Exchange bias for core/shell magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Lemos, C. G. O.; Figueiredo, W.; Santos, M.

2015-09-01

We study the properties of a finite magnetic system to model a magnetic nanoparticle, which is formed by a reduced number of magnetic dipole moments due to the spin of the atoms. The nanoparticle is of the type core/shell where the shell is formed by spins interacting through an antiferromagnetic exchange coupling while for the spins belonging to the core the coupling is ferromagnetic. The interaction between the spins at the interface core/shell can be either ferro or antiferromagnetic. To describe the states of the spins we used the XY model in which the spins are considered as continuous variables, free to point in any direction of the xy plane. We also consider a magnetocrystalline anisotropy, exchange anisotropy and the Zeeman effect. Our model is studied in a lattice with square symmetry, using the Monte Carlo method along with the Metropolis prescription. The results show that in the absence of an external magnetic field and exchange anisotropy, the system continuously goes to a disordered state from an ordered state at a well defined temperature. In the presence of external magnetic fields the system displays the exchange bias phenomenon, that is, the displacement of the hysteresis loops, due to the introduction of the exchange anisotropy term. However, this displacement depends on the core and shell sizes, as well as on the magnitude of the coupling between the shell and the core moments.

A mixed helium-oxygen shell in some core-collapse supernova progenitors

NASA Astrophysics Data System (ADS)

Gofman, Roni Anna; Gilkis, Avishai; Soker, Noam

2018-04-01

We evolve models of rotating massive stars up to the stage of iron core collapse using the MESA code and find a shell with a mixed composition of primarily helium and oxygen in some cases. In the parameter space of initial masses of 13-40M⊙ and initial rotation velocities of 0-450 kms-1 that we investigate, we find a mixed helium-oxygen (He-O) shell with a significant total He-O mass and with a helium to oxygen mass ratio in the range of 0.5-2 only for a small fraction of the models. While the shell formation due to mixing is instigated by rotation, the pre-collapse rotation rate is not very high. The fraction of models with a shell of He-O composition required for an energetic collapse-induced thermonuclear explosion is small, as is the fraction of models with high specific angular momentum, which can aid the thermonuclear explosion by retarding the collapse. Our results suggest that the collapse-induced thermonuclear explosion mechanism that was revisited recently can account for at most a small fraction of core-collapse supernovae. The presence of such a mixed He-O shell still might have some implications for core-collapse supernovae, such as some nucleosynthesis processes when jets are present, or might result in peculiar sub-luminous core-collapse supernovae.

A mixed helium-oxygen shell in some core-collapse supernova progenitors

NASA Astrophysics Data System (ADS)

Gofman, Roni Anna; Gilkis, Avishai; Soker, Noam

2018-07-01

We evolve models of rotating massive stars up to the stage of iron core collapse using the MESA code and find a shell with a mixed composition of primarily helium and oxygen in some cases. In the parameter space of initial masses of 13-40 M⊙ and initial rotation velocities of 0-450 km s-1 that we investigate, we find a mixed helium-oxygen (He-O) shell with a significant total He-O mass and with a helium to oxygen mass ratio in the range of 0.5-2 only for a small fraction of the models. While the shell formation due to mixing is instigated by rotation, the pre-collapse rotation rate is not very high. The fraction of models with a shell of He-O composition required for an energetic collapse-induced thermonuclear explosion is small, as is the fraction of models with high specific angular momentum, which can aid the thermonuclear explosion by retarding the collapse. Our results suggest that the collapse-induced thermonuclear explosion mechanism that was revisited recently can account for at most a small fraction of core-collapse supernovae. The presence of such a mixed He-O shell still might have some implications for core-collapse supernovae, such as some nucleosynthesis processes when jets are present, or might result in peculiar sub-luminous core-collapse supernovae.

Direct Evidence of Significant Cation Intermixing in Upconverting Core@Shell Nanocrystals: Toward a New Crystallochemical Model

DOE PAGES

Hudry, Damien; Busko, Dmitry; Popescu, Radian; ...

2017-11-02

Core@shell design represents an important class of architectures because of its capability to dramatically increase the absolute upconversion quantum yield (UCQY) of upconverting nanocrystals (UCNCs) but also to tune energy migration pathways. A relatively new trend towards the use of very thick optically inert shells affording significantly higher absolute UCQYs raises the question of the crystallographic and chemical characteristics of such nanocrystals (NCs). In this article, local chemical analyses performed by scanning transmission electron microscopy (STEM) combined with energy dispersive x-ray spectroscopy (EDXS) and x-ray total scattering experiments together with pair distribution function (PDF) analyses were used to probe themore » local chemical and structural characteristics of hexagonal β-NaGd0.78Yb0.2Er0.02F4@NaYF4 core@shell UCNCs. The investigations lead to a new crystallochemical model to describe core@shell UCNCs that considerably digresses from the commonly accepted epitaxial growth concept with sharp interfaces. The results obtained on ultra-small (4.8 ± 0.5 nm) optically active cores (β-NaGd0.78Yb0.2Er0.02F4) surrounded by an optically inert shell (NaYF4) of tunable thickness (roughly 0, 1, 2, and 3.5 nm) clearly indicate the massive dissolution of the starting seeds and the inter-diffusion of the shell element (such as Y) into the Gd/Yb/Er-containing core giving rise to the formation of a non-homogeneous solid solution characterized by concentration gradients and the lack of sharp interfaces. Independently of the inert shell thickness, core/interface/shell architectures were observed for all synthesized UCNCs. The presented results constitute a significant step towards the comprehensive understanding of the “structure - property” relationship of upconverting core@shell architectures, which is of prime interest not only in the development of more efficient structures but also to provide new physical insights at the nanoscale to better explain upconversion (UC) properties alterations.« less

Direct Evidence of Significant Cation Intermixing in Upconverting Core@Shell Nanocrystals: Toward a New Crystallochemical Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hudry, Damien; Busko, Dmitry; Popescu, Radian

Core@shell design represents an important class of architectures because of its capability to dramatically increase the absolute upconversion quantum yield (UCQY) of upconverting nanocrystals (UCNCs) but also to tune energy migration pathways. A relatively new trend towards the use of very thick optically inert shells affording significantly higher absolute UCQYs raises the question of the crystallographic and chemical characteristics of such nanocrystals (NCs). In this article, local chemical analyses performed by scanning transmission electron microscopy (STEM) combined with energy dispersive x-ray spectroscopy (EDXS) and x-ray total scattering experiments together with pair distribution function (PDF) analyses were used to probe themore » local chemical and structural characteristics of hexagonal β-NaGd0.78Yb0.2Er0.02F4@NaYF4 core@shell UCNCs. The investigations lead to a new crystallochemical model to describe core@shell UCNCs that considerably digresses from the commonly accepted epitaxial growth concept with sharp interfaces. The results obtained on ultra-small (4.8 ± 0.5 nm) optically active cores (β-NaGd0.78Yb0.2Er0.02F4) surrounded by an optically inert shell (NaYF4) of tunable thickness (roughly 0, 1, 2, and 3.5 nm) clearly indicate the massive dissolution of the starting seeds and the inter-diffusion of the shell element (such as Y) into the Gd/Yb/Er-containing core giving rise to the formation of a non-homogeneous solid solution characterized by concentration gradients and the lack of sharp interfaces. Independently of the inert shell thickness, core/interface/shell architectures were observed for all synthesized UCNCs. The presented results constitute a significant step towards the comprehensive understanding of the “structure - property” relationship of upconverting core@shell architectures, which is of prime interest not only in the development of more efficient structures but also to provide new physical insights at the nanoscale to better explain upconversion (UC) properties alterations.« less

Optical properties of light absorbing carbon aggregates mixed with sulfate: assessment of different model geometries for climate forcing calculations.

PubMed

Kahnert, Michael; Nousiainen, Timo; Lindqvist, Hannakaisa; Ebert, Martin

2012-04-23

Light scattering by light absorbing carbon (LAC) aggregates encapsulated into sulfate shells is computed by use of the discrete dipole method. Computations are performed for a UV, visible, and IR wavelength, different particle sizes, and volume fractions. Reference computations are compared to three classes of simplified model particles that have been proposed for climate modeling purposes. Neither model matches the reference results sufficiently well. Remarkably, more realistic core-shell geometries fall behind homogeneous mixture models. An extended model based on a core-shell-shell geometry is proposed and tested. Good agreement is found for total optical cross sections and the asymmetry parameter. © 2012 Optical Society of America

Anisotropic deformation of metallo-dielectric core shell colloids under MeV ion irradiation

NASA Astrophysics Data System (ADS)

Penninkhof, J. J.; van Dillen, T.; Roorda, S.; Graf, C.; van Blaaderen, A.; Vredenberg, A. M.; Polman, A.

2006-01-01

We have studied the deformation of metallo-dielectric core-shell colloids under 4 MeV Xe, 6 and 16 MeV Au, 30 MeV Si and 30 MeV Cu ion irradiation. Colloids of silica surrounded by a gold shell, with a typical diameter of 400 nm, show anisotropic plastic deformation under MeV ion irradiation, with the metal flowing conform the anisotropically deforming silica core. The 20 nm thick metal shell imposes a mechanical constraint on the deforming silica core, reducing the net deformation strain rate compared to that of pure silica. In colloids consisting of a Au core and a silica shell, the silica expands perpendicular to the ion beam, while the metal core shows a large elongation along the ion beam direction, provided the silica shell is thick enough (>40 nm). A minimum electronic energy loss of 3.3 keV/nm is required for shape transformation of the metal core. Silver cores embedded in a silica shell show no elongation, but rather disintegrate. Also in planar SiO2 films, Au and Ag colloids show entirely different behavior under MeV irradiation. We conclude that the deformation model of core-shell colloids must include ion-induced particle disintegration in combination with thermodynamical effects, possibly in combination with mechanical effects driven by stresses around the ion tracks.

X-ray and Neutron Scattering Study of the Formation of Core–Shell-Type Polyoxometalates

DOE PAGES

Yin, Panchao; Wu, Bin; Mamontov, Eugene; ...

2016-02-05

A typical type of core-shell polyoxometalates can be obtained through the Keggin-type polyoxometalate-templated growth of a layer of spherical shell structure of {Mo 72Fe 30}. Small angle X-ray scattering is used to study the structural features and stability of the core-shell structures in aqueous solutions. Time-resolved small angle X-ray scattering is applied to monitor the synthetic reactions and a three-stage formation mechanism is proposed to describe the synthesis of the core-shell polyoxometalates based on the monitoring results. Quasi-elastic and inelastic neutron scattering are used to probe the dynamics of water molecules in the core-shell structures and two different types ofmore » water molecules, the confined and structured water, are observed. These water molecules play an important role in bridging core and shell structures and stabilizing the cluster structures. A typical type of core shell polyoxometalates can be obtained through the Keggin-type polyoxometalate-templated growth of a layer of spherical shell structure of {Mo 72Fe 30}. Small-angle X-ray scattering is used to study the structural features and stability of the core shell structures in aqueous solutions. Time-resolved small-angle X-ray scattering is applied to monitor the synthetic reactions, and a three-stage formation mechanism is proposed to describe the synthesis of the core shell polyoxometalates based on the monitoring results. New protocols have been developed by fitting the X-ray data with custom physical models, which provide more convincing, objective, and completed data interpretation. Quasi-elastic and inelastic neutron scattering are used to probe the dynamics of water molecules in the core shell structures, and two different types of water molecules, the confined and structured water, are observed. These water molecules play an important role in bridging core and shell structures and stabilizing the cluster structures.« less

One-pot facile synthesis of reusable tremella-like M1@M2@M1(OH)2 (M1 = Co, Ni, M2 = Pt/Pd, Pt, Pd and Au) three layers core-shell nanostructures as highly efficient catalysts

NASA Astrophysics Data System (ADS)

Liu, Yadong; Fang, Zhen; Kuai, Long; Geng, Baoyou

2014-07-01

In this work, a general, facile, successive and eco-friendly method for multilayer nanostructures has been established for the first time. We take full advantage of the structural and compositional character of M1@M2 (M1 = Co, Ni, M2 = Pt/Pd, Pt, Pd and Au) core-shell nanostructures to prepare a series of reusable tremella-like M1@M2@M1(OH)2 three layer core-shell or yolk-shell nanocomposites with a magnetic core, a porous noble metal shell, and an ultrathin cobalt or nickel hydroxide shell. We evaluated their catalytic performance using a model reaction based on the reduction of 4-nitrophenol. These novel M1@M2@M1(OH)2 nanomaterials with a unique internal micro environment promoted the efficiency of the catalytic reaction, prolonged the service life of the catalyst and enhanced the overall activity of the catalyst in the catalytic process. The novel three layer core-shell nanocomposites can be extended to other applications such as biomedical detection, energy conversion and storage systems.In this work, a general, facile, successive and eco-friendly method for multilayer nanostructures has been established for the first time. We take full advantage of the structural and compositional character of M1@M2 (M1 = Co, Ni, M2 = Pt/Pd, Pt, Pd and Au) core-shell nanostructures to prepare a series of reusable tremella-like M1@M2@M1(OH)2 three layer core-shell or yolk-shell nanocomposites with a magnetic core, a porous noble metal shell, and an ultrathin cobalt or nickel hydroxide shell. We evaluated their catalytic performance using a model reaction based on the reduction of 4-nitrophenol. These novel M1@M2@M1(OH)2 nanomaterials with a unique internal micro environment promoted the efficiency of the catalytic reaction, prolonged the service life of the catalyst and enhanced the overall activity of the catalyst in the catalytic process. The novel three layer core-shell nanocomposites can be extended to other applications such as biomedical detection, energy conversion and storage systems. Electronic supplementary information (ESI) available: Fig. S1-S6. See DOI: 10.1039/c4nr01470g

Effects of core/shell structure on magnetic induction heating promotion in Fe3O4/γ-Fe2O3 magnetic nanoparticles for hyperthermia

NASA Astrophysics Data System (ADS)

Lee, Shih-Chi; Fu, Chao-Ming; Chang, Fu-Hsiung

2013-10-01

Fe3O4/γ-Fe2O3 core-shell magnetic nanoparticles have demonstrated superior heating efficiency by applying the alternating magnetic field. The magnetic induction heating properties of core-shell magnetic nanoparticles were analyzed by the rate-dependent hysteresis model, taken into account the magnetic anisotropies and actual size distribution of particles. The analyzed results have disclosed the significance of magnetic anisotropies and shell-thickness to the promotion of magnetic induction heating performance. Further experiments about the cancer cells with uptake of these core-shell magnetic nanoparticles conjugated biocompatible cationic liposomes have achieved in vitro intracellular magnetically induced hyperthermia under a weak alternating magnetic field.

Control of the Speed of a Light-Induced Spin Transition through Mesoscale Core-Shell Architecture.

PubMed

Felts, Ashley C; Slimani, Ahmed; Cain, John M; Andrus, Matthew J; Ahir, Akhil R; Abboud, Khalil A; Meisel, Mark W; Boukheddaden, Kamel; Talham, Daniel R

2018-05-02

The rate of the light-induced spin transition in a coordination polymer network solid dramatically increases when included as the core in mesoscale core-shell particles. A series of photomagnetic coordination polymer core-shell heterostructures, based on the light-switchable Rb a Co b [Fe(CN) 6 ] c · mH 2 O (RbCoFe-PBA) as core with the isostructural K j Ni k [Cr(CN) 6 ] l · nH 2 O (KNiCr-PBA) as shell, are studied using temperature-dependent powder X-ray diffraction and SQUID magnetometry. The core RbCoFe-PBA exhibits a charge transfer-induced spin transition (CTIST), which can be thermally and optically induced. When coupled to the shell, the rate of the optically induced transition from low spin to high spin increases. Isothermal relaxation from the optically induced high spin state of the core back to the low spin state and activation energies associated with the transition between these states were measured. The presence of a shell decreases the activation energy, which is associated with the elastic properties of the core. Numerical simulations using an electro-elastic model for the spin transition in core-shell particles supports the findings, demonstrating how coupling of the core to the shell changes the elastic properties of the system. The ability to tune the rate of optically induced magnetic and structural phase transitions through control of mesoscale architecture presents a new approach to the development of photoswitchable materials with tailored properties.

Cooperative effects in spherical spasers: Ab initio analytical model

NASA Astrophysics Data System (ADS)

Bordo, V. G.

2017-06-01

A fully analytical semiclassical theory of cooperative optical processes which occur in an ensemble of molecules embedded in a spherical core-shell nanoparticle is developed from first principles. Both the plasmonic Dicke effect and spaser generation are investigated for the designs in which a shell/core contains an arbitrarily large number of active molecules in the vicinity of a metallic core/shell. An essential aspect of the theory is an ab initio account of the feedback from the core/shell boundaries which significantly modifies the molecular dynamics. The theory provides rigorous, albeit simple and physically transparent, criteria for both plasmonic superradiance and surface plasmon generation.

Resource Letter NSM-1: New insights into the nuclear shell model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dean, David Jarvis; Hamilton, J. H.

2011-01-01

This Resource Letter provides a guide to the literature on the spherical shell model as applied to nuclei. The nuclear shell model describes the structure of nuclei starting with a nuclear core developed by the classical neutron and proton magic numbers N,Z=2,8,20,28,50,82, 126, where gaps occur in the single-particle energies as a shell is filled, and the interactions of valence nucleons that reside beyond that core. Various modern extensions of this model for spherical nuclei are likewise described. Significant extensions of the nuclear shell model include new magic numbers for spherical nuclei and now for deformed nuclei as well. Whenmore » both protons and neutrons have shell gaps at the same spherical or deformed shapes, they can reinforce each other to give added stability to that shape and lead to new magic numbers. The vanishings of the classical spherical shell model energy gaps and magic numbers in new neutron-rich nuclei are described. Spherical and deformed shell gaps are seen to be critical for the existence of elements with Z > 100.« less

Shell morphology and Raman spectra of epitaxial Ge-SixGe1-x and Si-SixGe1-x core-shell nanowires

NASA Astrophysics Data System (ADS)

Wen, Feng; Dillen, David C.; Kim, Kyounghwan; Tutuc, Emanuel

2017-06-01

We investigate the shell morphology and Raman spectra of epitaxial Ge-SixGe1-x and Si-SixGe1-x core-shell nanowire heterostructures grown using a combination of a vapor-liquid-solid (VLS) growth mechanism for the core, followed by in-situ epitaxial shell growth using ultra-high vacuum chemical vapor deposition. Cross-sectional transmission electron microscopy reveals that the VLS growth yields cylindrical Ge, and Si nanowire cores grown along the ⟨111⟩, and ⟨110⟩ or ⟨112⟩ directions, respectively. A hexagonal cross-sectional morphology is observed for Ge-SixGe1-x core-shell nanowires terminated by six {112} facets. Two distinct morphologies are observed for Si-SixGe1-x core-shell nanowires that are either terminated by four {111} and two {100} planes associated with the ⟨110⟩ growth direction or four {113} and two {111} planes associated with the ⟨112⟩ growth direction. We show that the Raman spectra of Si- SixGe1-x are correlated with the shell morphology thanks to epitaxial growth-induced strain, with the core Si-Si mode showing a larger red shift in ⟨112⟩ core-shell nanowires compared to their ⟨110⟩ counterparts. We compare the Si-Si Raman mode value with calculations based on a continuum elasticity model coupled with the lattice dynamic theory.

Radiative Properties of Carriers in Cdse-Cds Core-Shell Heterostructured Nanocrystals of Various Geometries

NASA Astrophysics Data System (ADS)

Zhou, S.; Dong, L.; Popov, S.; Friberg, A. T.

2013-07-01

We report a model on core-shell heterostructured nanocrystals with CdSe as the core and CdS as the shell. The model is based on one-band Schrödinger equation. Three different geometries, nanodot, nanorod, and nanobone, are implemented. The carrier localization regimes with these structures are simulated, compared, and analyzed. Based on the electron and hole wave functions, the carrier overlap integral that has a great impact on stimulated emission is further investigated numerically by a novel approach. Furthermore, the relation between the nanocrystal size and electron-hole recombination energy is also examined.

