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4. Induced Ferromagnetism in bilayer Hexagonal Boron Nitride (h-BN) on vacancy defects at B and N sites

Author

Chettri, B., Patra, P. K., Vu, Tuan V., Lalrinkima, Yaya, Abu, Obodo, Kingsley O., Tran, Ngoc Thanh Thuy, Laref, A., and Rai, D. P.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Disordered Systems and Neural Networks
Abstract

We investigated the electronic and optical properties of bilayer AB stacked Boron and Nitrogen vacancies in hexagonal Boron Nitride (h-BN) using density functional theory (DFT). The density of states (DOS) and electronic band structure showed that Boron vacancy in bilayer h-BN results in a magnetic and conducting ground state. The band gap energy ranges from 4.56 eV for the pristine BN bilayer to 0.12 eV for a single Nitrogen vacancy in the bilayer. Considering the presence of 1,3,4-Boron vacancy, half metallic character is observed. However, the 2-boron vacancy configuration resulted in metallic character. The bilayers with 1,2,3,4- Nitrogen vacancy has a band gap of 0.39, 0.33, 0.28 and 0.12eV respectively, which is significantly less than the pristine band gap. Also B and N vacancy induces ferromagnetism in the h-BN bilayer. The maximum total magnetic moment for the Boron vacant system is 6.583uB in case of 4-Boron vacancy configuration. In case of Nitrogen vacancy system it is 3.926uB for 4-Nitrogen vacancy configuration. The optical response of the system is presented in terms of the absorption coefficient, refractive index and dielectric constant for pristine as well as the defective configurations. Negative value of dielectric constant for Boron vacant system in the energy range 0.9-1.4 eV and for Nitrogen vacant system in the energy range 0.5-0.8 eV opens an opportunity for it to be utilized for negative index optical materials. The current study shows that B and N vacancies in bilayer h-BN could have potential applications in nano-structure based electronics, optoelectronics and spintronic devices.

Published
2020
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13. Hydroxyapatite nano‐pillars on TI‐6Al‐4V: Enhancements in cell spreading and proliferation during cell/surface integration.

Author

Osafo, Sarah Akua, Etinosa, Precious Osayamen, Obayemi, John David, Salifu, Ali Azeko, Asumadu, Tabiri, Klenam, Desmond, Agyei‐Tuffour, Benjamin, Dodoo‐Arhin, David, Yaya, Abu, and Soboyejo, Winston Oluwole

Abstract

Despite the attractive combinations of cell/surface interactions, biocompatibility, and good mechanical properties of Ti‐6Al‐4V, there is still a need to enhance the early stages of cell/surface integration that are associated with the implantation of biomedical devices into the human body. This paper presents a novel, easy and reproducible method of nanoscale and nanostructured hydroxyapatite (HA) coatings on Ti‐6Al‐4V. The resulting nanoscale coatings/nanostructures are characterized using a combination of Raman spectroscopy, scanning electron microscopy equipped with energy dispersive x‐ray spectroscopy. The nanostructured/nanoscale coatings are shown to enhance the early stages of cell spreading and integration of bone cells (hFOB cells) on Ti‐6Al‐4V surfaces. The improvements include the acceleration of extra‐cellular matrix, cell spreading and proliferation by nanoscale HA structures on the coated surfaces. The implications of the results are discussed for the development of HA nanostructures for the improved osseointegration of Ti‐6Al‐4V in orthopedic and dental applications. [ABSTRACT FROM AUTHOR]

Published
2024
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16. Chemical Reactivity and Alteration of Pyrite Mineral in the Kubi Gold Concession in Ghana

Author

Nzulu, Gabriel Kofi, Högberg, Hans, Eklund, Per, Hultman, Lars, Nude, Prosper M., Yaya, Abu, Magnuson, Martin, Nzulu, Gabriel Kofi, Högberg, Hans, Eklund, Per, Hultman, Lars, Nude, Prosper M., Yaya, Abu, and Magnuson, Martin

Abstract

Pyrite is the most common among the group of sulfide minerals in the Earth and abundant in most geological settings. This gangue mineral in association with garnet, hematite, magnetite, and other sulfide minerals acts as an indicator mineral in the Kubi concession of the Asante Gold corporation in Ghana. X-ray diffraction (XRD), air annealing in a furnace, energy-dispersive x-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) were applied to investigate the crystal structure, identify individual elements, permanence, transformation, and chemical/electronic properties of such pyrite. The study aims to identify individual elements and to gain an understanding of the surface reaction mechanisms, as well as the properties of precipitated pyrite particles observed during the hydrothermal formation of the ore deposit. XRD shows that pristine and annealed samples contain some hematite and quartz besides pyrite. Results from air annealing indicate that the relationship between pyrite and hematite-magnetite is controlled by temperature. EDX reveals that the sample has O and C as contaminants, while XPS in addition reveals Ba, Au, P, Al, and N. These elements are attributed to pyrite that bonds metallically or covalently to neighboring ligands/impurity minerals such as oxides, chalcogenide sulfides, as well as the gangue alteration minerals of magnetite and hematite in the pyrite sample. These findings suggest that during the hydrothermal flow regime, pyrite, pathfinder elements, and impurity minerals/metals were in contact with quartz minerals before undergoing hematite transformation, which thus becomes an indicator mineral in the Kubi gold concession., Funding Agencies|Linkoping University

