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2. Electron spin mediated distortion in metallic systems

Author

Anand, G., Eisenbach, Markus, Goodall, Russell, and Freeman, Colin L.

Subjects
Condensed Matter - Materials Science
Abstract

The deviation of positions of atoms from their ideal lattice sites in crystalline solid state systems causes distortion and can lead to variation in structural [1] and functional properties [2]. Distortion in molecular systems has been traditionally understood in the term of Jahn-Teller distortion [3], while for the one-dimensional chain of metals, the Peierls distortion mechanism has been proposed [4]. In a real three dimensional metallic systems, a fundamental description of the distortion is missing, which we need to design alloys with attractive structural properties. The present investigation presents the evolution of distortion in metallic systems in terms of magnetovolume effects arising due to magnetic ground-state of the system. Particularly the significant distortion in the case of Cr due to presence of other transition metals is seen. Cr alloyed with transition metals as a candidate system to study the correlation between charge disproportion, spin-flip, magnetovolume effects and Fermi surface nesting. This study provides a novel explanation of strengthening effect of Cr observed in alloys due to its unique magnetic properties.

Published
2019

6. A general method for calculating solid/liquid interfacial free energies from atomistic simulations: Application to CaSO4·xH2O.

Author

Yeandel, Stephen R., Freeman, Colin L., and Harding, John H.

Subjects
*GYPSUM, *SOLIDS, *LIQUIDS, *CRYSTALS, *SALT, *EQUILIBRIUM
Abstract

We present a general method for computing interfacial free energies from atomistic simulations, which is particularly suitable for solid/liquid interfaces. Our method uses an Einstein crystal as a universal reference state and is more flexible than previous approaches. Surfaces with dipoles, complex reconstructions, and miscible species are all easily accommodated within the framework. It may also be extended to calculating the relative free energies of different phases and other types of defect. We have applied our method to interfaces of bassanite and gypsum with water and obtained interfacial free energies of the order of 0.12 J/m2, of which ∼45% is due to entropic contributions. Our calculations of the interfacial free energy of NaCl with water obtained a value of 0.13 J/m2, of which only 19% is from entropic contributions. We have also predicted equilibrium morphologies for bassanite and gypsum that compare well with experiments and previous calculations. [ABSTRACT FROM AUTHOR]

Published
2022
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9. Dynamic tilting in perovskites

Author

Handley, Christopher M., primary, Ward, Robyn E., additional, Freeman, Colin L., additional, Reaney, Ian M., additional, Sinclair, Derek C., additional, and Harding, John H., additional

Published
2023
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10. Electron transparent nanotubes reveal crystallization pathways in confinement

Author

Galloway, Johanna M., primary, Aslam, Zabeada P., additional, Yeandel, Stephen R., additional, Kulak, Alexander, additional, Ilett, Martha A., additional, Kim, Yi-Yeoun, additional, Bejarano-Villafuerte, Angela, additional, Pokroy, Boaz, additional, Drummond-Brydson, Rik M., additional, Freeman, Colin L., additional, Harding, John H., additional, Kapur, Nikil, additional, and Meldrum, Fiona C., additional

Published
2023
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17. Complexities of atomic structure at CdO/MgO and CdO/Al2O3 interfaces.

Author

Grimley, Everett D., Wynn, Alex P., Kelley, Kyle P., Sachet, Edward, Dean, Julian S., Freeman, Colin L., Maria, Jon-Paul, and LeBeau, James M.

Subjects
THIN films, CADMIUM oxide, MAGNESIUM oxide, SCANNING transmission electron microscopy, EPITAXY, MOLECULAR dynamics
Abstract

We report the interface structures of CdO thin films on 001 -MgO and 0001 -Al 2 O 3 substrates. Using aberration corrected scanning transmission electron microscopy, we show that epitaxial growth of (001)-CdO ∥ (001)-MgO occurs with a lattice misfit greater than 10%. A high density of interface misfit dislocations is found to form. In combination with molecular dynamics simulations, we show that dislocation strain fields form and overlap in very thin heterostructures of CdO and MgO (< 3 nm). On the c-Al 2 O 3 substrate, we find that CdO grows with a surface normal of 025. We show that three rotation variants form due to the symmetry of the sapphire surface. These results contribute insights into the epitaxial growth of these rock-salt oxides. [ABSTRACT FROM AUTHOR]

