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  • 1.
    Han, Yilin
    et al.
    School of Physical Science and Technology, Southwest University, Chongqing, China.
    Chen, Zongbin
    College of Science, North China University of Science and Technology, China.
    Kuang, Minquan
    School of Physical Science and Technology, Southwest University, Chongqing, China.
    Liu, Zhuhong
    University of Science and Technology Beijing (USTB), Beijing, China.
    Wang, Xiangjian
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Wang, Xiaotian
    School of Physical Science and Technology, Southwest University, Chongqing, China.
    171 Scandium-based full Heusler compounds: A comprehensive study of competition between XA and L21 atomic ordering2019Ingår i: Results in Physics, ISSN 2211-3797, Vol. 12, s. 435-446Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The site-preference rule (SPR), which is widely used to design and study the properties of full-Heusler alloys X2YZ, is applied to determine the positions of different transition-metal elements with various numbers of valence electrons in Heusler alloys. The scandium-based full Heusler alloys should form an XA structure according to the SPR, because the transition-metal element Sc with fewer valence electrons tends to occupy the Wyckoff sites A(0, 0, 0) and B(0.25, 0.25, 0.25). As opposed to previous investigations, L21-type scandium-based full Heusler alloys, which do not follow the SPR, are also considered in this work. Theoretical computations are used to study the atomic-site preferences of 171 scandium-based full Heusler alloys, and the results indicate that most of these alloys form L21-type structures rather than XA-type structures. Two possible orderings are also studied in terms of their difference in charge density. Furthermore, the ground state, electronic structure, and magnetic characteristics of these alloys are also investigated in detail in both XA and L21 structures. The results reveal dramatic differences between XA- and L21-type alloys. This study thus presents a counterexample of the SPR rule and should provide significant guidance for the future design of full-Heusler alloys.

  • 2.
    Zhang, Hanzhu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Luleå university of technology.
    Hedman, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Feng, Peizhong
    China University of Mining and Technology.
    Han, Gang
    University of Science and Technology Beijing.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite2019Ingår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, nr 16, s. 5161-5167Artikel i tidskrift (Refereegranskat)
    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.

  • 3.
    Bathen, M. E.
    et al.
    Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, Oslo, Norway.
    Coutinho, J.
    Department of Physics and I3N, University of Aveiro, Campus Santiag, Aveiro, Portugal.
    Ayedh, H. M.
    Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, Oslo, Norway.
    Hassan, J. Ul
    Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden.
    Farkas, I.
    Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Frodason, Y. K.
    Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, Oslo, Norway.
    Svensson, B. G.
    Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, Oslo, Norway.
    Vines, L.
    Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, Oslo, Norway.
    Anisotropic and plane-selective migration of the carbon vacancy in SiC: Theory and experiment2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 1, artikel-id 014103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the migration mechanism of the carbon vacancy (VC) in silicon carbide (SiC) using a combination of theoretical and experimental methodologies. The VC, commonly present even in state-of-the-art epitaxial SiC material, is known to be a carrier lifetime killer and therefore strongly detrimental to device performance. The desire for VC removal has prompted extensive investigations involving its stability and reactivity. Despite suggestions from theory that VC migrates exclusively on the C sublattice via vacancy-atom exchange, experimental support for such a picture is still unavailable. Moreover, the existence of two inequivalent locations for the vacancy in 4H-SiC [hexagonal, VC(h), and pseudocubic, VC(k)] and their consequences for VC migration have not been considered so far. The first part of the paper presents a theoretical study of VC migration in 3C- and 4H-SiC. We employ a combination of nudged elastic band (NEB) and dimer methods to identify the migration mechanisms, transition state geometries, and respective energy barriers for VC migration. In 3C-SiC, VC is found to migrate with an activation energy of EA=4.0 eV. In 4H-SiC, on the other hand, we anticipate that VC migration is both anisotropic and basal-plane selective. The consequence of these effects is a slower diffusivity along the axial direction, with a predicted activation energy of EA=4.2 eV, and a striking preference for basal migration within the h plane with a barrier of EA=3.7 eV, to the detriment of the k-basal plane. Both effects are rationalized in terms of coordination and bond angle changes near the transition state. In the second part, we provide experimental data that corroborates the above theoretical picture. Anisotropic migration of VC in 4H-SiC is demonstrated by deep level transient spectroscopy (DLTS) depth profiling of the Z1/2 electron trap in annealed samples that were subject to ion implantation. Activation energies of EA=(4.4±0.3) eV and EA=(3.6±0.3) eV were found for VC migration along the c and a directions, respectively, in excellent agreement with the analogous theoretical values. The corresponding prefactors of D0=0.54cm2/s and 0.017cm2/s are in line with a simple jump process, as expected for a primary vacancy point defect.

  • 4.
    Zhang, Hanzhu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Luleå university of technology.
    Hedman, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Feng, Peizhong
    China University of Mining and Technology.
    Han, Gang
    University of Science and Technology Beijing.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Correction: A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite2019Ingår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, nr 19, s. 6647-6647Artikel i tidskrift (Refereegranskat)
    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.

  • 5.
    Gorbatov, Oleg
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Materials Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden. Laboratory for Mechanics of Gradient Nanomaterials, Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia.
    Stroev, A. Yu.
    National Research Centre, Kurchatov Institute, Moscow, Russia. Moscow Institute of Physics and Technology (State University), Dolgoprudny, Moscow Region, Russia.
    Gornostyrev, Yu. N.
    Institute of Metal Physics, Ural Division RAS, Ekaterinburg, Russia. Institute of Quantum Materials Science, Ekaterinburg, Russia.
    Korzhavyi, P. A.
    Department of Materials Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden. Institute of Metal Physics, Ural Division RAS, Ekaterinburg, Russia.
    Effective cluster interactions and pre–precipitate morphology in binary Al-based alloys2019Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 179, s. 70-84Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The strengthening by coherent, nano-sized particles of metastable phases (pre-precipitates) continues to be the main design principle for new high-performance aluminium alloys. To describe the formation of such pre-precipitates in Al–Cu, Al–Mg, Al–Zn, and Al–Si alloys, we carry out cluster expansions of ab initio calculated energies for supercell models of the dilute binary Al-rich solid solutions. Effective cluster interactions, including many-body terms and strain-induced contributions due to the lattice relaxations around solute atoms, are thus systematically derived. Monte Carlo and statistical kinetic theory simulations, parameterized with the obtained effective cluster interactions, are then performed to study the early stages of decomposition in the binary Al-based solid solutions. We show that this systematic approach to multi-scale modelling is capable of incorporating the essential physical contributions (usually referred to as atomic size and electronic structure factors) to the free energy, and is therefore able to correctly describe the ordering temperatures, atomic structures, and morphologies of pre-precipitates in the four studied alloy systems.

  • 6.
    Wang, Xiangjian
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Frontier Institute of Science and Technology, and State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China.
    Gao, Hongcheng
    Inner Mongolia Key Laboratory of Ferroelectric-related New Energy Materials and Devices, School of Materials and Metallurgy, Inner Mongolia University of Science and Technology, Baotou 014010, China.
    Hao, Xihong
    Inner Mongolia Key Laboratory of Ferroelectric-related New Energy Materials and Devices, School of Materials and Metallurgy, Inner Mongolia University of Science and Technology, Baotou 014010, China.
    Lou, Xiaojie
    Frontier Institute of Science and Technology, and State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China.
    Enhanced piezoelectric, electrocaloric and energy storage properties at high temperature in lead-free Bi0.5(Na1-xKx)0.5TiO3ceramics2019Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 45, nr 4, s. 4274-4282Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The piezoelectric, electrocaloric and energy storage properties were systemically investigated in lead-free Bi0.5(Na1-xKx)0.5TiO3 ceramics from room temperature to high temperature region. These ceramics can be poled completely to obtain large piezoelectric coefficient (104–153 pC/N) at low electric field of ~30 kV/cm. The piezoelectric propertyshows good thermal stability due to high depolarization temperature (Td). For BNKT20, a large low electric field-induced strain of 0.36% is obtained at 120 °C under 50 kV/cm, the corresponding normalized strain coefficient is up to 720 pm/V, which is larger than other BNT-based ceramics at high temperature region. The electrocaloric properties of these ceramics are studied via indirect and direct methods. Large EC value (~1.08 K) in BNKT20ceramic is obtained at 50 kV/cm using indirect calculation. Above 100 °C, the dielectricenergy storage density and efficiency of BNKT20 is still up to ~0.85 J/cm3 and 0.75, respectively. The BNKTx ceramics may become promising candidates in the fields of actuators, electrocaloric cooling and energy storage at high temperature region.

  • 7.
    Öström, Jonatan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Bezrukov, Dmitry S.
    Department of Chemistry, M. V. Lomonosov Moscow State University.
    Nyman, Gunnar
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Erratum: “Reaction rate constant for radiative association of CF+” [J. Chem. Phys. 144, 044302 (2016)]2019Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, nr 24, artikel-id 249901Artikel i tidskrift (Refereegranskat)
  • 8.
    Szabo, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Formation of the NH molecule and its isotopologues through radiative association2019Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 483, nr 3, s. 3574-3578Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rate coefficients and the cross-sections for the formation of imidogen (NH) molecule (and its isotopologues: 15NH and ND) through radiative association are determined by employing quantum mechanical perturbation theory, classical Larmor formula, and Breit–Wigner theory. We suggest the radiative association process as possible route for NH production in diffuse interstellar clouds.

