Publikationen


Suche nach „[Stirner] [Thomas]“ hat 141 Publikationen gefunden
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    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    J. Sun, A. Matthews, Thomas Stirner

    Calculation of native defect energies in α-Al2O3 and α-Cr2O3 using a modified Matsui potential

    Posterpräsentation

    International Conference on Metallurgical Coatings and Thin Films (ICMCTF 2006), San Diego, CA, USA

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    J. Miao, W. Hagston, Thomas Stirner

    Towards a dynamical theory of magnetic polaron formation

    7th International Conference on II-VI Compounds and Devices, Edinburgh, Großbritannien

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    Thomas Stirner, S. Ahmed, W. Hagston

    Anisotropic magnetic field effects in diluted magnetic semiconductor quantum wells

    7th International Conference on II-VI Compounds and Devices, Edinburgh, Großbritannien

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    J. Fatah, I. Karla, J.H.C. Hogg, P. Harrison, W. Hagston, Thomas Stirner

    Defect induced diffusion mechanisms in ion implanted quantum well structures

    Posterpräsentation

    22nd International Conference on the Physics of Semiconductors (ICPS22), Vancouver, Kanada

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    T. Piorek, P. Harrison, W. Hagston, Thomas Stirner

    Magnetic field induced transitions in diluted magnetic semiconductor quantum wells

    7th International Conference on II-VI Compounds and Devices, Edinburgh, Großbritannien

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    S. Takeyama, H. Mino, S. Adachi, H. Yokoi, Y. Semenov, S. Tozer, G. Kim, G. Karczewski, J. Kossut, W. Hagston, Thomas Stirner

    Photoexcited spin states in diluted magnetic semiconductor quantum structures

    6th International Symposium on Research in High Magnetic Fields, Oporto, Portugal

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    S. Takeyama, G. Karczewski, J. Kossut, T. Wojtowicz, Thomas Stirner, W. Hagston

    Magnetic polaron bifurcation in asymmetric diluted magnetic semiconductor quantum wells

    Invited Lecture

    1st International Conference on the Physics and Applications of Spin-Related Phenomena in Semiconductors (PASPS 2000), Sendai, Japan

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    N. Cain, M. O’Neill, J. Nicholls, W. Hagston, D. Ashenford, Thomas Stirner

    Photoluminescence of highly excited CdTe/CdMnTe quantum wells

    European Quantum Electronics Conference (EQEC), Hamburg

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    Thomas Stirner, S. Takeyama, J. Miao, W. Hagston

    Asymmetric two-dimensional exciton magnetic polarons

    Posterpräsentation

    Autumn Meeting, Iwate, Japan

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    J. Sun, A. Matthews, Thomas Stirner

    Molecular dynamics simulation of the (0001) α-Al2O3 and α-Cr2O3 surfaces

    Surface Science, vol. 601, no. 5, pp. 1358-1364

    Abstract anzeigen

    A simple, rigid pair-potential model is applied to investigate the dynamics of the (0 0 0 1) α-Al2O3 and α-Cr2O3 surfaces using the molecular dynamics technique. The simulations employ a two-stage equilibration process: in the first stage the simulation-cell size is determined via the constant-stress ensemble, and in the second stage the equilibration of the size-corrected simulation cell is continued in the canonical ensemble. The thermal expansion coefficients of bulk alumina and chromia are evaluated as a function of temperature. Furthermore, the surface relaxation and mean-square displacement of the atoms versus depth into the slab are calculated, and their behaviour in the surface region analysed in detail. The calculations show that even moderate temperatures (∼400 °C) give rise to displacements of the atoms at the surface which are similar to the lattice mismatch between α-alumina and chromia. This will help in the initial nucleation stage during thin film growth, and thus facilitate the deposition of α-Al2O3 on (0 0 0 1) α-Cr2O3 templates.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    M. Carrasco-Or, D. Dong, R. Kelly, C. Ellis, M. O’Neill, Thomas Stirner, M.-O. M. Piepenbrock

    Superlattices of organic/inorganic semiconductor nanostructures from liquid-crystal templates

    Physical Review B - condensed matter and materials physics, vol. 75

    DOI: 10.1103/PhysRevB.75.035207

    Abstract anzeigen

    A lyotropic liquid-crystal-templated superlattice of inorganic CdSe semiconductor nanostructures within an organic semiconductor polymer-network film was fabricated by a self-assembly process. The film is characterized with small-angle x-ray diffraction experiments and ultraviolet-visible absorption measurements. Empirical pseudopotential calculations of the effective CdSe nanocrystal band gap show that the experimental observations are consistent with the formation of CdSe nanostructures inside lyotropic liquid-crystal nanotubes. A potential application of these nanocomposite supramolecular arrays is demonstrated via a photoconductive device.