Published
2018
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26. Stoichiometry-dependent local instability in MAPbI3 perovskite materials and devices

Author

Kumar, Vikas, Schmidt, Whitney L., Tsevas, Konstantinos, Ozkan, Buse, Handley, Christopher M., Freeman, Colin L., Sinclair, Derek C., Reaney, Ian M., Tsoi, Wing C., Dunbar, Alan, and Rodenburg, Cornelia

Subjects
Renewable Energy, Sustainability and the Environment, General Materials Science, General Chemistry
Abstract

Organometallic perovskite materials based on MAPbI3 achieve photovoltaic efficiencies as high as 22% for solar cells; however, the long-term stability of these perovskite materials is still a hurdle for applications. Here, we report the air and charge induced instabilities of MAPbI3 perovskite materials with different local stoichiometry using Secondary Electron Hyperspectral Imaging (SEHI). We find that individual grains which do not have the ideal ABX3 stoichiometry degrade faster than stoichiometric grains. We also observe that the degradation pathways depend on the local stoichiometry. Non-stoichiometric grains (with excess MAI) degrade from the centre of the grain and further degradation moves towards the grain boundary, whereas in stoichiometric grains degradation sets in at the grain boundary. We further use deliberately high doses of electron beam exposure to highlight the presence of local non-stoichiometry in device cross-sections of bias degraded devices which pinpoints different onset locations of degradation, depending on the local stoichiometry. These results, therefore, show that precise control of local stoichiometry is required to improve the stability of MAPbI3 and thus the lifetime of perovskite solar cells.

Published
2018

27. Simulation of Calcium Phosphate Prenucleation Clusters in Aqueous Solution: Association beyond Ion Pairing

Author

Garcia, Natalya A., Malini, Riccardo Innocenti, Freeman, Colin L., Demichelis, Raffaella, Raiteri, Paolo, Sommerdijk, N.A.J.M., Harding, John H., Gale, Julian D., Garcia, Natalya A., Malini, Riccardo Innocenti, Freeman, Colin L., Demichelis, Raffaella, Raiteri, Paolo, Sommerdijk, N.A.J.M., Harding, John H., and Gale, Julian D.

Abstract

Contains fulltext : 212286.pdf (publisher's version ) (Open Access)

Published
2019

32. The Role of Extracellular DNA in Microbial Attachment to Oxidized Silicon Surfaces in the Presence of Ca2+and Na+

Author

Morales-García, Ana L., Walton, Rachel, Blakeman, Jamie T., Banwart, Steven A., Harding, John H., Geoghegan, Mark, Freeman, Colin L., and Rolfe, Stephen A.

Abstract

Attachment assays of a Pseudomonasisolate to fused silica slides showed that treatment with DNaseI significantly inhibited cellular adsorption, which was restored upon DNA treatment. These assays confirmed the important role of extracellular DNA (eDNA) adsorption to a surface. To investigate the eDNA adsorption mechanism, single-molecule force spectroscopy (SMFS) was used to measure the adsorption of eDNA to silicon surfaces in the presence of different concentrations of sodium and calcium ions. SMFS reveals that the work of adhesion required to remove calcium-bound eDNA from the silicon oxide surface is substantially greater than that for sodium. Molecular dynamics simulations were also performed, and here, it was shown that the energy gain in eDNA adsorption to a silicon oxide surface in the presence of calcium ions is small and much less than that in the presence of sodium. The simulations show that the length scales involved in eDNA adsorption are less in the presence of sodium ions than those in the presence of calcium. In the presence of calcium, eDNA is pushed above the surface cations, whereas in the presence of sodium ions, short-range interactions with the surface dominate. Moreover, SMFS data show that increasing [Ca2+] from 1 to 10 mM increases the adsorption of the cations to the silicon oxide surface and consequently enhances the Stern layer, which in turn increases the length scale associated with eDNA adsorption.

Published
2021
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33. Using Metadynamics to Obtain the Free Energy Landscape for Cation Diffusion in Functional Ceramics: Dopant Distribution Control in Rare Earth‐Doped BaTiO3.

