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  • 1.
    Abbas, Ghulam
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Johansson, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Alay-e-Abbas, Syed Muhammad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad 38040, Pakistan.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, J. Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Quasi Three-Dimensional Tetragonal SiC Polymorphs as Efficient Anodes for Sodium-Ion Batteries2023In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 6, no 17, p. 8976-8988Article in journal (Refereed)
    Abstract [en]

    In the present work, we investigate, for the first time, quasi 3D porous tetragonal silicon–carbon polymorphs t(SiC)12 and t(SiC)20 on the basis of first-principles density functional theory calculations. The structural design of these q3-t(SiC)12 and q3-t(SiC)20 polymorphs follows an intuitive rational approach based on armchair nanotubes of a tetragonal SiC monolayer where C–C and Si–Si bonds are arranged in a paired configuration for retaining a 1:1 ratio of the two elements. Our calculations uncover that q3-t(SiC)12 and q3-t(SiC)20 polymorphs are thermally, dynamically, and mechanically stable with this lattice framework. The results demonstrate that the smaller polymorph q3-t(SiC)12 shows a small band gap (∼0.59 eV), while the larger polymorph of q3-t(SiC)20 displays a Dirac nodal line semimetal. Moreover, the 1D channels are favorable for accommodating Na ions with excellent (>300 mAh g–1) reversible theoretical capacities. Thus confirming potential suitability of the two porous polymorphs with an appropriate average voltage and vanishingly small volume change (<6%) as anodes for Na-ion batteries.

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  • 2.
    Ahmed, Shahbaz
    et al.
    Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Faisalabad, Pakistan.
    Zulfiqar, Waqas
    Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Faisalabad, Pakistan.
    Javed, Farrukh
    Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Faisalabad, Pakistan.
    Arshad, Hurriya
    Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Faisalabad, Pakistan.
    Abbas, Ghulam Gilani
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Laref, Amel
    Department of Physics and Astronomy, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia.
    Alay-e-Abbas, Syed Muhammad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Faisalabad, Pakistan.
    Accurate First-Principles Evaluation of Structural, Electronic, Optical and Photocatalytic Properties of BaHfO3 and SrHfO3 Perovskites2022In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 892, article id 162071Article in journal (Refereed)
    Abstract [en]

    A reliable first-principles account of experimentally observed physical properties of perovskite oxides is crucial for realizing their employment in electronic and optical devices. In this context, SCAN meta-GGA functional of DFT offers good approximation for the exchange-correlation energy; facilitating accurate determination of structural and energetic properties. However, SCAN is unable to reproduce electronic and optical properties of wide bad gap materials. In the present study, we report systematic DFT calculations to show that structural, energetic, electronic and optical properties of hafnium based BaHfO3 and SrHfO3 perovskite oxides can be accurately determined through a combine application of SCAN and Tran-Blaha modified Becke-Johnson (TB-mBJ) meta-GGAs. The structural and energetic properties computed using SCAN functional for both BaHfO3 and SrHfO3 are found to be in good agreement with experimental data; achieving a level of accuracy comparable to computationally expansive hybrid DFT calculations. On the other hand, TB-mBJ calculated band gaps computed using the SCAN optimized lattice parameters provide better agreement with experimental data at a low computational cost. The optical properties, band edge potentials and effective masses of the charge carriers in BaHfO3 and SrHfO3 are also computed to examine the combined application of SCAN and TB-mBJ meta-GGAs in predicting the photocatalytic performance of these wide band gap materials. Our results clearly show that the combination of the two meta-GGAs provide a computationally economical route for evaluating the photocatalytic performance of alkaline-earth metal hafnates.

  • 3.
    Al-Jayyousi, Hiba
    et al.
    Department of Mechanical Engineering, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates.
    Eswaran, Mathan Kumar
    SRM Research Institute, SRM Institute of Science and Technology, Kattankulathur 603203, Tamil Nadu, India.
    Ray, Avijeet
    Department of Physics, Indian Institute of Technology Roorkee, Roorkee 247667, India.
    Sajjad, Muhammad
    Department of Physics, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates.
    Larsson, J. Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Singh, Nirpendra
    Department of Physics, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates; Center for Catalysis and Separations, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates.
    Exploring the Superior Anchoring Performance of the Two-Dimensional Nanosheets B2C4P2 and B3C2P3 for Lithium-Sulfur Batteries2022In: ACS Omega, E-ISSN 2470-1343, Vol. 7, no 43, p. 38543-38549Article in journal (Refereed)
    Abstract [en]

    Potential anchoring materials in lithium–sulfur batteries help overcome the shuttle effect and achieve long-term cycling stability and high-rate efficiency. The present study investigates the two-dimensional nanosheets B2C4P2 and B3C2P3 by employing density functional theory calculations for their promise as anchoring materials. The nanosheets B2C4P2 and B3C2P3 bind polysulfides with adsorption energies in the range from −2.22 to −0.75 and −2.43 to −0.74 eV, respectively. A significant charge transfer occurs from the polysulfides, varying from −0.74 to −0.02e and −0.55 to −0.02e for B2C4P2 and B3C2P3, respectively. Upon anchoring the polysulfides, the band gap of B3C2P3 reduces, leading to enhanced electrical conductivity of the sulfur cathode. Finally, the calculated barrier energies of B2C4P2 and B3C2P3 for Li2S indicate fast diffusion of Li when recharged. These enthralling characteristics propose that the nanosheets B2C4P2 and B3C2P3 could reduce the shuttle effect in Li–S batteries and significantly improve their cycle performance, suggesting their promise as anchoring materials.

  • 4.
    An, Rong
    et al.
    Herbert Gleiter Institute of Nanoscience, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing, China.
    Zheng, Hangbing
    Herbert Gleiter Institute of Nanoscience, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing, China.
    Dong, Yihui
    Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot, Israel.
    Liu, Chang
    State Key Laboratory of Materials-Oriented and Chemical Engineering, Nanjing Tech University, Nanjing, China.
    Zou, Luyu
    Herbert Gleiter Institute of Nanoscience, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing, China.
    Feng, Tao
    Herbert Gleiter Institute of Nanoscience, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing, China.
    Laaksonen, Aatto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. State Key Laboratory of Materials-Oriented and Chemical Engineering, Nanjing Tech University, Nanjing, China; Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Sweden; Centre of Advanced Research in Bionanoconjugates and Biopolymers, Petru Poni Institute of Macromolecular Chemistry, 41A, Romania; Department of Chemical and Geological Sciences, University of Cagliari, Campus Monserrato ,SS 554 Bivio per Sestu, Monserrato, Italy.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ti-Si-Zr-Zn Nanometallic Glass Substrate with a Tunable Zinc Composition for Surface-Enhanced Raman Scattering of Cytochrome c2023In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 15, no 21, p. 25275-25284Article in journal (Refereed)
  • 5.
    Andersson, B. M.
    et al.
    Dept. of Physics, Umeå University, 5-90187 Umeå, Sweden.
    Easterling, Kenneth E.
    Luleå University of Technology.
    Guo, S. J.
    Luleå University of Technology.
    Sundqvist, B.
    Dept. of Physics, Umeå University, 5-90187 Umeå, Sweden.
    Electrical resistivity and critical temperature of bi-based high-t superconductors to 1 GPa1990In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 3, no 1-6, p. 120-122Article in journal (Refereed)
  • 6.
    Andersson, B. M.
    et al.
    Dept. of Physics, Umeå University, Sweden.
    Easterling, Kenneth
    Luleå University of Technology.
    Loberg, Bengt
    Luleå University of Technology.
    Niska, J.
    Luleå University of Technology.
    Sundqvist, B.
    Dept. of Physics, Umeå University, Sweden.
    High-pressure properties of high-Tc superconductor samples produced by hot isostatic pressing1990In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 3, no 1-6, p. 123-125Article in journal (Refereed)
  • 7.
    Banari, Mohammad
    et al.
    Faculty of Physics, Semnan University, P.O. Box: 35195-363, Semnan, Iran.
    Memarian, Nafiseh
    Faculty of Physics, Semnan University, P.O. Box: 35195-363, Semnan, Iran.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, Via Torino 155, 30172 Venezia Mestre, Italy.
    Effect of the seed layer on the UV photodetection properties of ZnO nanorods2021In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 272, article id 115332Article in journal (Refereed)
    Abstract [en]

    The ZnO seed layer, acting as nucleation center for the growth of ZnO nanorods (NRs), has strong impact on the optical and photodetection properties of ZnO-based UV photodetectors (PDs). In this paper, vertically aligned ZnO NRs were grown by varying the thickness of the seed layer in the range 50–125 nm, to investigate its influence on the recovery time of the PD. Single crystalline ZnO NRs were obtained as indicated by combined electron microscopy and X-ray diffraction analysis. The photoluminescence (PL) spectra proved that the lowest PL intensity (i.e.: the lowest recombination) belongs to the sample with seed layer thickness of 100 nm (labeled as NR-7). The carrier concentration of ZnO NR films was estimated from the slope of the Mott–Schottky plot. It was 1.49 × 10+20 cm−3 for seed layer thickness of 65 nm (NR-5), which was dramatically reduced to 5.44 × 10+17 cm−3 in the sample NR-9 (seed layer thickness 125 nm). Furthermore, the current-voltage (I-V) and chronoamperometric (I-t) analysis indicate a high UV responsivity under a UV irradiation. The fastest recovery time (0.1 s time decay constant) occurs in sample NR-7 (seed layer 100 nm thick). These results indicate that effective control of the electronic and optical properties in ZnO NRs can be obtained by proper tuning of the seed layer, enabling a simple and straightforward strategy to optimize NR functionality, depending on their planned use.

  • 8.
    Batool, Javaria
    et al.
    Computational Materials Modeling Laboratory, Department of Physics, Government College University Faisalabad, 38040 Faisalabad, Pakistan; Department of Physics, Government College Women University Faisalabad, Faisalabad, Pakistan.
    Alay-e-Abbas, Syed Muhammad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Computational Materials Modeling Laboratory, Department of Physics, Government College University Faisalabad, 38040 Faisalabad, Pakistan.
    Johansson, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zulfiqar, Waqas
    Computational Materials Modeling Laboratory, Department of Physics, Government College University Faisalabad, 38040 Faisalabad, Pakistan.
    Danish, Muhammad Arsam
    Computational Materials Modeling Laboratory, Department of Physics, Government College University Faisalabad, 38040 Faisalabad, Pakistan.
    Bilal, Muhammad
    Computational Materials Modeling Laboratory, Department of Physics, Government College University Faisalabad, 38040 Faisalabad, Pakistan.
    Larsson, J. Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Amin, Nasir
    Computational Materials Modeling Laboratory, Department of Physics, Government College University Faisalabad, 38040 Faisalabad, Pakistan.
    Oxygen-vacancy-induced magnetism in anti-perovskite topological Dirac semimetal Ba3SnO2021In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 23, no 43, p. 24878-24891Article in journal (Refereed)
    Abstract [en]

    The thermodynamic, structural, magnetic and electronic properties of the pristine and intrinsic vacancy-defect-containing topological Dirac semimetal Ba3SnO are studied using first-principles density functional theory calculations. The thermodynamic stability of Ba3SnO has been evaluated with reference to its competing binary phases Ba2Sn, BaSn and BaO. Subsequently, valid limits of the atomic chemical potentials derived from the thermodynamic stability were used for assessing the formation of Ba, Sn and O vacancy defects in Ba3SnO under different synthesis environments. Based on the calculated defect-formation energies, we find that the charge-neutral oxygen vacancies are the most favourable type of vacancy defect under most chemical environments. The calculated electronic properties of pristine Ba3SnO show that inclusion of spin–orbit coupling in exchange–correlation potentials computed using generalized gradient approximation yields a semimetallic band structure exhibiting twin Dirac cones along the Γ–X path of the Brillouin zone. The effect of spin–polarization and spin–orbit coupling on the physical properties of intrinsic vacancy defects containing Ba3SnO has been examined in detail. Using Bader charges, electron localization function (ELF), electronic density of states (DOS) and spin density, we show that the isolated oxygen vacancy is a magnetic defect in anti-perovskite Ba3SnO. Our results show that the origin of magnetism in Ba3SnO is the accumulation of unpaired charges at the oxygen vacancy sites, which couple strongly with the 5d states of the Ba atom. Owing to the metastability observed in earlier theoretically predicted magnetic topological semimetals, the present study reveals the important role of intrinsic vacancy defects in giving rise to magnetism and also provides opportunities for engineering the electronic structure of a Dirac semimetal.