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    Zeitschriftenartikel

    M.-O. M. Piepenbrock, Thomas Stirner, M. O’Neill, S. Kelly

    Dynamics of the size distribution of CdTe quantum dot ensembles during growth in liquid and crystalline phases

    Physical Chemistry Chemical Physics (PCCP), vol. 9, no. 7, pp. 1057-1061

    Abstract anzeigen

    We recently reported that the growth rate of colloidal CdTe nanoparticles decreases by orders of magnitude when the particles undergo a phase transition from liquid to crystal. The dynamics of nanoparticle growth are dominated by this factor rather than the size dependence of the chemical potential. Herein we discuss how the phase transition affects the size distribution and photoluminescence quantum efficiency of the nanoparticles. We suggest that the absorption linewidth is a better monitor of size distribution than the photoluminescence linewidth because the photoluminescence quantum efficiency, which affects the latter via energy transfer, varies substantially with reaction time. We find that the size distribution broadens in the early stages of growth possibly because of inhomogeneities in the phase transition radius or because particles nucleated at later times coalesce with nanocrystals. The quantum efficiency is enhanced when tellurium is depleted in the reaction solution, giving a cadmium-enriched surface. Batches with high initial tellurium and cadmium concentrations show a substantial amount of delayed nucleation, lower quantum efficiency and some anisotropic growth.

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    Zeitschriftenartikel

    M.-O. M. Piepenbrock, Thomas Stirner, M. O’Neill, S. Kelly

    Growth dynamics of CdTe nanoparticles in liquid and crystalline phases

    Journal of the American Chemical Society (JACS), vol. 129, no. 24, pp. 7674-7679

    Abstract anzeigen

    Normally the size dependence of the chemical potential is used to explain the growth dynamics of semiconductor nanoparticles. Instead we show that very small CdTe nanoparticles continue to grow at high dilution, the growth rate is virtually independent of monomer concentration, nucleation continues after the growth of larger particles has saturated, and the growth rate has a much greater nonlinear dependence on particle size than predicted by theory. We suggest that nanoparticle growth is fast in the liquid phase and then saturates as the particles change phase from liquid to crystal at a threshold size which depends on the growth temperature and not the monomer concentration. The photoluminescence quantum efficiency becomes high when tellurium is depleted in the reaction solution giving a cadmium enriched surface.

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    Zeitschriftenartikel

    Thomas Stirner, J. Sun

    Non-equilibrium simulation of optically trapped colloidal particles at liquid interfaces

    Computational Materials Science, vol. 43, no. 4, pp. 769-801

    Abstract anzeigen

    A theoretical study of the non-equilibrium behaviour of colloidal particle monolayers under the influence of the displacement of a single, optically trapped colloidal particle is presented. Two different types of monolayer (i.e., one relatively rigid and the other relatively soft) confined to a liquid–liquid interface are investigated using the Stokesian dynamics simulation technique. An effective dipole–dipole interaction is assumed to act between the colloidal particles and viscous drag forces acting on the particles are taken into account. The calculations reveal periodic oscillations of the net force on the trapped particle for the soft monolayer and highly non-linear, non-monotonic variations for the rigid monolayer. The highly non-linear variations of the net force for the rigid monolayer are concomitant with rapid, cooperative particle rearrangements and large oscillations in the global orientational order parameter of the monolayer. These findings, combined with the results of optical-tweezer experiments, should be useful for the rheology of liquid interfaces and the investigation of Pickering emulsions.