Author

Ward, Robyn E., Freeman, Colin L., Dean, Julian S., Sinclair, Derek C., and Harding, John H.

Subjects
*CERAMIC capacitors, *RARE earth metals, *BARIUM titanate, *DOPING agents (Chemistry), *DIELECTRIC materials, *DIFFUSION, *DYSPROSIUM
Abstract

Barium titanate is the dielectric material of choice in most multilayer ceramic capacitors (MLCCs) and thus in the production of ≈3 trillion devices every year, with an estimated global market of ≈$8330 million per year. Rare earth dopants are regularly used to reduce leakage currents and improve the MLCC lifetime. Simulations are used to investigate the ability of yttrium, dysprosium, and gadolinium to reduce leakage currents by trapping mobile oxygen defects. All the rare earths investigated trap oxygen vacancies, however, dopant pairs are more effective traps than isolated dopants. The number of trapping sites increases with the ion size of the dopant, suggesting that gadolinium should be more effective than dysprosium, which contradicts experimental data. Additional simulations on diffusion of rare earths through the lattice during sintering show that dysprosium diffuses significantly faster than the other rare earths considered. As a consequence, its greater ability to reduce oxygen migration is a combination of thermodynamics (a strong ability to trap oxygen vacancies) and kinetics (sufficient distribution of the rare earth in the lattice to intercept the migrating defects). [ABSTRACT FROM AUTHOR]

Published
2020
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34. Using Metadynamics to Obtain the Free Energy Landscape for Cation Diffusion in Functional Ceramics: Dopant Distribution Control in Rare Earth‐Doped BaTiO3.

Author

Ward, Robyn E., Freeman, Colin L., Dean, Julian S., Sinclair, Derek C., and Harding, John H.

Subjects
CERAMIC capacitors, RARE earth metals, BARIUM titanate, DOPING agents (Chemistry), DIELECTRIC materials, DIFFUSION, DYSPROSIUM
Abstract

Barium titanate is the dielectric material of choice in most multilayer ceramic capacitors (MLCCs) and thus in the production of ≈3 trillion devices every year, with an estimated global market of ≈$8330 million per year. Rare earth dopants are regularly used to reduce leakage currents and improve the MLCC lifetime. Simulations are used to investigate the ability of yttrium, dysprosium, and gadolinium to reduce leakage currents by trapping mobile oxygen defects. All the rare earths investigated trap oxygen vacancies, however, dopant pairs are more effective traps than isolated dopants. The number of trapping sites increases with the ion size of the dopant, suggesting that gadolinium should be more effective than dysprosium, which contradicts experimental data. Additional simulations on diffusion of rare earths through the lattice during sintering show that dysprosium diffuses significantly faster than the other rare earths considered. As a consequence, its greater ability to reduce oxygen migration is a combination of thermodynamics (a strong ability to trap oxygen vacancies) and kinetics (sufficient distribution of the rare earth in the lattice to intercept the migrating defects). [ABSTRACT FROM AUTHOR]

Published
2020
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36. Stoichiometry-dependent local instability in MAPbI3perovskite materials and devices

Author

Kumar, Vikas, primary, Barbé, Jérémy, additional, Schmidt, Whitney L., additional, Tsevas, Konstantinos, additional, Ozkan, Buse, additional, Handley, Christopher M., additional, Freeman, Colin L., additional, Sinclair, Derek C., additional, Reaney, Ian M., additional, Tsoi, Wing C., additional, Dunbar, Alan, additional, and Rodenburg, Cornelia, additional

Published
2018
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37. Survival of eggshell peptides over millions of years in Africa is due to mineral binding

Author

Demarchi, Beatrice, Hall, Shaun, Roncal-Herrero, Teresa, Freeman, Colin L., Woolley, Jos, Crisp, Molly K., Wilson, Julie, Fotakis, Anna, Fischer, Roman, Kessler, Benedikt, Jersie-Christensen, Rosa Rakownikow, Olsen, Jesper V., Haile, James, Thomas, Jessica, Marean, Curtis W., Parkington, John, Presslee, Samantha, Lee-Thorp, Julia, Ditchfield, Peter, Hamilton, Jacqueline F., Ward, Martyn W., Wang, Chunting Michelle, Marvin David Shaw, Harrison, Terry, Domínguez-Rodrigo, Manuel, Macphee, Ross D. E., Kwekason, Amandus, Ecker, Michaela, Horwitz, Liora Kolska, Chazan, Michael, Kröger, Roland, Thomas-Oates, Jane, Harding, John H., Cappellini, Enrico, Penkman, Kirsty, and Collins, Matthew J.