  • 9.
    Benavides, Vicente
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Synthesis and characterization of nanocarbons as reinforced particles in metal composites2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this work, several scientific problems related to high pressure–high temperature (HP–HT) synthesis of new materials using fullerite as a precursor were studied: first, the mechanism of the transformation of C60 crystal into a nano-clustered graphene phase (NGP) at a pressure of 8 GPa; and second, the effect of disorder introduced into C60 crystals by ball milling prior to HP–HT synthesis on the structure and properties of the NGP. A separate set of experiments was devoted to compression of C60 precursor at unexplored before pressure of 25 GPa and elevated temperatures in search for new type of disordered carbon-based materials.

    In the first study, Raman spectroscopy, HRSTEM-EELS, and indentation hardness demonstrate that, under pressure, C60 exhibits a path of transformation from polymerized C60 to NGP. This phase exhibits a short-range order and preferential orientation of nano-clusters of graphene assembled in a highly disordered carbon matrix. In our studies, we observe that the mechanism of C60 transformation into NGP could be understood in terms of nucleation and growth mechanism as opposed to the pseudomartensitic mechanism. Changes in Raman intensity of the Ag(2) C60 mode monitored in polished incompletely transformed carbon particles reveal different steps of transformation. Moreover, the polishing reveals the distribution of shear bands resulting from plastic deformation of the C60 monomer and following the direction of the <110> slip planes in FCC system.

    HRSTEM analysis reveals the presence of disorder as an intermediate state between the parent C60 and the nano-graphene units. EELS spectra show that C60 molecules in such state are present as monomers, and the intermediate phase is an sp2–sp3 disordered phase, in which the sp2 fraction is by up to 20% lower than that of graphene nanoclusters. The findings suggest that, after the collapse, the polymer structure breaks down with the formation of a disordered (sp2–sp3) carbon phase containing some fraction of residual C60 molecules. The graphene nanoclusters further nucleate and grow in the intermediate disordered phase. Thus, a nucleation and growth mechanism is proposed for the formation of NGP phase from C60 upon HP-HT action.

    For the second problem, highly disordered systems were obtained from ball-milled C60 through HP–HT demonstrating a promising technique to create hard (hardness > 30 GPa) disordered carbons at relatively low pressure (up to 8 GPa).

    The nanoarchitecture of NGP and disordered systems was studied using multi-wavelength Raman spectroscopy, HRSTEM, and indentation techniques. The Raman data treatment was carefully studied following the three-stage amorphization trajectory of amorphous carbon. The Raman model consists of G and D bands and data from semi-empirical models that include peak position, FWHM, and intensity ratio. A new approach proposed by the research team includes the presence of carbon pentagons (F band) and carbon heptagons as defects in the graphene clusters and are eventually present in the disordered carbon matrix as well. A peak deconvolution considering the G, D, F and heptagon bands is the model that allows building an empirical correlation between the Raman spectra features and hardness. Using peak deconvolution model based on G, D, F heptagon and sp3 carbon-derived bands allowed us to build an empirical correlation that can be used for a semi-quantitative estimation/prediction of hardness of an arbitrary disordered sp2 carbon-based system based on their spectroscopic (Raman) data.

    Finally, experiments on compressed C60 at 25 GPa, previously unexplored pressure, produce superhard 3D-C60 polymers at temperatures below 600 oC. As the temperature increases, sp3 carbon starts dominating the disordered structures. The synthesized materials are semiconductors exhibiting ultra-high hardness that in a particular case exceeds that of single crystalline diamond. UV-Raman spectroscopy reveals a high intensity of T band and a G band position typically observed in tetrahedral amorphous carbon (ta-C)-based thin films. The phase has a residual fraction of sp2 carbons, mainly linear chains and fused aromatic rings.

    In summary, the results demonstrate that a whole class of novel materials with outstanding physical properties - superelastic-hard and ultrahard semiconducting carbons - can be produced for demanding technological applications at HP-HT by using C60 as a precursor and tuning its microstructure.

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  • 10.
    Benavides, Vicente
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Agafonov, S.
    Chernogorova, Olga Pavlovna
    Devaux, Xavier
    Université de Lorraine.
    Drozdova, Ekaterina
    Ushakova, Iraida
    Soldera, Flavio
    Saarland University.
    Mücklich, Frank
    Saarland University.
    Soldatov, Alexander V
    Luleå University of Technology, Department of Engineering Sciences and Mathematics. Physics Department, Harvard University.
    Tuning structure and mechanical properties of nanoclustered graphene phase by controlled disorder of precursor C60 fulleriteManuscript (preprint) (Other academic)
    Abstract [en]

    The paper compares the Raman spectroscopy, HRSTEM, and indentation hardness results of disordered systems synthesized by squeezing (8 GPa, 850 °C) C60 and ball-milled C60. Mechanical activation introduces substantial damage to the C60 crystal leading to the rupture of van der Waals interaction between the C60 units and a chemical reaction between the balls creating C60 dimers. The multi-wavelength Raman spectra of both, the compressed mechanical activated phase (MA-Phase) and without the mechanical activation phase (wMA phase) reveal that fused aromatic rings with a low fraction of nanographene clusters dominate the MA phase, whereas wMA phase is composed of nanographene clusters. Moreover, a Raman model is presented which introduces fullerene-like structures because of fivefold (F-band) and sevenfold carbon rings-like defects for the wMA phase and part of fused aromatic rings for the MA phase. HRSTEM-EELS data confirm that: nanographene clusters present in wMA (I) are smaller and not abundant in the MA phase (II). (III) EELS data reveal a higher fraction of sp3 bonds in the MA phase compared to that in wMA. The hardness of the MA Phase (37 GPa) is twice its value (18 GPa) in the wMA (IV). The extensive analysis of the Raman data yielded empirical dependences of Hardness vs ID/IG/Hardness vs ID/IF that can be useful for prediction of the hardness of sp2-dominant disordered carbon systems based on their spectroscopic data.         

  • 11.
    Benavides, Vicente
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Roa, Joan Josep
    Center for Research in Structural Integrity, Micromechanics and Reliability of Materials, Department of Materials Science and Engineering, Barcelona, Spain; Barcelona Research Center in Multiscale Science and Engineering, Barcelona, Spain; Universitat Politècnica de Catalunya, Escola d’Enginyeria de Barcelona Est (EEBE), Barcelona, Spain.
    Jimenez-Pique, Emilio
    Center for Research in Structural Integrity, Micromechanics and Reliability of Materials, Department of Materials Science and Engineering, Barcelona, Spain; Barcelona Research Center in Multiscale Science and Engineering, Barcelona, Spain; Universitat Politècnica de Catalunya, Escola d’Enginyeria de Barcelona Est (EEBE), Barcelona, Spain.
    Chernogorova, Olga Pavlovna
    A.A.Baikov Institute of Metallurgy and Materials Science (IMET), Russia.
    Drozdova, Ekaterina
    A.A.Baikov Institute of Metallurgy and Materials Science (IMET), Russia.
    Lukina, Ushakova
    A.A.Baikov Institute of Metallurgy and Materials Science (IMET), Russia.
    Ekimov, Eugene
    Vereshchagin Institute for High Pressure Physics HPPI RAS, Russia.
    Mücklich, Frank
    Department of Materials Science, Saarland University, Germany.
    Soldatov, Alexander V
    Luleå University of Technology, Department of Engineering Sciences and Mathematics. Department of Physics, Harvard University, USA.
    Raman spectroscopy and hardness study of C60 transformation into nanoclustered graphene phase at high pressure/high temperatureManuscript (preprint) (Other academic)
    Abstract [en]

    In this paper, a study of the C60 – nanoclustered graphene phase (NGP) transformation via characterization of non-completely transformed carbon particles is presented. High-resolution (∽ 1 µm) Raman spectroscopy and nanoindentation measurements were performed on the same pre-selected sample area. The results evidence different steps of the transformation that allows establishing correspondence between the NGP/C60 ratio and the nanohardness: an abrupt increase in nanohardness from 2 GPa to 20 GPa for a stepwise NGP/C60 ratio change in the transformation zone. These results demonstrate that (I) at a micro-level (1 µm), the transformation of C60 into NGP does not occur simultaneously in the entire volume and (II) the residual C60 polymer is not desirable in superhard amorphous carbon materials. This work demonstrates importance of advanced experimental methodologies to characterization of disordered carbon phases.

  • 12.
    Berezovsky, Vladimir
    et al.
    Department of Applied Mathematics and High-performance ComputingM.V.Lomonosov Northern (Arctic) Federal University, Arkhangelsk.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Computational study of the CO adsorption and diffusion in zeolites: validating the Reed–Ehrlich model2018In: Adsorption, ISSN 0929-5607, E-ISSN 1572-8757, Vol. 24, no 4, p. 403-413Article in journal (Refereed)
    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.