  • 9.
    Verkhoturov, Stanislav V.
    et al.
    Department of Chemistry, Texas A&M University, College Station, Texas, USA.
    Gołuński, Mikołaj
    Department of Physics, Jagiellonian University, Kraków, Poland.
    Verkhoturov, Dmitriy S.
    Department of Chemistry, Texas A&M University, College Station, Texas, USA.
    Czerwinski, Bartlomiej
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Eller, Michael J.
    Department of Chemistry, Texas A&M University, College Station, Texas, USA.
    Geng, Sheng
    Department of Chemistry, Texas A&M University, College Station, Texas, USA.
    Postawa, Zbigniew
    Department of Physics, Jagiellonian University, Kraków, Poland.
    Schweikert, Emile A.
    Department of Chemistry, Texas A&M University, College Station, Texas, USA.
    Hypervelocity cluster ion impacts on free standing graphene: Experiment, theory, and applications2019Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, nr 16, artikel-id 160901Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present results from experiments and molecular dynamics (MD) simulations obtained with C60 and Au400 impacting on free-standing graphene, graphene oxide (GO), and graphene-supported molecular layers. The experiments were run on custom-built ToF reflectron mass spectrometers with C60 and Au-LMIS sources with acceleration potentials generating 50 keV C2+ 60 and 440–540 keV Au4+ 400. Bombardmentdetection was in the same mode as MD simulation, i.e., a sequence of individual projectile impacts with separate collection/identification of the ejecta from each impact in either the forward (transmission) or backward (reflection) direction. For C60 impacts on single layer graphene, the secondary ion (SI) yields for C2 and C4 emitted in transmission are ∼0.1 (10%). Similar yields were observed for analyte-specific ions from submonolayer deposits of phenylalanine. MD simulations show that graphene acts as a trampoline, i.e., they can be ejected without destruction. Another topic investigated dealt with the chemical composition of free-standing GO. The elemental composition was found to be approximately COH2. We have also studied the impact of Au400 clusters on graphene. Again SI yields were high (e.g., 1.25 C /impact). 90–100 Au atoms evaporate off the exiting projectile which experiences an energy loss of ∼72 keV. The latter is a summation of energy spent on rupturing the graphene, ejecting carbon atoms and clusters and a dipole projectile/hole interaction. The charge distribution of the exiting projectiles is ∼50% neutrals and ∼25% either negatively or positively charged. We infer that free-standing graphene enables detection of attomole to zeptomole deposits of analyte via cluster-SI mass spectrometry

  • 10.
    Shi, P.
    et al.
    Xi'an Jiaotong University, Xi'an, China.
    Zhu, L.
    Xi'an Jiaotong University, Xi'an, China.
    Gao, W.
    Xi'an Jiaotong University, Xi'an, China.
    Yu, Z.
    Xi'an Jiaotong University, Xi'an, China.
    Lou, X.
    Xi'an Jiaotong University, Xi'an, China.
    Wang, Xiangjian
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Yang, Z.
    Xi'an Jiaotong University, Xi'an, China.
    Yang, S.
    Xi'an Jiaotong University, Xi'an, China.
    Large energy storage properties of lead-free (1-x)(0.72Bi0.5Na0.5TiO3-0.28SrTiO3)-xBiAlO3 ceramics at broad temperature range2019Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 784, s. 788-793Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    (1-x)(0.72Bi0.5Na0.5TiO3-0.28SrTiO3)-xBiAlO3 (BNT-ST-xBA) lead-free ceramics were prepared through solid-state sintering methods. The structural, dielectric and energy storage properties of the ceramics were studied in this work. A large energy storage density of BNT-ST-0.01BA ceramics exceeding 1.746 J/cm3 has been obtained. The ceramics exhibit a good thermal stability at the temperature ranging from 20 °C to 120 °C. In addition, energy storage properties are relatively stable after completing 10000 electrical cycles, which shows promising potential for energy storage devices at a high temperature region.

  • 11.
    Hansson, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Livet, Universum & Allting: Samlade Populärvetenskapliga Krönikor2019Bok (Övrig (populärvetenskap, debatt, mm))
  • 12.
    Sundbaum, Johanna
    et al.
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Medicinsk vetenskap. Department of Medical Sciences, Rheumatology, Uppsala University, Uppsala, Sweden.
    Eriksson, Niclas
    Department of Medical Sciences, Clinical Pharmacology and Science for Life Laboratory, Uppsala University, Uppsala, Sweden.
    Hallberg, Pär
    Department of Medical Sciences, Clinical Pharmacology and Science for Life Laboratory, Uppsala University, Uppsala, Sweden.
    Lehto, Niklas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Health Sciences, Luleå University of Technology, Luleå, Sweden.
    Wadelius, Mia
    Department of Medical Sciences, Clinical Pharmacology and Science for Life Laboratory, Uppsala University, Uppsala, Sweden.
    Baecklund, Eva
    Department of Medical Sciences, Rheumatology, Uppsala University, Uppsala, Sweden.
    Methotrexate treatment in rheumatoid arthritis and elevated liver enzymes: A long‐term follow‐up of predictors, surveillance, and outcome in clinical practice2019Ingår i: International Journal of Rheumatic Diseases, E-ISSN 1756-185X, Vol. 22, nr 7, s. 1226-1232Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aim

    To assess predictors of alanine aminotransferase (ALT) elevation in methotrexate (MTX) treated rheumatoid arthritis (RA) patients, and to describe the monitoring of liver enzymes, including handling and outcome of elevated ALT.

    Methods

    All RA patients starting MTX in January, 2005 to April, 2013 at a rheumatology clinic, (Uppsala University Hospital, Sweden) were identified from electronic medical records. Clinical and laboratory data were obtained from medical records, supplemented by telephone interviews. Predictors for ALT >1.5× over the upper limit of normal (ULN) were identified by multiple regression analysis.

    Results

    The study comprised 213 RA patients starting MTX. During a mean follow‐up of 4.3 years, 6288 ALT tests were performed; 7% of tests with ALT were >ULN. ALT >1.5× ULN was observed in 44 (21%) patients and the strongest predictor was a pre‐treatment elevation of ALT (adjusted odds ratio = 6.8, 95% CI 2.2‐20.5). Recurrent elevations occurred in 70% of patients who continued treatment, and the proportion was similar in those with and without interventions, for example MTX dose reduction (67% vs 73%, P = 0.43). Seven patients (3%) permanently stopped MTX due to ALT elevation, and two were eventually diagnosed with non‐alcoholic fatty liver disease. No patient developed hepatic failure.

    Conclusion

    Only a small number of ALT tests performed during MTX therapy in RA capture an elevation. A pre‐treatment elevation of ALT was the strongest predictor for early and recurrent ALT elevations during therapy. This study supports a more individualized approach to monitoring and handling of ALT elevations during MTX therapy in RA than recommended in current guidelines.

  • 13.
    Gustafsson, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Forrey, Robert C.
    Pennsylvania State University, Reading, USA.
    Semiclassical methods for calculating radiative association rate constants for different thermodynamic conditions: Application to formation of CO, CN, and SiN2019Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, ISSN 0021-9606, Vol. 150, nr 22, artikel-id 224301Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is well-known that resonances can serve as a catalyst for molecule formation. Rate constants for resonance-induced molecule formation are phenomenological as they depend upon the mechanism used to populate the resonances. Standard treatments assume tunneling from the continuum is the only available population mechanism, which means long-lived quasibound states are essentially unpopulated. However, if a fast resonance population mechanism exists, the long-lived quasibound states may be populated and give rise to a substantial increase in the molecule formation rate constant. In the present work, we show that the semiclassical formula of Kramers and ter Haar [Bull. Astron. Inst. Neth. 10, 137 (1946)] may be used to compute rate constants for radiative association in the limit of local thermodynamic equilibrium. Comparisons are made with quantum mechanical and standard semiclassical treatments, and results are shown for two limits which provide upper and lower bounds for the six most important radiative association reactions leading to the formation of CO, CN, and SiN. These results may have implications for interstellar chemistry in molecular clouds, where the environmental and thermodynamic conditions often are uncertain.

  • 14.
    Shmakov, I. G.
    et al.
    Institute of Metal Physics, Ural Division RAS, 620219, Ekaterinburg, Russia.
    Gorbatov, Oleg
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. KTH Royal Institute of Technology, Nosov Magnitogorsk State Technical University, 455000, Magnitogorsk, Russia.
    Serikov, V. V.
    Institute of Metal Physics, Ural Division RAS, 620219, Ekaterinburg, Russia.
    Kleinerman, N. M.
    Institute of Metal Physics, Ural Division RAS, 620219, Ekaterinburg, Russia.
    Golovnya, O. A.
    Institute of Metal Physics, Ural Division RAS, 620219, Ekaterinburg, Russia.
    Gornostyrev, Yu. N.
    Institute of Metal Physics, Ural Division RAS, 620219, Ekaterinburg, Russia.
    Short-range order formation in Fe-Co alloys: NMR study and first-principles calculations2019Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 782, s. 1008-1014Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The short/long-range order formation in Fe1-x-Cox (x < 0.3) alloys has been studied by the nuclear magnetic resonance (NMR) technique, as well as ab initio based atomistic simulation. The NMR measurements show up the formation of a certain short-range order (SRO) in dilute limit above the Curie temperature TC and of the D03-type SRO (with the dominance of 3rd Co-Co nearest neighbors) in the concentration range 0.2 < x < 0.3 after quenching and subsequent annealing in the ferromagnetic state. The results of Monte Carlo simulations of binary Fe-Co alloys with ab initio interatomic interactions predict SRO in agreement with the experiment for small concentrations of Co (CCo< 0.1), while the B2-type ordering is preferable in binary alloy in the ferromagnetic state. We demonstrate that the presence of point defects (vacancies, interstitial) can change essentially the ordering in alloys with the Co content 20-30% and result in the D03-type SRO formation in a reasonable agreement with the experiment.