Constraints on the design of core-shell resonators of locally resonant acoustic metamaterials

NASA Astrophysics Data System (ADS)

Bos, Lionel; Lukyanova, Lyubov; Wunenburger, Régis

2012-11-01

We perform a parametric study of the analytic model of Liu [Z. Liu , Phys. Rev. B10.1103/PhysRevB.71.014103 71, 014103 (2005)] describing the mechanical response of a core-shell particle to an acoustic excitation in order to help in selecting the constitutive materials and in designing innovative processes of fabrication of downsized core-shell resonators, which are key constituents of locally resonant acoustic metamaterials. We show that the value of the first Lamé coefficient of the material constituting the shell has no marked influence on the value of the resonance frequency of the core-shell resonator, that is, it does not necessarily need to be small for satisfying the condition of subwavelength resonator dimension at resonance. Moreover, we show that the larger the density contrast between the core and the shell and the thinner the shell, the broader is the frequency band over which the effective density of the resonator suspension is negative, but that it is practically useless to decrease the dimensionless shell thickness below 0.6. Finally, we show that the dissipation is also less perceptible the thinner is the shell and the larger is the density contrast. The effect of the density contrast between the core and the shell and of the dissipation on the resonance width are explained by comparing with the harmonic oscillator and the mass-in-mass 1D lattice.

Large-scale shell-model calculation with core excitations for neutron-rich nuclei beyond 132Sn

NASA Astrophysics Data System (ADS)

Jin, Hua; Hasegawa, Munetake; Tazaki, Shigeru; Kaneko, Kazunari; Sun, Yang

2011-10-01

The structure of neutron-rich nuclei with a few nucleons beyond 132Sn is investigated by means of large-scale shell-model calculations. For a considerably large model space, including neutron core excitations, a new effective interaction is determined by employing the extended pairing-plus-quadrupole model with monopole corrections. The model provides a systematical description for energy levels of A=133-135 nuclei up to high spins and reproduces available data of electromagnetic transitions. The structure of these nuclei is analyzed in detail, with emphasis of effects associated with core excitations. The results show evidence of hexadecupole correlation in addition to octupole correlation in this mass region. The suggested feature of magnetic rotation in 135Te occurs in the present shell-model calculation.

Strain-Driven Stacking Faults in CdSe/CdS Core/Shell Nanorods.

PubMed

Demortière, Arnaud; Leonard, Donovan N; Petkov, Valeri; Chapman, Karena; Chattopadhyay, Soma; She, Chunxing; Cullen, David A; Shibata, Tomohiro; Pelton, Matthew; Shevchenko, Elena V

2018-04-19

Colloidal semiconductor nanocrystals are commonly grown with a shell of a second semiconductor material to obtain desired physical properties, such as increased photoluminescence quantum yield. However, the growth of a lattice-mismatched shell results in strain within the nanocrystal, and this strain has the potential to produce crystalline defects. Here, we study CdSe/CdS core/shell nanorods as a model system to investigate the influence of core size and shape on the formation of stacking faults in the nanocrystal. Using a combination of high-angle annular dark-field scanning transmission electron microscopy and pair-distribution-function analysis of synchrotron X-ray scattering, we show that growth of the CdS shell on smaller, spherical CdSe cores results in relatively small strain and few stacking faults. By contrast, growth of the shell on larger, prolate spheroidal cores leads to significant strain in the CdS lattice, resulting in a high density of stacking faults.

An Efficient Analysis Methodology for Fluted-Core Composite Structures

NASA Technical Reports Server (NTRS)

Oremont, Leonard; Schultz, Marc R.

2012-01-01

The primary loading condition in launch-vehicle barrel sections is axial compression, and it is therefore important to understand the compression behavior of any structures, structural concepts, and materials considered in launch-vehicle designs. This understanding will necessarily come from a combination of test and analysis. However, certain potentially beneficial structures and structural concepts do not lend themselves to commonly used simplified analysis methods, and therefore innovative analysis methodologies must be developed if these structures and structural concepts are to be considered. This paper discusses such an analysis technique for the fluted-core sandwich composite structural concept. The presented technique is based on commercially available finite-element codes, and uses shell elements to capture behavior that would normally require solid elements to capture the detailed mechanical response of the structure. The shell thicknesses and offsets using this analysis technique are parameterized, and the parameters are adjusted through a heuristic procedure until this model matches the mechanical behavior of a more detailed shell-and-solid model. Additionally, the detailed shell-and-solid model can be strategically placed in a larger, global shell-only model to capture important local behavior. Comparisons between shell-only models, experiments, and more detailed shell-and-solid models show excellent agreement. The discussed analysis methodology, though only discussed in the context of fluted-core composites, is widely applicable to other concepts.

Effect of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal solar cells

NASA Astrophysics Data System (ADS)

Sahin, Mehmet

2018-05-01

In this study, the effects of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal (QDNC) solar cells have been investigated in detail. For this purpose, the conventional, i.e. original, detailed balance model, developed by Shockley and Queisser to calculate an upper limit for the conversion efficiency of silicon p–n junction solar cells, is modified in a simple and effective way to calculate the conversion efficiency of core/shell QDNC solar cells. Since the existing model relies on the gap energy () of the solar cell, it does not make an estimation about the effect of QDNC materials on the efficiency of the solar cells, and gives the same efficiency values for several QDNC solar cells with the same . The proposed modification, however, estimates a conversion efficiency in relation to the material properties and also the confinement type of the QDNCs. The results of the modified model show that, in contrast to the original one, the conversion efficiencies of different QDNC solar cells, even if they have the same , become different depending upon the confinement type and shell material of the core/shell QDNCs, and this is crucial in the design and fabrication of the new generation solar cells to predict the confinement type and also appropriate QDNC materials for better efficiency.

Dye-Sensitized Core/Active Shell Upconversion Nanoparticles for Optogenetics and Bioimaging Applications

DOE PAGES

Wu, Xiang; Zhang, Yuanwei; Takle, Kendra; ...

2016-01-06

A near-infrared (NIR) dye-sensitized upconversion nanoparticles (UCNPs) can broaden the absorption range and boost upconversion efficiency of UCNPs. We achieved significantly enhanced upconversion luminescence in dye-sensitized core/active shell UCNPs via the doping of ytterbium ions (Yb 3+ ) in the UCNP shell, which bridged the energy transfer from the dye to the UCNP core. As a result, we synergized the two most practical upconversion booster effectors (dye-sensitizing and core/shell enhancement) to amplify upconversion efficiency. We also demonstrated two biomedical applications using these UCNPs. By using dye-sensitized core/active shell UCNP embedded poly(methyl methacrylate) polymer implantable systems, we successfully shifted the optogeneticmore » neuron excitation window to a biocompatible and deep tissue penetrable 800 nm wavelength. Furthermore, UCNPs were water-solubilized with Pluronic F127 with high upconversion efficiency and can be imaged in a mouse model.« less

Evolution of a compound droplet attached to a core-shell nozzle under the action of a strong electric field

NASA Astrophysics Data System (ADS)

Reznik, S. N.; Yarin, A. L.; Zussman, E.; Bercovici, L.

2006-06-01

The shape evolution of small compound droplets at the exit of a core-shell system in the presence of a sufficiently strong electric field is studied both experimentally and theoretically. It is shown that the jetting effect at the tip of the shell nozzle does not necessarily cause entrainment of the core fluid, in which case the co-electrospinning process fails to produce core-shell nanofibers. The remedy lies in extending the core nozzle outside its shell counterpart by about half the radius of the latter. The results also show that the free charges migrate very rapidly from both fluids and their interface to the free surface of the shell. This reflects the fact that most of the prejetting evolution of the droplet can be effectively described in terms of the perfect conductor model, even though the fluids can be characterized as leaky dielectrics. The stress level at the core-shell interface is of the order of 5×103g/(cms2), the relevant value in assessing the viability of viruses, bacteria, DNA molecules, drugs, enzymes, chromophores, and proteins to be encapsulated in nanofibers via co-electrospinning.

Elastic stability of cylindrical shells with soft elastic cores: Biomimicking natural tubular structures

NASA Astrophysics Data System (ADS)

Karam, Gebran Nizar

1994-01-01

Thin walled cylindrical shell structures are widespread in nature: examples include plant stems, porcupine quills, and hedgehog spines. All have an outer shell of almost fully dense material supported by a low density, cellular core. In nature, all are loaded in combination of axial compression and bending: failure is typically by buckling. Natural structures are often optimized. Here we have analyzed the elastic buckling of a thin cylindrical shell supported by an elastic core to show that this structural configuration achieves significant weight saving over a hollow cylinder. The results of the analysis are compared with data from an extensive experimental program on uniaxial compression and four point bending tests on silicone rubber shells with and without compliant foam cores. The analysis describes the results of the mechanical tests well. Characterization of the microstructures of several natural tubular structures with foamlike cores (plant stems, quills, and spines) revealed them to be close to the optimal configurations predicted by the analytical model. Biomimicking of natural cylindrical shell structures and evolutionary design processes may offer the potential to increase the mechanical efficiency of engineering cylindrical shells.

Misfit stresses in a composite core-shell nanowire with an eccentric parallelepipedal core subjected to one-dimensional cross dilatation eigenstrain

NASA Astrophysics Data System (ADS)

Krasnitckii, S. A.; Kolomoetc, D. R.; Smirnov, A. M.; Gutkin, M. Yu

2017-05-01

The boundary-value problem in the classical theory of elasticity for a core-shell nanowire with an eccentric parallelepipedal core of an arbitrary rectangular cross section is solved. The core is subjected to one-dimensional cross dilatation eigenstrain. The misfit stresses are given in a closed analytical form suitable for theoretical modeling of misfit accommodation in relevant heterostructures.

Enhanced Electron Mobility in Nonplanar Tensile Strained Si Epitaxially Grown on SixGe1-x Nanowires.

PubMed

Wen, Feng; Tutuc, Emanuel

2018-01-10

We report the growth and characterization of epitaxial, coherently strained Si x Ge 1-x -Si core-shell nanowire heterostructure through vapor-liquid-solid growth mechanism for the Si x Ge 1-x core, followed by an in situ ultrahigh-vacuum chemical vapor deposition for the Si shell. Raman spectra acquired from individual nanowire reveal the Si-Si, Si-Ge, and Ge-Ge modes of the Si x Ge 1-x core and the Si-Si mode of the shell. Because of the compressive (tensile) strain induced by lattice mismatch, the core (shell) Raman modes are blue (red) shifted compared to those of unstrained bare Si x Ge 1-x (Si) nanowires, in good agreement with values calculated using continuum elasticity model coupled with lattice dynamic theory. A large tensile strain of up to 2.3% is achieved in the Si shell, which is expected to provide quantum confinement for electrons due to a positive core-to-shell conduction band offset. We demonstrate n-type metal-oxide-semiconductor field-effect transistors using Si x Ge 1-x -Si core-shell nanowires as channel and observe a 40% enhancement of the average electron mobility compared to control devices using Si nanowires due to an increased electron mobility in the tensile-strained Si shell.

Enhancing absorption in coated semiconductor nanowire/nanorod core-shell arrays using active host matrices

NASA Astrophysics Data System (ADS)

Jule, Leta; Dejene, Francis; Roro, Kittessa

2016-12-01

In the present work, we investigated theoretically and experimentally the interaction of radiation field phenomena interacting with arrays of nanowire/nanorod core-shell embedded in active host matrices. The optical properties of composites are explored including the case when the absorption of propagating wave by dissipative component is completely compensated by amplification in active (lasing) medium. On the basis of more elaborated modeling approach and extended effective medium theory, the effective polarizability and the refractive index of electromagnetic mode dispersion of the core-shell nanowire arrays are derived. ZnS(shell)-coated by sulphidation process on ZnO(shell) nanorod arrays grown on (100) silicon substrate by chemical bath deposition (CBD) has been used for theoretical comparison. Compared with the bare ZnO nanorods, ZnS-coated core/shell nanorods exhibit a strongly reduced ultraviolet (UV) emission and a dramatically enhanced deep level (DL) emission. Obviously, the UV and DL emission peaks are attributed to the emissions of ZnO nanorods within ZnO/ZnS core/shell nanorods. The reduction of UV emission after ZnS coating seems to agree with the charge separation mechanism of type-II band alignment that holes transfer from the core to shell, which would quench the UV emission to a certain extent. Our theoretical calculations and numerical simulation demonstrate that the use of active host (amplifying) medium to compensate absorption at metallic inclusions. Moreover the core-shell nanorod/nanowire arrays create the opportunity for broad band absorption and light harvesting applications.

The design and synthesis of heterostructured quantum dots with dual emission in the visible and infrared

DOE PAGES

Lin, Qianglu; Makarov, Nikolay S.; Koh, Weon-kyu; ...

2014-11-26

The unique optical properties exhibited by visible emitting core/shell quantum dots with especially thick shells are the focus of widespread study, but have yet to be realized in infrared (IR) -active nanostructures. We apply an effective-mass model to identify PbSe/CdSe core/shell quantum dots as a promising system for achieving this goal. We then synthesize colloidal PbSe/CdSe quantum dots with shell thicknesses of up to 4 nm that exhibit unusually slow hole intra-band relaxation from shell to core states, as evidenced by the emergence of dual emission, i.e., IR photoluminescence from the PbSe core observed simultaneously with visible emission from themore » CdSe shell. In addition to the large shell thickness, the development of slowed intraband relaxation is facilitated by the existence of a sharp core-shell interface without discernible alloying. Growth of thick shells without interfacial alloying or incidental formation of homogenous CdSe nanocrystals was accomplished using insights attained via a systematic study of the dynamics of the cation-exchange synthesis of both PbSe/CdSe as well as the related system PbS/CdS. Finally, we show that the efficiency of the visible photoluminescence can be greatly enhanced by inorganic passivation.« less

Frenkel pair recombinations in UO2: Importance of explicit description of polarizability in core-shell molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Devynck, Fabien; Iannuzzi, Marcella; Krack, Matthias

2012-05-01

The oxygen and uranium Frenkel pair (FP) recombination mechanisms are studied in UO2 using an empirical interatomic potential accounting for the polarizability of the ions, namely a dynamical core-shell model. The results are compared to a more conventional rigid-ion model. Both model types have been implemented into the cp2k program package and thoroughly validated. The overall picture indicates that the FP recombination mechanism is a complex process involving several phenomena. The FP recombination can happen instantaneously when the distance between the interstitial and the vacancy is small or can be thermally activated at larger separation distances. However, other criteria can prevail over the interstitial-vacancy distance. The surrounding environment of the FP defect, the mechanical stiffness of the matrix, and the orientation of the migration path are shown to be major factors acting on the FP lifetime. The core-shell and rigid-ion models provide a similar qualitative description of the FP recombination mechanism. However, the FP stabilities determined by both models significantly differ in the lower temperature range considered. Indeed, the recombination time of the oxygen and uranium FPs can be up to an order of magnitude lower in the core-shell model at T=600 K and T=1800 K, respectively. These differences highlight the importance of the explicit description of polarizability on some crucial properties such as the resistance to amorphization. This refined description of the interatomic interactions would certainly affect the description of the recrystallization process following a displacement cascade. In turn, the self-healing phase would be better accounted for in the core-shell model and the misestimate inherent to the lack of polarizability in the rigid-ion model corrected.

Effect of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal solar cells.

PubMed

Sahin, Mehmet

2018-05-23

In this study, the effects of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal (QDNC) solar cells have been investigated in detail. For this purpose, the conventional, i.e. original, detailed balance model, developed by Shockley and Queisser to calculate an upper limit for the conversion efficiency of silicon p-n junction solar cells, is modified in a simple and effective way to calculate the conversion efficiency of core/shell QDNC solar cells. Since the existing model relies on the gap energy ([Formula: see text]) of the solar cell, it does not make an estimation about the effect of QDNC materials on the efficiency of the solar cells, and gives the same efficiency values for several QDNC solar cells with the same [Formula: see text]. The proposed modification, however, estimates a conversion efficiency in relation to the material properties and also the confinement type of the QDNCs. The results of the modified model show that, in contrast to the original one, the conversion efficiencies of different QDNC solar cells, even if they have the same [Formula: see text], become different depending upon the confinement type and shell material of the core/shell QDNCs, and this is crucial in the design and fabrication of the new generation solar cells to predict the confinement type and also appropriate QDNC materials for better efficiency.

PLGA-lecithin-PEG core-shell nanoparticles for controlled drug delivery.

PubMed

Chan, Juliana M; Zhang, Liangfang; Yuet, Kai P; Liao, Grace; Rhee, June-Wha; Langer, Robert; Farokhzad, Omid C

2009-03-01

Current approaches to encapsulate and deliver therapeutic compounds have focused on developing liposomal and biodegradable polymeric nanoparticles (NPs), resulting in clinically approved therapeutics such as Doxil/Caelyx and Genexol-PM, respectively. Our group recently reported the development of biodegradable core-shell NP systems that combined the beneficial properties of liposomal and polymeric NPs for controlled drug delivery. Herein we report the parameters that alter the biological and physicochemical characteristics, stability, drug release properties and cytotoxicity of these core-shell NPs. We further define scalable processes for the formulation of these NPs in a reproducible manner. These core-shell NPs consist of (i) a poly(D,L-lactide-co-glycolide) hydrophobic core, (ii) a soybean lecithin monolayer, and (iii) a poly(ethylene glycol) shell, and were synthesized by a modified nanoprecipitation method combined with self-assembly. Preparation of the NPs showed that various formulation parameters such as the lipid/polymer mass ratio and lipid/lipid-PEG molar ratio controlled NP physical stability and size. We encapsulated a model chemotherapy drug, docetaxel, in the NPs and showed that the amount of lipid coverage affected its drug release kinetics. Next, we demonstrated a potentially scalable process for the formulation, purification, and storage of NPs. Finally, we tested the cytotoxicity using MTT assays on two model human cell lines, HeLa and HepG2, and demonstrated the biocompatibility of these particles in vitro. Our data suggest that the PLGA-lecithin-PEG core-shell NPs may be a useful new controlled release drug delivery system.

The role of ion exchange in the passivation of In(Zn)P nanocrystals with ZnS

PubMed Central

Cho, Deok-Yong; Xi, Lifei; Boothroyd, Chris; Kardynal, Beata; Lam, Yeng Ming

2016-01-01

We have investigated the chemical state of In(Zn)P/ZnS core/shell nanocrystals (NCs) for color conversion applications using hard X-ray absorption spectroscopy (XAS) and photoluminescence excitation (PLE). Analyses of the edge energies as well as the X-ray absorption fine structure (XAFS) reveal that the Zn2+ ions from ZnS remain in the shell while the S2− ions penetrate into the core at an early stage of the ZnS deposition. It is further demonstrated that for short growth times, the ZnS shell coverage on the core was incomplete, whereas the coverage improved gradually as the shell deposition time increased. Together with evidence from PLE spectra, where there is a strong indication of the presence of P vacancies, this suggests that the core-shell interface in the In(Zn)P/ZnS NCs are subject to substantial atomic exchanges and detailed models for the shell structure beyond simple layer coverage are needed. This substantial atomic exchange is very likely to be the reason for the improved photoluminescence behavior of the core-shell particles compare to In(Zn)P-only NCs as S can passivate the NCs surfaces. PMID:26972936

Colloidal-Quantum-Dot Ring Lasers with Active Color Control.