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  • 13.
    Bilal, Muhammad
    et al.
    Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Faisalabad, Pakistan.
    Alay-e-Abbas, Syed Muhammad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Faisalabad, Pakistan.
    Abbas, Ghulam Gilani
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Javed, Farrukh
    Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Faisalabad, Pakistan; Department of Chemical Engineering, McGill University, 845 Sherbrooke St. W, Montreal, Quebec, Canada.
    Zulfiqar, Waqas
    Department of Physics & Namur Institute of Structured Matter (NISM), University of Namur, 61 Rue de Bruxelles, 5000, Namur, Belgium.
    Amin, Nasir
    Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Faisalabad, Pakistan.
    Elucidating the Surface Properties of Sr3PbO Inverse-Perovskite Topological Insulator: A First-Principles Study2023In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951Article in journal (Refereed)
  • 14.
    Bilal, Muhammad
    et al.
    Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Faisalabad, Pakistan.
    Alay-e-Abbas, Syed Muhammad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Faisalabad, Pakistan.
    Sluydts, Michael
    Center for Molecular Modeling, Ghent University, 9052 Zwijnaarde, Belgium; Department of Electromechanical, Systems and Metal Engineering, Ghent University, 9052 Zwijnaarde, Belgium; ePotentia, 2600 Antwerp, Belgium.
    Batool, Javaria
    Department of Physics, Government College Women University, Faisalabad, Faisalabad, Pakistan.
    Laref, Amel
    Department of Physics and Astronomy, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia.
    Abbas, Ghulam
    School of Materials Science and Engineering, Hanshan Normal University, Chaozhou 521041, China; College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
    Amin, Nasir
    Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Faisalabad, Pakistan.
    DFT insights into surface properties of anti-perovskite 3D topological crystalline insulators: A case study of (001) surfaces of Ca3SnO2021In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 408, article id 127469Article in journal (Refereed)
    Abstract [en]

    In this letter density functional theory calculations are used for investigating the structural, energetic and electronic properties of CaSn- and Ca2O-terminated (001) surfaces of anti-perovskite Ca3SnO. Our calculations indicate larger structural changes in case of the CaSn-terminated (001) surface of Ca3SnO, however, both CaSn- and Ca2O-terminated surfaces of Ca3SnO are found to be energetically stable. The electronic properties of (001) surfaces of Ca3SnO are examined by taking spin-orbit coupling into account. Comparison of the simulated results of electronic properties for the two (001) surfaces of Ca3SnO with experimentally reported hole carrier densities observed in p-type polycrystalline samples show good agreement.

  • 15.
    Busch, Michael
    et al.
    Institute of theoretical chemistry, Ulm University, Albert-Einstein Allee 11, 89069 Ulm, Germany; Department of chemistry and material science, School of chemical engineering, Aalto University, Kemistintie 1, 02150 Espoo, Finland.
    Ahlberg, Elisabet
    Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 41296 Gothenburg, Sweden.
    Laasonen, Kari
    Department of chemistry and material science, School of chemical engineering, Aalto University, Kemistintie 1, 02150 Espoo, Finland.
    Universal Trends between Acid Dissociation Constants in Protic and Aprotic Solvents2022In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 28, no 59, article id e202201667Article in journal (Refereed)
  • 16.
    Chen, Xu
    et al.
    School of Materials Science and Engineering, Xiangtan University, Xiangtan, 411105, China.
    Peng, Shaowen
    School of Materials Science and Engineering, Xiangtan University, Xiangtan, 411105, China.
    Liu, Ye
    School of Materials Science and Engineering, Xiangtan University, Xiangtan, 411105, China.
    Bai, Song
    State Key Laboratory of Powder Metallurgy, Central South University, Changsha, 410083, China.
    Zhang, Lin
    Beijing Advanced Innovation Center for Materials Genome Engineering, Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing, 100083, China.
    He, Shuang
    School of Materials Science and Engineering, Xiangtan University, Xiangtan, 411105, China.
    Gorbatov, Oleg I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Qu, Xuanhui
    Beijing Advanced Innovation Center for Materials Genome Engineering, Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing, 100083, China.
    Ductility deterioration induced by L21 phase in ferritic alloy through Ti addition2023In: Journal of Materials Research and Technology, ISSN 2238-7854, Vol. 25, p. 3273-3284Article in journal (Refereed)
    Abstract [en]

    Ductility deterioration induced by L21-Ni2AlTi precipitates in the aged ferritic alloys was examined systematically by using a combination of scanning transmission electron microscope (STEM), mechanical tests and first-principles thermodynamic calculations. The experimental studies revealed that the strength and hardness of the aged Fe–10Cr–5Ni–1Al–1Ti ferritic alloy containing B2–NiAl and L21-Ni2AlTi precipitates were higher than that of the aged Fe–10Cr–5Ni–1Al ferritic alloy containing NiAl precipitates, whereas the elongation-to-failure decreased dramatically from 9.3% to 0.3% indicating an obvious ductility deterioration due to the formation of L21-Ni2AlTi precipitates. This was also confirmed by the observation of fracture transition mode from dimpled failure to cleavage failure. The first-principles calculations, concerning the precipitate/matrix interface, were carried out to provide a theoretical analysis for the ductile–brittle transition by means of empirical ductility criteria ratios G/B and (C12–C44)/B as well as cleavage energy. The cleavage energy results indicated an intrinsic brittleness of the L21-Ni2AlTi phase and the L21-Ni2AlTi/BCC-Fe interface. Our analysis revealed that the intrinsic brittleness of L21-Ni2AlTi phase and L21-Ni2AlTi/BCC-Fe interface plays a vital role in determining the deformation behavior of the aged Fe–10Cr–5Ni–1Al–1Ti alloy.

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  • 17.
    Dong, Yihui
    et al.
    Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel.
    Gong, Mian
    Herbert Gleiter Institute of Nanoscience, Department of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China.
    Shah, Faiz Ullah
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Laaksonen, Aatto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm SE-10691, Sweden; Center of Advanced Research in Bionanoconjugates and Biopolymers, ‘‘Petru Poni” Institute of Macromolecular Chemistry, Iasi 700469, Romania; State Key Laboratory of Materials-Oriented and Chemical Engineering, Nanjing Tech University, Nanjing 211816, China.
    An, Rong
    Herbert Gleiter Institute of Nanoscience, Department of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Phosphonium-Based Ionic Liquid Significantly Enhances SERS of Cytochrome c on TiO2 Nanotube Arrays2022In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 14, no 23, p. 27456-27465Article in journal (Refereed)
    Abstract [en]

    Surface-enhanced Raman scattering (SERS) is an attractive technique for studying trace detection. It is of utmost importance to further improve the performance and understand the underlying mechanisms. An ionic liquid (IL), the anion of which is derived from biomass, [P6,6,6,14][FuA] was synthesized and used as a trace additive to improve the SERS performance of cytochrome c (Cyt c) on TiO2 nanotube arrays (TNAs). An increased and better enhancement factor (EF) by four to five times as compared to the system without an IL was obtained, which is better than that from using the choline-based amino acid IL previously reported by us. Dissociation of the ILs improved the ionic conductivity of the system, and the long hydrophobic tails of the [P6,6,6,14]+ cation contributed to a strong electrostatic interaction between Cyt c and the TNA surface, thereby enhancing the SERS performance. Atomic force microscopy did verify strong electrostatic interactions between the Cyt c molecules and TNAs after the addition of the IL. This work demonstrates the importance of introducing the phosphonium-based IL to enhance the SERS performance, which will stimulate further development of more effective ILs on SERS detection and other relevant applications in biology.

  • 18.
    Dong, Yihui
    et al.
    Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel.
    Lin, Weifeng
    Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel.
    Laaksonen, Aatto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Arrhenius Laboratory, Department of Materials and Environmental Chemistry, Stockholm University, 10691 Stockholm, Sweden; Center of Advanced Research in Bionanoconjugates and Biopolymers, ‘‘Petru Poni” Institute of Macromolecular Chemistry, 700469 Iasi, Romania; State Key Laboratory of Materials-Oriented and Chemical Engineering, Nanjing Tech University, Nanjing 211816, China.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Complementary Powerful Techniques for Investigating the Interactions of Proteins with Porous TiO2 and Its Hybrid Materials: A Tutorial Review2022In: Membranes, ISSN 2077-0375, E-ISSN 2077-0375, Vol. 12, no 4, article id 415Article, review/survey (Refereed)
    Abstract [en]

    Understanding the adsorption and interaction between porous materials and protein is of great importance in biomedical and interface sciences. Among the studied porous materials, TiO2 and its hybrid materials, featuring distinct, well-defined pore sizes, structural stability and excellent biocompatibility, are widely used. In this review, the use of four powerful, synergetic and complementary techniques to study protein-TiO2-based porous materials interactions at different scales is summarized, including high-performance liquid chromatography (HPLC), atomic force microscopy (AFM), surface-enhanced Raman scattering (SERS), and Molecular Dynamics (MD) simulations. We expect that this review could be helpful in optimizing the commonly used techniques to characterize the interfacial behavior of protein on porous TiO2 materials in different applications.

  • 19.
    Fadaei Naeini, Vahid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Unraveling the pressure-viscosity behavior and shear thinning in glycerol using atomic scale molecular dynamics simulations2023In: Journal of Molecular Liquids, ISSN 0167-7322, E-ISSN 1873-3166, Vol. 390, no part A, article id 122990Article in journal (Refereed)
    Abstract [en]

    In order to increase the usage and explore new applications of glycerol as a replacement for fossil-based lubricants its properties needs to be known at the fundamental level. In this study, the viscosity of pure glycerol at high pressures and strain rates has been investigated using of molecular dynamics (MD) simulations, utilizing both the Green-Kubo (GK) formalism and the SLLOD algorithm. Although the viscosity acquired by the GK method is in agreement with the corresponding experimental values at low pressure, a significant distinction was identified between the viscosity obtained by the GK method and the experimental values at higher pressures (P > 0.5 GPa). This results in a clear difference between the viscosity-pressure coefficient attained by the GK method and the corresponding experimental value. The SLLOD method using a non-equilibrium MD (NEMD) platform was exploited to take into account the simultaneous effects of strain rate and pressure on viscosity. As a result, the pressure-viscosity coefficient acquired by the SLLOD algorithm approaches the experimental value. By combining the experimental outputs for viscosity at low strain rates ( < 104 s−1) with the SLLOD outputs at higher rates ( > 105 s−1), the evolutions of glycerol viscosity with pressure and strain rate were ultimately achieved. Implementing this computational platform depicts the shear thinning process in pure glycerol in a wide range of pressures and strain rates.

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  • 20.
    Faiza-Rubab, S.
    et al.
    Department of Physics, University of Sargodha, Sargodha, Pakistan.
    Naseem, Shahnila
    Department of Physics, University of Sargodha, Sargodha, Pakistan.
    Alay-e-Abbas, Syed Muhammad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, Faisalabad, Pakistan.
    Zulfiqar, M.
    Department of Physics, University of Sargodha, Sargodha, Pakistan.
    Zhao, Y.
    Department of Physics, Yantai University, Yantai, People's Republic of China.
    Nazir, S.
    Department of Physics, University of Sargodha, Sargodha, Pakistan.
    Structural stability and evolution of half-metallicity in Ba2CaMoO6: interplay of hole- and electron-doping2021In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 23, p. 19472-19481Article in journal (Refereed)
    Abstract [en]

    Half-metallic ferromagnetic materials have attracted a lot of attention due to their probable technological applications in spintronics. In this respect, doping plays a crucial role in tailoring or controlling the physical properties of the system. Herein, the impact of both hole and electron doping on the structural, electronic and magnetic properties of the recent high pressure synthesized non-magnetic insulator Ba2CaMoO6 double perovskite oxide are investigated by replacing one of the Mo ions with Nb and Tc. The structural and mechanical stability of the undoped/doped materials are analyzed by calculating the formation energies and stiffness tensors, respectively, which confirm the system's stability. Interestingly, our results revealed that Nb- and Tc-doped systems display an electronic transition from insulating to p- and n-type half-metallic ferromagnetic states, respectively. The most striking feature of the present study is that oxygen ions become spin-polarized, with a magnetic moment of ∼0.12 μB per atom, and are mainly responsible for conductivity in the Nb-doped system. However, the admixture of Tc 4d non-degenerate orbitals are primarily contributing to the metallicity in the Tc-doped structure, with a moment of ∼0.59 μB. It is also found that Nb and Tc ions remain in the 5+ and 7+ states with electronic configurations of t22g↑t22g↓e0g↑e0g↓ and t32g↑t22g↓e0g↑e0g↓, with spin states of S = 0 and S = 1/2 in the individual doped systems, respectively. Hence, the present work proposes that a doping strategy with a suitable candidate could be beneficial to tune the physical properties of the materials for their potential utilization in advanced spin-based devices.