Published
2024
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17. Correction: Chemical Reactivity and Alteration of Pyrite Mineral in the Kubi Gold Concession in Ghana (27 Feb, 10.1007/s42461-024-00932-4, 2024)

Author

Nzulu, Gabriel Kofi, Högberg, Hans, Eklund, Per, Hultman, Lars, Nude, Prosper M., Yaya, Abu, Magnuson, Martin, Nzulu, Gabriel Kofi, Högberg, Hans, Eklund, Per, Hultman, Lars, Nude, Prosper M., Yaya, Abu, and Magnuson, Martin

Abstract

Funding Agencies|Swedish Research Council [2022-06725, 2018-05973]

Published
2024
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19. Graphene edge structures: Folding, scrolling, tubing, rippling and twisting

Author

Ivanovskaya, Viktoria V., Wagner, Philipp, Zobelli, Alberto, Suarez-Martinez, Irene, Yaya, Abu, and Ewels, Christopher P.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

Conventional three-dimensional crystal lattices are terminated by surfaces, which can demonstrate complex rebonding and rehybridisation, localised strain and dislocation formation. Two dimensional crystal lattices, of which graphene is the archetype, are terminated by lines. The additional available dimension at such interfaces opens up a range of new topological interface possibilities. We show that graphene sheet edges can adopt a range of topological distortions depending on their nature. Rehybridisation, local bond reordering, chemical functionalisation with bulky, charged, or multi-functional groups can lead to edge buckling to relieve strain, folding, rolling and even tube formation. We discuss the topological possibilities at a 2D graphene edge, and under what circumstances we expect different edge topologies to occur. Density functional calculations are used to explore in more depth different graphene edge types., Comment: Additional figure in published version

Published
2012
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20. A comparative study of density functional and density functional tight binding calculations of defects in graphene

Author

Zobelli, Alberto, Ivanovskaya, Viktoria V., Wagner, Philipp, Suarez-Martinez, Irene, Yaya, Abu, and Ewels, Chris P.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

The density functional tight binding approach (DFTB) is well adapted for the study of point and line defects in graphene based systems. After briefly reviewing the use of DFTB in this area, we present a comparative study of defect structures, energies and dynamics between DFTB results obtained using the dftb+ code, and density functional results using the localised Gaussian orbital code, AIMPRO. DFTB accurately reproduces structures and energies for a range of point defect structures such as vacancies and Stone-Wales defects in graphene, as well as various unfunctionalised and hydroxylated graphene sheet edges. Migration barriers for the vacancy and Stone-Wales defect formation barriers are accurately reproduced using a nudged elastic band approach. Finally we explore the potential for dynamic defect simulations using DFTB, taking as an example electron irradiation damage in graphene.

Published
2012
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27. Pathfinder elements and indicator minerals of Au from the Kubi Gold ore deposits in Ghana

Author

Nzulu, Gabriel Kofi, Högberg, Hans, Eklund, Per, Hultman, Lars, Nude, Prosper M., Yaya, Abu, Magnuson, Martin, Nzulu, Gabriel Kofi, Högberg, Hans, Eklund, Per, Hultman, Lars, Nude, Prosper M., Yaya, Abu, and Magnuson, Martin

Abstract

The Au mineralization in the Kubi Gold Mining Area in the Birimian of Ghana is associated with garnet (about 85 vol.%), magnetite, pyrrhotite, arsenopyrite, and sulfide minerals, as well as quartz with gold and calcite. These minerals and the included elements can act as indicator minerals or pathfinder elements. For the present work, we collected samples from drill holes at different depths, from the alluvial zone (0–45 m) to the ore zone (75–100 m). The distributions of minerals and elements in the rocks that act as indicator minerals and pathfinder elements in the concession area were investigated along the drill hole cross sections. X-ray diffraction shows that the samples contain garnet, pyrite, periclase, and quartz as the main indicator minerals. By energy-dispersive X-ray spectroscopy, Fe, Mg, Al, S, O, Mn, Na, Cu, Si, and K are identified as corresponding pathfinder elements. The results indicate that the Au mineralization in the Kubi Mine area correlates mostly with the occurrence of garnet, pyrite, goethite, and kaolinite in the host rocks, which show towards the surface increasingly hematitic and limonitic alteration in form of Fe(oxy-)hydroxides., Funding agencies:Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU no. 2009 00971).Swedish Energy Research(Grant no. 43606-1)Carl Tryggers Foundation (CTS20:272,CTS16:303, CTS14:310)Open access funding provided by Linköping University

Published
2023
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28. A study of the interactions of carbon based fillers in acrylonitrile butadiene rubber matrix for high deformation sensor applications.

