with Vasp; 20150219 (roblof)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-02-05Bibliographically approved
Silvearv, F., Larsson, P. O., Jones, S. L., Ahuja, R. B. & Larsson, A. (2015). Establishing the most favorable metal-carbon bond strength for carbon nanotube catalysts (ed.). Paper presented at . Journal of Materials Chemistry C, 3(14), 3422-3427
Open this publication in new window or tab >>Establishing the most favorable metal-carbon bond strength for carbon nanotube catalysts
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2015 (English)In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 3, no 14, p. 3422-3427Article in journal (Refereed) Published
Abstract [en]

We have studied a wide range of transition metals to find potential carbon nanotube (CNT) catalysts for chemical vapor deposition (CVD) production. The adhesion strengths between a CNT and a metal cluster were calculated using first principle density functional theory (DFT) for all 1st, 2nd and 3rd row transition metals. We have developed the criterion that the metal-carbon adhesion strength per bond must fulfill a Goldilocks principle for catalyzing CNT growth and used it to identify, besides the well known catalysts Fe, Co and Ni, a number of other potential catalysts, namely Y, Zr, Rh, Pd, La, Ce and Pt. Our results are consistent with previous experiments performed either in a carbon arc discharge environment or by a CVD-process with regard to CNT catalyst activity

National Category
Other Physics Topics
Research subject
Tillämpad fysik
Identifiers
urn:nbn:se:ltu:diva-7112 (URN)10.1039/c5tc00143a (DOI)000351871600025 ()2-s2.0-84925949919 (Scopus ID)56e881e9-25eb-4a08-819c-2dd21904c532 (Local ID)56e881e9-25eb-4a08-819c-2dd21904c532 (Archive number)56e881e9-25eb-4a08-819c-2dd21904c532 (OAI)
Note
Validerad; 2015; Nivå 2; 20150410 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Jarvis, S. P., Taylor, S., Baran, J. D., Champness, N. R., Larsson, A. & Moriarty, P. (2015). Measuring the mechanical properties of molecular conformers (ed.). Paper presented at . Nature Communications, 6, Article ID 8338.
Open this publication in new window or tab >>Measuring the mechanical properties of molecular conformers
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2015 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, article id 8338Article in journal (Refereed) Published
Abstract [en]

Scanning probe-actuated single molecule manipulation has proven to be an exceptionally powerful tool for the systematic atomic-scale interrogation of molecular adsorbates. To date, however, the extent to which molecular conformation affects the force required to push or pull a single molecule has not been explored. Here we probe the mechanochemical response of two tetra(4-bromophenyl)porphyrin conformers using non-contact atomic force microscopy where we find a large difference between the lateral forces required for manipulation. Remarkably, despite sharing very similar adsorption characteristics, variations in the potential energy surface are capable of prohibiting probe-induced positioning of one conformer, while simultaneously permitting manipulation of the alternative conformational form. Our results are interpreted in the context of dispersion-corrected density functional theory calculations which reveal significant differences in the diffusion barriers for each conformer. These results demonstrate that conformational variation significantly modifies the mechanical response of even simple porpyhrins, potentially affecting many other flexible molecules

National Category
Other Physics Topics
Research subject
Tillämpad fysik
Identifiers
urn:nbn:se:ltu:diva-9229 (URN)10.1038/ncomms9338 (DOI)000363021700002 ()26388232 (PubMedID)2-s2.0-84942155859 (Scopus ID)7cb8f2c9-5f82-4867-8f3c-9599d8222ed9 (Local ID)7cb8f2c9-5f82-4867-8f3c-9599d8222ed9 (Archive number)7cb8f2c9-5f82-4867-8f3c-9599d8222ed9 (OAI)
Note
Validerad; 2015; Nivå 2; 20150928 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically 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: 2018-07-10Bibliographically approved
Jarvis, S. P., Taylor, S., Baran, J. D., Thompson, D., Saywell, A., Mangham, B., . . . Moriarty, P. (2015). Physisorption Controls the Conformation and Density of States of an Adsorbed Porphyrin (ed.). Paper presented at . The Journal of Physical Chemistry C, 119(50), 27982-27994
Open this publication in new window or tab >>Physisorption Controls the Conformation and Density of States of an Adsorbed Porphyrin
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2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 50, p. 27982-27994Article in journal (Refereed) Published
Abstract [en]