  • 21.
    Friberg, Jakob
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Investigation of Metallic Dust formed on Steel Substrates in Solar Cell Sputtering Chambers2019Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Investigations have been done as of why dust particles appear in a circular pattern on the backside of solar cells produced in sputtering chambers at Midsummer AB. An experimental approach was conducted, where solar cells were produced at standard conditions and their backside studied by material analytical methods. The solar cells dust particles were analyzed by energy-dispersive x-ray spectroscopy and x-ray diffraction, deducing that they consisted of iron selenide (Fe0.89Se). Furthermore, the dust particles appear due to formation of a thin iron selenide film that cracks and delaminate upon cooling from process temperature to room temperature. Iron selenide film thickness was found by energy-dispersive x-ray spectroscopy to occur in a pattern with radial symmetry with respect to the cell center, correlating with the film delamination pattern. The reason to the film formation was due to selenium reacting with the substrate steel at high temperatures (>400 C) in deposition chambers having a selenium environment. The film delamination occurs at a critical film thickness at which stresses in the film is high enough for the film to yield and fracture.

    It was concluded that iron selenide film formation or delamination must be minimized in order to control dust particle formation. These two phenomena can be mitigated by protective substrate films, change of substrate material, selenium environment optimization or temperature profile optimization and should be researched further to find the most effective and viable solution.

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  • 22.
    Geng, Wenping
    et al.
    Science and Technology on Electronic Test and Measurement Laboratory, North University of China, Taiyuan 030051, China.
    Qiao, Xiaojun
    Science and Technology on Electronic Test and Measurement Laboratory, North University of China, Taiyuan 030051, China.
    He, Jinlong
    Science and Technology on Electronic Test and Measurement Laboratory, North University of China, Taiyuan 030051, China.
    Mei, Linyu
    School of Mechanical Engineering, North University of China, Taiyuan 030051, China.
    Bi, Kaixi
    Science and Technology on Electronic Test and Measurement Laboratory, North University of China, Taiyuan 030051, China.
    Wang, Xiangjian
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chou, Xiujian
    Science and Technology on Electronic Test and Measurement Laboratory, North University of China, Taiyuan 030051, China.
    Permanent charged domain walls under tip-poling engineering2021In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 9, no 44, p. 15797-15803Article in journal (Refereed)
    Abstract [en]

    Charged domain walls (CDWs) have attracted considerable attention owing to their tunable properties related to high-density information storage and nanoelectronics devices. The excellent time endurance of conductivity is a pressing need, which is directly related to the domain stability and boundary conditions. In this study, we propose an effective method to promote the permanent formation of charged domain walls aimed with tip-induced electric fields. The permanent domain structures and CDWs are attributed to the robust stimulus with tip dimensions combined with effective screening conditions. This interesting conductivity near the domain walls is three orders of magnitude higher than the domain inner, and exhibits attractive anti-fatigue properties with the value of ∼60 pA for the duration of more than one month. In addition, the tunable mechanism of CDWs in LiNbO3 thin films is related to carrier gathering near the domain walls for the inclined boundary. These inclined head-to-head domain walls exhibit conductive features only along the negative direction, which can be modulated by the application of a sub-coercive voltage. The results demonstrate the stable manipulation of domain reversal and charged domain walls in LiNbO3 thin films, highlighting them as a critical component, especially for multiple-state logic circuits and potential ferroelectric diode applications in non-volatile memories and nanoelectronics devices.

  • 23.
    Gilzad Kohan, Mojtaba
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    You, Shujie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Camellini, Andrea
    Dipartimento di Energia, Politecnico di Milano, Via G. Ponzio 34/3, Milano I-20133, Italy .
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rossi, Margherita Zavelani
    Dipartimento di Energia, Politecnico di Milano, Via G. Ponzio 34/3, Milano I-20133, Italy; IFN-CNR, piazza L. Da Vinci 32, 20133 Milano, Italy .
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, Via Torino 155, 30172 Venezia Mestre, Italy .
    Optical field coupling in ZnO nanorods decorated with silver plasmonic nanoparticles2021In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 9, no 43, p. 15452-15462Article in journal (Refereed)
    Abstract [en]

    Characterizing carrier redistribution due to optical field modulation in a plasmonic hot-electron/semiconductor junction can be used to raise the framework for harnessing the carrier decay of plasmonic metals in more efficient conversion systems. In this work we comprehensively studied the carrier redistribution mechanisms of a 1-dimensional (1D) metal-semiconductor Schottky architecture, holding the dual feature of a hot-electron plasmonic system and a simple metal/semiconductor junction. We obtained a strongly enhanced external quantum efficiency (EQE) of the plasmonic Ag decorated ZnO semiconductor in both the band-edge region of ZnO and the corresponding plasmonic absorption profile of the Ag NPs (visible region). Simultaneously, the insertion of an insulating Al2O3 intermediate layer between Ag NPs and ZnO resulted in a parallel distinction of the two main non-radiative carrier transfer mechanisms of plasmonic NPs, i.e. direct electron transfer (DET) and plasmonic induced resonance energy transfer (PIRET). The multi-wavelength transient pump-probe spectroscopy indicated the very fast plasmonic radiative transfer dynamics of the system in <500 fs below 389 nm. We demonstrate a 13% increase of photogenerated current in ZnO upon visible irradiation as a result of non-radiative plasmonic hot-electron injection from Ag NPs. Overall, our device encompasses several effective solutions for designing a plasmonic system featuring non-radiative electron-electron plasmonic dephasing and high photoconversion efficiencies.

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  • 24.
    Gorbatov, Oleg
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Laboratory for Mechanics of Gradient Nanomaterials, Nosov Magnitogorsk State Technical University, Magnitogorsk 455000, Russia.
    Johansson, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Jakobsson, Adam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mankovsky, S.
    Department of Chemistry/Physical Chemistry, LMU Munich, Butenandtstrasse 11, D-81377 Munich, Germany.
    Ebert, H.
    Department of Chemistry/Physical Chemistry, LMU Munich, Butenandtstrasse 11, D-81377 Munich, Germany.
    Di Marco, I.
    Asia Pacific Center for Theoretical Physics, Pohang, Gyeongbuk 790-784, Republic of Korea; Department of Physics, Pohang University of Science and Technology, Gyeongbuk 790-784, Republic of Korea; Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden.
    Minár, J.
    New Technologies–Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen, Czech Republic.
    Etz, Corina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Magnetic exchange interactions in yttrium iron garnet: A fully relativistic first-principles investigation2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 17, article id 174401Article in journal (Refereed)
    Abstract [en]

    Magnetic isotropic and Dzyaloshinskii-Moriya interactions in yttrium iron garnet have been obtained byab initio fully relativistic calculations. The calculated coupling constants are in agreement with availableexperimental data. Using linear spin-wave theory, we are able to reproduce the experimental magnon spectrumincluding the spin-wave gap and stiffness. The way to calculate the exchange coupling constants using theKorringa-Kohn-Rostoker formalism for large magnetic systems such as complex oxides is discussed in detail.

  • 25.
    Griesiute, Diana
    et al.
    Institute of Chemistry, Vilnius University, Naugarduko 24, 03225, Vilnius, Lithuania.
    Garskaite, Edita
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Antuzevics, Andris
    Institute of Solid State Physics, University of Latvia, Kengaraga 8, Riga, 1063, Latvia.
    Klimavicius, Vytautas
    Institute of Chemical Physics, Vilnius University, Sauletekio 3, 10257, Vilnius, Lithuania.
    Balevicius, Vytautas
    Institute of Chemical Physics, Vilnius University, Sauletekio 3, 10257, Vilnius, Lithuania.
    Zarkov, Aleksej
    Institute of Chemistry, Vilnius University, Naugarduko 24, 03225, Vilnius, Lithuania.
    Katelnikovas, Arturas
    Institute of Chemistry, Vilnius University, Naugarduko 24, 03225, Vilnius, Lithuania.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Kareiva, Aivaras
    Institute of Chemistry, Vilnius University, Naugarduko 24, 03225, Vilnius, Lithuania.
    Synthesis, structural and luminescent properties of Mn-doped calcium pyrophosphate (Ca2P2O7) polymorphs2022In: Scientific Reports, E-ISSN 2045-2322, Vol. 12, no 1, article id 7116Article in journal (Refereed)
    Abstract [en]

    In the present work, three different Mn2+-doped calcium pyrophosphate (CPP, Ca2P2O7) polymorphs were synthesized by wet co-precipitation method followed by annealing at different temperatures. The crystal structure and purity were studied by powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR), solid-state nuclear magnetic resonance (SS-NMR), and electron paramagnetic resonance (EPR) spectroscopies. Scanning electron microscopy (SEM) was used to investigate the morphological features of the synthesized products. Optical properties were investigated using photoluminescence measurements. Excitation spectra, emission spectra, and photoluminescence decay curves of the samples were studied. All Mn-doped polymorphs exhibited a broadband emission ranging from approximately 500 to 730 nm. The emission maximum was host-dependent and centered at around 580, 570, and 595 nm for γ-, β-, and α-CPP, respectively.

  • 26.
    Gustafsson, Magnus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    El-Kader, M.S.A.
    Department of Engineering Mathematics and Physics, Faculty of Engineering, Cairo University, Giza 12211, Egypt.
    Collision-induced absorption in Ar-Xe: a comparative study of empirical and ab initio interaction potentials and electric dipole moments2022In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 292, article id 108362Article in journal (Refereed)
    Abstract [en]

    Empirical Barker-Fisher-Watts and modified Tang-Toennies potential energy curves are obtained through fit to experimental vibrational transition energies for argon–argon, xenon–xenon, and argon–xenon pairs. The potentials are tested against experimental thermophysical and transport properties, and agreement is observed. Also, an interaction-induced electric dipole moment curve for the argon–xenon pair is determined through a fit to experimental spectral moments for collision-induced absorption. The argon–xenon potentials and dipole are tested in a complete quantum dynamical calculation of the collision-induced absorption profiles, which can be compared with a laboratory measurement. This provides further analysis of the accuracy of the empirical argon–xenon data, as calculations of absorption profiles are highly sensitive to the input of molecular data.