  • 15.
    Hedman, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Single-Walled Carbon Nanotubes: A theoretical study of stability, growth and properties2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Since their discovery over 25 years ago, scientists have explored the remarkable properties of single-walled carbon nanotubes (SWCNTs) for use in high-tech materials and devices, such as strong light-weight composites, efficient electrical wires, supercapacitors and high-speed transistors. However, the mass production of such materials and devices is still limited by the capability of producing uniform high-quality SWCNTs. The properties of a SWCNT are determined by the orientation of the hexagonal grid of carbon atoms constituting the tube wall, this is known as the chirality of the SWCNT.

    Today's large-scale methods for producing SWCNTs, commonly known as growth, give products with a large spread of different chiralities. A mixture of chiralities give products with a mixture of different properties. This is one of the major obstacles preventing large-scale use of SWCNTs in future materials and devices. The goal is to achieve growth where the resulting product is uniform, meaning that all SWCNTs have the same chirality, a process termed chirality-specific growth. To achieve this requires a deep fundamental understanding of how SWCNTs grow, both from an experimental and a theoretical perspective.

    This work focuses on theoretical studies of SWCNTs and their growth mechanisms. With the goal of achieving a deeper understanding of how chirality arises during growth and how to control it. Thus, taking us ever closer to the ultimate goal of achieving chirality-specific growth. In this thesis, an introduction to the field is given and the current research questions are stated. Followed by chapters on carbon nanomaterials, SWCNTs and computational physics. A review of the state-of-the-art experimental and theoretical works relating to chirality specific growth is also given.

    The results presented in this thesis are obtained using first principle density functional theory calculations. Results show that the stability of short SWCNT-fragments can be linked to the products observed in experiments. In 84% of the investigate cases, the chirality of experimental products matches the chirality of the most stable SWCNT-fragments (within 0.2 eV). Further studies also reveal a previously unknown link between the stability of SWCNT-fragments and their length. Calculations show that at specific lengths the most stable chirality changes. Thus, introducing the concept of a switching length for SWCNT stabilities.

    This newly found property of SWCNTs is used in combination with previously published works to create a state-of-the-art analytical model to investigate growth of SWCNTs any temperature. Results from the model show that the most stable chirality obtained is dependent on the diameter, length of the SWCNT, the growth temperature and the composition of the catalyst. Finally, a detailed study on the ability of catalyst metals to sustain SWCNT growth points to Pt as an interesting candidate to achieve growth of rarely seen chiralities. The new knowledge gained from these results takes us even closer to achieving chirality-specific growth.

  • 16.
    Wu, Mengxin
    et al.
    School of Physical Science and Technology, Southwest University, Chongqing, People’s Republic of China.
    Han, Yilin
    School of Physical Science and Technology, Southwest University, Chongqing, People’s Republic of China.
    Bouhemadou, A.
    Laboratory for Developing New Materials and Their Characterization, University Ferhat Abbas Setif 1, Setif, Algeria.
    Cheng, Zhenxiang
    Institute for Superconducting and Electronic Materials (ISEM), University of Wollongong, Wollongong, Australia.
    Khenata, R.
    Laboratoire de Physique Quantique de la Matie ` re et de Mode ́ lisation Mathe ́ matique (LPQ3M), Universite ́ de Mascara, Mascara, Algeria.
    Kuang, Minquan
    School of Physical Science and Technology, Southwest University, Chongqing, People’s Republic of China.
    Wang, Xiangjian
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Yang, Tie
    School of Physical Science and Technology, Southwest University, Chongqing, People’s Republic of China.
    Yuan, Hongkuan
    School of Physical Science and Technology, Southwest University, Chongqing, People’s Republic of China.
    Wang, Xiaotian
    School of Physical Science and Technology, Southwest University, Chongqing, People’s Republic of China.
    Site preference and tetragonal distortion inpalladium-rich Heusler alloys2019Ingår i: IUCrJ, ISSN 0972-6918, E-ISSN 2052-2525, Vol. 6, s. 218-225Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, two kinds of competition between different Heusler structure types are considered, one is the competition between XA and L2(1) structures based on the cubic system of full-Heusler alloys, Pd(2)YZ (Y = Co, Fe, Mn; Z = B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, Sb). Most alloys prefer the L2(1) structure; that is, Pd atoms tend to occupy the a (0, 0, 0) and c (0.5, 0.5, 0.5) Wyckoff sites, the Y atom is generally located at site b (0.25, 0.25, 0.25), and the main group element Z has a preference for site d (0.75, 0.75, 0.75), meeting the well known site-preference rule. The difference between these two cubic structures in terms of their magnetic and electronic properties is illustrated further by their phonon dispersion and density-of-states curves. The second type of competition that was subjected to systematic study was the competitive mechanism between the L2(1 )cubic system and its L1(0) tetragonal system. A series of potential tetragonal distortions in cubic full-Heusler alloys (Pd(2)YZ) have been predicted in this work. The valley-and-peak structure at, or in the vicinity of, the Fermi level in both spin channels is mainly attributed to the tetragonal ground states according to the density-of-states analysis. Delta E-M is defined as the difference between the most stable energy values of the cubic and tetragonal states; the larger the value, the easier the occurrence of tetragonal distortion, and the corresponding tetragonal structure is stable. Compared with the Delta E-M values of classic Mn-2 based tetragonal Heusler alloys, the Delta E(M )values of most Pd(2)CoZ alloys in this study indicate that they can overcome the energy barriers between cubic and tetragonal states, and possess possible tetragonal transformations. The uniform strain has also been taken into consideration to further investigate the tetragonal distortion of these alloys in detail. This work aims to provide guidance for researchers to further explore and study new magnetic functional tetragonal materials among the full-Heusler alloys.

  • 17.
    Löfgren, Robin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pawar, Ravinder
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Larsson, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    The bulk conversion depth of the NV-center in diamond: computing a charged defect in a neutral slab2019Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 21, artikel-id 053037Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The negatively charged nitrogen vacancy (NV-) center in diamond has properties that make it a promising candidate for applications such as a qubit in room temperature quantum computing, single-molecule photoluminescence and NMR sensor, and as a single photon source for quantum cryptography. For many of its uses it is desirable to have the NV-center close to the diamond surface. In this work, we use density functional theory simulations to investigate how the distance of the NV- center to a surface, and its orientation, affect its properties, including the zero-phonon-line. We study the three technologically important surfaces terminated with fluorine, oxygen/hydroxyl and nitrogen. Since the NV-center is charged it requires special measures to simulate within a slab-model. We use the recently proposed charging with a substitutional donor in the diamond lattice resulting in a neutral super-cell, which provides very satisfactory results. We have found that the NV-centers properties converge to bulk values already at 5 angstrom depth.

  • 18.
    Karman, Tijs
    et al.
    Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA. Radboud University, Nijmegen, the Netherlands. Durham University, United Kingdom.
    Gordon, Iouli
    Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
    van der Avoird, A.
    Radboud University, Nijmegen, the Netherlands.
    Baranov, Yury
    Institute of Experimental Meteorology, Obninsk, Russia.
    Boulet, Christian
    Université Paris-Sud, Orsay, France.
    Drouin, Brian
    Jet Propulsion Laboratory, Caltech, Pasadena, CA, USA.
    Groenenboom, Gerrit
    Radboud University, Nijmegen, the Netherlands.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hartmann, Jean-Michel
    Sorbonne Université, Palaiseau, France.
    Kurucz, Robert
    Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
    Rothman, Laurence
    Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
    Sun, Kang
    Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA. University at Buffalo, Buffalo, NY, USA.
    Sung, Keeyoon
    Jet Propulsion Laboratory, Caltech, Pasadena, CA, USA.
    Thalman, Ryan
    University of Colorado Boulder, Boulder, CO, USA. Snow College, Ephraim, UT, USA.
    Tran, Ha
    Sorbonne Université, Paris, France.
    Wishnow, Edward
    University of California Berkeley, Berkeley, CA, USA.
    Wordsworth, Robin
    Harvard University, Cambridge, MA, USA.
    Vigasin, Andrey
    Russian Academy of Sciences, Moscow, Russia.
    Volkamer, Rainer
    University of Colorado Boulder, Boulder, CO, USA.
    van der Zande, Wim
    Radboud University, Nijmegen, the Netherlands.
    Update of the HITRAN collision-induced absorption section2019Ingår i: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643, Vol. 328, s. 160-175Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Correct parameterization of the Collision-induced Absorption (CIA) phenomena is essential for accurate modeling of planetary atmospheres. The HITRAN spectroscopic database provides these parameters in a dedicated section. Here, we significantly revise and extend the HITRAN CIA data with respect to the original effort described in Richard et al. [JQSRT 113, 1276 (2012)]. The extension concerns new collisional pairs as well as wider spectral and temperature ranges for the existing pairs. The database now contains CIA for N2N2, N2H2, N2-CH4, N2H2O, N2O2, O2O2, O2-CO2, CO2-CO2, H2H2, H2He, H2-CH4, H2H, HHe, CH4-CH4, CH4-CO2, CH4He, and CH4Ar collision pairs. The sources of data as well as their validation and selection are discussed. A wish list to eliminate remaining deficiencies or lack of data from the astrophysics perspective is also presented.

  • 19.
    Koumpouras, Konstantinos
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Yudin, Dmitry
    Sankt Peterburgskij nacional'nyj issledovatel'skij universitet informacionnyh tehnologij mehaniki i optiki.
    Adelmann, Christoph
    IMEC, Heverlee, Vlaams .
    Bergman, Anders
    Uppsala University.
    Eriksson, Olle
    Uppsala University.
    Pereiro, Manuel
    Department of Physics and Astronomy, Uppsala Universitet.
    A majority gate with chiral magnetic solitons2018Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, nr 37, artikel-id 375801Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In magnetic materials, nontrivial spin textures may emerge due to the competition among different types of magnetic interactions. Among such spin textures, chiral magnetic solitons represent topologically protected spin configurations with particle-like properties. Based on atomistic spin dynamics simulations, we demonstrate that these chiral magnetic solitons are ideal to use for logical operations, and we demonstrate the functionality of a three-input majority gate, in which the input states can be controlled by applying an external electromagnetic field or spin-polarized currents. One of the main advantages of the proposed device is that the input and output signals are encoded in the chirality of solitons, that may be moved, allowing to perform logical operations using only minute electric currents. As an example we illustrate how the three input majority gate can be used to perform logical relations, such as Boolean AND and OR.