PubMed

le Feber, Boris; Prins, Ferry; De Leo, Eva; Rabouw, Freddy T; Norris, David J

2018-02-14

To improve the photophysical performance of colloidal quantum dots for laser applications, sophisticated core/shell geometries have been developed. Typically, a wider bandgap semiconductor is added as a shell to enhance the gain from the quantum-dot core. This shell is designed to electronically isolate the core, funnel excitons to it, and reduce nonradiative Auger recombination. However, the shell could also potentially provide a secondary source of gain, leading to further versatility in these materials. Here we develop high-quality quantum-dot ring lasers that not only exhibit lasing from both the core and the shell but also the ability to switch between them. We fabricate ring resonators (with quality factors up to ∼2500) consisting only of CdSe/CdS/ZnS core/shell/shell quantum dots using a simple template-stripping process. We then examine lasing as a function of the optical excitation power and ring radius. In resonators with quality factors >1000, excitons in the CdSe cores lead to red lasing with thresholds at ∼25 μJ/cm 2 . With increasing power, green lasing from the CdS shell emerges (>100 μJ/cm 2 ) and then the red lasing begins to disappear (>250 μJ/cm 2 ). We present a rate-equation model that can explain this color switching as a competition between exciton localization into the core and stimulated emission from excitons in the shell. Moreover, by lowering the quality factor of the cavity we can engineer the device to exhibit only green lasing. The mechanism demonstrated here provides a potential route toward color-switchable quantum-dot lasers.

PMMA/PS coaxial electrospinning: a statistical analysis on processing parameters

NASA Astrophysics Data System (ADS)

Rahmani, Shahrzad; Arefazar, Ahmad; Latifi, Masoud

2017-08-01

Coaxial electrospinning, as a versatile method for producing core-shell fibers, is known to be very sensitive to two classes of influential factors including material and processing parameters. Although coaxial electrospinning has been the focus of many studies, the effects of processing parameters on the outcomes of this method have not yet been well investigated. A good knowledge of the impacts of processing parameters and their interactions on coaxial electrospinning can make it possible to better control and optimize this process. Hence, in this study, the statistical technique of response surface method (RSM) using the design of experiments on four processing factors of voltage, distance, core and shell flow rates was applied. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), oil immersion and Fluorescent microscopy were used to characterize fiber morphology. The core and shell diameters of fibers were measured and the effects of all factors and their interactions were discussed. Two polynomial models with acceptable R-squares were proposed to describe the core and shell diameters as functions of the processing parameters. Voltage and distance were recognized as the most significant and influential factors on shell diameter, while core diameter was mainly under the influence of core and shell flow rates besides the voltage.

Misfit stresses in a composite core-shell nanowire with an eccentric parallelepipedal core subjected to one-dimensional cross dilatation eigenstrain

NASA Astrophysics Data System (ADS)

Krasnitckii, S. A.; Kolomoetc, D. R.; Smirnov, A. M.; Gutkin, M. Yu

2017-03-01

We present an analytical solution to the boundary-value problem in the classical theory of elasticity for a core-shell nanowire with an eccentric parallelepipedal core of an arbitrary rectangular cross section. The core is subjected to one-dimensional cross dilatation eigenstrain. The misfit stresses are found in a concise and transparent closed form which is convenient for practical use in theoretical modeling of misfit relaxation processes.

Study of spectroscopic properties of nanosized particles of core-shell morphology

NASA Astrophysics Data System (ADS)

Bzhalava, T. N.; Kervalishvili, P. J.

2018-03-01

Method of studying spectroscopic properties of nanosized particles and estimation of resonance wavelength range for determination of specific and unique “spectral” signatures in purpose of sensing, identification of nanobioparticles, viruses is proposed. Elaboration of relevant models of viruses, estimation of spectral response on interaction of electromagnetic (EM) field and viral nanoparticle is the goal of proposed methodology. Core-shell physical model is used as the first approximation of shape-structure of virion. Theoretical solution of EM wave scattering on single spherical virus-like particle (VLP) is applied for determination of EM fields in the areas of core, shell and surrounding medium of (VLP), as well as scattering and absorption characteristics. Numerical results obtained by computer simulation for estimation of EM “spectra” of bacteriophage T7 demonstrate the strong dependence of spectroscopic characteristics on core-shell related electric and geometric parameters of VLP in resonance wavelengths range. Expected spectral response is observable on far-field characterizations. Obtained analytical EM field expressions, modelling technique in complement with experimental spectroscopic methods should be the way of providing the virus spectral signatures, important in bioparticles characterization.

Improved open-circuit voltage in polymer/oxide-nanoarray hybrid solar cells by formation of homogeneous metal oxide core/shell structures.

PubMed

Wu, Fan; Cui, Qi; Qiu, Zeliang; Liu, Changwen; Zhang, Hui; Shen, Wei; Wang, Mingtai

2013-04-24

Incorporation of vertically aligned nanorod/nanowire arrays of metal oxide (oxide-NAs) with a polymer can produce efficient hybrid solar cells with an ideal bulk-heterojunction architecture. However, polymer/oxide-NAs solar cells still suffer from a rather low (normally, < 0.4 V) open-circuit voltage (Voc). Here we demonstrate, for the first time, a novel strategy to improve the Voc in polymer/oxide-NAs solar cells by formation of homogeneous core/shell structures and reveal the intrinsic principles involved therein. A feasible hydrothermal-solvothermal combined method is developed for preparing homogeneous core/shell nanoarrays of metal oxides with a single-crystalline nanorod as core and the aggregation layer of corresponding metal oxide quantum dots (QDs) as shell, and the shell thickness (L) is easily controlled by the solvothermal reaction time for growing QDs on the nanorod. The core/shell formation dramatically improves the device Voc up to ca. 0.7-0.8 V depending on L. Based on steady-state and dynamic measurements, as well as modeling by space-charge-limited current method, it is found that the improved Voc originates from the up-shifted conduction band edge in the core by the interfacial dipole field resulting from the decreased mobility difference between photogenerated electrons and holes after the shell growth, which increases the energy difference between the quasi-Fermi levels of photogenerated electrons in the core and holes in the polymer for a higher Voc. Our results indicate that increasing Voc by the core/shell strategy seems not to be dependent on the kinds of metal oxides.

Influence of particle size and shell thickness of core-shell packing materials on optimum experimental conditions in preparative chromatography.

PubMed

Horváth, Krisztián; Felinger, Attila

2015-08-14

The applicability of core-shell phases in preparative separations was studied by a modeling approach. The preparative separations were optimized for two compounds having bi-Langmuir isotherms. The differential mass balance equation of chromatography was solved by the Rouchon algorithm. The results show that as the size of the core increases, larger particles can be used in separations, resulting in higher applicable flow rates, shorter cycle times. Due to the decreasing volume of porous layer, the loadability of the column dropped significantly. As a result, the productivity and economy of the separation decreases. It is shown that if it is possible to optimize the size of stationary phase particles for the given separation task, the use of core-shell phases are not beneficial. The use of core-shell phases proved to be advantageous when the goal is to build preparative column for general purposes (e.g. for purification of different products) in small scale separations. Copyright © 2015 Elsevier B.V. All rights reserved.

The effects of staggered bandgap in the InP/CdSe and CdSe/InP core/shell quantum dots.

PubMed

Kim, Sunghoon; Park, Jaehyun; Kim, Sungwoo; Jung, Won; Sung, Jaeyoung; Kim, Sang-Wook

2010-06-15

New type-II structures of CdSe/InP and InP/CdSe core-shell nanocrystals which have staggered bandgap alignment were fabricated. Using a simple model for the wave function for electrons and holes in InP/CdSe and CdSe/InP core/shell nanocrystals showed the wave function of the electron and hole spread into the shell, respectively. The probability density of the InP/CdSe and CdSe/InP core/shell QDs also showed a similar tendency. As a result, the structure exhibits increased delocalization of electrons and holes, leading to a red-shift in absorption and emission. Quantum yield increased in the InP/CdSe, however decreased in the CdSe/InP. The reason may be due to the surface trap and high activation barrier for de-trapping in the InP shell. 2010 Elsevier Inc. All rights reserved.

Facile fabrication of core-in-shell particles by the slow removal of the core and its use in the encapsulation of metal nanoparticles.

PubMed

Choi, Won San; Koo, Hye Young; Kim, Dong-Yu

2008-05-06

Core-in-shell particles with controllable core size have been fabricated from core-shell particles by means of the controlled core-dissolution method. These cores in inorganic shells were employed as scaffolds for the synthesis of metal nanoparticles. After dissolution of the cores, metal nanoparticles embedded in cores were encapsulated into the interior of shell, without any damage or change. This article describes a very simple method for deriving core-in-shell particles with controllable core size and encapsulation of nanoparticles into the interior of shell.

Roles of nuclear weak rates on the evolution of degenerate cores in stars

NASA Astrophysics Data System (ADS)

Suzuki, Toshio; Tsunodaa, Naofumi; Tsunoda, Yuhsuke; Shimizu, Noritaka; Otsuka, Takaharu

2018-01-01

Electron-capture and β-decay rates in stellar environments are evaluated with the use of new shell-model Hamiltonians for sd-shell and pf-shell nuclei as well as for nuclei belonging to the island of inversion. Important role of the nuclear weak rates on the final evolution of stellar degenerate cores is presented. The weak interaction rates for sd-shell nuclei are calculated to study nuclear Urca processes in O-Ne-Mg cores of stars with 8-10 M⊙ (solar mass) and their effects on the final fate of the stars. Nucleosynthesis of iron-group elements in Type Ia supernova explosions are studied with the weak rates for pf-shell nuclei. The problem of the neutron-rich iron-group isotope over-production compared to the solar abundances is shown to be nearly solved with the use of the new rates and explosion model of slow defraglation with delayed detonation. Evaluation of the weak rates is extended to the island of inversion and the region of neutron-rich nuclei near 78Ni, where two major shells contribute to their configurations.

Synthesis of parallel and antiparallel core-shell triangular nanoparticles

NASA Astrophysics Data System (ADS)

Bhattacharjee, Gourab; Satpati, Biswarup

2018-04-01

Core-shell triangular nanoparticles were synthesized by seed mediated growth. Using triangular gold (Au) nanoparticle as template, we have grown silver (Ag) shellto get core-shell nanoparticle. Here by changing the chemistry we have grown two types of core-shell structures where core and shell is having same symmetry and also having opposite symmetry. Both core and core-shell nanoparticles were characterized using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) to know the crystal structure and composition of these synthesized core-shell nanoparticles. From diffraction pattern analysis and energy filtered TEM (EFTEM) we have confirmed the crystal facet in core is responsible for such two dimensional growth of core-shell nanostructures.

Atomistic Design of CdSe/CdS Core-Shell Quantum Dots with Suppressed Auger Recombination.

PubMed

Jain, Ankit; Voznyy, Oleksandr; Hoogland, Sjoerd; Korkusinski, Marek; Hawrylak, Pawel; Sargent, Edward H

2016-10-12

We design quasi-type-II CdSe/CdS core-shell colloidal quantum dots (CQDs) exhibiting a suppressed Auger recombination rate. We do so using fully atomistic tight-binding wave functions and microscopic Coulomb interactions. The recombination rate as a function of the core and shell size and shape is tested against experiments. Because of a higher density of deep hole states and stronger hole confinement, Auger recombination is found to be up to six times faster for positive trions compared to negative ones in 4 nm core/10 nm shell CQDs. Soft-confinement at the interface results in weak suppression of Auger recombination compared to same-bandgap sharp-interface CQDs. We find that the suppression is due to increased volume of the core resulting in delocalization of the wave functions, rather than due to soft-confinement itself. We show that our results are consistent with previous effective mass models with the same system parameters. Increasing the dot volume remains the most efficient way to suppress Auger recombination. We predict that a 4-fold suppression of Auger recombination can be achieved in 10 nm CQDs by increasing the core volume by using rodlike cores embedded in thick shells.

Design of Aerosol Particle Coating: Thickness, Texture and Efficiency

PubMed Central

Buesser, B.; Pratsinis, S.E.

2013-01-01

Core-shell particles preserve the performance (e.g. magnetic, plasmonic or opacifying) of a core material while modifying its surface with a shell that facilitates (e.g. by blocking its reactivity) their incorporation into a host liquid or polymer matrix. Here coating of titania (core) aerosol particles with thin silica shells (films or layers) is investigated at non-isothermal conditions by a trimodal aerosol dynamics model, accounting for SiO2 generation by gas phase and surface oxidation of hexamethyldisiloxane (HMDSO) vapor, coagulation and sintering. After TiO2 particles have reached their final primary particle size (e.g. upon completion of sintering during their flame synthesis), coating starts by uniformly mixing them with HMDSO vapor that is oxidized either in the gas phase or on the particles’ surface resulting in SiO2 aerosols or deposits, respectively. Sintering of SiO2 deposited onto the core TiO2 particles takes place transforming rough into smooth coating shells depending on process conditions. The core-shell characteristics (thickness, texture and efficiency) are calculated for two limiting cases of coating shells: perfectly smooth (e.g. hermetic) and fractal-like. At constant TiO2 core particle production rate, the influence of coating weight fraction, surface oxidation and core particle size on coating shell characteristics is investigated and compared to pertinent experimental data through coating diagrams. With an optimal temperature profile for complete precursor conversion, the TiO2 aerosol and SiO2-precursor (HMDSO) vapor concentrations have the strongest influence on product coating shell characteristics. PMID:23729833

Observation of hole accumulation in Ge/Si core/shell nanowires using off-axis electron holography.

PubMed

Li, Luying; Smith, David J; Dailey, Eric; Madras, Prashanth; Drucker, Jeff; McCartney, Martha R

2011-02-09

Hole accumulation in Ge/Si core/shell nanowires (NWs) has been observed and quantified using off-axis electron holography and other electron microscopy techniques. The epitaxial [110]-oriented Ge/Si core/shell NWs were grown on Si (111) substrates by chemical vapor deposition through the vapor-liquid-solid growth mechanism. High-angle annular-dark-field scanning transmission electron microscopy images and off-axis electron holograms were obtained from specific NWs. The excess phase shifts measured by electron holography across the NWs indicated the presence of holes inside the Ge cores. Calculations based on a simplified coaxial cylindrical model gave hole densities of (0.4 ± 0.2) /nm(3) in the core regions.

Micro-Raman investigations of InN-GaN core-shell nanowires on Si (111) substrate

NASA Astrophysics Data System (ADS)

Sangeetha, P.; Jeganathan, K.; Ramakrishnan, V.

2013-06-01

The electron-phonon interactions in InN-GaN core-shell nanowires grown by plasma assisted- molecular beam epitaxy (MBE) on Si (111) substrate have been analysed using micro-Raman spectroscopic technique with the excitation wavelength of 633, 488 and 325 nm. The Raman scattering at 633 nm reveals the characteristic E2 (high) and A1 (LO) phonon mode of InN core at 490 and 590 cm-1 respectively and E2 (high) phonon mode of GaN shell at 573 cm-1. The free carrier concentration of InN core is found to be low in the order ˜ 1016 cm-3 due to the screening of charge carriers by thin GaN shell. Diameter of InN core evaluated using the spatial correlation model is consistent with the transmission electron microscopic measurement of ˜15 nm. The phonon-life time of core-shell nanowire structure is estimated to be ˜0.4 ps. The micro-Raman mapping and its corresponding localised spectra for 325 nm excitation exhibit intense E2 (high) phonon mode of GaN shell at 573 cm-1 as the decrease of laser interaction length and the signal intensity is quenched at the voids due to high spacing of NWs.

Tracking the Magnetization Evolution in γ-Fe2O3 / Metallic Fe Core-Shell Nanoparticle Variants

NASA Astrophysics Data System (ADS)

Kons, C.; Nemati, Z.; Srikanth, H.; Phan, M.-H.; Krycka, K.; Borchers, J.; Keavney, D.; Arena, D. A.

Iron-core magnetic nanoparticles (MNPs) with oxide shells exhibit varying magnetic properties due to the different ordering temperatures of the core and shell spins, as well as the coupling across the metal/oxide interface. While spin coupling across two dimensional interfaces has been well explored, less is known about three dimensional interfaces such as those presented in the MNPs. In this work, MNPs were synthesized with a bcc Fe core and γ-Fe2O3 shell and placed in an oxygen rich environment to encourage the transition from cores shell (CS) to core void shell (CVS) to hollow (H) structures. Static magnetic measurements (MvT) and AC magnetometry were performed to explore the magnetic behavior of the various synthesized structures. To further understand the nature of the spin coupling in the MNPs, TEM and conventional magnetometry as well as variable-temperature small angle neutron scattering (SANS), x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy were performed. Modeling of the x-ray spectra and SANS data will enable us to develop a cohesive picture of spin coupling, freezing and frustration along the three-dimensional metal / oxide interface. Supported by Department of Energy award #DE-FG02-07ER46438; NSF Award #DMR-1508249.

Core-shell nanofibers of curcumin/cyclodextrin inclusion complex and polylactic acid: Enhanced water solubility and slow release of curcumin.

PubMed

Aytac, Zeynep; Uyar, Tamer

2017-02-25

Core-shell nanofibers were designed via electrospinning using inclusion complex (IC) of model hydrophobic drug (curcumin, CUR) with cyclodextrin (CD) in the core and polymer (polylactic acid, PLA) in the shell (cCUR/HPβCD-IC-sPLA-NF). CD-IC of CUR and HPβCD was formed at 1:2 molar ratio. The successful formation of core-shell nanofibers was revealed by TEM and CLSM images. cCUR/HPβCD-IC-sPLA-NF released CUR slowly but much more in total than PLA-CUR-NF at pH 1 and pH 7.4 due to the restriction of CUR in the core of nanofibers and solubility improvement shown in phase solubility diagram, respectively. Improved antioxidant activity of cCUR/HPβCD-IC-sPLA-NF in methanol:water (1:1) is related with the solubility enhancement achieved in water based system. The slow reaction of cCUR/HPβCD-IC-sPLA-NF in methanol is associated with the shell inhibiting the quick release of CUR. On the other hand, cCUR/HPβCD-IC-sPLA-NF exhibited slightly higher rate of antioxidant activity than PLA-CUR-NF in methanol:water (1:1) owing to the enhanced solubility. To conclude, slow release of CUR was achieved by core-shell nanofiber structure and inclusion complexation of CUR with HPβCD provides high solubility. Briefly, electrospinning of core-shell nanofibers with CD-IC core could offer slow release of drugs as well as solubility enhancement for hydrophobic drugs. Copyright © 2017 Elsevier B.V. All rights reserved.

Preparation and recognition of surface molecularly imprinted core-shell microbeads for protein in aqueous solutions

NASA Astrophysics Data System (ADS)

Lu, Yan; Yan, Chang-Ling; Gao, Shu-Yan

2009-04-01

In this paper, a surface molecular imprinting technique was reported for preparing core-shell microbeads of protein imprinting, and bovine hemoglobin or bovine serum albumin were used as model proteins for studying the imprinted core-shell microbeads. 3-Aminophenylboronic acid (APBA) was polymerized onto the surface of polystyrene microbead in the presence of the protein templates to create protein-imprinted core-shell microbeads. The various samples were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) methods. The effect of pH on rebinding of the template hemoglobin, the specific binding and selective recognition were studied for the imprinted microbeads. The results show that the bovine hemoglobin-imprinted core-shell microbeads were successfully created. The shell was a sort of imprinted thin films with porous structure and larger surface areas. The imprinted microbeads have good selectivity for templates and high stability. Due to the recognition sites locating at or closing to the surface, these imprinted microbeads have good property of mass-transport. Unfortunately, the imprint technology was not successfully applied to imprinting bovine serum albumin (BSA).

Silica-Coated Core-Shell Structured Polystyrene Nanospheres and Their Size-Dependent Mechanical Properties.