  • 27.
    Han, Sang Sub
    et al.
    NanoScience Technology Center, University of Central Florida, Orlando, Florida 32826, United States; Department of Materials Science and Engineering, Seoul National University, Seoul 08826, South Korea.
    Ko, Tae-Jun
    NanoScience Technology Center, University of Central Florida, Orlando, Florida 32826, United States.
    Shawkat, Mashiyat Sumaiya
    NanoScience Technology Center, University of Central Florida, Orlando, Florida 32826, United States; Department of Electrical and Computer Engineering, University of Central Florida, Orlando, Florida 32826, United States.
    Shum, Alex Ka
    Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, Florida 32826, United States.
    Bae, Tae-Sung
    Analytical Research Division, Korea Basic Science Institute, Jeonju 54907, South Korea.
    Chung, Hee-Suk
    Analytical Research Division, Korea Basic Science Institute, Jeonju 54907, South Korea.
    Ma, Jinwoo
    Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27606, United States.
    Sattar, Shahid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Physics and Electrical Engineering, Linnaeus University, SE-39231 Kalmar, Sweden.
    Hafiz, Shihab Bin
    Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, New Jersey 07102, United States.
    Mahfuz, Mohammad M. Al
    Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, New Jersey 07102, United States.
    Mofid, Sohrab Alex
    NanoScience Technology Center, University of Central Florida, Orlando, Florida 32826, United States.
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oh, Kyu Hwan
    Department of Materials Science and Engineering, Seoul National University, Seoul 08826, South Korea.
    Ko, Dong-Kyun
    Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, New Jersey 07102, United States.
    Jung, Yeonwoong
    NanoScience Technology Center, University of Central Florida, Orlando, Florida 32826, United States; Department of Electrical and Computer Engineering and Department of Materials Science and Engineering, University of Central Florida, Orlando, Florida 32826, United States.
    Peel-and-Stick Integration of Atomically Thin Nonlayered PtS Semiconductors for Multidimensionally Stretchable Electronic Devices2022In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 14, no 17, p. 20268-20279Article in journal (Refereed)
    Abstract [en]

    Various near-atom-thickness two-dimensional (2D) van der Waals (vdW) crystals with unparalleled electromechanical properties have been explored for transformative devices. Currently, the availability of 2D vdW crystals is rather limited in nature as they are only obtained from certain mother crystals with intrinsically possessed layered crystallinity and anisotropic molecular bonding. Recent efforts to transform conventionally non-vdW three-dimensional (3D) crystals into ultrathin 2D-like structures have seen rapid developments to explore device building blocks of unique form factors. Herein, we explore a “peel-and-stick” approach, where a nonlayered 3D platinum sulfide (PtS) crystal, traditionally known as a cooperate mineral material, is transformed into a freestanding 2D-like membrane for electromechanical applications. The ultrathin (∼10 nm) 3D PtS films grown on large-area (>cm2) silicon dioxide/silicon (SiO2/Si) wafers are precisely “peeled” inside water retaining desired geometries via a capillary-force-driven surface wettability control. Subsequently, they are “sticked” on strain-engineered patterned substrates presenting prominent semiconducting properties, i.e., p-type transport with an optical band gap of ∼1.24 eV. A variety of mechanically deformable strain-invariant electronic devices have been demonstrated by this peel-and-stick method, including biaxially stretchable photodetectors and respiratory sensing face masks. This study offers new opportunities of 2D-like nonlayered semiconducting crystals for emerging mechanically reconfigurable and stretchable device technologies.

  • 28.
    He, Shuang
    et al.
    School of Materials Science and Engineering, Xiangtan University, Xiangtan 411105, China.
    Tan, Qiankun
    School of Materials Science and Engineering, Xiangtan University, Xiangtan 411105, China.
    Chen, Xu
    School of Materials Science and Engineering, Xiangtan University, Xiangtan 411105, China.
    Liu, Ye
    School of Materials Science and Engineering, Xiangtan University, Xiangtan 411105, China.
    Gorbatov, Oleg I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Peng, Ping
    School of Materials Science and Engineering, Hunan University, Changsha 410082, China.
    First-principles study of Re-W interactions and their effects on the mechanical properties of γ/γ' interface in Ni-based single-crystal alloys2023In: Materials Today Communications, ISSN 2352-4928, Vol. 36, article id 106662Article in journal (Refereed)
    Abstract [en]

    The distribution of solutes and their interactions play a crucial role in determining the mechanical properties of the γ/γ′ interface in Ni-based single-crystal alloys. In this study, atomic interactions between Re and W and their alloying effects on the inter-phase cohesion of the γ/γ′ interface are investigated by first-principles calculations. Our results show that W atom exhibits a preference for partitioning into the γ phase, while the stability of the γ/γ′ interface can be enhanced due to the partitioning of W to the γ′ phase. Moreover, our results reveal that partitioned W atoms in the γ′ phase contribute to the strengthening of the γ/γ′ interface. Conversely, the dissolution of W atoms in the γ phase weakens the inter-phase cohesion. However, this detrimental effect can be mitigated by introducing of Re into the γ/γ′ interface. Partitioning of Re and W into separate phases yields minimal alterations in interaction energies, resulting in a notable enhancement of inter-phase cohesion when compared to the partitioning of Re and W within γ phase of the γ/γ′ interface. Additionally, the partitioning of solute atoms at the γ/γ′ interface leads to local lattice distortion and interfacial energy reduction, which contribute to the enhancement of inter-phase cohesion of the γ/γ′ interface. As a result, a model is proposed for interpretation of crack propagation at the γ/γ′ interface at the threshold region with the presence of tensile stress in Ni-based single-crystal alloys.

  • 29.
    Hedman, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    A Theoretical Study: The Connection between Stability of Single-Walled Carbon Nanotubes and Observed Products2017Licentiate thesis, comprehensive summary (Other academic)
    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.

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  • 30.
    Hedman, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Linking Stability of Single-Walled Carbon Nanotubes with Growth Products2017Conference paper (Other academic)
    Abstract [en]

    Many of the envisioned products and technologies using single-walled carbon nanotubes (SWCNTs) are only possible with a uniform product. Thus, control over the chirality during catalytical chemical vapor deposition (CCVD) growth of SWCNTs is necessary. Our highlighted works1,2 focuses on stabilities of SWCNTs and how that relates to growth, in order to reach the ultimate goal of chirality-specific growth. In ref.1 density functional theory (DFT) has been used to calculate the stability of SWCNT-fragments of all chiralities in the (n+m) = 8 to 18 series. The fragment stabilities are compare to the chiralities of actual CCVD products from all properly analysed experiments to date. The results show that in 84% of the cases the experimental products represent chiralities among the most stable SWCNT-fragments (within 0.2 eV) from the calculations. The analysed products from growth experiments show that diameters of SWCNTs are governed by the well-known relation to the size of the catalytic particle and that the specific chirality of SWCNT products are strongly dependent on the stability of the tubes within each series, suggesting thermodynamic control at the early stage of growth. Analysis of the relative energy show that for the lower series 8 to 10, zigzag SWCNTs are the most stable and for the higher series 11 to 18 the most stable chirality changes from zigzag to armchair. This switch in stability between armchair and zigzag chiralities is studied further in ref.2, where DFT was used to calculate the stability of armchair and zigzag SWCNTs and graphene nanoribbons (GNRs) of different lengths. The calculations show that the stability of armchair and zigzag tubes has different linear dependence with regard to their length, with switches in the most stable chirality occurring at specific lengths for each SWCNT-series. These dependencies are explained by competing edge and curvature energies. Within each series armchair nanotubes are the most stable at short lengths, while zigzag nanotubes are the most stable at long lengths, this sheds new light into why armchair and near-armchair tubes are the dominant product from CCVD growth, if templating is not used. Paradoxically, the stability of armchair nanotubes at short lengths favors their growth although zigzag nanotubes are more stable at long lengths, resulting in the production of the least stable SWCNTs.

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  • 31.
    Hedman, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    On the Stability of Single-Walled Carbon Nanotubes and how it relates to Growth2017In: CCTN17: 12th International Symposium on Computational Challenges and Tools for Nanotubes, 2017Conference paper (Other academic)
    Abstract [en]

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

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

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  • 32.
    Hedman, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Single-Walled Carbon Nanotubes: A theoretical study of stability, growth and properties2019Doctoral thesis, comprehensive summary (Other academic)
    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.

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  • 33.
    Hedman, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Research Center for Computational Design of Advanced Functional Materials, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
    Rothe, Tom
    Institute of Physics, Faculty of Natural Sciences, Chemnitz University of Technology, Chemnitz 09126, Germany.
    Johansson, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sandin, Fredrik
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Larsson, J. Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Miyamoto, Yoshiyuki
    Research Center for Computational Design of Advanced Functional Materials, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
    Impact of training and validation data on the performance of neural network potentials: A case study on carbon using the CA-9 dataset2021In: Carbon Trends, ISSN 2667-0569, Vol. 3, article id 100027Article in journal (Refereed)
    Abstract [en]

    The use of machine learning to accelerate computer simulations is on the rise. In atomistic simulations, the use of machine learning interatomic potentials (ML-IAPs) can significantly reduce computational costs while maintaining accuracy close to that of ab initio methods. To achieve this, ML-IAPs are trained on large datasets of images, which are atomistic configurations labeled with data from ab initio calculations. Focusing on carbon, we use deep learning to train neural network potentials (NNPs), a form of ML-IAP, based on the state-of-the-art end-to-end NNP architecture SchNet and investigate how the choice of training and validation data affects the performance of the NNPs. Training is performed on the CA-9 dataset, a 9-carbon allotrope dataset constructed using data obtained via ab initio molecular dynamics (AIMD). Our results show that image generation with AIMD causes a high degree of similarity between the generated images, which has a detrimental effect on the performance of the NNPs. But by carefully choosing which images from the dataset are included in the training and validation data, this effect can be mitigated. We conclude by benchmarking our trained NNPs in applications such as relaxation and phonon calculation, where we can reproduce ab initio results with high accuracy.

  • 34.
    Ibrahim, Kassa Belay
    et al.
    Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, Venezia Mestre, 30170 Italy.
    Shifa, Tofik Ahmed
    Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, Venezia Mestre, 30170 Italy.
    Moras, Paolo
    Istituto di Struttura della Materia-CNR (ISM-CNR), SS 14, Km 163.5, Trieste, 34149 Italy.
    Moretti, Elisa
    Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, Venezia Mestre, 30170 Italy.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, Venezia Mestre, 30170 Italy.
    Facile Electron Transfer in Atomically Coupled Heterointerface for Accelerated Oxygen Evolution2023In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 19, no 1, article id 2204765Article in journal (Refereed)
    Abstract [en]

    An efficient and cost-effective approach for the development of advanced catalysts has been regarded as a sustainable way for green energy utilization. The general guideline to design active and efficient catalysts for oxygen evolution reaction (OER) is to achieve high intrinsic activity and the exposure of more density of the interfacial active sites. The heterointerface is one of the most attractive ways that plays a key role in electrochemical water oxidation. Herein, atomically cluster-based heterointerface catalysts with strong metal support interaction (SMSI) between WMn2O4 and TiO2 are designed. In this case, the WMn2O4 nanoflakes are uniformly decorated by TiO2 particles to create electronic effect on WMn2O4 nanoflakes as confirmed by X-ray absorption near edge fine structure. As a result, the engineered heterointerface requires an OER onset overpotential as low as 200 mV versus reversible hydrogen electrode, which is stable for up to 30 h of test. The outstanding performance and long-term durability are due to SMSI, the exposure of interfacial active sites, and accelerated reaction kinetics. To confirm the synergistic interaction between WMn2O4 and TiO2, and the modification of the electronic structure, high-resolution transmission electron microscopy (HR-TEM), X-ray photoemission spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) are used.