Conformational changes caused by adsorption can dramatically affect a molecule's properties. Despite extensive study, however, the exact mechanisms underpinning conformational switching are often unclear. Here we show that the conformation of a prototypical flexible molecule, the free-base tetra(4-bromophenyl) porphyrin, adsorbed on Cu(111), depends critically on its precise adsorption site and that, remarkably, large conformational changes are dominated by van der Waals interactions between the molecule and the substrate surface. A combination of scanning probe microscopy, single-molecule manipulation, DFT with dispersion density functional theory, and molecular dynamics simulations show that van der Waals forces drive significant distortions of the molecular architecture so that the porphyrin can adopt one of two low-energy conformations. We find that adsorption driven by van der Waals forces alone is capable of causing large shifts in the molecular density of states, despite the apparent absence of chemical interactions. These findings highlight the essential role that van der Waals forces play in determining key molecular properties.

National Category
Other Physics Topics
Research subject
Tillämpad fysik
Identifiers
urn:nbn:se:ltu:diva-5740 (URN)10.1021/acs.jpcc.5b08350 (DOI)000366878500013 ()2-s2.0-84951775016 (Scopus ID)3eb60648-3b7f-4e25-b1e7-0d7f633e14db (Local ID)3eb60648-3b7f-4e25-b1e7-0d7f633e14db (Archive number)3eb60648-3b7f-4e25-b1e7-0d7f633e14db (OAI)
Note
Validerad; 2016; Nivå 2; 20160107 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically 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
Li, Y., Ahuja, R. B. & Larsson, A. (2014). Communication: Origin of the difference between carbon nanotube armchair and zigzag ends (ed.). Paper presented at . Journal of Chemical Physics, 140(9), Article ID 91102.
Open this publication in new window or tab >>Communication: Origin of the difference between carbon nanotube armchair and zigzag ends
2014 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 9, article id 91102Article in journal (Refereed) Published
Abstract [en]

In this work, we have found that the difference between armchair and zigzag ends of carbon nanotubes (CNTs) does not pertain at close study for individual bonds and thus alternative strategies need to be developed to reach the ultimate goals in selective growth. Based on first-principles simulations, the difference between binding strengths for CNTs of different chirality was investigated using hydrogen dissociation energies at their passivated ends. When all H atoms are removed collectively we find the well-known difference: that armchair bonds are much weaker than zigzag ones, which is typically seen for both CNT ends and graphene edges. However, when individual H atoms are removed we find almost no difference in hydrogen dissociation energies, small difference in bond lengths, which by association means small difference in C-C and M-C binding energies. We show convincingly that the difference in binding energy between armchair and zigzag ends is due to a fragment stabilization effect that is only manifested when all (or several neighbouring) bonds are broken. This is because at armchair ends/edges neighbouring dangling bonds can pair-up to form C≡C triple bonds that constitute a considerable stabilization effect compared to the isolated dangling bonds at zigzag ends/edges. Consequently, in many processes, e.g., catalytic growth where bonds are normally created/broken sequentially, not collectively, the difference between armchair and zigzag ends/edges cannot be used to discriminate growth of one type over the other to achieve chiral selective growth. Strategies are discussed to realize chirality selective growth in the light of the results presented, including addition of C2-fragments to favor armchair tubes

National Category
Other Physics Topics
Research subject
Tillämpad fysik
Identifiers
urn:nbn:se:ltu:diva-15192 (URN)10.1063/1.4867744 (DOI)000334067400003 ()2-s2.0-84896775010 (Scopus ID)eaf7245e-874b-4732-bb57-448859eb8733 (Local ID)eaf7245e-874b-4732-bb57-448859eb8733 (Archive number)eaf7245e-874b-4732-bb57-448859eb8733 (OAI)
Note
Validerad; 2014; 20140407 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-3455-2877

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