PubMed

Cao, Xu; Pan, Guoshun; Huang, Peng; Guo, Dan; Xie, Guoxin

2017-08-22

The core-shell structured PS/SiO 2 composite nanospheres were synthesized on the basis of a modified Stöber method. The mechanical properties of monodisperse nanospheres were characterized with nanoindentation on the basis of the atomic force microscopy (AFM). The surface morphologies of PS/SiO 2 composite nanospheres was scanned with the tapping mode of AFM, and the force-distance curves were measured with the contact mode of AFM. Different contact models were compared for the analyses of experimental data. The elastic moduli of PS/SiO 2 composite nanosphere (4-40 GPa) and PS nanosphere (∼3.4 GPa) were obtained with the Hertz and Johnson-Kendall-Roberts (JKR) models, respectively, and the JKR model was proven to be more appropriate for calculating the elastic modulus of PS/SiO 2 nanospheres. The elastic modulus of SiO 2 shell gradually approached a constant value (∼46 GPa) with the increase of SiO 2 shell thickness. A core-shell model was proposed for describing the relationship between PS/SiO 2 composite nanosphere's elastic modulus and shell thickness. The mechanical properties of the composite nanospheres were reasonably explained on the basis of the growth mechanism of PS/SiO 2 composite nanospheres, in particular the SiO 2 shell's formation process. Available research data of PS/SiO 2 composite nanospheres in this work can provide valuable guidance for their effective application in surface engineering, micro/nanomanufacturing, lubrication, and so on.

Structure analysis for hole-nuclei close to 132Sn by a large-scale shell-model calculation

NASA Astrophysics Data System (ADS)

Wang, Han-Kui; Sun, Yang; Jin, Hua; Kaneko, Kazunari; Tazaki, Shigeru

2013-11-01

The structure of neutron-rich nuclei with a few holes in respect of the doubly magic nucleus 132Sn is investigated by means of large-scale shell-model calculations. For a considerably large model space, including orbitals allowing both neutron and proton core excitations, an effective interaction for the extended pairing-plus-quadrupole model with monopole corrections is tested through detailed comparison between the calculation and experimental data. By using the experimental energy of the core-excited 21/2+ level in 131In as a benchmark, monopole corrections are determined that describe the size of the neutron N=82 shell gap. The level spectra, up to 5 MeV of excitation in 131In, 131Sn, 130In, 130Cd, and 130Sn, are well described and clearly explained by couplings of single-hole orbitals and by core excitations.

Ultrafast Three-Dimensional Integrated Imaging of Strain in Core/Shell Semiconductor/Metal Nanostructures

DOE PAGES

Cherukara, Mathew J.; Sasikumar, Kiran; DiChiara, Anthony; ...

2017-11-07

Visualizing the dynamical response of material heterointerfaces is increasingly important for the design of hybrid materials and structures with tailored properties for use in functional devices. In situ characterization of nanoscale heterointerfaces such as metal-semiconductor interfaces, which exhibit a complex interplay between lattice strain, electric potential, and heat transport at subnanosecond time scales, is particularly challenging. Here in this work, we use a laser pump/X-ray probe form of Bragg coherent diffraction imaging (BCDI) to visualize in three-dimension the deformation of the core of a model core/shell semiconductor-metal (ZnO/Ni) nanorod following laser heating of the shell. We observe a rich interplaymore » of radial, axial, and shear deformation modes acting at different time scales that are induced by the strain from the Ni shell. We construct experimentally informed models by directly importing the reconstructed crystal from the ultrafast experiment into a thermo-electromechanical continuum model. The model elucidates the origin of the deformation modes observed experimentally. Our integrated imaging approach represents an invaluable tool to probe strain dynamics across mixed interfaces under operando conditions.« less

Ultrafast Three-Dimensional Integrated Imaging of Strain in Core/Shell Semiconductor/Metal Nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cherukara, Mathew J.; Sasikumar, Kiran; DiChiara, Anthony

Visualizing the dynamical response of material heterointerfaces is increasingly important for the design of hybrid materials and structures with tailored properties for use in functional devices. In situ characterization of nanoscale heterointerfaces such as metal-semiconductor interfaces, which exhibit a complex interplay between lattice strain, electric potential, and heat transport at subnanosecond time scales, is particularly challenging. Here in this work, we use a laser pump/X-ray probe form of Bragg coherent diffraction imaging (BCDI) to visualize in three-dimension the deformation of the core of a model core/shell semiconductor-metal (ZnO/Ni) nanorod following laser heating of the shell. We observe a rich interplaymore » of radial, axial, and shear deformation modes acting at different time scales that are induced by the strain from the Ni shell. We construct experimentally informed models by directly importing the reconstructed crystal from the ultrafast experiment into a thermo-electromechanical continuum model. The model elucidates the origin of the deformation modes observed experimentally. Our integrated imaging approach represents an invaluable tool to probe strain dynamics across mixed interfaces under operando conditions.« less

Ultrafast Three-Dimensional Integrated Imaging of Strain in Core/Shell Semiconductor/Metal Nanostructures.

PubMed

Cherukara, Mathew J; Sasikumar, Kiran; DiChiara, Anthony; Leake, Steven J; Cha, Wonsuk; Dufresne, Eric M; Peterka, Tom; McNulty, Ian; Walko, Donald A; Wen, Haidan; Sankaranarayanan, Subramanian K R S; Harder, Ross J

2017-12-13

Visualizing the dynamical response of material heterointerfaces is increasingly important for the design of hybrid materials and structures with tailored properties for use in functional devices. In situ characterization of nanoscale heterointerfaces such as metal-semiconductor interfaces, which exhibit a complex interplay between lattice strain, electric potential, and heat transport at subnanosecond time scales, is particularly challenging. In this work, we use a laser pump/X-ray probe form of Bragg coherent diffraction imaging (BCDI) to visualize in three-dimension the deformation of the core of a model core/shell semiconductor-metal (ZnO/Ni) nanorod following laser heating of the shell. We observe a rich interplay of radial, axial, and shear deformation modes acting at different time scales that are induced by the strain from the Ni shell. We construct experimentally informed models by directly importing the reconstructed crystal from the ultrafast experiment into a thermo-electromechanical continuum model. The model elucidates the origin of the deformation modes observed experimentally. Our integrated imaging approach represents an invaluable tool to probe strain dynamics across mixed interfaces under operando conditions.

Surface passivation and self-regulated shell growth in selective area-grown GaN-(Al,Ga)N core-shell nanowires.

PubMed

Hetzl, Martin; Winnerl, Julia; Francaviglia, Luca; Kraut, Max; Döblinger, Markus; Matich, Sonja; Fontcuberta I Morral, Anna; Stutzmann, Martin

2017-06-01

The large surface-to-volume ratio of GaN nanowires implicates sensitivity of the optical and electrical properties of the nanowires to their surroundings. The implementation of an (Al,Ga)N shell with a larger band gap around the GaN nanowire core is a promising geometry to seal the GaN surface. We investigate the luminescence and structural properties of selective area-grown GaN-(Al,Ga)N core-shell nanowires grown on Si and diamond substrates. While the (Al,Ga)N shell allows a suppression of yellow defect luminescence from the GaN core, an overall intensity loss due to Si-related defects at the GaN/(Al,Ga)N interface has been observed in the case of Si substrates. Scanning transmission electron microscopy measurements indicate a superior crystal quality of the (Al,Ga)N shell along the nanowire side facets compared to the (Al,Ga)N cap at the top facet. A nucleation study of the (Al,Ga)N shell reveals a pronounced bowing of the nanowires along the c-direction after a short deposition time which disappears for longer growth times. This is assigned to an initially inhomogeneous shell nucleation. A detailed study of the proceeding shell growth allows the formulation of a strain-driven self-regulating (Al,Ga)N shell nucleation model.

Core@shell@shell structured carbon-based magnetic ternary nanohybrids: Synthesis and their enhanced microwave absorption properties

NASA Astrophysics Data System (ADS)

Yang, Erqi; Qi, Xiaosi; Xie, Ren; Bai, Zhongchen; Jiang, Yang; Qin, Shuijie; Zhong, Wei; Du, Youwei

2018-05-01

High encapsulation efficiency of core@shell@shell structured carbon-based magnetic ternary nanohybrids have been synthesized in high yield by chemical vapor deposition of acetylene directly over octahedral-shaped Fe2O3 nanoparticles. By controlling the pyrolysis temperature, Fe3O4@Fe3C@carbon nanotubes (CNTs) and Fe@Fe3C@CNTs ternary nanohybrids could be selectively produced. The optimal RL values for the as-prepared ternary nanohybrids could reach up to ca. -46.7, -52.7 and -29.5 dB, respectively. The excellent microwave absorption properties of the obtaiend ternary nanohybrids were proved to ascribe to the quarter-wavelength matching model. Moreover, the as-prepared Fe@Fe3C@CNTs ternary nanohybrids displayed remarkably enhanced EM wave absorption capabilities compared to Fe3O4@Fe3C@CNTs due to their excellent dielectric loss abilities, good complementarities between the dielectric loss and the magnetic loss, and high attenuation constant. Generally, this strategy can be extended to explore other categories of core@shell or core@shell@shell structured carbon-based nanohybrids, which is very beneficial to accelerate the advancements of high performance MAMs.

Refined hierarchical kinematics quasi-3D Ritz models for free vibration analysis of doubly curved FGM shells and sandwich shells with FGM core

NASA Astrophysics Data System (ADS)

Fazzolari, Fiorenzo A.; Carrera, Erasmo

2014-02-01

In this paper, the Ritz minimum energy method, based on the use of the Principle of Virtual Displacements (PVD), is combined with refined Equivalent Single Layer (ESL) and Zig Zag (ZZ) shell models hierarchically generated by exploiting the use of Carrera's Unified Formulation (CUF), in order to engender the Hierarchical Trigonometric Ritz Formulation (HTRF). The HTRF is then employed to carry out the free vibration analysis of doubly curved shallow and deep functionally graded material (FGM) shells. The PVD is further used in conjunction with the Gauss theorem to derive the governing differential equations and related natural boundary conditions. Donnell-Mushtari's shallow shell-type equations are given as a particular case. Doubly curved FGM shells and doubly curved sandwich shells made up of isotropic face sheets and FGM core are investigated. The proposed shell models are widely assessed by comparison with the literature results. Two benchmarks are provided and the effects of significant parameters such as stacking sequence, boundary conditions, length-to-thickness ratio, radius-to-length ratio and volume fraction index on the circular frequency parameters and modal displacements are discussed.

Effect of core-shell structure on optical properties of Au-Cu2O nanoparticles

NASA Astrophysics Data System (ADS)

Sai, Cong Doanh; Ngac, An Bang

2018-03-01

Solid Au-Cu2O core-shell nanoparticles were synthesized using gold nanoparticles of 16.6 nm in size as the core. The core-shell structure of the synthesized particles was confirmed and characterized by TEM and HRTEM images. Due to their similar crystal structure, the (111) planes of Cu2O are nucleated and grown epitaxially on the {111} facets of Au nanoparticles with the lattice mismatch of about 4.3% resulting in a polycrystallized Cu2O shell covering the Au nanocore. Due to the quantum confinement effect, the band gap energy Eg of the synthesized Cu2O shells is blue-shifted from 2.35 to 2.70 eV as the shell thickness decreases from of 24.6±3.6 to 9.0±1.7 nm. The localized SPR (Surface Plasmon Resonance) peak of the Au nanocore undergoes a large red shift of the order of a hundred of nm due to both the high refractive index and the increase of the thickness of Cu2O shell. Theoretical models within the Drude framework significantly underestimate the experimental data and predict a wrong rate of change of the SPR peak position with respect to the shell thickness.

Core–shell interaction and its impact on the optical absorption of pure and doped core-shell CdSe/ZnSe nanoclusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xinqin; Cui, Yingqi; Zeng, Qun

The structural, electronic, and optical properties of core-shell nanoclusters, (CdSe){sub x}@(CdSe){sub y} and their Zn-substituted complexes of x = 2–4 and y = 16–28, were studied with density functional theory calculations. The substitution was applied in the cores, the shells, and/or the whole clusters. All these clusters are characterized by their core-shell structures in which the core-shell interaction was found different from those in core or in shell, as reflected by their bondlengths, volumes, and binding energies. Moreover, the core and shell combine together to compose a new cluster with electronic and optical properties different from those of separated individuals,more » as reflected by their HOMO-LUMO gaps and optical absorptions. With the substitution of Cd by Zn, the structural, electronic, and optical properties of clusters change regularly. The binding energy increases with Zn content, attributed to the strong Zn–Se bonding. For the same core/shell, the structure with a CdSe shell/core has a narrower gap than that with a ZnSe shell/core. The optical absorption spectra also change accordingly with Zn substitution. The peaks blueshift with increasing Zn concentration, accompanying with shape variations in case large number of Cd atoms are substituted. Our calculations reveal the core-shell interaction and its influence on the electronic and optical properties of the core-shell clusters, suggesting a composition–structure–property relationship for the design of core-shell CdSe and ZnSe nanoclusters.« less

Soft particles at fluid interfaces: wetting, structure, and rheology

NASA Astrophysics Data System (ADS)

Isa, Lucio

Most of our current knowledge concerning the behavior of colloidal particles at fluid interfaces is limited to model spherical, hard and uniform objects. Introducing additional complexity, in terms of shape, composition or surface chemistry or by introducing particle softness, opens up a vast range of possibilities to address new fundamental and applied questions in soft matter systems at fluid interfaces. In this talk I will focus on the role of particle softness, taking the case of core-shell microgels as a paradigmatic example. Microgels are highly swollen and cross-linked hydrogel particles that, in parallel with their practical applications, e.g. for emulsion stabilization and surface patterning, are increasingly used as model systems to capture fundamental properties of bulk materials. Most microgel particles develop a core-shell morphology during synthesis, with a more cross-linked core surrounded by a corona of loosely linked and dangling polymer chains. I will first discuss the difference between the wetting of a hard spherical colloid and a core-shell microgel at an oil-water interface, pinpointing the interplay between adsorption at the interface and particle deformation. I will then move on to discuss the interplay between particle morphology and the microstructure and rheological properties of the interface. In particular, I will demonstrate that synchronizing the compression of a core-shell microgel-laden fluid interface with the deposition of the interfacial monolayer makes it possible to transfer the 2D phase diagram of the particles onto a solid substrate, where different positions correspond to different values of the surface pressure and the specific area. Using atomic force microscopy, we analyzed the microstructure of the monolayer and discovered a phase transition between two crystalline phases with the same hexagonal symmetry, but with two different lattice constants. The two phases correspond to shell-shell or core-core inter-particle contacts, respectively, where with increasing surface pressure the former mechanically fail enabling the particle cores to come into contact. In the phase-transition region, clusters of particles in core-core contacts nucleate, melting the surrounding shell-shell crystal, until the whole monolayer moves into the second phase. We furthermore extended our analysis to measure the interfacial rheology of the monolayers as a function of the surface pressure using an interfacial microdisk rheometer; the interfaces always show a strong elastic response, with a dip in the elastic modulus in correspondence of the melting of the shell-shell phase, followed by a steep increase upon formation of a percolating network of the core-core contacts. The presented results highlight the complex interplay between the wetting and deformation of individual soft particles at fluid interfaces and the overall interface microstructure and mechanics. They show strong connections to fundamental studies on phase transitions in two-dimensional systems and pave the way for novel nanoscale surface patterning routes. The author acknowledges financial support from the Swiss National Science Foundation Grant PP00P2-144646/1.

Influence of dimensionality and interface type on optical and electronic properties of CdS/ZnS core-shell nanocrystals—A first-principles study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kocevski, V., E-mail: vancho.vk@gmail.com, E-mail: vancho.kocevski@physics.uu.se; Eriksson, O.; Gerard, C.

2015-10-28

Semiconducting nanocrystals (NCs) have become one of the leading materials in a variety of applications, mainly due to their size tunable band gap and high intensity emission. Their photoluminescence (PL) properties can be notably improved by capping the nanocrystals with a shell of another semiconductor, making core-shell structures. We focus our study on the CdS/ZnS core-shell nanocrystals that are closely related to extensively studied CdSe/CdS NCs, albeit exhibiting rather different photoluminescence properties. We employ density functional theory to investigate the changes in the electronic and optical properties of these nanocrystals with size, core/shell ratio, and interface structure between the coremore » and the shell. We have found that both the lowest unoccupied eigenstate (LUES) and the highest occupied eigenstate (HOES) wavefunction (WF) are localized in the core of the NCs, with the distribution of the LUES WF being more sensitive to the size and the core/shell ratio. We show that the radiative lifetimes are increasing, and the Coulomb interaction energies decrease with increasing NC size. Furthermore, we investigated the electronic and optical properties of the NCs with different interfaces between the core and the shell and different core types. We find that the different interfaces and core types have rather small influence on the band gaps and the absorption indexes, as well as on the confinement of the HOES and LUES WFs. Also the radiative lifetimes are found to be only slightly influenced by the different structural models. In addition, we compare these results with the previous results for CdSe/CdS NCs, reflecting the different PL properties of these two types of NCs. We argue that the difference in their Coulomb interaction energies is one of the main reasons for their distinct PL properties.« less

Atomistic tight-binding computations of the structural and optical properties of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals

NASA Astrophysics Data System (ADS)

Sukkabot, Worasak

2018-05-01

A study of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals is carried out using atomistic tight-binding theory and the configuration interaction method to provide information for applications in bioimaging, biolabeling, display devices and near-infrared electronic instruments. The calculations yield the dependences of the internal and external passivated shells on the natural behaviours of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals. The reduction of the optical band gaps is observed with increasing numbers of monolayers in the external ZnS shell due to quantum confinement. Interestingly, the optical band gaps of CdTe/CdS/ZnS core/shell/shell nanocrystals are greater than those of CdTe/CdSe/ZnS core/shell/shell nanocrystals. In the presence of an external ZnS-coated shell, electron-hole wave function overlaps, oscillation strengths, ground-state exchange energies and Stokes shift are improved, whereas ground-state coulomb energies and fine-structure splitting are reduced. The oscillation strengths, Stokes shift and fine-structure splitting are reduced with the increase in external ZnS shell thickness. The oscillation strengths, Stokes shift and fine-structure splitting of CdTe/CdS/ZnS core/shell/shell nanocrystals are larger than those of CdTe/CdSe/ZnS core/shell/shell nanocrystals. Reduction of the atomistic electron-hole interactions is observed with increasing external ZnS shell size. The strong electron-hole interactions are more probed in CdTe/CdS/ZnS core/shell/shell nanocrystals than in CdTe/CdSe/ZnS core/shell/shell nanocrystals.

Tenofovir Containing Thiolated Chitosan Core/Shell Nanofibers: In Vitro and in Vivo Evaluations.

PubMed

Meng, Jianing; Agrahari, Vivek; Ezoulin, Miezan J; Zhang, Chi; Purohit, Sudhaunshu S; Molteni, Agostino; Dim, Daniel; Oyler, Nathan A; Youan, Bi-Botti C

2016-12-05

It is hypothesized that thiolated chitosan (TCS) core/shell nanofibers (NFs) can enhance the drug loading of tenofovir, a model low molecular weight and highly water-soluble drug molecule, and improve its mucoadhesivity and in vivo safety. To test this hypothesis, poly(ethylene oxide) (PEO) core with TCS and polylactic acid (PLA) shell NFs are fabricated by a coaxial electrospinning technique. The morphology, drug loading, drug release profiles, cytotoxicity and mucoadhesion of the NFs are analyzed using scanning and transmission electron microscopies, liquid chromatography, cytotoxicity assays on VK2/E6E7 and End1/E6E7 cell lines and Lactobacilli crispatus, fluorescence imaging and periodic acid colorimetric method, respectively. In vivo safety studies are performed in C57BL/6 mice followed by H&E and immunohistochemical (CD45) staining analysis of genital tract. The mean diameters of PEO, PEO/TCS, and PEO/TCS-PLA NFs are 118.56, 9.95, and 99.53 nm, respectively. The NFs exhibit smooth surface. The drug loading (13%-25%, w/w) increased by 10-fold compared to a nanoparticle formulation due to the application of the electrospinning technique. The NFs are noncytotoxic at the concentration of 1 mg/mL. The PEO/TCS-PLA core/shell NFs mostly exhibit a release kinetic following Weibull model (r 2 = 0.9914), indicating the drug release from a matrix system. The core/shell NFs are 40-60-fold more bioadhesive than the pure PEO based NFs. The NFs are nontoxic and noninflammatory in vivo after daily treatment for up to 7 days. Owing to their enhanced drug loading and preliminary safety profile, the TCS core/shell NFs are promising candidates for the topical delivery of HIV/AIDS microbicides such as tenofovir.