  • 20.
    Hosseinzadeh Delandar, A.
    et al.
    Department of Materials Science and Engineering, KTH Royal Institute of Technology.
    Gorbatov, Oleg I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Materials Science and Engineering, KTH Royal Institute of Technology.
    Snelleby, M.
    Department of Materials Science and Engineering, KTH Royal Institute of Technology.
    Gornostyrev, Yu. N.
    Institute of Metal Physics, Ural Division RAS.
    Korzvavyi, P.A.
    Department of Materials Science and Engineering, KTH Royal Institute of Technology.
    Ab-initio based search for late blooming phase compositions in iron alloys2018Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 509, s. 225-236Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a systematic analysis, based on ab initio calculations, of concentrated solute arrangements and precipitate phases in Fe-based alloys. The input data for our analysis are the calculated formation and interaction energies of point defects in the iron matrix, as well as the energies of ordered compounds that represent end-members in the 4-sublattice compound energy model of a multicomponent solid solution of Mg, Al, Si, P, S, Mn, Ni, and Cu elements and also vacancies in bcc Fe. The list of compounds also includes crystal structures obtained by geometric relaxation of the end-member compounds that in the cubic structure show weak mechanical instabilities (negative elastic constants) and also the G-phase Mn6(Ni,Fe)16(Si,P)7 having a complex cubic structure. A database of calculated thermodynamic properties (crystal structure, molar volume, enthalpy of formation, and elastic constants) of the most stable late-blooming-phase candidates is thus obtained. The results of this ab initio based theoretical analysis compare well with the recent experimental observations and predictions of thermodynamic calculations employing Calphad methodology.

  • 21.
    Allali, Naoual
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. LCPME, UMR CNRS-Université de Lorraine, Villers-lès-Nancy, France. SRSMC, UMR CNRS-Université de Lorraine, Faculté des Sciences et Technologies, Vandoeuvre-lès-Nancy, France.
    Urbanova, Veronika
    LCPME, UMR CNRS-Université de Lorraine, Villers-lès-Nancy, France.
    Etienne, Mathieu
    LCPME, UMR CNRS-Université de Lorraine, Villers-lès-Nancy, France.
    Devaux, Xavier
    IJL, UMR CNRS-Université de Lorraine, Nancy Cedex, France.
    Mallet, Martine
    LCPME, UMR CNRS-Université de Lorraine, Villers-lès-Nancy, France.
    Vigolo, Brigitte
    IJL, UMR CNRS-Université de Lorraine, Faculté des Sciences et Technologies, Vandoeuvre-lès-Nancy Cedex, France.
    Adjizian, Jean-Joseph
    IMN, UMR CNRS-Université de Nantes, Nantes, France.
    Ewels, Chris
    IMN, UMR CNRS-Université de Nantes, Nantes, France.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Soldatov, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    McRae, Edward
    IJL, UMR CNRS-Université de Lorraine, Faculté des Sciences et Technologies,Vandoeuvre-lès-Nancy Cedex, France.
    Fort, Yves
    SRSMC, UMR CNRS-Université de Lorraine, Faculté des Sciences et Technologies, Vandoeuvre-lès-Nancy, France.
    Dossot, Manuel
    LCPME, UMR CNRS-Université de Lorraine, Villers-lès-Nancy, France.
    Mamane, Victor
    Institut de Chimie de Strasbourg, UMR CNRS-Université de Strasbourg, Strasbourg, France.
    Accurate control of the covalent functionalization of single-walled carbon nanotubes for the electro-enzymatically controlled oxidation of biomolecules2018Ingår i: Beilstein Journal of Nanotechnology, ISSN 2190-4286, Vol. 9, s. 2750-2762Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Single-walled carbon nanotubes (SWCNTs) were functionalized by ferrocene through ethyleneglycol chains of different lengths (FcETGn) and the functionalized SWCNTs (f-SWCNTs) were characterized by different complementary analytical techniques. In particular, high-resolution scanning electron transmission microscopy (HRSTEM) and electron energy loss spectroscopy (EELS) analyses support that the outer tubes of the carbon-nanotube bundles were covalently grafted with FcETGn groups. This result confirms that the electrocatalytic effect observed during the oxidation of the reduced form of nicotinamide adenine dinucleotide (NADH) co-factor by the f-SWCNTs is due to the presence of grafted ferrocene derivatives playing the role of a mediator. This work clearly proves that residual impurities present in our SWCNT sample (below 5 wt. %) play no role in the electrocatalytic oxidation of NADH. Moreover, molecular dynamic simulations confirm the essential role of the PEG linker in the efficiency of the bioelectrochemical device in water, due to the favorable interaction between the ETG units and water molecules that prevents π-stacking of the ferrocene unit on the surface of the CNTs. This system can be applied to biosensing, as exemplified for glucose detection. The well-controlled and well-characterized functionalization of essentially clean SWCNTs enabled us to establish the maximum level of impurity content, below which the f-SWCNT intrinsic electrochemical activity is not jeopardized.

  • 22.
    Löfgren, Robin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pawar, Ravinder
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Larsson, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Charged dopants in neutral supercells through substitutional donor (acceptor): nitrogen donor charging of the nitrogen-vacancy center in diamond2018Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 20, artikel-id 023002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Charged defects are traditionally computed by adding (subtracting) electrons for negative (positive) impurities. When using periodic boundary conditions this results in artificially charged supercells that also require a compensating background charge of the opposite sign, which makes slab supercells problematic because of an arbitrary dependence on the vacuum thickness. In this work, we test the method of using neutral supercells through the use of a substitutional electron donor (acceptor) to describe charged systems. We use density functional theory (DFT) to compare the effects of charging the well-studied NV-center in diamond by a substitutional donor nitrogen. We investigate the influence of the donor-N on the NV-center properties as a function of the distance between them, and find that they converge toward those obtained when adding an electron. We analyze the spin density and conclude that the donor-N has a zero magnetic moment, and thus, will not be seen in electron spin resonance. We validate our DFT energies through comparison to GW simulations. Charging the NV-center with a substitutional donor-N enables accurate calculations of slabs, without the ambiguity of using charged supercells. Implantation of donor-N atoms opens up the possibility to engineer NV-centers with the desired charge state for future ICT and sensor applications.

  • 23.
    Berezovsky, Vladimir
    et al.
    Department of Applied Mathematics and High-performance ComputingM.V.Lomonosov Northern (Arctic) Federal University, Arkhangelsk.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Computational study of the CO adsorption and diffusion in zeolites: validating the Reed–Ehrlich model2018Ingår i: Adsorption, ISSN 0929-5607, E-ISSN 1572-8757, Vol. 24, nr 4, s. 403-413Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Molecular simulations have been employed to explore at the microscopic scale the adsorption of CO in zeolites (MFI, CHA and DDR). On the basis of classical force fields, grand canonical Monte Carlo simulations are performed to predict the adsorption properties (isotherms) of these types of zeolites up to high pressure. Subsequent careful analysis yields details the microscopic mechanism in play, along the whole adsorption process, together with a considering of the arrangements of CO in MFI at high pressure. This work also summarizes an approach which uses single component diffusion data in prediction of multicomponent diffusion.

  • 24.
    Urbán, Béla
    et al.
    University of Pannonia, Institute of Chemistry, Department of Organic Chemistry, Egyetem u, Hungary.
    Szabó, Péter
    University of Pannonia, Institute of Chemistry, Department of Analytical Chemistry, Egyetem u, Hungary.
    Srankó, Dávid
    Hungarian Academy of Sciences, Centre for Energy Research, Department of Surface Chemistry and Catalysis, Hungary.
    Sáfrán, György
    Hungarian Academy of Sciences, Research Institute for Technical Physics and Materials Science, Hungary.
    Kollár, László
    University of Pécs, Department of Inorganic Chemistry and MTA-PTE Research Group for Selective Chemical Syntheses, Hungary.
    Skoda-Földes, Rita
    University of Pannonia, Institute of Chemistry, Department of Organic Chemistry, Egyetem u, Hungary.
    Double carbonylation of iodoarenes in the presence of reusable palladium catalysts immobilised on supported phosphonium ionic liquid phases2018Ingår i: Molecular Catalysis, ISSN 2468-8231, Vol. 445, s. 195-205Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The first heterogeneous carbonylation reaction carried out with palladium catalysts immobilised on phosphonium ion modified silica supports is reported. The supported ionic liquid phases were characterised by solid state NMR and FT-IR measurements. The presence of the phosphonium ions on the surface made it possible to carry out double carbonylation in apolar toluene efficiently that resulted in reduced metal leaching. The introduction of dicationic moieties on the solid support has been proved to lead to a further increase in catalyst stability. The catalysts were proved to produce α-ketoamide products with excellent selectivity in the carbonylation of iodoarenes with aliphatic amines while monocarbonylation was the only reaction observed with aniline derivatives. The catalysts could be recycled and used in at least 10 subsequent runs under optimised conditions.

  • 25.
    Grenman, Tiia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Dusty Globules and Globulettes2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Interstellar gas and dust can condense into clouds of very different size, ranging from giant molecular cloud complexes to massive, isolated, dark cloudlets, called globules with a few solar masses.