Published
2016

40. Stoichiometry-dependent local instability in MAPbI3 perovskite materials and devices.

Author

Kumar, Vikas, Barbé, Jérémy, Schmidt, Whitney L., Tsevas, Konstantinos, Ozkan, Buse, Handley, Christopher M., Freeman, Colin L., Sinclair, Derek C., Reaney, Ian M., Tsoi, Wing C., Dunbar, Alan, and Rodenburg, Cornelia

Abstract

Organometallic perovskite materials based on MAPbI3 achieve photovoltaic efficiencies as high as 22% for solar cells; however, the long-term stability of these perovskite materials is still a hurdle for applications. Here, we report the air and charge induced instabilities of MAPbI3 perovskite materials with different local stoichiometry using Secondary Electron Hyperspectral Imaging (SEHI). We find that individual grains which do not have the ideal ABX3 stoichiometry degrade faster than stoichiometric grains. We also observe that the degradation pathways depend on the local stoichiometry. Non-stoichiometric grains (with excess MAI) degrade from the centre of the grain and further degradation moves towards the grain boundary, whereas in stoichiometric grains degradation sets in at the grain boundary. We further use deliberately high doses of electron beam exposure to highlight the presence of local non-stoichiometry in device cross-sections of bias degraded devices which pinpoints different onset locations of degradation, depending on the local stoichiometry. These results, therefore, show that precise control of local stoichiometry is required to improve the stability of MAPbI3 and thus the lifetime of perovskite solar cells. [ABSTRACT FROM AUTHOR]

Published
2018
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41. Protein sequences bound to mineral surfaces persist into deep time

Author

Demarchi, Beatrice, Hall, Shaun, Roncal-herrero, Teresa, Freeman, Colin L., Woolley, Jos, Crisp, Molly K., Wilson, Julie, Fotakis, Anna, Fischer, Roman, Kessler, Benedikt M., Jersie-christensens, Rosa Rakownikow, Olsen, Jesper V., Haile, James, Thomas, Jessica, Marean, Curtis W., Parkington, John, Presslee, Samantha, Lee-thorp, Julia, Ditchfield, Peter, Hamilton, Jacqueline F., Ward, Martyn W., Wang, Chunting Michelle, Shaw, Marvin D., Harrison, Terry, Dominguez-rodrigo, Manuel, Macphee, Ross De, Kwekason, Amandus, Ecker, Michaels, Horwitz, Liora Kolska, Chazan, Michael, Kröger, Roland, Thomas-oates, Jane, Harding, John H., Cappellini, Enrico, Penkman, Kirsty, Collins, Matthew J., Demarchi, Beatrice, Hall, Shaun, Roncal-herrero, Teresa, Freeman, Colin L., Woolley, Jos, Crisp, Molly K., Wilson, Julie, Fotakis, Anna, Fischer, Roman, Kessler, Benedikt M., Jersie-christensens, Rosa Rakownikow, Olsen, Jesper V., Haile, James, Thomas, Jessica, Marean, Curtis W., Parkington, John, Presslee, Samantha, Lee-thorp, Julia, Ditchfield, Peter, Hamilton, Jacqueline F., Ward, Martyn W., Wang, Chunting Michelle, Shaw, Marvin D., Harrison, Terry, Dominguez-rodrigo, Manuel, Macphee, Ross De, Kwekason, Amandus, Ecker, Michaels, Horwitz, Liora Kolska, Chazan, Michael, Kröger, Roland, Thomas-oates, Jane, Harding, John H., Cappellini, Enrico, Penkman, Kirsty, and Collins, Matthew J.

