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Anisotropic Shell

The Experts below are selected from a list of 162 Experts worldwide ranked by ideXlab platform

Chao Zhang – 1st expert on this subject based on the ideXlab platform

  • prevalence of Anisotropic Shell growth in rare earth core Shell upconversion nanocrystals
    ACS Nano, 2013
    Co-Authors: Chao Zhang

    Abstract:

    Through a series of carefully executed experiments, we discovered the prevalence of Anisotropic Shell growth in many upconversion NaREF4 systems caused by a combination of factors: selective adsorption of ligands on the core surface due to the core crystal structure, ligand etching, and the lattice mismatch between core and Shell components. This could lead to incomplete Shell formation in core–Shell nanocrystals under certain conditions. Shell growth is always faster in the a and b crystallographic directions than in the c direction. In the case of a larger lattice mismatch between the core and Shell, Shell growth only occurs in the a and b directions resulting in an oblong core–Shell structure. These findings are useful for rationalizing Shell-dependent emission properties, understanding the emission mechanisms in complex core–Shell nanostructures, and for creating accurate models of core–Shell designs for multifunctionality and optimal performance in applications.

  • Prevalence of Anisotropic Shell Growth in Rare Earth Core–Shell Upconversion Nanocrystals
    ACS Nano, 2013
    Co-Authors: Chao Zhang

    Abstract:

    Through a series of carefully executed experiments, we discovered the prevalence of Anisotropic Shell growth in many upconversion NaREF4 systems caused by a combination of factors: selective adsorption of ligands on the core surface due to the core crystal structure, ligand etching, and the lattice mismatch between core and Shell components. This could lead to incomplete Shell formation in core–Shell nanocrystals under certain conditions. Shell growth is always faster in the a and b crystallographic directions than in the c direction. In the case of a larger lattice mismatch between the core and Shell, Shell growth only occurs in the a and b directions resulting in an oblong core–Shell structure. These findings are useful for rationalizing Shell-dependent emission properties, understanding the emission mechanisms in complex core–Shell nanostructures, and for creating accurate models of core–Shell designs for multifunctionality and optimal performance in applications.

Zhen-sen Wu – 2nd expert on this subject based on the ideXlab platform

  • Scattering by a conducting elliptic cylinder coated with a nonconfocal homogeneous Anisotropic Shell
    Waves in Random and Complex Media, 2013
    Co-Authors: Zhen-sen Wu

    Abstract:

    The problem of scattering by an Anisotropic-coated nonconfocal conducting elliptic cylinder is investigated. In order to solve the boundary condition on the surface of the conducting cylinder, the transmitted field in the homogeneous Anisotropic Shell is described in the local coordinates. The addition theorem of Mathieu functions is used to transfer from the local coordinates to the global ones. Only the transverse magnetic case is presented. The result is in agreement with that available, as expected when the coated elliptic cylinder degenerates to a coated circular one.

  • Off-Axis Gaussian Beam Scattering by an Anisotropic Coated Sphere
    IEEE Transactions on Antennas and Propagation, 2011
    Co-Authors: Zhen-sen Wu, Zheng-jun Li, Huan Li, Qiong-kun Yuan, Hai-ying Li

    Abstract:

    An analytical solution to the scattering of an off-axis Gaussian beam incident on an Anisotropic coated sphere is proposed. Based on the local approximation of the off-axis beam shape coefficients, the field of the incident Gaussian beam is expanded using first spherical vector wave functions. By introducing the Fourier transform, the electromagnetic fields in the Anisotropic layer are expressed as the addition of the first and the second spherical vector wave functions. The expansion coefficients are analytically derived by applying the continuous tangential boundary conditions to each interface among the internal isotropic dielectric or conducting sphere, the Anisotropic Shell, and the free space. The influence of the beam widths, the beam waist center positioning, and the size parameters of the spherical structure on the field distributions are analyzed. The applications of this theoretical development in the fields of biomedicine, target shielding, and anti-radar coating are numerically discussed. The accuracy of the theory is verified by comparing the numerical results reduced to the special cases of a plane wave incidence and the case of a homogeneous Anisotropic sphere with results from a CST simulation and references.