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  • 35.
    Jacobsson, Adam
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Johansson, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gorbatov, Oleg I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ležaić, M.
    Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425, Jülich, Germany.
    Sanyal, B.
    Department of Physics and Astronomy, Uppsala University, Box 516, 75120, Uppsala, Sweden.
    Blügel, S.
    Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425, Jülich, Germany.
    Etz, Corina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Efficient parameterisation of non-collinear energy landscapes in itinerant magnets2022In: Scientific Reports, E-ISSN 2045-2322, Vol. 12, article id 18987Article in journal (Refereed)
    Abstract [en]

    Magnetic exchange interactions determine the magnetic groundstate, as well as magnetic excitations of materials and are thus essential to the emerging and fast evolving fields of spintronics and magnonics. The magnetic force theorem has been used extensively for studying magnetic exchange interactions. However, short-ranged interactions in itinerant magnetic systems are poorly described by this method and numerous strategies have been developed over the years to overcome this deficiency. The present study supplies a fully self-consistent method for systematic investigations of exchange interactions beyond the standard Heisenberg model. In order to better describe finite deviations from the magnetic ground state, an extended Heisenberg model, including multi-spin interactions, is suggested. Using cross-validation analysis, we show that this extended Heisenberg model gives a superior description for non-collinear magnetic configurations. This parameterisation method allows us to describe many different itinerant magnetic systems and can be useful for high-throughput calculations.

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  • 36.
    Jain, Preeti
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. Department of Materials and Environmental Chemistry, Stockholm University, SE-10691, Stockholm, Sweden.
    Antzutkin, Oleg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. Department of Physics, Warwick University, CV47AL, Covertly, United Kingdom.
    2-Ethylhexylsulfate Anion-based Surface-Active Ionic Liquids (SAILs) as Temperature Persistent Electrolytes for Supercapacitors2022In: Journal of Ionic Liquids, ISSN 2772-4220, Vol. 2, no 2, article id 100034Article in journal (Refereed)
    Abstract [en]

    We report on a comparative study of three novel non-halogenated surface-active ionic liquids (SAILs), which contain a surface-active anion, 2-ethylhexyl sulfate ([EHS]−), and phosphonium or imidazolium cations: tetrabutylphosphonium ([P4,4,4,4]+), trihexyl(tetradecyl)phosphonium ([P6,6,6,14]+), and 1-methyl-3-hexylimidazolium ([C6C1Im]+). Thermal and electrochemical properties i.e., ionic conductivities at different temperatures and electrochemical potential windows of these SAILs were thoroughly studied. SAIL's electrochemical performance as electrolytes was also examined in a multi-walled-carbon- nanotubes (MWCNT)-based supercapacitor over a wide range of temperatures from 253 to 373 K. We observed that the electrode material in the supercapacitor cell with [C6C1Im][EHS] as an electrolyte has a higher specific capacitance (Celec in F g−1), a higher electric energy density (E in W h kg−1), and a higher electric power density (P in kW kg−1) as compared to the other studied SAILs, [P4,4,4,4][EHS], [P6,6,6,14][EHS] and [N8,8,8,8][EHS] (from our preceding study) in a temperature range from 253 to 373 K: At the scan rate of 2 mV s−1 a supercapacitor cell with a MWCNT-based electrode and [C6C1Im][EHS], [P4,4,4,4][EHS] and [P6,6,6,14][EHS] as electrolytes has the specific capacitance, Celec = 148, 90 and 47 F g−1 and the energy density, E = 82, 50 and 26 W h kg−1, respectively, when measured at 298 K. For the named three SAILs at the scan rate of 2 mV s−1, a two- to three-fold increase in the specific capacitance and the energy density values was measured at 373 K: Celec = 290, 198 and 114 F g−1 and E = 161, 110 and 63 Wh kg−1, respectively. The solution resistance (Rs), charge transfer resistance (Rct) and equivalent series resistance (ESR) all decreased two- to three-fold with an increase in temperature from 298 to 373 K. With the high specific capacitance and enhanced energy and power density and wider electrochemical potential window as compared to the molecular organic and aqueous electrolytes, these SAILs can be used for high-temperature electrochemical applications, such as high power and energy storage devices. In particular, up to now, [C6C1Im][EHS] and [P4,4,4,4][EHS] are the most appropriate candidates for such applications.

  • 37.
    Jiang, Chongyang
    et al.
    Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering Chinese Academy of Sciences, Beijing China; School of Future Technology University of Chinese Academy of Sciences, Beijing China.
    Zeng, Shaojuan
    Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering Chinese Academy of Sciences, Beijing China.
    Ma, Xifei
    Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering Chinese Academy of Sciences, Beijing China.
    Feng, Jiaqi
    Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering Chinese Academy of Sciences, Beijing China.
    Li, Guilin
    Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering Chinese Academy of Sciences, Beijing China.
    Bai, Lu
    Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering Chinese Academy of Sciences, Beijing China.
    Li, Fangfang
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Zhang, Xiangping
    Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering Chinese Academy of Sciences, Beijing China; School of Future Technology University of Chinese Academy of Sciences Beijing China.
    Aprotic phosphonium‐based ionic liquid as electrolyte for high CO2 electroreduction to oxalate2023In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 69, no 2, article id e17859Article in journal (Refereed)
    Abstract [en]

    In this study, a new CO2 electroreduction electrolyte system consisting of tetrabutylphosphonium 4-(methoxycarbonyl) phenol ([P4444][4-MF-PhO]) ionic liquid (IL) and acetonitrile (AcN) was designed to produce oxalate, and the electroreduction mechanism was studied. The results show that using the new IL-based electrolyte, the electroreduction system exhibits 93.8% Faradaic efficiency and 12.6 mA cm−2 partial current density of oxalate at −2.6 V. The formation rate of oxalate is 234.4 μmol cm−2 h−1, which is better than those reported in the literature. The mechanism study using density functional theory (DFT) calculations reveals that [P4444][4-MF-PhO] can effectively activate CO2 molecule through ester and phenoxy double active sites. In addition, in the phosphonium-based ionic environment, the potential barriers of the key intermediates *CO2 and *C2O42− are reduced by the induced electric field, which greatly facilitates the activation and conversion of CO2 molecule to oxalate.

  • 38.
    Johansson, Gustav
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gorbatov, Oleg I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Etz, Corina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Theoretical investigation of magnons in Fe-Ga alloys2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 18, article id 184410Article in journal (Refereed)
    Abstract [en]

    Fe-Ga alloys show an unusually large increase in magnetostriction compared to pure Fe and are one of the most interesting Fe-based alloys for this reason. However, the origin of the large magnetostriction and its relation to the chemical ordering on the underlying bcc phase is still under debate. To gain further understanding of the extraordinary magnetoelastic characteristics of this system, we investigate the effect of Ga-concentration and ordering on the spin-wave spectra and stiffness. The magnetic interactions in the Fe-Ga alloys are obtained by ab initio electronic structure calculations and the magnon spectra are modeled using atomistic spin dynamics modeling. Our results agree with available experimental data and show softening of the magnon modes with increasing Ga-concentration and a strong reduction of the spin-wave stiffness due to atomic ordering.

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  • 39.
    Jovanović, Aleksandar Z.
    et al.
    University of Belgrade – Faculty of Physical Chemistry, Studentski trg 12-16, 11000 Belgrade, Serbia.
    Dobrota, Ana S.
    University of Belgrade – Faculty of Physical Chemistry, Studentski trg 12-16, 11000 Belgrade, Serbia.
    Skorodumova, Natalia V.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Materials Science and Engineering, School of Industrial Engineering and Management, KTH – Royal Institute of Technology, Brinellvägen 23, 100 44 Stockholm, Sweden.
    Pašti, Igor A.
    University of Belgrade – Faculty of Physical Chemistry, Studentski trg 12-16, 11000 Belgrade, Serbia.
    Reactivity of Stone-Wales defect in graphene lattice – DFT study2023In: FlatChem, E-ISSN 2452-2627, Vol. 42, article id 100573Article in journal (Refereed)
    Abstract [en]

    Understanding the reactivity of carbon surfaces is crucial for the development of advanced functional materials. The SW defect is commonly present in carbon materials, but a comprehensive understanding of its effects on the reactivity of carbons is missing. In this study, we systematically investigate the reactivity of graphene surfaces with the Stone-Wales (SW) defect using Density Functional Theory calculations. We explore the atomic adsorption of various elements, including rows 1–3 of the Periodic Table, potassium, calcium, and selected transition metals. Our results demonstrate that the SW defect enhances binding with the studied adsorbates when compared to pristine graphene, with carbon and silicon showing the most significant differences. Additionally, we examine the effects of mechanical deformation on the lattice by constraining the system with the SW defect to the pristine graphene cell. Interestingly, these constraints lead to even stronger binding interactions. Furthermore, for carbon, nitrogen, and oxygen adsorbates, we observe that mechanical deformation triggers the incorporation of adatoms into the carbon bond network, leading to the reorganization of the SW defect structure. This work establishes a foundation for future studies in the defect and strain engineering of graphene, opening avenues for developing advanced materials and catalysts with enhanced reactivity and performance.

  • 40.
    Kurak, Johan-Michael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Theoretical investigation of Co-dependence in magnetic high-entropy alloys2023Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    High-entropy alloys (HEA) is a class of materials consisting of multiple principal elements that often crystallize in simple lattices such as body-centered cubic, face-centered cubic and hexagonal close-packed structures. Many HEAsexhibit exceptional mechanical properties, e.g., impact toughness and ductility at cryogenic temperatures and high temperature creep strength.

    Out of the known magnetic HEAs, the Cantor alloy, consisting of equalparts of Co, Cr, Fe, Mn, and Ni, is by far the most investigated. The influenceof magnetism on the stability and mechanical properties for these alloys isintricate and very interesting for that reason. The concentration dependencein this alloy is, however, fairly unexplored and it would be beneficial if onecould avoid including critical elements such as Co.

    As such, the purpose of this work was to find a suitable replacement forCo in the Cantor alloy. Using density functional theory, the Co-concentrationwas investigated by replacing Co with the other constituent elements in different ways. It was discovered that the most energetically stable configurations,with magnetic and structural properties similar to the equiatomic alloy, werefound in the body-centered cubic phase when replacing Co with Fe.

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  • 41.
    Landström, Anton
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gradone, Alessandro
    National Research Council, Institute for Microelectronics and Microsystems, Via Piero Gobetti 101, 40129, Bologna, Italy. Department of Chemistry “G. Ciamician”, University of Bologna, Via Francesco Selmi 2, 40126, Bologna, Italy.
    Mazzaro, Raffaello
    National Research Council, Institute for Microelectronics and Microsystems, Via Piero Gobetti 101, 40129, Bologna, Italy.
    Morandi, Vittorio
    National Research Council, Institute for Microelectronics and Microsystems, Via Piero Gobetti 101, 40129, Bologna, Italy.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Reduced graphene oxide-ZnO hybrid composites as photocatalysts: The role of nature of the molecular target in catalytic performance2021In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 47, no 14, p. 19346-19355Article in journal (Refereed)
    Abstract [en]

    Spurred by controversial literature findings, we enwrapped reduced graphene oxide (rGO) in ZnO hierarchical microstructures (rGO loadings spanning from 0.01 to 2 wt%) using an in situ synthetic procedure. The obtained hybrid composites were carefully characterized, aiming at shining light on the possible role of rGO on the claimed increased performance as photocatalysts. Several characterization tools were exploited to unveil the effect exerted by rGO, including steady state and time resolved photoluminescence, electron microscopies and electrochemical techniques, in order to evaluate the physical, optical and electrical features involved in determining the catalytic degradation of rhodamine B and phenol in water.