    This thesis focuses on a new category of small globules, named globulettes.These have been found in the bright surroundings of H II regions of young, massive stellar clusters. The globulettes are much smaller and less massive than normal globules. The analysis is based on H-alpha images ofe.g., the Rosette Nebula and the Carina Nebula collected with the Nordic Optical Tele-scope and the Hubble Space Telescope.

    Most globulettes found in different H II regions have distinct contours and are well isolated from the surrounding molecular shell structures. Masses and densities were derived from the extinction of light through the globulettes and the measured shape of the objects. A majority of the globulettes have planetary masses,<13MJ (Jupiter masses). Very few objects have masses above 100MJ≈0.1M(Solar masses). Hence, there is no smooth overlap between globulettes and globules, which makes us conclude that globulettes represent a distinct, new class of objects.

    Globulettes might have been formed either by the fragmentation of larger filaments, or by the disintegration of large molecular clouds originally hosting compact and small cores. At a later stage, globulettes expand, disrupt or evaporate. However, preliminary calculations of their lifetimes show that some might survive for a relatively long time, in several cases even longer than their estimated contraction time.

    The tiny high density globulettes in the Carina Nebula indicate that they are in a more evolved state than those in the Rosette Nebula, and hence they may have survived for a longer time. It is possible that the globulettes could host low mass brown dwarfs or planets.

    Using the virial theorem on the Rosette Nebula globulettes and including only the thermal and gravitational potential energy indicated that the 133 found globulettes are all either expanding or disrupting. When the ram and the radiation pressure were included, we found that about half of our objectsare gravitationally bound or unstable to contraction and could collapse to form brown dwarfs or free floating planets.

    We also estimated the amount of globulettes and the number of free floating planetary mass objects, originating from globulettes, during the history of the Milky Way. We found that a conservative value of the number of globulettes formed is 5.7×1010. A less conservative estimate gave 2×1011globulettes andif 10% of these forms free floating planets then the globulettes have contributed about 0.2 free floating planets per star.

    In the Crab Nebula, which is a supernova remnant from the explosion of a massive old star, one can find dusty globules appearing as dark spots against the background nebulosity. These globules are very similar to the globulettes we have found in H II regions. The total mass of dust in globules was estimated to be 4.5×10−4M, which corresponds to.2% of the total dust content of the nebula. These globules move outward from the center with transversal velocities of 60–1600 km s−1. Using the extinction law for globules, we found that the dust grains are similar to the interstellar dust grains. This means that they contribute to the ISM dust population. We concluded that the majority of the globules are not located in bright filaments and we proposed that these globules may be products of cell-like blobs or granules in the atmosphere of the progenitor star. Theses blobs collapse and form globules during the passage of the blast wave during the explosion.

  • 26.
    Råsander, Mikael
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Materials, Imperial College London.
    Moram, M.A.
    Department of Physics, Cavendish Laboratory, University of Cambridge.
    Elastic constants of the II–IV nitride semiconductors MgSiN2, MgGeN2 and MgSnN22018Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, artikel-id 375101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The single crystal elastic constants, polycrystalline elastic moduli and related properties of orthorhombic MgSiN2, MgGeN2 and MgSnN2 have been calculated using density functional theory and compared to the related wurtzite structured AlN, GaN and InN. Since there are no experimental studies of single crystal elastic properties of neither MgSiN2, MgGeN2 or MgSnN2, we have established the accuracy of the calculations by comparison with experimental data for AlN, GaN and InN. The calculated polycrystalline elastic moduli of MgSiN2 are found to be in good agreement with available experimental elastic moduli. It will be shown that MgSiN2 and MgGeN2 have a small xy-plane lattice mismatch with AlN and GaN, respectively, while at the same time being significantly softer than both AlN and GaN. This shows that MgSiN2 and MgGeN2 should be possible to be grown on AlN and GaN without significant lattice mismatch or strain.

  • 27.
    Hosseinzadeh Delandar, Arash
    et al.
    Department of Materials Science and Engineering, KTH Royal Institute of Technology.
    Gorbatov, Oleg I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Materials Science and Engineering, KTH Royal Institute of Technology.
    Selleby, Malin
    Department of Materials Science and Engineering, KTH Royal Institute of Technology.
    Gornostyrev, Yury N.
    Institute of Metal Physics, Ural Division RAS.
    Korzhavyi, Pavel A.
    Department of Materials Science and Engineering, KTH Royal Institute of Technology.
    End-member compounds of a 4-sublattice model of multicomponent BCC solid solutions2018Ingår i: Data in Brief, E-ISSN 2352-3409, Vol. 20, s. 1018-1022Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    he article presents ab initio calculated properties (total energies, lattice parameters, and elastic properties) for the complete set of 1540 end-member compounds within a 4-sublattice model of Fe-based solid solutions. The compounds are symmetry-distinct cases of integral site occupancy for superstructure Y (space group #227, type LiMgPdSn) chosen to represent the ordered arrangements of solvent atoms (Fe), solute atoms (Fe, Mg, Al, Si, P, S, Mn, Ni, Cu), and vacancies (Va) on the sites of a body-centered cubic lattice. The model is employed in the research article “Ab-initio based search for late blooming phase compositions in iron alloys” (A. Hosseinzadeh Delandar et al., 2018) [1].

  • 28.
    Santos, Paolo
    et al.
    Department of Physics and I3N, University of Aveiro, Campus Santiago, 3810-193 Aveiro, Portugal.
    Coutinho, Jose
    Department of Physics and I3N, University of Aveiro, Campus Santiago, 3810-193 Aveiro, Portugal.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    First-principles calculations of iron-hydrogen reactions in silicon2018Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 123, nr 24, artikel-id 245703Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Controlling the contamination of silicon materials by iron, especially dissolved interstitial iron (Fe-i), is a longstanding problem with recent developments and several open issues. Among these, we have the question whether hydrogen can assist iron diffusion or if significant amounts of substitutional iron (Fe-s) can be created. Using density functional calculations, we explore the structure, formation energies, binding energies, migration, and electronic levels of several FeH complexes in Si. We find that a weakly bound FeiH pair has a migration barrier close to that of isolated Fe-i and a donor level at E-v + 0.5 eV. Conversely, FeiH2 (0/+) is estimated at E-v + 0.33 eV. These findings suggest that the hole trap at E-v + 0.32 eV obtained by capacitance measurements should be assigned to FeiH2 . FesH-related complexes show only deep acceptor activity and are expected to have little effect on minority carrier life-time in p-type Si. The opposite conclusion can be drawn for n-type Si. We find that while in H-free material Fe i defects have lower formation energy than Fe-s , in hydrogenated samples Fe-s -related defects become considerably more stable. This would explain the observation of an electron paramagnetic resonance signal attributed to a FesH-related complex in hydrogenated Si, which was quenched from above 1000 degrees C to iced-water temperature.

  • 29.
    Góger, Szabolcs
    et al.
    Department of General and Inorganic Chemistry, University of Pannonia. Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences.
    Szabo, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Czakó, Gábor
    Department of Physical Chemistry and Materials Science, Institute of Chemistry, University of Szeged.
    Lendvay, György
    Department of General and Inorganic Chemistry, University of Pannonia. Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Hungary.
    Flame Inhibition Chemistry: Rate Coefficients of the Reactions of HBr with CH3 and OH Radicals at High Temperatures Determined by Quasiclassical Trajectory Calculations2018Ingår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 32, nr 10, s. 10100-10105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Reactions of HBr with radicals are involved in atmospheric chemistry and in the mechanism of operation of bromine-containing flame retardants. The rate coefficients for two such reactions, HBr + OH and HBr + CH3, are available from earlier experiments at near or below room temperature, relevant for atmospheric chemistry, and in this domain, the activation energy for both has been found to be negative. However, no experimental data are available at combustion temperatures. In this work, to provide reliable data needed for modeling the action of brominated flame suppressants, we used the quasiclassical trajectory (QCT) method in combination with high-level ab initio potential energy surfaces to evaluate the rate coefficients of the two title reactions at combustion temperatures. The QCT calculations have been validated by reproducing the experimental rate coefficients at room temperature. At temperatures between 600 and 3200 K, the QCT rate coefficients display positive activation energies. We recommend the following extended Arrhenius expressions to describe the temperature dependence of the thermal rate coefficients: k6 = (9.86 ± 2.38) × 10–16T(1.23±0.03) exp[(5.93 ± 0.33) kJ mol–1/RT] cm3 molecule–1 s–1 for the HBr + OH → H2O + Br reaction, and k–2 = (4.06 ± 2.72) × 10–18T(1.83±0.08) exp[(7.53 ± 0.18) kJ mol–1/RT] cm3 molecule–1 s–1 for the HBr + CH3 → CH4 + Br reaction. The latter is in very good agreement with the formula proposed by Burgess et al. [Burgess, D. R., Jr.; Babushok, V. I.; Linteris, G. T.; Manion, J. A. A Chemical Kinetic Mechanism for 2-Bromo-3,3,3-trifluoropropene (2-BTP) Flame Inhibition. Int. J. Chem. Kinet. 2015, 47, 533−619, DOI: 10.1002/kin.20923]. The conventional transition state theory has been tested against the rate data obtained by the QCT method and was found to overestimate not only the rate coefficients but also the activation energies