Iridium-decorated palladium-platinum core-shell catalysts for oxygen reduction reaction in proton exchange membrane fuel cell.

PubMed

Wang, Chen-Hao; Hsu, Hsin-Cheng; Wang, Kai-Ching

2014-08-01

Carbon-supported Pt, Pd, Pd-Pt core-shell (Pt(shell)-Pd(core)/C) and Ir-decorated Pd-Pt core-shell (Ir-decorated Pt(shell)-Pd(core)/C) catalysts were synthesized, and their physical properties, electrochemical behaviors, oxygen reduction reaction (ORR) characteristics and proton exchange membrane fuel cell (PEMFC) performances were investigated herein. From the XRD patterns and TEM images, Ir-decorated Pt(shell)-Pd(core)/C has been confirmed that Pt was deposited on the Pd nanoparticle which had the core-shell structure. Ir-decorated Pt(shell)-Pd(core)/C has more positive OH reduction peak than Pt/C, which is beneficial to weaken the binding energy of Pt-OH during the ORR. Thus, Ir-decorated Pt(shell)-Pd(core)/C has higher ORR activity than Pt/C. The maximum power density of H2-O2 PEMFC using Ir-decorated Pt(shell)-Pd(core)/C is 792.2 mW cm(-2) at 70°C, which is 24% higher than that using Pt/C. The single-cell accelerated degradation test of PEMFC using Ir-decorated Pt(shell)-Pd(core)/C shows good durability by the potential cycling of 40,000 cycles. This study concludes that Ir-decorated Pt(shell)-Pd(core)/C has the low Pt content, but it can facilitate the low-cost and high-efficient PEMFC. Copyright © 2013 Elsevier Inc. All rights reserved.

Design and intestinal mucus penetration mechanism of core-shell nanocomplex.

PubMed

Zhang, Xin; Cheng, Hongbo; Dong, Wei; Zhang, Meixia; Liu, Qiaoyu; Wang, Xiuhua; Guan, Jian; Wu, Haiyang; Mao, Shirui

2018-02-28

The objective of this study was to design intestinal mucus-penetrating core-shell nanocomplex by functionally mimicking the surface of virus, which can be used as the carrier for peroral delivery of macromolecules, and further understand the influence of nanocomplex surface properties on the mucosal permeation capacity. Taking insulin as a model drug, the core was formed by the self-assembly among positively charged chitosan, insulin and negatively charged sodium tripolyphosphate, different types of alginates were used as the shell forming material. The nanocomplex was characterized by dynamic light scattering (DLS), atomic force microscopy (AFM) and FTIR. Nanocomplex movement in mucus was recorded using multiple particle tracking (MPT) method. Permeation and uptake of different nanocomplex were studied in rat intestine. It was demonstrated that alginate coating layer was successfully formed on the core and the core-shell nanocomplex showed a good physical stability and improved enzymatic degradation protection. The mucus penetration and MPT study showed that the mucus penetration capacity of the nanocomplex was surface charge and coating polymer structure dependent, nanocomplex with negative alginate coating had 1.6-2.5 times higher mucus penetration ability than that of positively charged chitosan-insulin nanocomplex. Moreover, the mucus penetration ability of the core-shell nanocomplex was alginate structure dependent, whereas alginate with lower G content and lower molecular weight showed the best permeation enhancing ability. The improvement of intestine permeation and intestinal villi uptake of the core-shell nanocomplex were further confirmed in rat intestine and multiple uptake mechanisms were involved in the transport process. In conclusion, core-shell nanocomplex composed of oppositely charged materials could provide a strategy to overcome the mucus barrier and enhance the mucosal permeability. Copyright © 2018 Elsevier B.V. All rights reserved.

Fabrication and investigation of effect of core size in heterostructure PbS/CdS core/shell nanoparticles

NASA Astrophysics Data System (ADS)

Das, D.; Hussain, A. M. P.

2018-04-01

PbS/CdS core/shell (CS) nanoparticles (NPs) were fabricated with three different concentrations of PbS core and CdS shell. Formation of core/shell heterostructure was confirmed from X-ray diffraction studies. The diffraction patterns exhibited formation of cubic phase and polycrystalline core/shell nanostructure. The crystalline sizes calculated from Williamson-Hall plot exhibited increase with molar concentration of precursors with decrease in strain. High resolution electron microscopy studies also confirm the formation of core/shell structure with particle size around 10 nm. A large blue-shift for PbS core compared to its bulk and small red-shift for the PbS/CdS core/shell as compared to the core is being observed in absorption spectra.

Application of Powder Diffraction Methods to the Analysis of the Atomic Structure of Nanocrystals: The Concept of the Apparent Lattice Parameter (ALP)

NASA Technical Reports Server (NTRS)

Palosz, B.; Grzanka, E.; Gierlotka, S.; Stelmakh, S.; Pielaszek, R.; Bismayer, U.; Weber, H.-P.; Palosz, W.; Curreri, Peter A. (Technical Monitor)

2002-01-01

The applicability of standard methods of elaboration of powder diffraction data for determination of the structure of nano-size crystallites is analysed. Based on our theoretical calculations of powder diffraction data we show, that the assumption of the infinite crystal lattice for nanocrystals smaller than 20 nm in size is not justified. Application of conventional tools developed for elaboration of powder diffraction data, like the Rietveld method, may lead to erroneous interpretation of the experimental results. An alternate evaluation of diffraction data of nanoparticles, based on the so-called 'apparent lattice parameter' (alp) is introduced. We assume a model of nanocrystal having a grain core with well-defined crystal structure, surrounded by a surface shell with the atomic structure similar to that of the core but being under a strain (compressive or tensile). The two structural components, the core and the shell, form essentially a composite crystal with interfering, inseparable diffraction properties. Because the structure of such a nanocrystal is not uniform, it defies the basic definitions of an unambiguous crystallographic phase. Consequently, a set of lattice parameters used for characterization of simple crystal phases is insufficient for a proper description of the complex structure of nanocrystals. We developed a method of evaluation of powder diffraction data of nanocrystals, which refers to a core-shell model and is based on the 'apparent lattice parameter' methodology. For a given diffraction pattem, the alp values are calculated for every individual Bragg reflection. For nanocrystals the alp values depend on the diffraction vector Q. By modeling different a0tomic structures of nanocrystals and calculating theoretically corresponding diffraction patterns using the Debye functions we showed, that alp-Q plots show characteristic shapes which can be used for evaluation of the atomic structure of the core-shell system. We show, that using a simple model of a nanocrystal with spherical shape and centro-symmetric strain at the surface shell we obtain theoretical alp-Q values which match very well the alp-Q plots determined experimentally for Sic, GaN, and diamond nanopowders. The theoretical models are defined by the lattice parameter of the grain core, thickness of the surface shell, and the magnitude and distribution of the strain field in the surface shell. According to our calculations, the part of the diffraction pattern measured at relatively low diffraction vectors Q (below 10/angstrom) provides information on the surface strain, whle determination of the lattice parameters in the grain core requires measurements at large Q-values (above 15 - 20/angstrom).

Magnetic field insensitive photoluminescence decay of ZnSe/CdS core/shell type-II colloidal quantum dots

NASA Astrophysics Data System (ADS)

Lee, Woojin; Park, Seongho; Murayama, Akihiro; Lee, Jong-soo; Kyhm, Kwangseuk

2018-06-01

We have synthesized ZnSe/CdS core/shell type-II colloidal quantum dots, where an electron and a hole are separated in the CdS shell and the ZnSe core, respectively. Our theoretical model has revealed that absorbance spectrum of bare ZnSe quantum dots in 2 nm radius becomes broadened with a large redshift (∼1.15 eV) when the electron in ZnSe core is separated by 3.2 nm CdS shell. Also, we found that our type-II QDs are insensitive to an external magnetic field up to 5 T in terms of central emission energy, degree of polarization, and photoluminescence decay time. This can be attributed to the electron–hole charge separation in a type-II structure, whereby the suppressed exchange interaction gives rise to a magnetic insensitivity with a small energy difference between the bright and dark exciton states.

Wave Function Engineering in CdSe/PbS Core/Shell Quantum Dots.

PubMed

Wieliczka, Brian M; Kaledin, Alexey L; Buhro, William E; Loomis, Richard A

2018-05-25

The synthesis of epitaxial CdSe/PbS core/shell quantum dots (QDs) is reported. The PbS shell grows in a rock salt structure on the zinc blende CdSe core, thereby creating a crystal structure mismatch through additive growth. Absorption and photoluminescence (PL) band edge features shift to lower energies with increasing shell thickness, but remain above the CdSe bulk band gap. Nevertheless, the profiles of the absorption spectra vary with shell growth, indicating that the overlap of the electron and hole wave functions is changing significantly. This leads to over an order of magnitude reduction of absorption near the band gap and a large, tunable energy shift, of up to 550 meV, between the onset of strong absorption and the band edge PL. While the bulk valence and conduction bands adopt an inverse type-I alignment, the observed spectroscopic behavior is consistent with a transition between quasi-type-I and quasi-type-II behavior depending on shell thickness. Three effective mass approximation models support this hypothesis and suggest that the large difference in effective masses between the core and shell results in hole localization in the CdSe core and a delocalization of the electron across the entire QD. These results show the tuning of wave functions and transition energies in CdSe/PbS nanoheterostructures with prospects for use in optoelectronic devices for luminescent solar concentration or multiexciton generation.

The Last Minutes of Oxygen Shell Burning in a Massive Star

NASA Astrophysics Data System (ADS)

Müller, Bernhard; Viallet, Maxime; Heger, Alexander; Janka, Hans-Thomas

2016-12-01

We present the first 4π-three-dimensional (3D) simulation of the last minutes of oxygen shell burning in an 18 M ⊙ supernova progenitor up to the onset of core collapse. A moving inner boundary is used to accurately model the contraction of the silicon and iron core according to a one-dimensional stellar evolution model with a self-consistent treatment of core deleptonization and nuclear quasi-equilibrium. The simulation covers the full solid angle to allow the emergence of large-scale convective modes. Due to core contraction and the concomitant acceleration of nuclear burning, the convective Mach number increases to ˜0.1 at collapse, and an ℓ = 2 mode emerges shortly before the end of the simulation. Aside from a growth of the oxygen shell from 0.51 M ⊙ to 0.56 M ⊙ due to entrainment from the carbon shell, the convective flow is reasonably well described by mixing-length theory, and the dominant scales are compatible with estimates from linear stability analysis. We deduce that artificial changes in the physics, such as accelerated core contraction, can have precarious consequences for the state of convection at collapse. We argue that scaling laws for the convective velocities and eddy sizes furnish good estimates for the state of shell convection at collapse and develop a simple analytic theory for the impact of convective seed perturbations on shock revival in the ensuing supernova. We predict a reduction of the critical luminosity for explosion by 12%-24% due to seed asphericities for our 3D progenitor model relative to the case without large seed perturbations.

Wide-range tuning of the surface plasmon resonance of silver/gold core shell and alloyed nanoparticles

NASA Astrophysics Data System (ADS)

Hubenthal, Frank; Ziegler, Torsten; Hendrich, Christian; Träger, Frank

2004-03-01

For many applications like surface enhanced Raman scattering in which the optical field enhancement associated with surface plasmon excitation is exploited, tunability of this collective resonance over a wide range is required. For this purpose we have prepared Ag/Au core shell and Ag/Au alloyed nanoparticles with different shell thicknesses and different percentages of the two metals. The nanoparticles were made by subsequent deposition of Ag and Au atoms on dielectric substrates followed by diffusion and nucleation or heat treatment. Depending on the Au shell thickness the plasmon frequency can be tuned, e.g. from 2.8 eV (442 nm) to 2.1 eV (590 nm). Annealing of the core-shell nanoparticles causes a shift of the resonance frequency to 2.6 eV. Theoretical modelling allows us to attribute this observation to the production of alloyed nanoparticles. Possible application of the Ag/Au nanoparticles will be discussed.

Seed-Surface Grafting Precipitation Polymerization for Preparing Microsized Optically Active Helical Polymer Core/Shell Particles and Their Application in Enantioselective Crystallization.

PubMed

Zhao, Biao; Lin, Jiangfeng; Deng, Jianping; Liu, Dong

2018-05-14

Core/shell particles constructed by polymer shell and silica core have constituted a significant category of advanced functional materials. However, constructing microsized optically active helical polymer core/shell particles still remains as a big academic challenge due to the lack of effective and universal preparation methods. In this study, a seed-surface grafting precipitation polymerization (SSGPP) strategy is developed for preparing microsized core/shell particles with SiO 2 as core on which helically substituted polyacetylene is covalently bonded as shell. The resulting core/shell particles exhibit fascinating optical activity and efficiently induce enantioselective crystallization of racemic threonine. Taking advantage of the preparation strategy, novel achiral polymeric and hybrid core/shell particles are also expected. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Design, synthesis and applications of core-shell, hollow core, and nanorattle multifunctional nanostructures.

PubMed

El-Toni, Ahmed Mohamed; Habila, Mohamed A; Labis, Joselito Puzon; ALOthman, Zeid A; Alhoshan, Mansour; Elzatahry, Ahmed A; Zhang, Fan

2016-02-07

With the evolution of nanoscience and nanotechnology, studies have been focused on manipulating nanoparticle properties through the control of their size, composition, and morphology. As nanomaterial research has progressed, the foremost focus has gradually shifted from synthesis, morphology control, and characterization of properties to the investigation of function and the utility of integrating these materials and chemical sciences with the physical, biological, and medical fields, which therefore necessitates the development of novel materials that are capable of performing multiple tasks and functions. The construction of multifunctional nanomaterials that integrate two or more functions into a single geometry has been achieved through the surface-coating technique, which created a new class of substances designated as core-shell nanoparticles. Core-shell materials have growing and expanding applications due to the multifunctionality that is achieved through the formation of multiple shells as well as the manipulation of core/shell materials. Moreover, core removal from core-shell-based structures offers excellent opportunities to construct multifunctional hollow core architectures that possess huge storage capacities, low densities, and tunable optical properties. Furthermore, the fabrication of nanomaterials that have the combined properties of a core-shell structure with that of a hollow one has resulted in the creation of a new and important class of substances, known as the rattle core-shell nanoparticles, or nanorattles. The design strategies of these new multifunctional nanostructures (core-shell, hollow core, and nanorattle) are discussed in the first part of this review. In the second part, different synthesis and fabrication approaches for multifunctional core-shell, hollow core-shell and rattle core-shell architectures are highlighted. Finally, in the last part of the article, the versatile and diverse applications of these nanoarchitectures in catalysis, energy storage, sensing, and biomedicine are presented.

Predictable Particle Engineering: Programming the Energy Level, Carrier Generation, and Conductivity of Core-Shell Particles.

PubMed

Yuan, Conghui; Wu, Tong; Mao, Jie; Chen, Ting; Li, Yuntong; Li, Min; Xu, Yiting; Zeng, Birong; Luo, Weiang; Yu, Lingke; Zheng, Gaofeng; Dai, Lizong

2018-06-20

Core-shell structures are of particular interest in the development of advanced composite materials as they can efficiently bring different components together at nanoscale. The advantage of this structure greatly relies on the crucial design of both core and shell, thus achieving an intercomponent synergistic effect. In this report, we show that decorating semiconductor nanocrystals with a boronate polymer shell can easily achieve programmable core-shell interactions. Taking ZnO and anatase TiO 2 nanocrystals as inner core examples, the effective core-shell interactions can narrow the band gap of semiconductor nanocrystals, change the HOMO and LUMO levels of boronate polymer shell, and significantly improve the carrier density of core-shell particles. The hole mobility of core-shell particles can be improved by almost 9 orders of magnitude in comparison with net boronate polymer, while the conductivity of core-shell particles is at most 30-fold of nanocrystals. The particle engineering strategy is based on two driving forces: catechol-surface binding and B-N dative bonding and having a high ability to control and predict the shell thickness. Also, this approach is applicable to various inorganic nanoparticles with different components, sizes, and shapes.

Double-detonation Sub-Chandrasekhar Supernovae: Synthetic Observables for Minimum Helium Shell Mass Models

NASA Astrophysics Data System (ADS)

Kromer, M.; Sim, S. A.; Fink, M.; Röpke, F. K.; Seitenzahl, I. R.; Hillebrandt, W.

2010-08-01

In the double-detonation scenario for Type Ia supernovae, it is suggested that a detonation initiates in a shell of helium-rich material accreted from a companion star by a sub-Chandrasekhar-mass white dwarf. This shell detonation drives a shock front into the carbon-oxygen white dwarf that triggers a secondary detonation in the core. The core detonation results in a complete disruption of the white dwarf. Earlier studies concluded that this scenario has difficulties in accounting for the observed properties of Type Ia supernovae since the explosion ejecta are surrounded by the products of explosive helium burning in the shell. Recently, however, it was proposed that detonations might be possible for much less massive helium shells than previously assumed (Bildsten et al.). Moreover, it was shown that even detonations of these minimum helium shell masses robustly trigger detonations of the carbon-oxygen core (Fink et al.). Therefore, it is possible that the impact of the helium layer on observables is less than previously thought. Here, we present time-dependent multi-wavelength radiative transfer calculations for models with minimum helium shell mass and derive synthetic observables for both the optical and γ-ray spectral regions. These differ strongly from those found in earlier simulations of sub-Chandrasekhar-mass explosions in which more massive helium shells were considered. Our models predict light curves that cover both the range of brightnesses and the rise and decline times of observed Type Ia supernovae. However, their colors and spectra do not match the observations. In particular, their B - V colors are generally too red. We show that this discrepancy is mainly due to the composition of the burning products of the helium shell of the Fink et al. models which contain significant amounts of titanium and chromium. Using a toy model, we also show that the burning products of the helium shell depend crucially on its initial composition. This leads us to conclude that good agreement between sub-Chandrasekhar-mass explosions and observed Type Ia supernovae may still be feasible but further study of the shell properties is required.

Ag@ZnO core-shell nanoparticles study by first principle: The structural, magnetic and optical properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Hai-Xia; Wang, Xiao-Xu; Beijing Computing Center, Beijing 100094

Ag@ZnO core-shell nanoparticles of around 72 atoms have been investigated by the density functional theory, revealing proving for the first time that the core-shell structure exhibits a shrinkage phenomenon from outer shell in agreement with the other studies in literatures. Our calculations predict that the Ag@ZnO core-shell structure is a ferromagnetic spin polarized state, and the magnetism mainly stems from the spin splitting of 2p electrons of O atoms. In addition, the total and partial DOS of Ag@ZnO indicate that the nanostructure is a half-metallic nanoparticle and has the characters of the p-type semiconductor. Furthermore, the optical properties calculations showmore » that the absorption edge of Ag@ZnO have a red shift and good photocatalysis compare to that of the bulk ZnO. These results of the Ag@ZnO core-shell structure obtain a well agreement with the experimental measurement. - Graphical abstract: Geometric structure of (a) Ag@ZnO core-shell nanostructure; (b) the core of Ag; (c) the shell of ZnO The core-shell nanoparticle Ag@ZnO contains Ag inner core of radius of 4 Å and ZnO outer shell with thickness of 2 Å. Ag@ZnO core-shell nanoparticles of around 72 atoms have been proved for the first time that the core-shell structure exhibit a shrinkage phenomenon from outer shell. Our calculations predict that the Ag@ZnO core-shell structure is a half-metallic nanoparticle and has the characters of the p-type semiconductor. The absorption edge of Ag@ZnO have a red shift and get good photo-catalysis compare to that of the bulk ZnO.« less

Control of the shell structural properties and cavity diameter of hollow magnesium fluoride particles.