Abstract

Proteins persist longer in the fossil record than DNA, but the longevity, survival mechanisms and substrates remain contested. Here, we demonstrate the role of mineral binding in preserving the protein sequence in ostrich (Struthionidae) eggshell, including from thepalaeontological sites of Laetoli (3.8 Ma) and Olduvai Gorge (1.3 Ma) in Tanzania. By tracking protein diagenesis back in time we find consistent patterns of preservation, demonstrating authenticity of the surviving sequences. Molecular dynamics simulations of struthiocalcin-1 and -2, the dominant proteins within the eggshell, reveal that distinct domains bind to the mineral surface. It is the domain with the strongest calculated binding energy to the calcite surface that is selectively preserved. Thermal age calculations demonstrate that the Laetoli and Olduvai peptides are 50 times older than any previously authenticated sequence (equivalent to similar to 16 Ma at a constant 10 degrees C).

Published
2016
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43. Protein sequences bound to mineral surfaces persist into deep time

Author

Demarchi, Beatrice, primary, Hall, Shaun, additional, Roncal-Herrero, Teresa, additional, Freeman, Colin L, additional, Woolley, Jos, additional, Crisp, Molly K, additional, Wilson, Julie, additional, Fotakis, Anna, additional, Fischer, Roman, additional, Kessler, Benedikt M, additional, Rakownikow Jersie-Christensen, Rosa, additional, Olsen, Jesper V, additional, Haile, James, additional, Thomas, Jessica, additional, Marean, Curtis W, additional, Parkington, John, additional, Presslee, Samantha, additional, Lee-Thorp, Julia, additional, Ditchfield, Peter, additional, Hamilton, Jacqueline F, additional, Ward, Martyn W, additional, Wang, Chunting Michelle, additional, Shaw, Marvin D, additional, Harrison, Terry, additional, Domínguez-Rodrigo, Manuel, additional, MacPhee, Ross DE, additional, Kwekason, Amandus, additional, Ecker, Michaela, additional, Kolska Horwitz, Liora, additional, Chazan, Michael, additional, Kröger, Roland, additional, Thomas-Oates, Jane, additional, Harding, John H, additional, Cappellini, Enrico, additional, Penkman, Kirsty, additional, and Collins, Matthew J, additional

Published
2016
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44. Author response: Protein sequences bound to mineral surfaces persist into deep time

Author

Demarchi, Beatrice, primary, Hall, Shaun, additional, Roncal-Herrero, Teresa, additional, Freeman, Colin L, additional, Woolley, Jos, additional, Crisp, Molly K, additional, Wilson, Julie, additional, Fotakis, Anna, additional, Fischer, Roman, additional, Kessler, Benedikt M, additional, Rakownikow Jersie-Christensen, Rosa, additional, Olsen, Jesper V, additional, Haile, James, additional, Thomas, Jessica, additional, Marean, Curtis W, additional, Parkington, John, additional, Presslee, Samantha, additional, Lee-Thorp, Julia, additional, Ditchfield, Peter, additional, Hamilton, Jacqueline F, additional, Ward, Martyn W, additional, Wang, Chunting Michelle, additional, Shaw, Marvin D, additional, Harrison, Terry, additional, Domínguez-Rodrigo, Manuel, additional, MacPhee, Ross DE, additional, Kwekason, Amandus, additional, Ecker, Michaela, additional, Kolska Horwitz, Liora, additional, Chazan, Michael, additional, Kröger, Roland, additional, Thomas-Oates, Jane, additional, Harding, John H, additional, Cappellini, Enrico, additional, Penkman, Kirsty, additional, and Collins, Matthew J, additional

Published
2016
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45. Tuning hardness in calcite by incorporation of amino acids

Author

Kim, Yi-Yeoun, primary, Carloni, Joseph D., additional, Demarchi, Beatrice, additional, Sparks, David, additional, Reid, David G., additional, Kunitake, Miki E., additional, Tang, Chiu C., additional, Duer, Melinda J., additional, Freeman, Colin L., additional, Pokroy, Boaz, additional, Penkman, Kirsty, additional, Harding, John H., additional, Estroff, Lara A., additional, Baker, Shefford P., additional, and Meldrum, Fiona C., additional

Published
2016
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