  • 30.
    Fehér, Klaudia
    et al.
    Department of Organic Chemistry University of Pannonia, Institute of Chemistry Egyetem, Veszprém, Hungary.
    Nagy, Eniko
    Department of Organic Chemistry University of Pannonia, Institute of Chemistry Egyetem, Veszprém, Hungary.
    Szabo, Peter
    Department of Analytical Chemistry University of Pannonia, Institute of Chemistry Egyetem, Veszprém, Hungary.
    Juzsakova, Tatjana
    University of Pannonia, Institute of Environmental Engineering Egyetem, Veszprém Hungary.
    Srankó, David
    Department of Surface Chemistry and Catalysis Hungarian Academy of Sciences, Centre for Energy Research, Budapest, Hungary.
    Gömöry, Ágnes
    Research Centre for Natural Sciences Hungarian Academy of Sciences, Budapest, Hungary.
    Kollár, Lazslo
    Department of Inorganic Chemistry and MTA-PTE Research Group for Selective Chemical Syntheses University of Pécs, Pécs, Hungary.
    Skoda-Földes, Rita
    Department of Organic Chemistry University of Pannonia, Institute of Chemistry Egyetem, Veszprém, Hungary.
    Heterogeneous azide–alkyne cycloaddition in the presence of a copper catalyst supported on an ionic liquid polymer/silica hybrid material2018Ingår i: Applied organometallic chemistry, ISSN 0268-2605, E-ISSN 1099-0739, Vol. 32, nr 6, artikel-id e4343Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Heterogeneous copper catalysts were prepared by the deposition of CuI on a hybrid material consisting of silica and a polymer with imidazolium moieties. The solid materials were characterised using solid‐phase NMR, Fourier transform infrared, Raman and X‐ray photoelectron spectroscopies and Brunauer–Emmett–Teller measurements. The formation of copper–carbene complexes was proved from Raman spectra and the results were supported by density functional theory calculations. The catalyst could be recycled efficiently with low loss of copper. Metal leaching was proved to be facilitated by the use of conditions typical for a homogeneous system (the presence of a polar solvent or the addition of a tertiary amine). Besides simple model reactions, the best catalyst was found to be suitable for the synthesis of triazoles of more elaborate structure, such as ferrocene or steroid derivatives.

  • 31.
    Grenman, Tiia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Elfgren, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Weber, Hans
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    History of Globulettes in the Milky Way2018Ingår i: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 363, nr 2, artikel-id 28Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Globulettes are small (radii $< 10$ kAU) dark dust clouds, seen against the background of bright nebulae.

    A majority of the objects have planetary mass.

    These objects may be a source of brown dwarfs and free floating planetary mass objects in the galaxy.

    In this paper we investigate how many globulettes could have formed in the Milky Way and how they could contribute to the total population of free floating planets.

    In order to do that we examine H-alpha images of 27 H~II regions. In these images, we find 778 globulettes.

    We find that a conservative value of the number of globulettes formed is $5.7\times 10^{10}$.

    If 10 \% of the globulettes form free floating planets then they have contributed with $5.7\times 10^{9}$ free floating planets in the Milky Way. A less conservative number of globulettes would mean that the globulettes could contribute $2.0\times 10^{10}$ free floating planets.

    Thus the globulettes could represent a non-negligible source of free floating planets in the Milky Way.

  • 32.
    Fletcher, Leigh N.
    et al.
    Department of Physics and Astronomy, University of Leicester.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Orton, Glenn S.
    Jet Propulsion Laboratory, California Institute of Technology.
    Hydrogen Dimers in Giant-planet Infrared Spectra2018Ingår i: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 235, nr 1, artikel-id 24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Despite being one of the weakest dimers in nature, low-spectral-resolution Voyager/IRIS observations revealed the presence of (H2)2 dimers on Jupiter and Saturn in the 1980s. However, the collision-induced H2-H2 opacity databases widely used in planetary science have thus far only included free-to-free transitions and have neglected the contributions of dimers. Dimer spectra have both fine-scale structure near the S(0) and S(1) quadrupole lines (354 and 587 cm-1, respectively), and broad continuum absorption contributions up to ±50 cm-1 from the line centers. We develop a new ab initio model for the free-to-bound, bound-to-free, and bound-to-bound transitions of the hydrogen dimer for a range of temperatures (40-400 K) and para-hydrogen fractions (0.25-1.0). The model is validated against low-temperature laboratory experiments, and used to simulate the spectra of the giant planets. The new collision-induced opacity database permits high-resolution (0.5-1.0 cm-1) spectral modeling of dimer spectra near S(0) and S(1) in both Cassini Composite Infrared Spectrometer observations of Jupiter and Saturn, and in Spitzer Infrared Spectrometer (IRS) observations of Uranus and Neptune for the first time. Furthermore, the model reproduces the dimer signatures observed in Voyager/IRIS data near S(0) on Jupiter and Saturn, and generally lowers the amount of para-H2 (and the extent of disequilibrium) required to reproduce IRIS observations.

  • 33.
    Gergely, Andras
    et al.
    Department of Physical Chemistry, Institute of Chemistry, University of Pannonia, Egyetem, Hungary .
    Szabó, Péter
    Department of General and Inorganic Chemistry, Institute of Chemistry, University of Pannonia, Egyetem, Hungary .
    Krojer, Antal
    Department of Inspection and Maintenance, Mol Nyrt., Olajmunkás, Hungary .
    Nagy, Bence
    Refining Research and Innovation, Mol Nyrt., Hungary .
    Kristof, Tamas
    Department of Physical Chemistry, Institute of Chemistry, University of Pannonia, Egyetem, Hungary .
    Hydrogen Sulfide Corrosion of Carbon and Stainless Steel Alloys in Mixtures of Renewable Fuel Sources under Co-Processing Conditions2018Ingår i: Modern Applied Science, ISSN 1913-1844, E-ISSN 1913-1852, Vol. 12, nr 4, s. 227-255Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Corrosion rates of steel alloys were investigated in gas oil and its mixture with waste cooking oil and animal waste lard over 1, 3, 7 and 21 days under desulfurizing condition. Co-processing conditions were attempted to simulate by batch-reactor experiment at temperatures between 200 and 300oC and pressures between 20 and 90 bar in the presence of 2 volume% hydrogen sulfide. Integral and differential corrosion rates were defined by weight losses. Intense sulfide corrosion of carbon steels was less impacted by the biomass sources. Thinner scales in gas oil was probably due to frequent cohesive failure, whereas thicker layers in biomass mixtures were allowed to form to afford limited physical protection. The high corrosion rate of low alloy steel with temperature over time is related to inefficient protection by the metal sulfide scales. Greater activation energy and enthalpy balance in the formation of activated complex is expected to reflect in thick cohesive scales. Loose layers and the less unfavorable entropy balance in the transition state did not lead to valuable barrier protection. High sulfide corrosion resistance of stainless steels is in chemical in nature markedly impacted by the biomass fuel sources and contributed especially by the acidic species. Corrosion rates increased with temperature by magnitude similar to those of carbon steels, which probably owes to the less unfavorable entropy and free energy balance between the initial and transition states of the reactants.

  • 34.
    Zarshenas, Mohammad
    et al.
    Institute of Condensed Matter and Nanosciences - Bio & Soft Matter (IMCN/BSMA), Université Catholique de Louvain.
    Moshkunov, Konstantin
    Institute of Condensed Matter and Nanosciences - Bio & Soft Matter (IMCN/BSMA), Université Catholique de Louvain.
    Czerwinski, Bartlomiej
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Leyssens, Tom
    Institute of Condensed Matter and Nanosciences - Molecules, Solids and Reactivity (IMCN/MOST) Université Catholique de Louvain.
    Delcorte, Amaud
    Institute of Condensed Matter and Nanosciences - Bio & Soft Matter (IMCN/BSMA), Université Catholique de Louvain.
    Molecular Dynamics Simulations of Hydrocarbon Film Growth from Acetylene Monomers and Radicals: Effect of Substrate Temperature2018Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 27, s. 15252-15263Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In an attempt to rationalize the mechanisms occurring during plasma polymerization of acetylene, classical molecular dynamics (MD) computer simulations investigating the deposition and reaction of a mixed gas of acetylene molecules and radicals on the Ag(111) substrate were performed for a wide range of substrate temperatures. Prior to that, this article establishes a methodology for film deposition and identifies the appropriate potentials for hydrocarbons by comparison with electronic calculations using the density functional theory (DFT). Based on this preliminary study, simulations of films growth are carried out at different temperatures using the REBO potential. Our results show that the rates of creation of new C-C and C-H bonds are higher at the beginning of the film growth when the substrate is still exposed, than when it is covered with polymeric chains, and these initial reaction rates are proportional to temperature. The analysis of the hybridization of carbon atoms in the films shows that the substrate temperature increase leads to the formation of coatings containing more carbon atoms in the sp2 and sp3 configurations and less in the sp configuration with sp2 becoming dominant at high temperatures. We establish a polymerization-connectivity formalism that describes the structural transformation of the film during the deposition on the basis of each atom hybridization and bonding. Within this formalism the evolution of the polymerization and the connection character of the polymers is observed and discussed.

  • 35.
    El-Kader, M.S.A.
    et al.
    Department of Engineering Mathematics and Physics, Faculty of Engineering, Cairo University.
    Godet, J-L
    Laboratoire de photonique d'Angers, Université d'Angers.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Maroulis, G.
    Department of Chemistry, University of Patras.
    Multi-property isotropic intermolecular potentials and predicted spectral lineshapes of collision-induced absorption (CIA), collision-induced light scattering (CILS) and collision-induced hyper-Rayleigh scattering (CIHR) for H2Ne, −Kr and −Xe2018Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 209, s. 232-242Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quantum mechanical lineshapes of collision-induced absorption (CIA), collision-induced light scattering (CILS) and collision-induced hyper-Rayleigh scattering (CIHR) at room temperature (295 K) are computed for gaseous mixtures of molecular hydrogen with neon, krypton and xenon. The induced spectra are detected using theoretical values for induced dipole moment, pair-polarizability trace and anisotropy, hyper-polarizability and updated intermolecular potentials. Good agreement is observed for all spectra when the literature and the present potentials which are constructed from the transport and thermo-physical properties are used.