PubMed

Nandiyanto, Asep Bayu Dani; Ogi, Takashi; Okuyama, Kikuo

2014-03-26

Control of the shell structural properties [i.e., thickness (8-25 nm) and morphology (dense and raspberry)] and cavity diameter (100-350 nm) of hollow particles was investigated experimentally, and the results were qualitatively explained based on the available theory. We found that the selective deposition size and formation of the shell component on the surface of a core template played important roles in controlling the structure of the resulting shell. To achieve the selective deposition size and formation of the shell component, various process parameters (i.e., reaction temperature and charge, size, and composition of the core template and shell components) were tested. Magnesium fluoride (MgF2) and polystyrene spheres were used as models for shell and core components, respectively. MgF2 was selected because, to the best of our knowledge, the current reported approaches to date were limited to synthesis of MgF2 in film and particle forms only. Therefore, understanding how to control the formation of MgF2 with various structures (both the thickness and morphology) is a prospective for advanced lens synthesis and applications.

A coarse grained molecular dynamics simulation study on the structural properties of carbon nanotube-dendrimer composites.

PubMed

Kavyani, Sajjad; Dadvar, Mitra; Modarress, Hamid; Amjad-Iranagh, Sepideh

2018-04-25

By employing coarse grained (CG) molecular dynamics (MD) simulation, the effect of the size and hydrophilic/hydrophobic properties of the interior/exterior structures of the dendrimers in carbon nanotube (CNT)-dendrimer composites has been studied, to find a stable composite with high solubility in water and the capability to be used in drug delivery applications. For this purpose, composites consisting of core-shell dendrimer complexes including: [PPI{core}-PAMAM{shell}], [PAMAM{core}-polyethyleneglycol (PEG){shell}] and [PAMAM{core}-fattyacid (FTA){shell}] were constructed. A new CG model for the fatty acid (FTA) molecules as functionalized to the dendrimer was developed, which, unlike the previous models, could generate the structural conformations of the FTA properly. The obtained results indicated that the dendrimer complexes with short FTA chains can form stable composites with the CNT. Also, it was found that the pristine PAMAM and PPI-PAMAM with small PPI, and PAMAM-PEG dendrimers with short PEG chains, can distribute their chains into the water medium and interact with the CNT efficiently, to form a stable water-soluble CNT-dendrimer composite. The results demonstrated that the structural difference between the interior and exterior of a core-shell dendrimer complex can prevent the core and the interior layers of the dendrimer complex from interacting with the CNT. An overall analysis of the results manifested that the CNT-PAMAM:4-PEG:4 is the most stable composite, due to strong binding of the dendrimer with the CNT while also having high solubility in water, and its core retains its structure properly and unchanged, suitable for encapsulating drugs in the targeted delivery applications.

Charge symmetry breaking in light Λ hypernuclei

NASA Astrophysics Data System (ADS)

Gal, Avraham; Gazda, Daniel

2018-02-01

Charge symmetry breaking (CSB) is particularly strong in the A = 4 mirror hypernuclei {}14\\text{H}-Λ 4\\text{He}. Recent four-body no-core shell model calculations that confront this CSB by introducing Λ-Σ0 mixing to leading-order chiral effective field theory hyperon-nucleon potentials are reviewed, and a shell-model approach to CSB in p-shell Λ hypernuclei is outlined.

Porous Core-Shell Nanostructures for Catalytic Applications

NASA Astrophysics Data System (ADS)

Ewers, Trevor David

Porous core-shell nanostructures have recently received much attention for their enhanced thermal stability. They show great potential in the field of catalysis, as reactant gases can diffuse in and out of the porous shell while the core particle is protected from sintering, a process in which particles coalesce to form larger particles. Sintering is a large problem in industry and is the primary cause of irreversible deactivation. Despite the obvious advantages of high thermal stability, porous core-shell nanoparticles can be developed to have additional interactive properties from the combination of the core and shell together, rather than just the core particle alone. This dissertation focuses on developing new porous core-shell systems in which both the core and shell take part in catalysis. Two types of systems are explored; (1) yolk-shell nanostructures with reducible oxide shells formed using the Kirkendall effect and (2) ceramic-based porous oxide shells formed using sol-gel chemistry. Of the Kirkendall-based systems, Au FexOy and Cu CoO were synthesized and studied for catalytic applications. Additionally, ZnO was explored as a potential shelling material. Sol-gel work focused on optimizing synthetic methods to allow for coating of small gold particles, which remains a challenge today. Mixed metal oxides were explored as a shelling material to make dual catalysts in which the product of a reaction on the core particle becomes a reactant within the shell.

Photocatalytic activity of Ag/ZnO core-shell nanoparticles with shell thickness as controlling parameter under green environment

NASA Astrophysics Data System (ADS)

Rajbongshi, Himanshu; Bhattacharjee, Suparna; Datta, Pranayee

2017-02-01

Plasmonic Ag/ZnO core-shell nanoparticles have been synthesized via a simple two-step wet chemical method for application in Photocatalysis. The morphology, size, crystal structure, composition and optical properties of the nanoparticles are investigated by x-ray diffraction, transmission electron microscopy (TEM), FTIR spectroscopy, ultraviolet-visible (UV-Vis) absorption spectroscopy and photoluminescence (PL) spectroscopy. The shell thicknesses are varied by varying the concentration of zinc nitrate hexa-hydrate and triethanolamine. The ZnO shell coating over Ag core enhances the charge separation, whereas the larger shell thickness and increased refractive index of surrounding medium cause red shifts of surface Plasmon resonance (SPR) peak of Ag core. The photoluminescence (PL) spectra of Ag/ZnO core-shell show that the larger shell thickness quenches the near band edge UV emission of ZnO. The electrochemical impedance spectra (EIS) i.e. Nyquist plots also confirm the higher charge transfer efficiency of the Ag/ZnO core-shell nanoparticles. The Photocatalytic activities of Ag/ZnO core-shell nanoparticles are investigated by the degradation of methylene blue (MB) dye under direct sunlight irradiation. Compared to pure ZnO nanoparticles (NPs), Ag/ZnO core-shell NPs display efficient sunlight plasmonic photocatalytic activity because of the influence of SPR of Ag core and the electron sink effect. The photocatalytic activity of Ag/ZnO core-shell NPs is found to be enhanced with increase in shell thickness.

Finite Element Modeling of the Buckling Response of Sandwich Panels

NASA Technical Reports Server (NTRS)

Rose, Cheryl A.; Moore, David F.; Knight, Norman F., Jr.; Rankin, Charles C.

2002-01-01

A comparative study of different modeling approaches for predicting sandwich panel buckling response is described. The study considers sandwich panels with anisotropic face sheets and a very thick core. Results from conventional analytical solutions for sandwich panel overall buckling and face-sheet-wrinkling type modes are compared with solutions obtained using different finite element modeling approaches. Finite element solutions are obtained using layered shell element models, with and without transverse shear flexibility, layered shell/solid element models, with shell elements for the face sheets and solid elements for the core, and sandwich models using a recently developed specialty sandwich element. Convergence characteristics of the shell/solid and sandwich element modeling approaches with respect to in-plane and through-the-thickness discretization, are demonstrated. Results of the study indicate that the specialty sandwich element provides an accurate and effective modeling approach for predicting both overall and localized sandwich panel buckling response. Furthermore, results indicate that anisotropy of the face sheets, along with the ratio of principle elastic moduli, affect the buckling response and these effects may not be represented accurately by analytical solutions. Modeling recommendations are also provided.

Highly aqueous soluble CaF2:Ce/Tb nanocrystals: effect of surface functionalization on structural, optical band gap, and photoluminescence properties.

PubMed

Ansari, Anees A; Parchur, Abdul K; Kumar, Brijesh; Rai, S B

2016-12-01

The design of nanostructured materials with highly stable water-dispersion and luminescence efficiency is an important concern in nanotechnology and nanomedicine. In this paper, we described the synthesis and distinct surface modification on the morphological structure and optical (optical absorption, band gap energy, excitation, emission, decay time, etc.) properties of highly crystalline water-dispersible CaF 2 :Ce/Tb nanocrystals (core-nanocrystals). The epitaxial growth of inert CaF 2 and silica shell, respectively, on their surface forming as CaF 2 :Ce/Tb@CaF 2 (core/shell) and CaF 2 :Ce/Tb@CaF 2 @SiO 2 (core/shell/SiO 2 ) nanoarchitecture. X-ray diffraction and transmission electron microscope image shows that the nanocrystals were in irregular spherical phase, highly crystalline (~20 nm) with narrow size distribution. The core/shell nanocrystals confirm that the surface coating is responsible in the change of symmetrical nanostructure, which was determined from the band gap energy and luminescent properties. It was found that an inert inorganic shell formation effectively enhances the luminescence efficiency and silica shell makes the nanocrystals highly water-dispersible. In addition, Ce 3+ /Tb 3+ -co-doped CaF 2 nanocrystals show efficient energy transfer from Ce 3+ to Tb 3+ ion and strong green luminescence of Tb 3+ ion at 541 nm( 5 D 4 → 7 F 5 ). Luminescence decay curves of core and core/shell nanocrystals were fitted using mono and biexponential equations, and R 2 regression coefficient criteria were used to discriminate the goodness of the fitted model. The lifetime values for the core/shell nanocrystals are higher than core-nanocrystals. Considering the high stable water-dispersion and intensive luminescence emission in the visible region, these luminescent core/shell nanocrystals could be potential candidates for luminescent bio-imaging, optical bio-probe, displays, staining, and multianalyte optical sensing. A newly designed CaF 2 :Ce/Tb nanoparticles via metal complex decomposition rout shows high dispersibility in aqueous solvents with enhanced photoluminescence. The epitaxial growth of inert CaF 2 shell and further amorphous silica, respectively, enhanced their optical and luminescence properties, which is highly usable for luminescent biolabeling, and optical bioprobe etc.

Fabrication of sub-micrometer-sized jingle bell-shaped hollow spheres from multilayered core-shell particles.

PubMed

Gu, Shunchao; Kondo, Tomohiro; Mine, Eiichi; Nagao, Daisuke; Kobayashi, Yoshio; Konno, Mikio

2004-11-01

Jingle bell-shaped hollow spheres were fabricated starting from multilayered particles composed of a silica core, a polystyrene inner shell, and a titania outer shell. Composite particles of silica core-polystyrene shell, synthesized by coating a 339-nm-sized silica core with a polystyrene shell of thickness 238 nm in emulsion polymerization, were used as core particles for a succeeding titania-coating. A sol-gel method was employed to form the titania outer shell with a thickness of 37 nm. The inner polystyrene shell in the multilayered particles was removed by immersing them in tetrahydrofuran. These successive procedures could produce jingle bell-shaped hollow spheres that contained a silica core in the titania shell.

Core-shell microspheres with porous nanostructured shells for liquid chromatography.

PubMed

Ahmed, Adham; Skinley, Kevin; Herodotou, Stephanie; Zhang, Haifei

2018-01-01

The development of new stationary phases has been the key aspect for fast and efficient high-performance liquid chromatography separation with relatively low backpressure. Core-shell particles, with a solid core and porous shell, have been extensively investigated and commercially manufactured in the last decade. The excellent performance of core-shell particles columns has been recorded for a wide range of analytes, covering small and large molecules, neutral and ionic (acidic and basic), biomolecules and metabolites. In this review, we first introduce the advance and advantages of core-shell particles (or more widely known as superficially porous particles) against non-porous particles and fully porous particles. This is followed by the detailed description of various methods used to fabricate core-shell particles. We then discuss the applications of common silica core-shell particles (mostly commercially manufactured), spheres-on-sphere particles and core-shell particles with a non-silica shell. This review concludes with a summary and perspective on the development of stationary phase materials for high-performance liquid chromatography applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of shell thickness on the exchange bias blocking temperature and coercivity in Co-CoO core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Thomas, S.; Reethu, K.; Thanveer, T.; Myint, M. T. Z.; Al-Harthi, S. H.

2017-08-01

The exchange bias blocking temperature distribution of naturally oxidized Co-CoO core-shell nanoparticles exhibits two distinct signatures. These are associated with the existence of two magnetic entities which are responsible for the temperature dependence of an exchange bias field. One is from the CoO grains which undergo thermally activated magnetization reversal. The other is from the disordered spins at the Co-CoO interface which exhibits spin-glass-like behavior. We investigated the oxide shell thickness dependence of the exchange bias effect. For particles with a 3 nm thick CoO shell, the predominant contribution to the temperature dependence of exchange bias is the interfacial spin-glass layer. On increasing the shell thickness to 4 nm, the contribution from the spin-glass layer decreases, while upholding the antiferromagnetic grain contribution. For samples with a 4 nm CoO shell, the exchange bias training was minimal. On the other hand, 3 nm samples exhibited both the training effect and a peak in coercivity at an intermediate set temperature Ta. This is explained using a magnetic core-shell model including disordered spins at the interface.

A model study of aggregates composed of spherical soot monomers with an acentric carbon shell

NASA Astrophysics Data System (ADS)

Luo, Jie; Zhang, Yongming; Zhang, Qixing

2018-01-01

Influences of morphology on the optical properties of soot particles have gained increasing attentions. However, studies on the effect of the way primary particles are coated on the optical properties is few. Aimed to understand how the primary particles are coated affect the optical properties of soot particles, the coated soot particle was simulated using the acentric core-shell monomers model (ACM), which was generated by randomly moving the cores of concentric core-shell monomers (CCM) model. Single scattering properties of the CCM model with identical fractal parameters were calculated 50 times at first to evaluate the optical diversities of different realizations of fractal aggregates with identical parameters. The results show that optical diversities of different realizations for fractal aggregates with identical parameters cannot be eliminated by averaging over ten random realizations. To preserve the fractal characteristics, 10 realizations of each model were generated based on the identical 10 parent fractal aggregates, and then the results were averaged over each 10 realizations, respectively. The single scattering properties of all models were calculated using the numerically exact multiple-sphere T-matrix (MSTM) method. It is found that the single scattering properties of randomly coated soot particles calculated using the ACM model are extremely close to those using CCM model and homogeneous aggregate (HA) model using Maxwell-Garnett effective medium theory. Our results are different from previous studies. The reason may be that the differences in previous studies were caused by fractal characteristics but not models. Our findings indicate that how the individual primary particles are coated has little effect on the single scattering properties of soot particles with acentric core-shell monomers. This work provides a suggestion for scattering model simplification and model selection.

Characterization of core–shell MOF particles by depth profiling experiments using on-line single particle mass spectrometry

DOE PAGES

Cahill, J. F.; Fei, H.; Cohen, S. M.; ...

2015-01-05

Materials with core-shell structures have distinct properties that lend themselves to a variety of potential applications. Characterization of small particle core-shell materials presents a unique analytical challenge. Herein, single particles of solid-state materials with core-shell structures were measured using on-line aerosol time-of-flight mass spectrometry (ATOFMS). Laser 'depth profiling' experiments verified the core-shell nature of two known core-shell particle configurations (< 2 mu m diameter) that possessed inverted, complimentary core-shell compositions (ZrO2@SiO2 versus SiO2@ZrO2). The average peak area ratios of Si and Zr ions were calculated to definitively show their core-shell composition. These ratio curves acted as a calibrant for anmore » uncharacterized sample - a metal-organic framework (MOF) material surround by silica (UiO-66(Zr)@SiO2; UiO = University of Oslo). ATOFMS depth profiling was used to show that these particles did indeed exhibit a core-shell architecture. The results presented here show that ATOFMS can provide unique insights into core-shell solid-state materials with particle diameters between 0.2-3 mu m.« less

Photoresponse and Field Effect Transport Studies in InAsP-InP Core-Shell Nanowires

NASA Astrophysics Data System (ADS)

Lee, Rochelle; Jo, Min Hyeok; Kim, TaeWan; Kim, Hyo Jin; Kim, Doo Gun; Shin, Jae Cheol

2018-05-01

A ternary InAsyP1-y alloy is suitable for an application to near-infrared (NIR) optical devices as their direct bandgap energy covers the entire NIR band. A nanowire (NW) system allows an epitaxial integration of InAsyP1-y alloy on any type of substrate since the lattice mismatch strain can be relieved through the NW sidewall. Nevertheless, the very large surface to volume ratio feature of the NWs leads to enormous surface states which are susceptible to surface recombination of free carriers. Here, ternary InAs0.75P0.25 NWs are grown with InP passivation layer (i.e., core-shell structure) to minimize the influence of the surface states, thus increasing their optical and electrical properties. A photoresponse study was achieved through the modeled band structure of the grown NWs. The model and experimental results suggest that 5-nm-thick InP shell efficiently passivates the surface states of the InAs0.75P0.25 NWs. The fabricated core-shell photodetectors and field-effect transistors exhibit improved photoresponse and transport properties compared to its counterpart core-only structure.

Photoresponse and Field Effect Transport Studies in InAsP-InP Core-Shell Nanowires

NASA Astrophysics Data System (ADS)

Lee, Rochelle; Jo, Min Hyeok; Kim, TaeWan; Kim, Hyo Jin; Kim, Doo Gun; Shin, Jae Cheol

2018-03-01

A ternary InAsyP1-y alloy is suitable for an application to near-infrared (NIR) optical devices as their direct bandgap energy covers the entire NIR band. A nanowire (NW) system allows an epitaxial integration of InAsyP1-y alloy on any type of substrate since the lattice mismatch strain can be relieved through the NW sidewall. Nevertheless, the very large surface to volume ratio feature of the NWs leads to enormous surface states which are susceptible to surface recombination of free carriers. Here, ternary InAs0.75P0.25 NWs are grown with InP passivation layer (i.e., core-shell structure) to minimize the influence of the surface states, thus increasing their optical and electrical properties. A photoresponse study was achieved through the modeled band structure of the grown NWs. The model and experimental results suggest that 5-nm-thick InP shell efficiently passivates the surface states of the InAs0.75P0.25 NWs. The fabricated core-shell photodetectors and field-effect transistors exhibit improved photoresponse and transport properties compared to its counterpart core-only structure.