  • Two-Dimensional Scattering by a Conducting Elliptic Cylinder Coated With a Homogeneous Anisotropic Shell
    IEEE Transactions on Antennas and Propagation, 2009
    Co-Authors: Zhen-sen Wu, Li Yang

    Abstract:

    A solution to the two-dimensional scattering properties of a conducting elliptic cylinder coated with a confocal homogeneous Anisotropic elliptical Shell is obtained. The transmitted field of the Anisotropic Shell is expressed as an integral equation based on waves with different wave numbers and different directions of propagation. The waves in all directions are represented as the eigenfunction expansion in elliptic coordinates in terms of Mathieu functions. In order to solve the nonorthogonality properties of Mathieu functions, Galerkin’s method is applied and a matrix is required for the computation of unknown expansion coefficients of the scattered and transmitted fields. Only the transverse magnetic (TM) polarization is presented, while the transverse electric (TE) polarization can be obtained in the same way. Some numerical results are presented in graphical forms. The result is in agreement with that available as expected when a coated elliptic cylinder degenerates to the coated circular one.

Balaji Dhanabalan – 3rd expert on this subject based on the ideXlab platform

  • core Shell cdse cds bone shaped nanocrystals with a thick and Anisotropic Shell as optical emitters
    Advanced Optical Materials, 2020
    Co-Authors: Andrea Castelli, Balaji Dhanabalan, Anatolii Polovitsyn, Vincenzo Caligiuri, Francesco Di Stasio, Alice Scarpellini, Rosaria Brescia, Milan Palei, Beatriz Martingarcia

    Abstract:

    Colloidal core/Shell nanocrystals are key materials for optoelectronics, enabling control over essential properties via precise engineering of the shape, thickness, and crystal lattice structure of their Shell. Here, we apply the growth protocol for CdS branched nanocrystals on CdSe nanoplatelet seeds and obtain bone-shaped heterostructures with a highly Anisotropic Shell. Surprisingly, the nanoplatelets withstand the high growth temperature of 350 °C and we obtain structures with a CdSe nanoplatelet core that is overcoated by a Shell of cubic CdS, on top of which tetrahedral CdS structures with hexagonal lattice are formed. These complex core/Shell nanocrystals show a bandedge emission around 657 nm with a photoluminescence quantum yield of ca. 42 % in solution, which is also retained in thin films. Interestingly, the nanocrystals manifest simultaneous red and green emission, and the relatively long wavelength of the green emission indicates charge recombination at the cubic/hexagonal interface of the CdS Shell. The nanocrystal films show amplified spontaneous emission, random lasing, and distributed feedback lasing when the material is deposited on suitable gratings. Our work stimulates the design and fabrication of more exotic core/Shell heterostructures where charge carrier delocalization, dipole moment, and other optical and electrical properties can be engineered.

  • Core/Shell CdSe/CdS Bone‐Shaped Nanocrystals with a Thick and Anisotropic Shell as Optical Emitters
    Advanced Optical Materials, 2019
    Co-Authors: Andrea Castelli, Balaji Dhanabalan, Anatolii Polovitsyn, Vincenzo Caligiuri, Francesco Di Stasio, Alice Scarpellini, Rosaria Brescia, Milan Palei, Beatriz Martín-garcía, Mirko Prato

    Abstract:

    Colloidal core/Shell nanocrystals are key materials for optoelectronics, enabling control over essential properties via precise engineering of the shape, thickness, and crystal lattice structure of their Shell. Here, we apply the growth protocol for CdS branched nanocrystals on CdSe nanoplatelet seeds and obtain bone-shaped heterostructures with a highly Anisotropic Shell. Surprisingly, the nanoplatelets withstand the high growth temperature of 350 °C and we obtain structures with a CdSe nanoplatelet core that is overcoated by a Shell of cubic CdS, on top of which tetrahedral CdS structures with hexagonal lattice are formed. These complex core/Shell nanocrystals show a bandedge emission around 657 nm with a photoluminescence quantum yield of ca. 42 % in solution, which is also retained in thin films. Interestingly, the nanocrystals manifest simultaneous red and green emission, and the relatively long wavelength of the green emission indicates charge recombination at the cubic/hexagonal interface of the CdS Shell. The nanocrystal films show amplified spontaneous emission, random lasing, and distributed feedback lasing when the material is deposited on suitable gratings. Our work stimulates the design and fabrication of more exotic core/Shell heterostructures where charge carrier delocalization, dipole moment, and other optical and electrical properties can be engineered.