  • 36.
    Hansson, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Dols Duxans, Jaime
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Svensson, Martin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nonlinear Effects of Gravity in Cosmology2018Ingår i: Advanced Studies in Theoretical Physics, ISSN 1313-1311, E-ISSN 1314-7609, Vol. 12, nr 4, s. 157-172Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider some nonlinear effects of gravity in cosmology. Possible physically interesting consequences include: non-requirement of dark matter and dark energy, asymmetric gravitational matter-creation, emergent homogeneity/isotropy & asymptotic flatness, resolution of "cosmic coincidence" Omega_m \sim Omega_lambda, effective cutoff of gravitational interaction at the scale of cosmic voids.

  • 37.
    Avakyan, Leon
    et al.
    Department of Physics and I3N, University of Aveiro, Aveiro, Portugal.
    Paramonova, Ekaterina
    Institute of Mathematical Problems of Biology, Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, 142290 Moscow Region, Russian Federation.
    Coutinho, José
    Department of Physics and I3N, University of Aveiro, Aveiro, Portugal.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Bystrov, Vladimir
    Institute of Mathematical Problems of Biology, Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, 142290 Moscow Region, Russian Federation.
    Bugaev, Lusegen
    Physics Faculty, Southern Federal University, Rostov-on-Don 344090, Russian Federation.
    Optoelectronics and defect levels in hydroxyapatite by first-principles2018Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, nr 15, artikel-id 154706Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hydroxyapatite (HAp) is an important component of mammal bones and teeth, being widely used in prosthetic implants. Despite the importance of HAp in medicine, several promising applications involving this material (e.g., in photo-catalysis) depend on how well we understand its fundamental properties. Among the ones that are either unknown or not known accurately, we have the electronic band structure and all that relates to it, including the bandgap width. We employ state-of-the-art methodologies, including density hybrid-functional theory and many-body perturbation theory within the dynamically screened single-particle Green's function approximation, to look at the optoelectronic properties of HAp. These methods are also applied to the calculation of defect levels. We find that the use of a mix of (semi-)local and exact exchange in the exchange-correlation functional brings a drastic improvement to the band structure. Important side effects include improvements in the description of dielectric and optical properties not only involving conduction band (excited) states but also the valence. We find that the highly dispersive conduction band bottom of HAp originates from anti-bonding σ* states along the ⋯OH-OH-⋯ infinite chain, suggesting the formation of a conductive 1D-ice phase. The choice of the exchange-correlation treatment to the calculation of defect levels was also investigated by using the OH-vacancy as a testing model. We find that donor and acceptor transitions obtained within semi-local density functional theory (DFT) differ from those of hybrid-DFT by almost 2 eV. Such a large discrepancy emphasizes the importance of using a high-quality description of the electron-electron interactions in the calculation of electronic and optical transitions of defects in HAp.

  • 38.
    Hartmann, Jean-Michel
    et al.
    Laboratoire de Météorologie Dynamique/IPSL, CNRS, École polytechnique, Sorbonne Université, École normale supérieure, PSL Research University.
    Tran, Ha
    Laboratoire de Météorologie Dynamique/IPSL, CNRS, Sorbonne Université, École normale supérieure, PSL Research University, École polytechnique.
    Armante, Raymond
    Laboratoire de Météorologie Dynamique/IPSL, CNRS, École polytechnique, Sorbonne Université, École normale supérieure, PSL Research University.
    Boulet, Christian
    Institut des Sciences Moléculaires d'Orsay, CNRS, Université Paris-Sud, Université Paris-Saclay.
    Campargue, Alain
    Univ. Grenoble Alpes, CNRS.
    Forget, François
    Laboratoire de Météorologie Dynamique/IPSL, CNRS, Sorbonne Université, École normale supérieure, PSL Research University, École polytechnique.
    Gianfrani, Livio
    Dipartimento di Matematica e Fisica, Università degli Studi della Campania "Luigi Vanvitelli".
    Gordon, Iouli
    Harvard-Smithsonian Center for Astrophysics, Atomic and Molecular Physics Division, Cambridge, MA .
    Guerlet, Sandrine
    Laboratoire de Météorologie Dynamique/IPSL, CNRS, Sorbonne Université, École normale supérieure, PSL Research University, École polytechnique.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hodges, Joseph T.
    National Institute of Standards and Technology.
    Kassi, Samir
    Univ. Grenoble Alpes, CNRS.
    Lisak, Daniel
    Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University.
    Thibault, Franck
    Institut de Physique de Rennes, UMR CNRS 6251, Université de Rennes .
    Toon, Geoffrey C.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California.
    Recent advances in collisional effects on spectra of molecular gases and their practical consequences2018Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 213, s. 178-227Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We review progress, since publication of the book "Collisional effects on molecular spectra: Laboratory experiments and models, consequences for applications" (Elsevier, Amsterdam, 2008), on measuring, modeling and predicting the influence of pressure (ie of intermolecular collisions) on the spectra of gas molecules. We first introduce recently developed experimental techniques of high accuracy and sensitivity. We then complement the above mentioned book by presenting the theoretical approaches, results and data proposed (mostly) in the last decade on the topics of isolated line shapes, line-broadening and -shifting, line-mixing, the far wings and associated continua, and collision-induced absorption. Examples of recently demonstrated consequences of the progress in the description of spectral shapes for some practical applications (metrology, probing of gas media, climate predictions) are then given. Remaining issues and directions for future research are finally discussed.

  • 39.
    Wu, Bo
    et al.
    School of Physics and Electronic Science, Zunyi Normal University, Zunyi, China. School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an, China.
    Huang, Haishen
    School of Physics and Electronic Science, Zunyi Normal University, Zunyi, China. School of Physics, Beijing Institute of Technology, Beijing, China.
    Zhou, Guangdong
    Guizhou Institute of Technology, Guiyang, China.
    Feng, Yu
    School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou, China.
    Chen, Ying
    School of Mathematics and Physics, Anshun University, Anshun, China.
    Wang, Xiangjian
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Structure, Magnetism, and Electronic Properties of Inverse Heusler Alloy Ti2CoAl/MgO(100) Herterojuction: the Role of Interfaces2018Ingår i: Applied Sciences, E-ISSN 2076-3417, Vol. 8, nr 12, artikel-id 2336Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, the interface structures, atom-resolved magnetism, density of states, and spin polarization of 10 possible atomic terminations in the Ti2CoAl/MgO(100) heterojunction were comprehensively investigated using first-principle calculations. In the equilibrium interface structures, the length of the alloy-Mg bond was found to be much longer than that of the alloy-O bond because of the forceful repulsion interactions between theHeusler interface atoms andMg atoms. The competition among d-electronic hybridization, d-electronic localization, and the moving effect of the interface metal atoms played an important role in the interface atomic magnetic moment. Unexpected interface states appeared in the half-metallic gap for all terminations. The "ideal" half-metallicity observed in the bulk had been destroyed. In TiAl-Mg and AlAl-O terminations, the maximal spin polarization of about 65% could be reserved. The tunnel magnetoresistance (TMR) value was deduced to be lower than 150% in the Ti2CoAl/MgO(100) heterojunction at low temperature.

  • 40.
    Wright, E.
    et al.
    Department of Physics and I3N, University of Aveiro, Campus Santiago.
    Coutinho, J.
    Department of Physics and I3N, University of Aveiro, Campus Santiago.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Torres, V.J.B.
    Department of Physics and I3N, University of Aveiro, Campus Santiago.
    A first-principles model of copper-boron interactions in Si: for the light-induced degradation of solar Si2017Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, nr 6, artikel-id 065701Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The recent discovery that Cu contamination of Si combined with light exposure has a significant detrimental impact on carrier life-time has drawn much concern within the solar-Si community. The effect, known as the copper-related light-induced degradation (Cu-LID) of Si solar cells, has been connected to the release of Cu interstitials within the bulk (2016 Sol. Energy Mater. Sol. Cells 147 115-26). In this paper, we describe a comprehensive analysis of the formation/dissociation process of the CuB pair in Si by means of first-principles modelling, as well as the interaction of CuB defects with photo-excited minority carriers. We confirm that the long-range interaction between the Cu-i(+) cation and the B-s(-) anion has a Coulomb-like behaviour, in line with the trapping-limited diffusivity of Cu observed by transient ion drift measurements. On the other hand, the short-range interaction between the d-electrons of Cu and the excess of negative charge on B-s(-) produces a repulsive effect, thereby decreasing the binding energy of the pair when compared to the ideal point-charge Coulomb model. We also find that metastable CuB pairs produce acceptor states just below the conduction band minimum, which arise from the Cu level emptied by the B acceptor. Based on these results, we argue that photo-generated minority carriers trapped by the metastable pairs can switch off the Coulomb interaction that holds the pairs together, enhancing the release of Cu interstitials, and acting as a catalyst for Cu-LID.

