The Experts below are selected from a list of 51 Experts worldwide ranked by ideXlab platform

Changhong Xiao - One of the best experts on this subject based on the ideXlab platform.

Xiao Changhong - One of the best experts on this subject based on the ideXlab platform.

  • A structural investigation into the complexity of mesoporous silica crystals : From a view of curvature and micellar interaction to Quasicrystallinity
    Stockholm : Department of Materials and Environmental Chemistry (MMK) Stockholm University, 2012
    Co-Authors: Xiao Changhong
    Abstract:

    Mesoporous silica crystals have a large variety of structures mainly due to the versatility of their structure template. The configuration and the chemical state of the templating micellar surfactants, together with the kinetic process of silica will determine the final outcome of the synthesis. Increasing the understanding of the complex formation processes involved will enable a possibilityto fine tune the material for specific uses, today focused into the fields of photoniccrystals, drug delivery, catalysis and separation technology. In this thesis emphasis is put on (1) increasing the understanding the formation mechanism yielding the different species of mesoporous silica crystals through an in depth study of Quasicrystallinity (2) Characterization and description of the structural complexity through various characterization techniquesand also by studying the kinetic structural transformation phenomenon related to the minimal G- and D-surfaces. (3) The structural studies of the versatile surfactant liquid crystals for establishing a thermodynamically stable basis to evaluate the kinetic mesoporous silica growth processes. Furthermorethe thesis both enlightens the possibilities of and contributes to the developmentof electron microscopy characterization techniques. In these studies, electron microscopy is largely employed in the characterization to give a thorough picture of the mesoporous structures. This is combined with the sample preparation techniques cross-section polishing and ionslicing. Low voltage scanning electron microscopy is utilized for studying the surfaces and cross-sections of various materials at the limit of the resolution. Here, a deep understanding of the electron beam-material interaction is used for a better interpretation of the detected signals. Transmission electron microscopyis combined with electron crystallographic reconstruction to yield a three dimensional structural model. For determination of the Quasicrystallinity level for a structure of dodecagonal tiling, revealed in the scope of this study,a phason strain analysis was made.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 7: Manuscript.

Holger Stark - One of the best experts on this subject based on the ideXlab platform.

  • Quasicrystalline Order in Binary Dipolar Systems
    2004
    Co-Authors: Falk Scheffler, Johannes Roth, Holger Stark
    Abstract:

    Motivated by recent experimental findings, we investigate the possible occurrence and characteristics of quasicrystalline order in two-dimensional mixtures of point dipoles with two sorts of dipole moments. Despite the fact that the dipolar interaction potential does not exhibit an intrinsic length scale and cannot be tuned a priori to support the formation of quasicrystalline order, we find that configurations with long–range Quasicrystallinity yield minima in the potential energy surface of the many particle system. These configurations emanate from an ideal or perturbed ideal decoration of a binary tiling by steepest descent relaxation. Ground state energy calculations of alternative ordered states and parallel tempering Monte-Carlo simulations reveal that the quasicrystalline configurations do not correspond to a thermodynamically stable state. On the other hand, steepest descent relaxations and conventional Monte-Carlo simulations suggest that they are rather robust against fluctuations. Local quasicrystalline order in the disordered equilibrium states can be strong. I

  • Quasicrystalline order in binary dipolar systems
    2026
    Co-Authors: Falk Scheffler, Johannes Roth, P. Maass, Holger Stark
    Abstract:

    Motivated by recent experimental findings, we investigate the possible occurrence and characteristics of quasicrystalline order in two-dimensional mixtures of point dipoles with two sorts of dipole moments. Despite the fact that the dipolar interaction potential does not exhibit an intrinsic length scale and cannot be tuned a priori to support the formation of quasicrystalline order, we find that configurations with long-range Quasicrystallinity yield minima in the potential energy surface of the many particle system. These configurations emanate from an ideal or perturbed ideal decoration of a binary tiling by steepest descent relaxation. Ground state energy calculations of alternative ordered states and parallel tempering Monte-Carlo simulations reveal that the quasicrystalline configurations do not correspond to a thermodynamically stable state. On the other hand, steepest descent relaxations and conventional Monte-Carlo simulations suggest that they are rather robust against fluctuations. Local quasicrystalline order in the disordered equilibrium states can be strong. Copyright Springer-Verlag Berlin/Heidelberg 2004

Wolf Widdra - One of the best experts on this subject based on the ideXlab platform.