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    Zeitschriftenartikel

    J. Sun, A. Matthews, Thomas Stirner

    Structure and electronic properties calculation of ultrathin α-Al2O3 films on (0001) α-Cr2O3 templates

    Surface Science, vol. 601, no. 21, pp. 5050-5056

    Abstract anzeigen

    Ab initio total energy Hartree–Fock calculations of ultrathin films of α-Al2O3 on (0 0 0 1) α-Cr2O3 templates are presented. The surface relaxation, the in-plane reconstruction and the surface and strain energies of the slabs are studied as a function of alumina film thickness. The surface Al layer is found to relax inwards considerably, with the magnitude of the inwards relaxation depending on the thickness of the ultrathin alumina film in a non-linear manner. The calculations also reveal that ultrathin films of alumina lower the surface energy of (0 0 0 1) α-chromia substrates. This indicates that the (0 0 0 1) α-chromia surface provides favourable conditions for the templated growth of α-alumina. However, increasing the alumina film thickness is found to give rise to a significant increase in strain energy. Finally, the electronic properties at the surface of the (0 0 0 1) α-Al2O3/α-Cr2O3 slabs are investigated. Here it is found that the alumina coating gives rise to an increase in the covalency of the bonds at the surface of the slabs. In contrast, the influence of an alumina layer on the electrostatic potential at the surface of the chromia slab is relatively minor, which should also be beneficial for the templated growth of α-alumina on (0 0 0 1) α-chromia substrates.

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    Zeitschriftenartikel

    A. Löbbert, S. Kitney, M. O’Neill, S. Kelly, Thomas Stirner

    Terminal end-group efficiency for the nematic phase using model bicyclo[2.2.2]octanes

    Liquid Crystals, vol. 34, no. 12, pp. 1357-1367

    Abstract anzeigen

    The synthesis is reported of new liquid crystals incorporating the 1,4-disubstituted bicyclo[2.2.2] octane ring and a series of substituents in a terminal position on the molecular core. The nature of the terminal substituent is varied from apolar with a small dipole moment to polar with a strong dipole moment. The angle of the dipole moment with respect to the molecular axis is also varied. An updated order of terminal group efficiency for substituents in a terminal position for the nematic phase is provided. The bicyclo[2.2.2] octane ring shields halogen substituents in a lateral position on phenyl rings attached to the bicyclooctane ring to a small degree and reduces the steric efects of these substituents, giving rise to high relative nematic - isotropic transition temperatures.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    J. Sun, Thomas Stirner

    Ab initio supercell calculations of the (0001) alpha-Cr203 surface with a partially or totally Al-substituted external layer

    Thin Solid Films, vol. 517, pp. 5512-5515

    Abstract anzeigen

    Ab initio supercell calculations employing the periodic Hartree–Fock formalism are presented of the (0001) α-Cr2O3 surface with a partially or totally Al-substituted external layer. In the simulations a fraction of the Cr atoms at the surface of the chromia slab are replaced by Al atoms, and the Al surface coverage is varied between zero (pure chromia) and 100% (Al-terminated chromia). The surface Al atoms are found to relax inwards considerably, with the magnitude of the relaxation decreasing with increasing Al surface coverage. The calculations also reveal that the surface energy of the slab decreases with increasing Al coverage. Finally, the electronic properties at the surface of the Al-substituted (0001) α-Cr2O3 slabs are investigated. Here the calculations show that the substitution of Cr by Al gives rise to an increase in the covalency of the AlO bonds compared to slabs of pure alumina. In contrast, the influence of the surface Al atoms on the electrostatic potential in the (0001) plane of metal ions is relatively small. These findings support the utilisation of α-chromia substrates for the templated growth of α-alumina, which is consistent with recent experiments.

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    Vortrag

    Thomas Stirner

    Free and localized magnetic polarons in diluted magnetic semiconductors

    National II-VI Semiconductor Interaction Meeting, Norwich, Großbritannien

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    Thomas Stirner

    Magnetic polarons in diluted magnetic semiconductors

    Highlights of UK Research and R&D in Physics and Physics-based Technologies by Young Physicists, London, Großbritannien

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    Thomas Stirner

    Computer simulation of colloidal particle monolayers at liquid-liquid interfaces

    Simulation and Modelling of Colloidal Systems (Meeting of the RSC Colloids and Interface Science Group, the RSC Statistical Mechanics and Thermodynamics Group and the IoP Complex Fluids Group), Sheffield, Großbritannien