Author

Mensah, Bismark, Yaya, Abu, Onwona-Agyeman, Boateng, Ofori, Ralph Abakah, and Dompreh, Clive

Subjects
*NITRILE rubber, *RUBBER, *STYRENE-butadiene rubber, *ACRYLONITRILE butadiene styrene resins, *CARBON-black, *STRAIN sensors, *CYCLIC loads, *DENSITY functional theory
Abstract

A strain sensor was prepared by reinforcing acrylonitrile butadiene rubber (NBR)-5 parts per hundred of rubber (phr) carbon black (CBH) separately with small concentration (∼0.1phr) of reduced graphene oxide (GL), multi-walled, and carbon nanotube (NTL) via a combination of conventional solution and solid processing techniques. The interactions and the electronic properties among carbon based fillers NT, CB, G and their synergy effects (NBR-CBH-GL and NBR-CBH-NTL) were investigated by using density functional theory (DFT) modeling approach. The DFT predictions were in correspondence with the experimental results. The optimum design (NBR-CBH-GL) was found to show high curing, mechanical and improved electrical properties. On account of strain sensing performance, NBR-CBH-GL exhibited high gauge factor (GF) ∼105 at 0–40% strain, which was over 900% than NBR-CBH (GF ∼104 at 0–30% strain) and the highest reported so far. This was explained by the breaking of CB networks caused by tight NBR-G structures on straining, leading to high electrical resistance. The NBR-CBH-GL also demonstrated high stability and repeatability in the cyclic loading. In terms of applications, NBR-CBH-GL exhibited high capability for vibration detections and wearable sensing, especially for detection of human bodily motions like speeches, facial deformations, bending, and relaxation of the fingers. [ABSTRACT FROM AUTHOR]

Published
2023
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32. Electronic and Magnetic Properties of Transition Metal‐Doped MoS2 Monolayer: First‐Principles Calculations.

Author

Boakye, Dennis, Martin, Henry, Labik, Linus K., Britwum, Akyana, Nunoo, Oswald Ashirifi, Elloh, Van W., Kwakye-Awuah, Bright, Yaya, Abu, and Abavare, Eric K. K.

Subjects
MAGNETIC transitions, MAGNETIC properties, DENSITY functional theory, MAGNETIC moments, SPIN polarization, MONOMOLECULAR films, RARE earth metal alloys, HEUSLER alloys
Abstract

Density functional theory in the framework of generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof to investigate the effects of some selected transition metal (TM) and rare‐earth metal (RE) dopants on the electronic and magnetic properties of a 2D molybdenum disulfide (MoS2) monolayer is reported. The results demonstrate that it is energetically stable to incorporate Ni and Cu in MoS2 structure under Mo‐rich conditions. The pristine MoS2 monolayer has a calculated direct bandgap of 1.70 eV and experiences significant reduction in the gap due to the defects. There is observed induced magnetic behavior due to the tight binding effect originating from the localized dopants and the nearest‐neighbor Mo atoms, with magnetic moments ranging between 0.82 and 3.00 μB. Some of the dopants result in 100%$$ spin polarization which is useful for engineering spin filter devices on magnetic MoS2 nanostructures. [ABSTRACT FROM AUTHOR]

Published
2023
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36. Computational Modelling of Poly(9-Vinylcarbazole)/Fullerene Nanoheterojunction for Organic Solar Cells and Photovoltaics Applications – a Dft Approach

Author

Elloh, Van Wellington, primary, Elloh, V. W., additional, Kan-Dapaah, K., additional, Gebreyesus, G. H., additional, Boadu, E. Okoampa, additional, Arhin, I., additional, Ofosuhene, D. F., additional, Abbeyquaye, D., additional, Anderson, D. E., additional, Dodoo-Arhin, D., additional, Abhishek, Kumar Mishra M., additional, Abavare, Eric K. K., additional, and Yaya, Abu, additional

Published
2022
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39. Comparative analyses of rice husk cellulose fiber and kaolin particulate reinforced thermoplastic cassava starch biocomposites using the solution casting technique

Author

Agyei‐Tuffour, Benjamin, primary, Asante, Joshua Tuah, additional, Nyankson, Emmanuel, additional, Dodoo‐Arhin, David, additional, Oteng‐Peprah, Michael, additional, Azeko, Salifu T., additional, Azeko, Ali Salifu, additional, Oyewole, Oluwaseun K., additional, and Yaya, Abu, additional

Published
2021
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