  • quasicrystalline structure formation in a classical crystalline thin film system
    Nature, 2013
    Co-Authors: Stefan Forster, K Meinel, Rene Hammer, Martin Trautmann, Wolf Widdra
    Abstract:

    The unusual ordering of quasicrystals can be induced in thin films of a regular crystalline material; here a two-dimensional quasicrystal has been achieved by growing thin films of the perovskite barium titanate on an appropriately oriented crystalline platinum substrate. Quasicrystals are quite distinct from conventional crystals: their component parts are ordered, but they do not display the precise repeating patterns seen in crystals. These unusual structures can give quasicrystals novel — and potentially useful — properties. Quasicrystallinity is rare, restricted to a few specific materials, but Wolf Widdra and co-workers now show that Quasicrystallinity can be induced in thin films of a regular crystalline material by exploiting the geometric mismatch between two different periodic systems. Specifically, they find that thin perovskite films made of barium titanate can be driven to adopt a quasicrystalline dodecahedral structure when grown on an appropriately oriented crystalline platinum substrate. Further development of this methodology might bring the concept of Quasicrystallinity to a wider range of materials and technical applications. The discovery of quasicrystals1—crystalline structures that show order while lacking periodicity—forced a paradigm shift in crystallography. Initially limited to intermetallic systems1,2,3,4, the observation of quasicrystalline structures has recently expanded to include ‘soft’ quasicrystals in the fields of colloidal and supermolecular chemistry5,6,7,8,9. Here we report an aperiodic oxide that grows as a two-dimensional quasicrystal on a periodic single-element substrate. On a Pt(111) substrate with 3-fold symmetry, the perovskite barium titanate BaTiO3 forms a high-temperature interface-driven structure with 12-fold symmetry. The building blocks of this dodecagonal structure assemble with the theoretically predicted Stampfli–Gahler tiling10,11 having a fundamental length-scale of 0.69 nm. This example of interface-driven formation of ultrathin quasicrystals from a typical periodic perovskite oxide potentially extends the quasicrystal concept to a broader range of materials. In addition, it demonstrates that frustration at the interface between two periodic materials can drive a thin film into an aperiodic quasicrystalline phase, as proposed previously12. Such structures might also find use as ultrathin buffer layers for the accommodation of large lattice mismatches in conventional epitaxy13.

Falk Scheffler - One of the best experts on this subject based on the ideXlab platform.

  • Quasicrystalline Order in Binary Dipolar Systems
    2004
    Co-Authors: Falk Scheffler, Johannes Roth, Holger Stark
    Abstract:

    Motivated by recent experimental findings, we investigate the possible occurrence and characteristics of quasicrystalline order in two-dimensional mixtures of point dipoles with two sorts of dipole moments. Despite the fact that the dipolar interaction potential does not exhibit an intrinsic length scale and cannot be tuned a priori to support the formation of quasicrystalline order, we find that configurations with long–range Quasicrystallinity yield minima in the potential energy surface of the many particle system. These configurations emanate from an ideal or perturbed ideal decoration of a binary tiling by steepest descent relaxation. Ground state energy calculations of alternative ordered states and parallel tempering Monte-Carlo simulations reveal that the quasicrystalline configurations do not correspond to a thermodynamically stable state. On the other hand, steepest descent relaxations and conventional Monte-Carlo simulations suggest that they are rather robust against fluctuations. Local quasicrystalline order in the disordered equilibrium states can be strong. I

  • Quasicrystalline order in binary dipolar systems
    2026
    Co-Authors: Falk Scheffler, Johannes Roth, P. Maass, Holger Stark
    Abstract:

    Motivated by recent experimental findings, we investigate the possible occurrence and characteristics of quasicrystalline order in two-dimensional mixtures of point dipoles with two sorts of dipole moments. Despite the fact that the dipolar interaction potential does not exhibit an intrinsic length scale and cannot be tuned a priori to support the formation of quasicrystalline order, we find that configurations with long-range Quasicrystallinity yield minima in the potential energy surface of the many particle system. These configurations emanate from an ideal or perturbed ideal decoration of a binary tiling by steepest descent relaxation. Ground state energy calculations of alternative ordered states and parallel tempering Monte-Carlo simulations reveal that the quasicrystalline configurations do not correspond to a thermodynamically stable state. On the other hand, steepest descent relaxations and conventional Monte-Carlo simulations suggest that they are rather robust against fluctuations. Local quasicrystalline order in the disordered equilibrium states can be strong. Copyright Springer-Verlag Berlin/Heidelberg 2004