Surfactant mediated hydrothermal synthesis, characterization and luminescent properties of GdPO{sub 4}: Ce{sup 3+}/Tb{sup 3+} @ GdPO{sub 4} core shell nanorods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khajuria, Heena; Ladol, Jigmet; Khajuria, Sonika

Highlights: • Core shell nanorods were synthesised by surfactant assisted hydrothermal method. • Morphology of core shell nanorods resembles those of core nanorods indicating coating of shell on cores. • More uniform and non-aggregated core shell nanorods were prepared in presence of surfactants. • Surfactant assisted prepared core shell nanorods show intense emission as compared to uncoated core nanorods. - Abstract: Core shell GdPO{sub 4}: Ce{sup 3+}/Tb{sup 3+} @ GdPO{sub 4} nanorods were synthesized via hydrothermal route in the presence of different surfactants [cetyltrimethyl ammonium bromide (CTAB) and Sodium dodecyl sulphate (SDS)]. The nanorods were characterized by powder X-ray diffractionmore » (PXRD), fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and photoluminescence (PL) studies. The X-ray diffraction results indicate good crystallinity and effective doping in core and core shell nanorods. SEM and TEM micrographs show that all of the as prepared gadolinium phosphate products have rod like shape. The compositional analysis of GdPO{sub 4}: Ce{sup 3+}/Tb{sup 3+} core was done by EDS. The emission intensity of the GdPO{sub 4}: Ce{sup 3+}/Tb{sup 3+} @ GdPO{sub 4} core shell increased significantly with respect to those of GdPO{sub 4}: Ce{sup 3+}/Tb{sup 3+} core nanorods. The effect of surfactant on the uniformity, thickness and luminescence of the core shell nanorods was investigated.« less

THE LAST MINUTES OF OXYGEN SHELL BURNING IN A MASSIVE STAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Müller, Bernhard; Viallet, Maxime; Janka, Hans-Thomas

We present the first  4 π– three-dimensional (3D) simulation of the last minutes of oxygen shell burning in an 18 M {sub ⊙} supernova progenitor up to the onset of core collapse. A moving inner boundary is used to accurately model the contraction of the silicon and iron core according to a one-dimensional stellar evolution model with a self-consistent treatment of core deleptonization and nuclear quasi-equilibrium. The simulation covers the full solid angle to allow the emergence of large-scale convective modes. Due to core contraction and the concomitant acceleration of nuclear burning, the convective Mach number increases to ∼0.1 at collapse,more » and an ℓ  = 2 mode emerges shortly before the end of the simulation. Aside from a growth of the oxygen shell from 0.51 M {sub ⊙} to 0.56 M {sub ⊙} due to entrainment from the carbon shell, the convective flow is reasonably well described by mixing-length theory, and the dominant scales are compatible with estimates from linear stability analysis. We deduce that artificial changes in the physics, such as accelerated core contraction, can have precarious consequences for the state of convection at collapse. We argue that scaling laws for the convective velocities and eddy sizes furnish good estimates for the state of shell convection at collapse and develop a simple analytic theory for the impact of convective seed perturbations on shock revival in the ensuing supernova. We predict a reduction of the critical luminosity for explosion by 12% – 24% due to seed asphericities for our 3D progenitor model relative to the case without large seed perturbations.« less

Liquid-phase pulsed laser ablation synthesis of graphitized carbon-encapsulated palladium core-shell nanospheres for catalytic reduction of nitrobenzene to aniline

NASA Astrophysics Data System (ADS)

Kim, Yu-jin; Ma, Rory; Reddy, D. Amaranatha; Kim, Tae Kyu

2015-12-01

Graphitized carbon-encapsulated palladium (Pd) core-shell nanospheres were produced via pulsed laser ablation of a solid Pd foil target submerged in acetonitrile. The microstructural features and optical properties of these nanospheres were characterized via high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-visible spectroscopy. Microstructural analysis indicated that the core-shell nanostructures consisted of single-crystalline cubic metallic Pd spheres that serve as the core material, over which graphitized carbon was anchored as a heterogeneous shell. The absorbance spectrum of the synthesized nanostructures exhibited a broad (absorption) band at ∼264 nm; this band corresponded to the typical inter-band transition of a metallic system and resulted possibly from the absorbance of the ionic Pd2+. The catalytic properties of the Pd and Pd@C core-shell nanostructures were investigated using the reduction of nitrobenzene to aniline by an excess amount of NaBH4 in an aqueous solution at room temperature, as a model reaction. Owing to the graphitized carbon-layered structure and the high specific surface area, the resulting Pd@C nanostructures exhibited higher conversion efficiencies than their bare Pd counterparts. In fact, the layered structure provided access to the surface of the Pd nanostructures for the hydrogenation reaction, owing to the synergistic effect between graphitized carbon and the nanostructures. Their unique structure and excellent catalytic performance render Pd@C core-shell nanostructures highly promising candidates for catalysis applications.

Multiple Interfacial Fe3O4@BaTiO3/P(VDF-HFP) Core-Shell-Matrix Films with Internal Barrier Layer Capacitor (IBLC) Effects and High Energy Storage Density.

PubMed

Zhou, Ling; Fu, Qiuyun; Xue, Fei; Tang, Xiahui; Zhou, Dongxiang; Tian, Yahui; Wang, Geng; Wang, Chaohong; Gou, Haibo; Xu, Lei

2017-11-22

Flexible nanocomposites composed of high dielectric constant fillers and polymer matrix have shown great potential for electrostatic capacitors and energy storage applications. To obtain the composited material with high dielectric constant and high breakdown strength, multi-interfacial composited particles, which composed of conductive cores and insulating shells and possessed the internal barrier layer capacitor (IBLC) effect, were adopted as fillers. Thus, Fe 3 O 4 @BaTiO 3 core-shell particles were prepared and loaded into the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) polymer matrix. As the mass fraction of core-shell fillers increased from 2.5 wt % to 30 wt %, the dielectric constant of the films increased, while the loss tangent remained at a low level (<0.05 at 1 kHz). Both high electric displacement and high electric breakdown strength were achieved in the films with 10 wt % core-shell fillers loaded. The maximum energy storage density of 7.018 J/cm 3 was measured at 2350 kV/cm, which shows significant enhancement than those of the pure P(VDF-HFP) films and analogous composited films with converse insulating-conductive core-shell fillers. A Maxwell-Wagner capacitor model was also adopted to interpret the efficiency of IBLC effects on the suppressed loss tangent and the superior breakdown strength. This work explored an effective approach to prepare dielectric nanocomposites for energy storage applications experimentally and theoretically.

Alloy and heterostructure architectures as promising tools for controlling electronic properties of semiconductor quantum dots

NASA Astrophysics Data System (ADS)

Vaxenburg, Roman; Lifshitz, Efrat

2012-02-01

Tunability of energy levels and wavefunctions of carriers in colloidal quantum dots (CQDs) has a marked effect on numerous physical aspects, such as Coulomb interactions and charge separation, which in turn has a direct impact on the functioning of CQD-based opto-electronic devices. The electronic properties of CQDs are conventionally controlled by variation of their size. Here we demonstrate a theoretical approach to engineer the electronic properties of IV-VI CQDs by introducing an alloy composition in core and core/shell heterostructures, having the general chemical formula PbSexS1-x/PbSeyS1-y (0 ≤ x ≤ 1, 0 ≤ y ≤ 1), while maintaining a constant size. The theoretical model considered an effective mass anisotropy and smooth potential step at the core/shell interface. The model revealed the influence induced by variation of chemical composition and core-to-shell division on the band-gap energy, remote states’ density, internal charge separation, electron-hole Coulomb interaction, and optical transition oscillator strength.

A solar-thermal energy harvesting scheme: enhanced heat capacity of molten HITEC salt mixed with Sn/SiOx core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Lai, Chih-Chung; Chang, Wen-Chih; Hu, Wen-Liang; Wang, Zhiming M.; Lu, Ming-Chang; Chueh, Yu-Lun

2014-04-01

We demonstrated enhanced solar-thermal storage by releasing the latent heat of Sn/SiOx core-shell nanoparticles (NPs) embedded in a eutectic salt. The microstructures and chemical compositions of Sn/SiOx core-shell NPs were characterized. In situ heating XRD provides dynamic crystalline information about the Sn/SiOx core-shell NPs during cyclic heating processes. The latent heat of ~29 J g-1 for Sn/SiOx core-shell NPs was measured, and 30% enhanced heat capacity was achieved from 1.57 to 2.03 J g-1 K-1 for the HITEC solar salt without and with, respectively, a mixture of 5% Sn/SiOx core-shell NPs. In addition, an endurance cycle test was performed to prove a stable operation in practical applications. The approach provides a method to enhance energy storage in solar-thermal power plants.We demonstrated enhanced solar-thermal storage by releasing the latent heat of Sn/SiOx core-shell nanoparticles (NPs) embedded in a eutectic salt. The microstructures and chemical compositions of Sn/SiOx core-shell NPs were characterized. In situ heating XRD provides dynamic crystalline information about the Sn/SiOx core-shell NPs during cyclic heating processes. The latent heat of ~29 J g-1 for Sn/SiOx core-shell NPs was measured, and 30% enhanced heat capacity was achieved from 1.57 to 2.03 J g-1 K-1 for the HITEC solar salt without and with, respectively, a mixture of 5% Sn/SiOx core-shell NPs. In addition, an endurance cycle test was performed to prove a stable operation in practical applications. The approach provides a method to enhance energy storage in solar-thermal power plants. Electronic supplementary information (ESI) available: Detailed experimental results are included for the following: SEM images of the HITEC molten salt with and without a mixture of Sn/SiOx core-shell NPs; statistical diameter distribution of pure Sn and Sn/SiOx core-shell NPs; the HAADF image and EDS linescan profile of a Sn/SiOx core-shell NP; XRD analysis for Sn NPs annealing at different heating temperatures; the XRD spectra of Sn/SiOx core-shell NPs before and after RTA for the shell protection test. See DOI: 10.1039/c3nr06810b

Biomimetic synthesis of chiral erbium-doped silver/peptide/silica core-shell nanoparticles (ESPN)

NASA Astrophysics Data System (ADS)

Mantion, Alexandre; Graf, Philipp; Florea, Ileana; Haase, Andrea; Thünemann, Andreas F.; Mašić, Admir; Ersen, Ovidiu; Rabu, Pierre; Meier, Wolfgang; Luch, Andreas; Taubert, Andreas

2011-12-01

Peptide-modified silver nanoparticles have been coated with an erbium-doped silica layer using a method inspired by silica biomineralization. Electron microscopy and small-angle X-ray scattering confirm the presence of an Ag/peptide core and silica shell. The erbium is present as small Er2O3 particles in and on the silica shell. Raman, IR, UV-Vis, and circular dichroism spectroscopies show that the peptide is still present after shell formation and the nanoparticles conserve a chiral plasmon resonance. Magnetic measurements find a paramagnetic behavior. In vitro tests using a macrophage cell line model show that the resulting multicomponent nanoparticles have a low toxicity for macrophages, even on partial dissolution of the silica shell.Peptide-modified silver nanoparticles have been coated with an erbium-doped silica layer using a method inspired by silica biomineralization. Electron microscopy and small-angle X-ray scattering confirm the presence of an Ag/peptide core and silica shell. The erbium is present as small Er2O3 particles in and on the silica shell. Raman, IR, UV-Vis, and circular dichroism spectroscopies show that the peptide is still present after shell formation and the nanoparticles conserve a chiral plasmon resonance. Magnetic measurements find a paramagnetic behavior. In vitro tests using a macrophage cell line model show that the resulting multicomponent nanoparticles have a low toxicity for macrophages, even on partial dissolution of the silica shell. Electronic supplementary information (ESI) available: Figures S1 to S12, Tables S1 and S2. See DOI: 10.1039/c1nr10930h

Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells

DOE PAGES

Zhang, Xiaoming; Liu, Ping; Yu, Shansheng; ...

2015-05-21

We employed density functional theory (DFT) to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt 1ML) supported on an M surface, Pt 1ML/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt 1ML shell depending on the conditions. In vacuum conditions, the Pt 1ML shell can be stabilized on the mostmore » of M cores except Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the Pt ML shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt 1ML/M 1ML/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt 1ML shell were also discussed.« less

Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xiaoming; Yu, Shansheng; Zheng, Weitao, E-mail: wtzheng@jlu.edu.cn, E-mail: pingliu3@bnl.gov

2015-05-21

We employed density functional theory to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt{sub 1ML}) supported on an M surface, Pt{sub 1ML}/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt{sub 1ML} shell depending on the conditions. In vacuum conditions, the Pt{sub 1ML} shell can be stabilized on the most ofmore » M cores except Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the Pt{sub ML} shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt{sub 1ML}/M{sub 1ML}/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt{sub 1ML} shell were also discussed.« less

Recombination energy for negatively charged excitons inside type-II core/shell spherical quantum dots

NASA Astrophysics Data System (ADS)

Chafai, A.; Essaoudi, I.; Ainane, A.; Dujardin, F.; Ahuja, R.

2018-07-01

The recombination energy of isolated neutral exciton and that of isolated negatively charged exciton inside a type-II core/shell spherical quantum dot are studied. Our investigation considers the charge-carriers effective mass discontinuity at the surface contact between the core and shell materials. Although our model omits the effect of the surface polarization, the dielectric-constant mismatch at the nanodot boundaries was taken into account. In order to achieve the exciton and negative trion energies, we proceed by a variational calculation in the framework of the envelope approximation. Our results reveal a strong correlation between the nanodot morphology and the energy spectrum of the neutral and negatively charged exciton.

A Study on Dielectric Properties of Cadmium Sulfide-Zinc Sulfide Core-Shell Nanocomposites for Application as Nanoelectronic Filter Component in the Microwave Domain

NASA Astrophysics Data System (ADS)

Devi, Jutika; Datta, Pranayee

2018-07-01

Complex permittivities of cadmium sulfide (CdS), zinc sulfide (ZnS), and of cadmium sulfide-zinc sulfide (CdS/ZnS) core-shell nanoparticles embedded in a polyvinyl alcohol matrix (PVA) were measured in liquid phase using a VectorNetwork Analyzer in the frequency range of 500 MHz-10 GHz. These nanocomposites are modeled as an embedded capacitor, and their electric field distribution and polarization have been studied using COMSOL Multiphysics software. By varying the thickness of the shell and the number of inclusions, the capacitance values were estimated. It was observed that CdS, ZnS and CdS/ZnS core-shell nanoparticles embedded in a polyvinyl alcohol matrix show capacitive behavior. There is a strong influence of the dielectric properties in the capacitive behavior of the embedded nanocapacitor. The capping matrix, position and filling factors of nanoinclusions all affect the capacitive behavior of the tested nanocomposites. Application of the CdS, ZnS and CdS/ZnS core-shell nanocomposite as the passive low-pass filter circuit has also been investigated. From the present study, it has been found that CdS/ZnS core-shell nanoparticles embedded in PVA matrix are potential structures for application as nanoelectronic filter components in different areas of communication.

A Study on Dielectric Properties of Cadmium Sulfide-Zinc Sulfide Core-Shell Nanocomposites for Application as Nanoelectronic Filter Component in the Microwave Domain

NASA Astrophysics Data System (ADS)

Devi, Jutika; Datta, Pranayee

2018-03-01

Complex permittivities of cadmium sulfide (CdS), zinc sulfide (ZnS), and of cadmium sulfide-zinc sulfide (CdS/ZnS) core-shell nanoparticles embedded in a polyvinyl alcohol matrix (PVA) were measured in liquid phase using a VectorNetwork Analyzer in the frequency range of 500 MHz-10 GHz. These nanocomposites are modeled as an embedded capacitor, and their electric field distribution and polarization have been studied using COMSOL Multiphysics software. By varying the thickness of the shell and the number of inclusions, the capacitance values were estimated. It was observed that CdS, ZnS and CdS/ZnS core-shell nanoparticles embedded in a polyvinyl alcohol matrix show capacitive behavior. There is a strong influence of the dielectric properties in the capacitive behavior of the embedded nanocapacitor. The capping matrix, position and filling factors of nanoinclusions all affect the capacitive behavior of the tested nanocomposites. Application of the CdS, ZnS and CdS/ZnS core-shell nanocomposite as the passive low-pass filter circuit has also been investigated. From the present study, it has been found that CdS/ZnS core-shell nanoparticles embedded in PVA matrix are potential structures for application as nanoelectronic filter components in different areas of communication.

Press-coated tablets for time-programmed release of drugs.

PubMed

Conte, U; Maggi, L; Torre, M L; Giunchedi, P; La Manna, A

1993-10-01

A new dry-coated device for the release of drug after a programmable period of time is proposed. It is intended to be used mainly in the therapy of those diseases which depend on circadian rhythms. Some core formulations, characterized by different release rates and mechanisms (containing diltiazem hydrochloride or sodium diclofenac as model drugs), were coated by compression with different polymeric barrier layers (press-coated systems). The shell formulations tested contained either gellable or erodible polymers. The dissolution profiles of uncoated cores and press-coated devices were compared. The gellable and/or erodible characteristics (properties) of the barrier formulations were also examined by means of a penetrometer. The coatings prevent drug release from the core until the polymeric shell is completely eroded or swollen. This delay in release start is not influenced by the core composition and depends only on the shell formulation. Except for the time-lag, the release kinetics of the drug contained in the core are not significantly influenced by the presence of the erodible barrier, but can be widely modulated using a swellable polymeric shell.

Bi-metallic nanoparticles as cathode electrocatalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Jun; Amine, Khalil; Wang, Xiaoping

A lithium-air battery cathode catalyst includes core-shell nanoparticles on a carbon support, wherein: a core of the core-shell nanoparticles is platinum metal; and a shell of the core-shell nanoparticles is copper metal; wherein: the core-shell nanoparticles have a weight ratio of the copper metal to the platinum metal from about 4% to about 6% copper to from about 2% to about 12% platinum, with a remaining percentage being the carbon support.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hansen, Stephanie B.; Harding, Eric C.; Knapp, Patrick F.

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. In this work, we show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated bymore » the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Lastly, analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 10 24 e/cm 3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.« less

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

NASA Astrophysics Data System (ADS)

Hansen, S. B.; Harding, E. C.; Knapp, P. F.; Gomez, M. R.; Nagayama, T.; Bailey, J. E.

2018-05-01

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. We show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated by the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 1024 e/cm3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.

Synthesis and cytotoxicity study of magnesium ferrite-gold core-shell nanoparticles.

PubMed

Nonkumwong, Jeeranan; Pakawanit, Phakkhananan; Wipatanawin, Angkana; Jantaratana, Pongsakorn; Ananta, Supon; Srisombat, Laongnuan

2016-04-01

In this work, the core-magnesium ferrite (MgFe2O4) nanoparticles were prepared by hydrothermal technique. Completed gold (Au) shell coating on the surfaces of MgFe2O4 nanoparticles was obtained by varying core/shell ratios via a reduction method. Phase identification, morphological evolution, optical properties, magnetic properties and cytotoxicity to mammalian cells of these MgFe2O4 core coated with Au nanoparticles were examined by using a combination of X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy, UV-visible spectroscopy (UV-vis), vibrating sample magnetometry and resazurin microplate assay techniques. In general, TEM images revealed different sizes of the core-shell nanoparticles generated from various core/shell ratios and confirmed the completed Au shell coating on MgFe2O4 core nanoparticles via suitable core/shell ratio with particle size less than 100 nm. The core-shell nanoparticle size and the quality of coating influence the optical properties of the products. The UV-vis spectra of complete coated MgFe2O4-Au core-shell nanoparticles exhibit the absorption bands in the near-Infrared (NIR) region indicating high potential for therapeutic applications. Based on the magnetic property measurement, it was found that the obtained MgFe2O4-Au core-shell nanoparticles still exhibit superparamagnetism with lower saturation magnetization value, compared with MgFe2O4 core. Both of MgFe2O4 and MgFe2O4-Au core-shell also showed in vitro non-cytotoxicity to mouse areola fibroblast (L-929) cell line. Copyright © 2015 Elsevier B.V. All rights reserved.

The microstructure and magnetic properties of Cu/CuO/Ni core/multi-shell nanowire arrays

NASA Astrophysics Data System (ADS)

Yang, Feng; Shi, Jie; Zhang, Xiaofeng; Hao, Shijie; Liu, Yinong; Feng, Chun; Cui, Lishan

2018-04-01

Multifunctional metal/oxide/metal core/multi-shell nanowire arrays were prepared mostly by physical or chemical vapor deposition. In our study, the Cu/CuO/Ni core/multi-shell nanowire arrays were prepared by AAO template-electrodeposition and oxidation processes. The Cu/Ni core/shell nanowire arrays were prepared by AAO template-electrodeposition method. The microstructure and chemical compositions of the core/multi-shell nanowires and core/shell nanowires have been characterized using transmission electron microscopy with HADDF-STEM and X-ray diffraction. Magnetization measurements revealed that the Cu/CuO/Ni and Cu/Ni nanowire arrays have high coercivity and remanence ratio.

Long term stability of nanowire nanoelectronics in physiological environments.