    Several properties of native ZnO structures were found changed upon the rGO enwrapping (including optical absorbance, concentration of native defects in the ZnO matrix and double-layer capacitance), which are all involved in determining the photocatalytic performance of the hybrid composites. The findings discussed in the present work highlight the high complexity of the field of application of graphene-derivatives as supporters of semiconducting metal oxides functionality, which has to be analyzed through a multi-parametric approach.

  • 42.
    Liu, Peijie
    et al.
    College of Materials Science and Engineering, Shenzhen Key Laboratory of Special Functional Materials, Shenzhen Engineering Laboratory for Advanced Technology of Ceramics, Guangdong Research Center for Interfacial Engineering of Functional Materials, Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization, Shenzhen University, Shenzhen 518060, China.
    Wu, Mengnan
    College of Materials Science and Engineering, Shenzhen Key Laboratory of Special Functional Materials, Shenzhen Engineering Laboratory for Advanced Technology of Ceramics, Guangdong Research Center for Interfacial Engineering of Functional Materials, Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization, Shenzhen University, Shenzhen 518060, China.
    Abbas, Ghulam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. College of Materials Science and Engineering, Shenzhen Key Laboratory of Special Functional Materials, Shenzhen Engineering Laboratory for Advanced Technology of Ceramics, Guangdong Research Center for Interfacial Engineering of Functional Materials, Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization, Shenzhen University, Shenzhen 518060, China.
    Yang, Weifan
    College of Materials Science and Engineering, Shenzhen Key Laboratory of Special Functional Materials, Shenzhen Engineering Laboratory for Advanced Technology of Ceramics, Guangdong Research Center for Interfacial Engineering of Functional Materials, Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization, Shenzhen University, Shenzhen 518060, China.
    Liu, Fusheng
    College of Materials Science and Engineering, Shenzhen Key Laboratory of Special Functional Materials, Shenzhen Engineering Laboratory for Advanced Technology of Ceramics, Guangdong Research Center for Interfacial Engineering of Functional Materials, Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization, Shenzhen University, Shenzhen 518060, China.
    Li, Yu
    College of Materials Science and Engineering, Shenzhen Key Laboratory of Special Functional Materials, Shenzhen Engineering Laboratory for Advanced Technology of Ceramics, Guangdong Research Center for Interfacial Engineering of Functional Materials, Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization, Shenzhen University, Shenzhen 518060, China.
    Transport behavior and thermoelectric properties of SnSe/SnS heterostructure modulated with asymmetric strain engineering2022In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 207, article id 111271Article in journal (Refereed)
    Abstract [en]

    Strain engineering of two-dimensional materials provides specific regulation method for the crystal structure, electric transport behavior and hence thermoelectric properties. Since the layer components of the van der Waals heterojunction exhibit discrepant response to strains, it provides a platform for manipulation of emergent electronic and thermoelectric properties. Here, motivated by the promising thermoelectric materials SnSe and its analogue, we design a specific high-promising thermoelectric candidate based on SnSe-SnS heterostructures, focusing on the strain induced asymmetric bonding-transition and its effect on thermoelectric properties. The compressed SnS/SnSe hetero-bilayer shows significantly enhanced anisotropic electrical transport properties, due to depressed carrier scattering rate along the robust weak bonding direction. In this armchair direction, extremely high power factor values (3600 μW/(cm⋅K2)  for n-type and 4000 μW/(cm⋅K2) for p-type) are predicted at ∼1021 cm−3 at 700 K. We obtain a new state-of-the-art thermoelectric material with extremely high thermoelectric power factor and pave the way for strain engineering of thermoelectric van der Waals heterostructures with robust in-plane weak bonding.

  • 43.
    Lukina, I N
    et al.
    A.A. Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, Leninskii pr., 49, 119334, Moscow, Russia.
    Chernogorova, O P
    A.A. Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, Leninskii pr., 49, 119334, Moscow, Russia.
    Drozdova, E I
    A.A. Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, Leninskii pr., 49, 119334, Moscow, Russia.
    Stupnikov, V A
    MSU Faculty of Chemistry, Lomonosov Moscow State University, Leninskiye Gory, 1-3, 119991, Moscow, Russia.
    Soldatov, Alexander V
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Physics, Harvard University, Cambridge, MA 02138, USA.
    Effect of high-pressure treatment temperature on the structure of carbon phases formed from C60 fullerites under pressure2019In: Fourth interdisciplinary scientific forum with international participation "New materials and promising technologies" 27–30 November 2018, Moscow, Russian Federation, Institute of Physics (IOP), 2019, article id 012034Conference paper (Refereed)
    Abstract [en]

    The synthesis of metal-matrix composite materials reinforced with superelastic hard carbon particles formed from C60 fullerites includes heating of the metal-fullerite powder mixture to temperatures above 800C under pressure. The structure evolution of the carbon particles upon heating from 700 to 800 C at a pressure of 5 GPa has been studied in detail by Raman spectroscopy and indentation hardness measurements. It is shown that the structure of the carbon particle passes the stage of a nanoscale mixture of one- and two-dimensional polymers with the resulting atomic superelastic solid phase. The determining properties of the carbon particles such as superplasticity and high hardness are attained before the complete disappearance of polymerized fullerites, the remnants of which are responsible for the disintegration of the material upon scratching.

  • 44.
    Löfgren, Robin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    A Theoretical Investigation of the Nitrogen-Vacancy Center in Diamond as a Single Molecule Sensor and Qubit: Charging through Explicit Electron Donors2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The NV-center in diamond is one of the most well researched defects to date. Since its discovery in the 1960’s, a large body of experimental as well as theoretical work have been produced, investigating its properties and applications. The reason for the attention on this defect are its properties that are well suited for a number of applications. Some of those properties are: 1) photostable at room temperature; 2) long spin coherence time; 3) spin-flipping during the process of optical excitation and decay; 4) Optical readout of spin state. Some of the applications include qubits in quantum computers and sensors for single molecule properties. In order for the NV-center to function well, it is important to decouple its interaction with other defects in the diamond lattice or with the surface of the diamond, that could have a detrimental effect on the NV-center properties. In this work, we theoretically investigate how the NV-center properties are affected by some nearby defects. Those defects include: a nitrogen point defect in the diamond lattice, diamond surfaces, and an extended intrinsic stacking fault defect in the diamond lattice. It is the negative charge state of the NV-center that has the properties mentioned above, and therefore it is this charge state that is interesting for the applications. Here, we investigate our new theoretical method of charging the NV-center through an electron donor nitrogen in the diamond lattice. By instead charging with an explicit electron donor/acceptor, we avoid the complicated correction schemes associated with the tra-ditional theoretical method of introducing an artificial background charge density in a supercell for simulating charged defects. It can also be argued that our new method is a more physically correct method, as negatively charged NV-centers in diamond get their charge by accepting electrons from nearby nitrogens in the diamond lattice. In addition to the NV-center, we further test the method for other point defects in diamond.In this thesis, an introduction to the field is given and the current research questions are stated in chapter 1. Followed by chapters reviewing the current experimental and theoret-ical work regarding the NV-center, computational physics and density functional theory, and an overview of the software used in this work. The results presented in this thesis are obtained using density functional theory computations.Our results show that the method of charging the NV-center with a donor-nitrogen is viable for an NV-N distance of 7.5 ˚A or greater.When placing the NV-center in the vicinity to a terminated surface (F- H/O/OH- and N-terminated), its properties converge to bulk values already at 5 ˚A depth. This is great news when compared with the recent experimentally achieved distance of 1 nm, meaning that NV-centers could possibly be placed even closer to the surface without being affected. When placing the NV-center in the vicinity of an intrinsic stacking fault (ISF), our results show that the NV-center is not greatly affected down to a distance of 4.2 ˚A. However, when the NV-center is placed 3.8 ˚A or closer to the ISF, the ZPL is perturbed between 2.0 and 11.3 %. It is perturbed the most when placed inside the ISF glide plane. This is great news for the technical applications; some diamonds contain high densities of ISFs, and our results show that a NV-center can be placed really close to such an ISF without losing its sensitivity as a sensor of magnetic fields.We have also found that the excitation from the NVground state into donor-N+ (one-photon process) requires 2.31 eV and lead to a meta-stable NV0 and donor-N0 charge state, both of which are electron spin resonance (ESR) active and, thus, this transition could be investigated experimentally. The excitation to the neutral state can also be achieved through a two-photon process with the first step at 2.19 eV and the second step at 0.81 eV.When placing the NV-center in the vicinity to two nitrogens (one neutrally charged, and one positively charged acting as electron donor), we find that it is almost unaffected, with changes in the ZPL of 1-8 meV when the distance to the nitrogens is 9.40-12.52 ˚A. This means that a nearby nitrogen, whether it is neutral or positively charged does not affect the NV-center in a detrimental way.Our tests on charging defects through electron donors/acceptors reveals that our method also works for the following defect-donor/acceptor pairs: NV-P+, NV-B+, N+-B, SiV-N+, Be-O+, Be2−-N+-N+.

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  • 45.
    Löfgren, Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, J. Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    The diamond NV-center transition energies in the vicinity of an intrinsic stacking fault2022In: AIP Advances, E-ISSN 2158-3226, Vol. 12, no 3, article id 035009Article in journal (Refereed)
    Abstract [en]

    The negatively charged nitrogen vacancy (NV−) center in a diamond is a nanometer-sized defect with very sensitive properties that can be manipulated, for example, for single-molecule photoluminescence and nuclear magnetic resonance sensing, as a single photon source for quantum cryptography and as a qubit in room temperature quantum computing. To have a minimal perturbation of its properties, it is important to isolate the NV-center from other defects. One type of the extended defects that can be common in diamonds is the intrinsic stacking fault (ISF) associated with dislocations. In this work, we use density functional theory simulations to investigate how the distance between the NV− center and an ISF affects its properties, including the transition energies, spin density, and energy eigenvalues in the Kohn–Sham bandgap. We have found that the NV-center properties are only slightly perturbed when placed in the vicinity of an ISF. Even for an interdistance of only 3.8 Å between the NV-center and the ISF, the decrease in its zero phonon line (ZPL) energy is less than 6.8%. To more significantly perturb the ZPL, the NV-center has to be placed inside the stacking fault glide plane (11.3% decrease). The changes in ZPL are in the majority of cases lower than the bulk value, which can be used to guide experimental observations. We find that the NV-center is only weakly interacting with ISFs, which in addition to a small bulk conversion depth of 5 Å to a diamond surface is important for their technological use.

  • 46.
    Magnusson, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Training Neural Network Potentials for Atomistic Calculations on Carbon Materials: An initial study on diamond structures2018Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Machine Learning (ML) and especially implementations of  Neural Networks (NNs) is growing in popularity  across numerous application areas. One of which is the use of a trained NN as an interatomic potential in Atomistic Simulations (AS), a NN applied in this manner is referred to as a Neural Network Potential (NNP).