  • 41.
    Szabo, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    A surface-hopping method for semiclassical calculations of cross sectionsfor radiative association with electronic transitions2017Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, artikel-id 094308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A semiclassical method based on surface-hopping techniques is developed to model the dynamics of radiative association with electronic transitions. It can be proven that this method is an extension of the established semiclassical formula used in the characterization of diatomic molecule-formation. Our method is tested for diatomic molecules. It gives the same cross sections as the former semiclassical formula but, contrary to the former method, it allows us to follow the fate of the trajectories after the emission of a photon. This means that we can characterize the rovibrational states of the stabilized molecules. Using semiclassical quantization, we can obtain quantum state-resolved cross sections or emission spectra for the radiative association process. The calculated semiclassical state-resolved spectra show general agreement with the result of quantum mechanical perturbation theory. Furthermore, our surface-hopping model is not only applicable for the description of radiative association but it can be used for semiclassical characterization of any molecular process where spontaneous emission occurs

  • 42.
    Hedman, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    A Theoretical Study: The Connection between Stability of Single-Walled Carbon Nanotubes and Observed Products2017Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 43.
    Pinto, H.
    et al.
    COMP, Department of Applied Physics, Aalto University.
    Haapasilta, Ville
    COMP, Department of Applied Physics, Aalto University.
    Lokhandwala, M.
    COMP, Department of Applied Physics, Aalto University.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Foster, Adam S.
    COMP, Department of Applied Physics, Aalto University.
    Adsorption and migration of single metal atoms on the calcite (10.4) surface2017Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, nr 13, artikel-id 135001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transition metal atoms are one of the key ingredients in the formation of functional 2D metal organic coordination networks. Additionally, the co-deposition of metal atoms can play an important role in anchoring the molecular structures to the surface at room temperature. To gain control of such processes requires the understanding of adsorption and diffusion properties of the different transition metals on the target surface. Here, we used density functional theory to investigate the adsorption of 3d (Ti, Cr, Fe, Ni, Cu), 4d (Zr, Nb, Mo, Pd, Ag) and 5d (Hf, W, Ir, Pt, Au) transition metal adatoms on the insulating calcite (10.4) surface. We identified the most stable adsorption sites and calculated binding energies and corresponding ground state structures. We find that the preferential adsorption sites are the Ca–Ca bridge sites. Apart from the Cr, Mo, Cu, Ag and Au all the studied metals bind strongly to the calcite surface. The calculated migration barriers for the representative Ag and Fe atoms indicates that the metal adatoms are mobile on the calcite surface at room temperature. Bader analysis suggests that there is no significant charge transfer between the metal adatoms and the calcite surface.

  • 44.
    Szabo, Peter
    et al.
    Department of Analytical Chemistry, University of Pannonia.
    Zsirka, Balázs
    Institute of Environmental Engineering, University of Pannonia.
    Fertig, Dávid
    Department of Analytical Chemistry, University of Pannonia.
    Horváth, Erzsébet
    Institute of Environmental Engineering, University of Pannonia.
    Csizmadia, Tamás
    Department of Anatomy, Cell and Developmental Biology, Eötvös Loránd University.
    Kristóf, János
    Institute of Environmental Engineering, University of Pannonia.
    Delaminated kaolinites as potential photocatalysts: Tracking degradation of Na-benzenesulfonate test compound adsorbed on the dry surface of kaolinite nanostructures2017Ingår i: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 287, nr Supplement C, s. 37-44Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Abstract Based on their bandgap values, kaolins can have semiconductive and photocatalytic properties enabling them to use as potential photocatalysts. Kaolinite nanostructures (Knano) and silver-coated kaolinite nanohybrids (Knano(Ag)) were made of ordered (Hinkley Index, HI=1.4) and disordered (HI=0.3) kaolins via intercalation/deintercalation. The book-type kaolin built up from tetrahedral(T)-octahedral(O) double layers has very low photocatalytic activity. At the same time the nanostructures made of individual TO layers show photochemical activity in spite of the fact that their bandgap values are comparable to those of the book-type ones. The presence of Ag on the surface significantly reduced the bandgap and shifted the excitation wavelength towards the visible range. This phenomenon supports the supposition that kaolinite has some semiconductive character. This work presents the connection between photocatalytic activity and morphology for the first time. The surface activity of kaolinite nanostructures and their Ag-hybrids was studied through the decomposition of sodium-benzenesulfonate (BS) test compound with attenuated total reflection Fourier transform infrared spectroscopy (FT-IR/ATR). BS decomposition can be detected on the Knano surface but with low efficiency. The presence of silver can significantly improve the mineralization efficiency. No correlation was found between the activity and the quantity of Ti and Fe contaminants and the amount of Ag on the surface. However, the activity could be correlated with the order-dependent morphology (mixture of semi-hexagonal and nanoscroll-type structures), the pore size and with the increase of the surface coverage.

  • 45.
    Grenman, Tiia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gahm, Gösta F.
    Stockholm Observatory, AlbaNova University Centre, Stockholm University.
    Elfgren, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Dusty globules in the Crab Nebula2017Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 599, artikel-id A110Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Dust grains are widespread in the Crab Nebula. A number of small, dusty globules, are visible as dark spots against the background of continuous synchrotron emission in optical images. Aims. Our aim is to catalogue such dusty globules and investigate their properties. Methods. From existing broad-band images obtained with the Hubble Space Telescope, we located 92 globules, for which we derived positions, dimensions, orientations, extinctions, masses, proper motions, and their distributions. Results. The globules have mean radii ranging from 400 to 2000 AU and are not resolved in current infrared images of the nebula. The extinction law for dust grains in these globules matches a normal interstellar extinction law. Derived masses of dust range from 1 to 60 × 10-6M, and the total mass contained in globules constitute a fraction of approximately 2% or less of the total dust content of the nebula. The globules are spread over the outer part of the nebula, and a fraction of them coincide in position with emission filaments, where we find elongated globules that are aligned with these filaments. Only 10% of the globules are coincident in position with the numerous H2-emitting knots found in previous studies. All globules move outwards from the centre with transversal velocities of 60 to 1600 km s-1, along with the general expansion of the remnant. We discuss various hypotheses for the formation of globules in the Crab Nebula

  • 46.
    Verkhoturov, Stanislav V.
    et al.
    Department of Chemistry, Texas A&M University.
    Czerwinski, Bartlomiej
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Verkhoturov, Dmitriy S.
    Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.
    Geng, Sheng
    Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.
    Delcorte, Arnaud
    nstitute of Condensed Matter and Nanosciences - Bio and Soft Matter (IMCN/BSMA), Universit ́ e Catholique de Louvain, 1 Croix du Sud, B-1348 Louvain-la-Neuve, Belgium.
    Schweikert, Emile A.
    Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.
    Ejection-ionization of molecules from free standing graphene2017Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, nr 8, artikel-id 084308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the first data on emission of C60stimulated by single impacts of 50 keV C602+on the self-assembled molecular layer of C60deposited on free standing 2 layer graphene. The yield,Y, of C60emitted in the transmission direction is 1.7%. To characterize the ejection and ionization of molecules,we have measured the emission of C60from the surface of bulk C60(Y= 3.7%) and from a singlelayer of C60deposited on bulk pyrolytic graphite (Y= 3.3%). To gain insight into the mechanism(s) ofejection, molecular dynamic simulations were performed. The scenario of the energy deposition andejection of molecules is different for the case of graphene due to the confined volume of projectile-analyte interaction. In the case of 50 keV C602+impacts on graphene plus C60, the C atoms of theprojectile collide with those of the target. The knocked-on atoms take on a part of the kinetic energyof the projectile atoms. Another part of the kinetic energy is deposited into the rim around the impactsite. The ejection of molecules from the rim is a result of collective movement of the molecules andgraphene membrane, where the membrane movement provides the impulse for ejection. The efficientemission of the intact molecular ions implies an effective ionization probability of intact C60. Theproposed mechanism of ionization involves the tunneling of electrons from the vibrationally exitedarea around the hole to the ejecta

  • 47.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hydrogen dimer features in low temperature collision-induced spectra2017Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 810, nr 1, artikel-id 012017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The absorption of radiation in pure hydrogen (H2) gas around the S(0) and S(1) rotational transitions is computed at 20 K and compared with laboratory data. All transitions involving free state are included in the calculations of the absolute absorption. These calculations are done with an isotropic approximation for the H2–H2 pair potential. Agreement with the experiment is observed around the S(0) transition, while the computational approach appears to be slightly worse around the S(1) transition. The positions for bound-to-bound transitions are computed including the full anisotropic pair potential. The anisotropy seems to be crucial to achieve agreement with the measured bound-to-bound transition frequencies. However, those transitions contribute little to the total absorption. The present computed absolute absorptions will provide improved input for radiative transfer models of planetary atmospheres.

  • 48.
    Hegedűs, Péter
    et al.
    Department of General and Inorganic Chemistry, Institute of Chemistry, University of Pannonia, Hungary.
    Szabó-Bárdos, Erzsébet
    Department of General and Inorganic Chemistry, Institute of Chemistry, University of Pannonia, Hungary.
    Horváth, Ottó
    Department of General and Inorganic Chemistry, Institute of Chemistry, University of Pannonia, Hungary.
    Szabó, Péter
    Department of Analytical Chemistry, Institute of Chemistry, University of Pannonia, Hungary.
    Horváth, Krisztián
    Department of Analytical Chemistry, Institute of Chemistry, University of Pannonia, Hungary.
    Investigation of a TiO2 photocatalyst immobilized with poly(vinyl alcohol)2017Ingår i: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 284, s. 179-186Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Immobilization of TiO2 photocatalyst was realized with application of poly(vinyl alcohol) (PVA). However, these PVA-based foils were too instable to be used for photocatalytic water cleaning. Their stability could be significantly enhanced by a thermal treatment, but this procedure generated various water-soluble derivatives such as aldehydes, ketones, and aromatic species. Photocatalytic pre-treatment of the foils proved to be suitable to remove these products from the surface of the composite. After three subsequent pre-treating cycles of irradiation and rinsing, the PVA-TiO2 foil became applicable for photocatalytic degradation of Triton X-100, a widely used non-ionic detergent. The composite catalyst kept its stability and efficiency even after some cycles of re-usage, while its surface underwent a perceptible, although quantitatively negligible degradation.

  • 49.
    Hedman, Daniel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Larsson, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Length dependent stability of single-walled carbon nanotubes and how it affects their growth2017Ingår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 116, s. 443-447Artikel i tidskrift (Refereegranskat)
    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.

  • 50.
    Hedman, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Linking Stability of Single-Walled Carbon Nanotubes with Growth Products2017Konferensbidrag (Övrigt vetenskapligt)
    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.