    A well established method of atomistic calculations is the use of the first principle Density Functional Theory (DFT). DFT can very precisely model properties of nanomaterials, but for large systems of atoms DFT is not a feasible method because of its heavy computational load. The use of NNPs enables accurate simulations of big systems of atoms with a reasonable low computational cost.

    Previous work by students at Luleå University of Technology (LTU) where NNs were trained on fullerenes and carbon nanotubes (CNTs) demonstrated promising results. The NNs trained by the use of Atomistic Machine-Learning Package (AMP) managed to predict energies with considerable accuracy (100 meV/atom), but the force predictions were problematic and did not reach desired accuracy (the force RMSE reached was 6 eV/Å). Attempts made to run AS such as Molecular Dynamics (MD) and Geometry Optimization (GO) were unsuccessful, likely due to a poor representation of forces. 

    This work aims to improve the performance of NNs on carbon materials by studying diamond structures using AMP, such that working AS can be achieved.This was done in two stages, first a feasibility study was made to find appropriate hyperparameters. Moreover a study was made, where NNs was trained with the hyperparameters found. Two types of feature mapping descriptors were considered here, Gaussian and Zernike.The NNs trained was used as NNPs to perform MD and GO simulations as a mean of evaluation. The NNPs were also used to calculate the phonon dispersion curve of diamond.The trained NNPs in this work managed to perform AS and calculate the phonon dispersion curve with varying success. The best performing NN trained on 333 super-cells of diamond reached an accuracy of 120 meV/atom when predicting energies, and 640 meV/Å predicting forces. A NNP trained with Gaussian descriptors turned out to be 10 times faster than the reference simulation done with DFT, compared while performing a single step in a GO. The phonon dispersion curve produced by the Gaussian NNP displayed a striking resemblance to the reference produced by using DFT. Phonon dispersion curves produced by the Zernike NNP was distorted and involved a great deal of imaginary frequencies, but the correct amplitude was reached.The Gaussian NNPs trained in this work turned out to be faster and better in almost all regards compared to the Zernike alternative. The only time Zernike outperformed Gaussian descriptors were in the total energy reached in a GO simulation applying the NNPs from the study. Compared to DFT results the Zernike error was 0.26 eV (0.05%) and the Gaussian error was 0.855 eV (0.17%). MD simulations where the NNPs was used worked well for the Gaussian variant but not for the Zernike.With the AS up and running (at least for the Gaussian NNP) the following step is either to improve the performance on diamond structures. Or to include more carbon materials in the studies such as CNT and fullerenes.

  • 47.
    Migas, Dmitry B.
    et al.
    Belarusian State University of Informatics and Radioelectronics, P. Browki 6, 220013 Minsk, Belarus; National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe shosse 31, 115409 Moscow, Russia.
    Turchenko, Vitaliy A.
    Joint Institute for Nuclear Research, 6 Joliot-Curie Str., Dubna, Russia.
    Rutkauskas, A. V.
    Joint Institute for Nuclear Research, 6 Joliot-Curie Str., Dubna, Russia.
    Trukhanov, Sergey V.
    SSPA Scientific-Practical Materials Research Centre of the NAS of Belarus, Minsk, Belarus; Smart Sensors Laboratory, NUST MISiS, Moscow, Russia.
    Zubar, Tatiana I.
    SSPA Scientific-Practical Materials Research Centre of the NAS of Belarus, Minsk, Belarus.
    Tishkevich, Daria I.
    SSPA Scientific-Practical Materials Research Centre of the NAS of Belarus, Minsk, Belarus.
    Trukhanov, Alex V.
    SSPA Scientific-Practical Materials Research Centre of the NAS of Belarus, Minsk, Belarus; Smart Sensors Laboratory, NUST MISiS, Moscow, Russia; L.N. Gumilyov Eurasian National University, Astana, Kazakhstan.
    Skorodumova, Natalia V.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-10044 Stockholm, Sweden.
    Temperature induced structural and polarization features in BaFe12O192023In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 11, no 36, p. 12406-12414Article in journal (Refereed)
  • 48.
    Mondal, Aniruddha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, Venezia Mestre, 30172 Italy.
    2D Transition Metal Dichalcogenides‐Based Electrocatalysts for Hydrogen Evolution Reaction2022In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 32, no 52, article id 2208994Article, review/survey (Refereed)
    Abstract [en]

    Hydrogen is an efficient, clean, and economical energy source, owing to its huge energy density. Electrochemical water splitting is a potential candidate for inexpensive and eco-friendly hydrogen production. Recently, the development of 2D transition metal chalcogenides (TMDs) nanomaterials with a variety of physicochemical properties has shown their potential as eminent non-noble metal-based nanoscale electrocatalysts for hydrogen evolution. Nanostructuring such materials induces deep modification of their functionalities, compared to their bulk counterparts. High density of different types of exposed active sites is formed, and the small diffusion paths, which enhances the electron transfer in the 2D structures, can successfully aid the charge collection process in the electrocatalytic hydrogen evolution reactions. In this review, the key parameters to improve the catalyst performance of 2D TMDs in electrochemical hydrogen evolution reaction (HER) processes are discussed in detail and the most recent developments in the field are summarized, focusing on the improvement of the electrocatalytic activity of 2D TMDs. This review delivers deep insight for the clear understanding of the potential of 2D TMDs nanoscale materials as electrocatalysts for HER, suggesting the development of new type of catalyst with efficient activity in HER as well as other renewable energy fields.

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  • 49.
    Muhammad, Zahir
    et al.
    Hefei Innovation Research Institute, School of Microelectronics, Beihang University, Hefei 230013, P. R. China.
    Li, Yuliang
    National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, P. R. China.
    Abbas, Ghulam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Usman, Muhammad
    College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
    Sun, Zhe
    National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, P. R. China.
    Zhang, Yue
    Hefei Innovation Research Institute, School of Microelectronics, Beihang University, Hefei 230013, P. R. China.
    Lv, Ziyu
    College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
    Wang, Yan
    Hefei Innovation Research Institute, School of Microelectronics, Beihang University, Hefei 230013, P. R. China.
    Zhao, Weisheng
    Hefei Innovation Research Institute, School of Microelectronics, Beihang University, Hefei 230013, P. R. China.
    Temperature Modulating Fermi Level Pinning in 2D GeSe for High‐Performance Transistor2022In: Advanced Electronic Materials, E-ISSN 2199-160X, Vol. 8, no 7, article id 2101112Article in journal (Refereed)
    Abstract [en]

    2D layered germanium selenide (GeSe) material possesses in-plane anisotropy because of low-symmetry crystal structure with a new degree of freedom for enhanced optical and electronic properties. However, their systematic vibrational and electronics properties are still under the scope to study. Herein, the vibrational properties of GeSe sheets are studied by Raman spectroscopy. Whereas, the temperature-dependent electronic band structure is studied using angle-resolved photoemission spectroscopy (ARPES) combined with density functional theory calculations. Moreover, the field-effect transistor (FET) is fabricated on a few-layer GeSe with high performance. The vibrational modes (Formula presented.) and (Formula presented.) demonstrates linear softening as the temperature increases, with temperature coefficient value associated by anharmonic phonon–phonon/electron coupling. Besides, the enhanced dielectric screening effect of long-range Coulomb and interlayer interaction is observed from bulk to monolayer. Similarly, ARPES results further show Fermi level movement toward the valance band as increased temperature represents hole doping to pining the Fermi level, which indicates superior carrier concentration for electronic properties. The fabricated FET device on six layers GeSe exhibits high carrier mobility of 52.89 cm2 V−1 s−1 with an on/off ratio above 4 × 105 at room temperature, while it decreased below the room temperature. Our results provide the important figure of merit for GeSe-based novel nanoelectronic and thermoelectric devices.

  • 50.
    Muhammad, Zahir
    et al.
    Hefei Innovation Research Institute, School of Integrated Circuit Science and Engineering, Beihang University, Hefei 230013, People’s Republic of China.
    Szpakowski, Jan
    Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland.
    Abbas, Ghulam Gilani
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zu, Lin
    Hefei Innovation Research Institute, School of Integrated Circuit Science and Engineering, Beihang University, Hefei 230013, People’s Republic of China.
    Islam, Rajibul
    International Research Centre Magtop, Institute of Physics, Polish Academy of Sciences, Aleja Lotników 32/46, PL-02668 Warsaw, Poland.
    Wang, Yan
    School of Microelectronics, Hefei University of Technology, Hefei 230009, People’s Republic of China.
    Wali, Faiz
    College of Physics and Optoelectronic Engineering, Shenzhen University, Nanhai Ave. 3688, Shenzhen, Guangdong 518060, People’s Republic of China.
    Karmakar, Arka
    Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland.
    Molas, Maciej R.
    Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland.
    Zhang, Yue
    Hefei Innovation Research Institute, School of Integrated Circuit Science and Engineering, Beihang University, Hefei 230013, People’s Republic of China.
    Zhu, Ling
    College of Physics and Optoelectronic Engineering, Shenzhen University, Nanhai Ave. 3688, Shenzhen, Guangdong 518060, People’s Republic of China.
    Zhao, Weisheng
    Hefei Innovation Research Institute, School of Integrated Circuit Science and Engineering, Beihang University, Hefei 230013, People’s Republic of China.
    Zhang, Han
    College of Physics and Optoelectronic Engineering, Shenzhen University, Nanhai Ave. 3688, Shenzhen, Guangdong 518060, People’s Republic of China.
    Anisotropic phonon and magnon vibration and gate-tunable optoelectronic properties of nickel thiophosphite2023In: 2D Materials, E-ISSN 2053-1583, Vol. 10, no 2, article id 025001Article in journal (Refereed)
    Abstract [en]

    Transition metal phosphorus trichalcogenides retain spin-charge coupling and lattice vibrations in different layers, which are useful for spintronic and optoelectronic devices. The phonon, magnons and excitonic properties of two-dimensional ternary nickel-phosphorus trisulfides (NiPS3) are investigated using Raman spectroscopy and photoluminescence (PL) study. With magnetic exchange interaction, an exotic phonon scattering degenerates the optical phonons into in-plane Ag and Bg modes. We have observed eight Raman modes with two acoustic anisotropic magnon modes (M1, M2) below the critical temperature for co-(XX), while only M1 at cross (XY) polarizations. The M1 mode is coupled with the phonon Bg mode that can survive after transition temperature. The phonon and magnon modes soften with variations in temperature, which is attributed to anharmonic phonon–phonon coupling and interlayer forces. The polarized Raman shows the two-fold and four-fold symmetry orientations of the phonon and magnon modes, respectively, which exhibit strong in-plane anisotropic phonon/magnon. The PL spectra revealed the existence of bound excitonic features and ensemble emitters in NiPS3. The robust interlayer excitation and structural stability further revealed the optothermal properties. Moreover, the fabricated field-effect transistor on NiPS3 reveals p-type semiconducting nature with an ON/OFF ratio of 5 × 106 and mobility of ∼16.34 cm2 V−1 s−1. In contrast, the rectification ratio indicates their diode characteristics. Similarly, the photocurrent is enhanced by changing the wavelength of light, which shows the potential for optoelectronics. The strong spin-charge interaction provides new insights into these materials’ magneto-optical and thermal properties for memory devices.

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