PubMed

Zhou, Wei; Dai, Xiaochuan; Fu, Tian-Ming; Xie, Chong; Liu, Jia; Lieber, Charles M

2014-03-12

Nanowire nanoelectronic devices have been exploited as highly sensitive subcellular resolution detectors for recording extracellular and intracellular signals from cells, as well as from natural and engineered/cyborg tissues, and in this capacity open many opportunities for fundamental biological research and biomedical applications. Here we demonstrate the capability to take full advantage of the attractive capabilities of nanowire nanoelectronic devices for long term physiological studies by passivating the nanowire elements with ultrathin metal oxide shells. Studies of Si and Si/aluminum oxide (Al2O3) core/shell nanowires in physiological solutions at 37 °C demonstrate long-term stability extending for at least 100 days in samples coated with 10 nm thick Al2O3 shells. In addition, investigations of nanowires configured as field-effect transistors (FETs) demonstrate that the Si/Al2O3 core/shell nanowire FETs exhibit good device performance for at least 4 months in physiological model solutions at 37 °C. The generality of this approach was also tested with in studies of Ge/Si and InAs nanowires, where Ge/Si/Al2O3 and InAs/Al2O3 core/shell materials exhibited stability for at least 100 days in physiological model solutions at 37 °C. In addition, investigations of hafnium oxide-Al2O3 nanolaminated shells indicate the potential to extend nanowire stability well beyond 1 year time scale in vivo. These studies demonstrate that straightforward core/shell nanowire nanoelectronic devices can exhibit the long term stability needed for a range of chronic in vivo studies in animals as well as powerful biomedical implants that could improve monitoring and treatment of disease.

Long Term Stability of Nanowire Nanoelectronics in Physiological Environments

PubMed Central

2015-01-01

Nanowire nanoelectronic devices have been exploited as highly sensitive subcellular resolution detectors for recording extracellular and intracellular signals from cells, as well as from natural and engineered/cyborg tissues, and in this capacity open many opportunities for fundamental biological research and biomedical applications. Here we demonstrate the capability to take full advantage of the attractive capabilities of nanowire nanoelectronic devices for long term physiological studies by passivating the nanowire elements with ultrathin metal oxide shells. Studies of Si and Si/aluminum oxide (Al2O3) core/shell nanowires in physiological solutions at 37 °C demonstrate long-term stability extending for at least 100 days in samples coated with 10 nm thick Al2O3 shells. In addition, investigations of nanowires configured as field-effect transistors (FETs) demonstrate that the Si/Al2O3 core/shell nanowire FETs exhibit good device performance for at least 4 months in physiological model solutions at 37 °C. The generality of this approach was also tested with in studies of Ge/Si and InAs nanowires, where Ge/Si/Al2O3 and InAs/Al2O3 core/shell materials exhibited stability for at least 100 days in physiological model solutions at 37 °C. In addition, investigations of hafnium oxide-Al2O3 nanolaminated shells indicate the potential to extend nanowire stability well beyond 1 year time scale in vivo. These studies demonstrate that straightforward core/shell nanowire nanoelectronic devices can exhibit the long term stability needed for a range of chronic in vivo studies in animals as well as powerful biomedical implants that could improve monitoring and treatment of disease. PMID:24479700

Strain-induced structural defects and their effects on the electrochemical performances of silicon core/germanium shell nanowire heterostructures

DOE PAGES

Lin, Yung-Chen; Kim, Dongheun; Li, Zhen; ...

2016-12-14

Here we report on strain-induced structural defect formation in core Si nanowire of Si/Ge core/shell nanowire heterostructure and influences of the structural defects on the electrochemical performances in lithium-ion battery anodes based on Si/Ge core/shell nanowire heterostructures. The induced structural defects consisting of stacking faults and dislocations in the core Si nanowire were observed for the first time. The generation of stacking faults in Si/Ge core/shell nanowire heterostructure is observed to prefer settling in either only Ge shell region or in both Ge shell and Si core regions and is associated with the increase of the shell volume fraction. Themore » relax of misfit strain in [112] oriented core/shell nanowire heterostructure leads to subsequent gliding of Shockley partial dislocations, preferentially forming the twins. The observation of cross-over defect formation is of great importance for the understanding of heteroepitaxy in radial heterostructures at nanoscale and building the three dimensional heterostructures for the various applications. In addition, the effect of the defect formation on nanomaterial’s functionality is investigated by electrochemical performance test. The Si/Ge core/shell nanowire heterostructures enhance the gravimetric capacity of lithium ion battery anodes under fast charging/discharging rates compared to Si nanowires. However, the induced structural defects hamper lithiation of the Si/Ge core/shell nanowire heterostructure.« less

Strain-induced structural defects and their effects on the electrochemical performances of silicon core/germanium shell nanowire heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Yung-Chen; Kim, Dongheun; Li, Zhen

Here we report on strain-induced structural defect formation in core Si nanowire of Si/Ge core/shell nanowire heterostructure and influences of the structural defects on the electrochemical performances in lithium-ion battery anodes based on Si/Ge core/shell nanowire heterostructures. The induced structural defects consisting of stacking faults and dislocations in the core Si nanowire were observed for the first time. The generation of stacking faults in Si/Ge core/shell nanowire heterostructure is observed to prefer settling in either only Ge shell region or in both Ge shell and Si core regions and is associated with the increase of the shell volume fraction. Themore » relax of misfit strain in [112] oriented core/shell nanowire heterostructure leads to subsequent gliding of Shockley partial dislocations, preferentially forming the twins. The observation of cross-over defect formation is of great importance for the understanding of heteroepitaxy in radial heterostructures at nanoscale and building the three dimensional heterostructures for the various applications. In addition, the effect of the defect formation on nanomaterial’s functionality is investigated by electrochemical performance test. The Si/Ge core/shell nanowire heterostructures enhance the gravimetric capacity of lithium ion battery anodes under fast charging/discharging rates compared to Si nanowires. However, the induced structural defects hamper lithiation of the Si/Ge core/shell nanowire heterostructure.« less

Modeling of rapid shutdown in the DIII-D tokamak by core deposition of high-Z material

DOE PAGES

Izzo, Valerie A.; Parks, Paul B.

2017-06-22

MHD modeling of shell-pellet injection for disruption mitigation is carried out under the assumption of idealized delivery of the radiating payload to the core, neglecting the physics of shell ablation. The shell pellet method is designed to produce an inside-out thermal quench in which core thermal heat is radiated while outer flux surfaces remain intact, protecting the divertor from large conducted heat loads. In the simulation, good outer surfaces remain until the thermal quench is nearly complete, and a high radiated energy fraction is achieved. As a result, when the outermost surfaces are destroyed, runaway electron test orbits indicate thatmore » the rate of runaway electron loss is very fast compared with prior massive gas injection simulations, which is attributed to the very different current profile evolution that occurs with central cooling.« less

ZnSe based semiconductor core-shell structures: From preparation to application

NASA Astrophysics Data System (ADS)

Sun, Chengcheng; Gu, Yarong; Wen, Weijia; Zhao, Lijuan

2018-07-01

Inorganic core-shell semiconductor materials have attracted increasing interest in recent years because of the unique structure, stable chemical properties and high performance in devices. With special properties such as a direct band-gap and excellent photoelectrical characteristics, ZnSe based semiconductor core-shell structures are promising materials for applications in such fields as photocatalysts, light-emitting diodes, solar cells, photodetectors, biomedical science and so on. However, few reviews on ZnSe based semiconductor core-shell structures have been reported so far. Therefore this manuscript mainly focuses on the research activities on ZnSe based semiconductor core-shell composites including various preparation methods and the applications of these core-shell structures, especially in photocatalysts, light emitting, solar cells and photodetectors. The possibilities and limitations of studies on ZnSe based semiconductor core-shell composites are also highlighted.

Facile synthesis of mercaptosuccinic acid-capped CdTe/CdS/ZnS core/double shell quantum dots with improved cell viability on different cancer cells and normal cells

NASA Astrophysics Data System (ADS)

Parani, Sundararajan; Bupesh, Giridharan; Manikandan, Elayaperumal; Pandian, Kannaiyan; Oluwafemi, Oluwatobi Samuel

2016-11-01

Water-soluble, mercaptosuccinic acid (MSA)-capped CdTe/CdS/ZnS core/double shell quantum dots (QDs) were prepared by successive growth of CdS and ZnS shells on the as-synthesized CdTe/CdSthin core/shell quantum dots. The formation of core/double shell structured QDs was investigated by ultraviolet-visible (UV-Vis) absorption and photoluminescence (PL) spectroscopy, PL decay studies, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The core/double shell QDs exhibited good photoluminescence quantum yield (PLQY) which is 70% higher than that of the parent core/shell QDs, and they are stable for months. The average particle size of the core/double shell QDs was ˜3 nm as calculated from the transmission electron microscope (TEM) images. The cytotoxicity of the QDs was evaluated on a variety of cancer cells such as HeLa, MCF-7, A549, and normal Vero cells by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell viability assay. The results showed that core/double shell QDs were less toxic to the cells when compared to the parent core/shell QDs. MCF-7 cells showed proliferation on incubation with QDs, and this is attributed to the metalloestrogenic activity of cadmium ions released from QDs. The core/double shell CdTe/CdS/ZnS (CSS) QDs were conjugated with transferrin and successfully employed for the biolabeling and fluorescent imaging of HeLa cells. These core/double shell QDs are highly promising fluorescent probe for cancer cell labeling and imaging applications.

Synthesis and Plasmonic Understanding of Core/Satellite and Core Shell Nanostructures

NASA Astrophysics Data System (ADS)

Ruan, Qifeng

Localized surface plasmon resonance, which stems from the collective oscillations of conduction-band electrons, endows Au nanocrystals with unique optical properties. Au nanocrystals possess extremely large scattering/absorption cross-sections and enhanced local electromagnetic field, both of which are synthetically tunable. Moreover, when Au nanocrystals are closely placed or hybridized with semiconductors, the coupling and interaction between the individual components bring about more fascinating phenomena and promising applications, including plasmon-enhanced spectroscopies, solar energy harvesting, and cancer therapy. The continuous development in the field of plasmonics calls for further advancements in the preparation of high-quality plasmonic nanocrystals, the facile construction of hybrid plasmonic nanostructures with desired functionalities, as well as deeper understanding and efficient utilization of the interaction between plasmonic nanocrystals and semiconductor components. In this thesis, I developed a seed-mediated growth method for producing size-controlled Au nanospheres with high monodispersity and assembled Au nanospheres of different sizes into core/satellite nanostructures for enhancing Raman signals. For investigating the interactions between Au nanocrystals and semiconductors, I first prepared (Au core) (TiO2 shell) nanostructures, and then studied their synthetically controlled plasmonic properties and light-harvesting applications. Au nanocrystals with spherical shapes are desirable in plasmon-coupled systems owing to their high geometrical symmetry, which facilitates the analysis of electrodynamic responses in a classical electromagnetic framework and the investigation of quantum tunneling and nonlocal effects. I prepared remarkably uniform Au nanospheres with diameters ranging from 20 nm to 220 nm using a simple seed-mediated growth method associated with mild oxidation. Core/satellite nanostructures were assembled out of differently sized Au nanospheres with molecular linkers. The plasmon resonances of the core/satellite nanostructures undergo red shifts in comparison to those of the sole Au cores, which is consistent with Mie theory analysis. As predicted by finite-difference time-domain simulations, the assembled core/satellite nanostructures exhibit large enhancements for Raman scattering. The facile growth of Au nanospheres and assembly of core/satellite nanostructures blaze a new way to the design of nanoarchitectures with desired plasmonic properties and functions. Coating semiconductors onto Au nanocrystals to form core shell configurations can increase the interactions between the two materials, benefiting from their large active interfacial area. The shell can also protect the Au nanocrystal core from aggregation, reshaping, and chemical corrosion. In this thesis, (Au nanocrystal core) (titania shell) nanostructures with tunable shell thicknesses were prepared by a facile wetchemistry method. Au nanocrystals with strong and tunable plasmon resonances in the visible and near-infrared regions can enhance and broaden the light utilization of TiO2 through the scattering/absorption enhancement, sensitization, and hot-electron injection. The integration of Au nanocrystals therefore hold the prospect of breaking the light-harvesting limit of TiO2 arising from its wide band gap. The resultant (Au core) (TiO2 shell) nanostructures were examined to be capable of efficiently generating reactive oxygen species under near-infrared resonant excitation. On the other hand, the transverse plasmon modes of Au nanorods, which are often too weak to be observed on scattering spectra, are enhanced by the TiO2 shell through energy transfer. With the increment of the shell thickness, the intensity of the transverse plasmon mode increases significantly and even becomes comparable with the longitudinal plasmon mode. Interestingly, both the transverse and longitudinal modes of the (Au core) (TiO2 shell) nanostructures exhibit asymmetric Fano line shapes. The Fano resonances result from the coupling between the core and shell, as understood by the mechanical oscillator model. Besides varying the shell thickness, the plasmonic bands of the core shell nanostructures can also be tailored by employing Au nanorods with different aspect ratios. The synthetically tunable plasmonic properties and synergistic interactions between the gold core and the titania shell make the hybrid nanostructure a multifunctional nanomaterial and ideal system for studying the plasmonic hybrid nanostructures.

A general and high-yield galvanic displacement approach to Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells and enhanced electrocatalytic performances.

PubMed

Kuai, Long; Geng, Baoyou; Wang, Shaozhen; Sang, Yan

2012-07-23

In this work, we utilize the galvanic displacement synthesis and make it a general and efficient method for the preparation of Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells, which consist of multilayer nanoparticles. The method is generally applicable to the preparation of Au-Au, Au-Pd, and Au-Pt core-shell nanostructures with typical porous shells. Moreover, the Au-Au isomeric core-shell nanostructure is reported for the first time. The lower oxidation states of Au(I), Pd(II), and Pt(II) are supposed to contribute to the formation of porous core-shell nanostructures instead of yolk-shell nanostructures. The electrocatalytic ethanol oxidation and oxygen reduction reaction (ORR) performance of porous Au-Pd core-shell nanostructures are assessed as a typical example for the investigation of the advantages of the obtained core-shell nanostructures. As expected, the Au-Pd core-shell nanostructure indeed exhibits a significantly reduced overpotential (the peak potential is shifted in the positive direction by 44 mV and 32 mV), a much improved CO tolerance (I(f)/I(b) is 3.6 and 1.63 times higher), and an enhanced catalytic stability in comparison with Pd nanoparticles and Pt/C catalysts. Thus, porous Au-M (M = Au, Pd, and Pt) core-shell nanostructures may provide many opportunities in the fields of organic catalysis, direct alcohol fuel cells, surface-enhanced Raman scattering, and so forth. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tuning exchange bias in Fe/γ-Fe{sub 2}O{sub 3} core-shell nanoparticles: Impacts of interface and surface spins

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khurshid, Hafsa, E-mail: hkhurshi@usf.edu, E-mail: phanm@usf.edu, E-mail: sharihar@usf.edu; Phan, Manh-Huong, E-mail: hkhurshi@usf.edu, E-mail: phanm@usf.edu, E-mail: sharihar@usf.edu; Mukherjee, Pritish

A comparative study has been performed of the exchange bias (EB) effect in Fe/γ-Fe{sub 2}O{sub 3} core-shell nanoparticles with the same thickness of the γ-Fe{sub 2}O{sub 3} shell (∼2 nm) and the diameter of the Fe core varying from 4 nm to 11 nm. Transmission electron microscopy (TEM) and high-resolution TEM confirmed the high quality of the core-shell nanostructures. A systematic analysis of magnetization versus magnetic field measurements under zero-field-cooled and field-cooled regimes using the Meiklejohn-Bean model and deconvoluting superparamagnetic and paramagnetic contribution to the total magnetic moment Langevin function shows that there exists a critical particle size (∼10 nm), above which the spinsmore » at the interface between Fe and γ-Fe{sub 2}O{sub 3} contribute primarily to the EB, but below which the surface spin effect is dominant. Our finding yields deeper insight into the collective contributions of interface and surface spins to the EB in core-shell nanoparticle systems, knowledge of which is the key to manipulating EB in magnetic nanostructures for spintronics applications.« less

Synthesis of Multicolor Core/Shell NaLuF4:Yb3+/Ln3+@CaF2 Upconversion Nanocrystals

PubMed Central

Li, Hui; Hao, Shuwei; Yang, Chunhui; Chen, Guanying

2017-01-01

The ability to synthesize high-quality hierarchical core/shell nanocrystals from an efficient host lattice is important to realize efficacious photon upconversion for applications ranging from bioimaging to solar cells. Here, we describe a strategy to fabricate multicolor core @ shell α-NaLuF4:Yb3+/Ln3+@CaF2 (Ln = Er, Ho, Tm) upconversion nanocrystals (UCNCs) based on the newly established host lattice of sodium lutetium fluoride (NaLuF4). We exploited the liquid-solid-solution method to synthesize the NaLuF4 core of pure cubic phase and the thermal decomposition approach to expitaxially grow the calcium fluoride (CaF2) shell onto the core UCNCs, yielding cubic core/shell nanocrystals with a size of 15.6 ± 1.2 nm (the core ~9 ± 0.9 nm, the shell ~3.3 ± 0.3 nm). We showed that those core/shell UCNCs could emit activator-defined multicolor emissions up to about 772 times more efficient than the core nanocrystals due to effective suppression of surface-related quenching effects. Our results provide a new paradigm on heterogeneous core/shell structure for enhanced multicolor upconversion photoluminescence from colloidal nanocrystals. PMID:28336867

Inflation of a magma chamber surrounded by poroelastic mush shell

NASA Astrophysics Data System (ADS)

Liao, Y.; Soule, S. A.; Jones, M.

2017-12-01

Recent studies have highlighted the importance of crystal-rich mush in crustal magmatic system [Cashman et. al. 2017]. This potential paradigm shift from isolated melt bodies in elastic crust poses new challenges to our previous understanding of igneous processes. Existing models describing the physical processes in a conventional magma plumbing system may require modification to account for the properties of mush. In this study, we demonstrate that the abundance of very crystalline mush between magma lenses and the crustal rocks influences the mechanical coupling between pressurized magma lenses and their surroundings with regard to deformation and melt transport. We develop a conceptual model invoking a simplified geometry and presumed rheological properties of liquid magma, mush and country rock. In our preliminary study, a magma chamber is modeled as a spherical liquid core enveloped by a shell of poroelastic, magma-(and/or)-gas-bearing mush in an infinite domain of elastic country rock. We interrogate the effect of varying physical properties of the system (e.g., geometry) and mush material (e.g., elastic moduli) on the deformation in the liquid core, mush shell and host rock, as well as pressure built-up in the chamber, upon injection of magma into the liquid core. When we allow the pore spaces to be connected in the mush shell, melt can migrate within the permeable matrix, thereby promoting melt segregation or `leaking' from the core to the shell. These initial results highlight the importance of constraining the physical properties of crystal mush in order for us to properly evaluate the mechanics of magmatic system.

Synthesis of Ag@TiO2 core-shells using a rapid microwave irradiation and study of their nonlinear optical properties

NASA Astrophysics Data System (ADS)

Karimipour, M.; Ebrahimi, M.; Abafat, Z.; Molaei, M.

2016-07-01

Ag@TiO2 core-shells were synthesized by employing oleylamine as capping agent and using a rapid microwave method. The shell growth was optimized first based on the variation of oleylamine content in the reaction solution. Thereafter the shell thickness was varied just by varying titanium isopropoxide (TiTP) with 25, 50, 100 and 200 μl as TiO2 precursor. The prepared core-shells were characterized by means of XRD, FTIR spectroscopy, transmission electron microscopy, and UV-Vis spectroscopy. XRD analysis revealed a cubic crystal structure for Ag and Anatase phase for TiO2. TEM images clearly indicated that the size of Ag core is roughly 15 nm and with the increase of TiTP, the shell thickness increases and varies between 5 nm and 15 nm. UV-Vis spectroscopy indicated that the plasmon resonance of Ag nanoparticles shifts from 407 nm up to 454 nm with the increase of TiTP precursor. Using a low power laser diode at a 532 nm wavelength, the magnitude and the sign of the nonlinear refractive index were determined by the Z-scan technique and Sheik-Bahae model. The results show that the enhancement of nonlinear optical properties originates from the quality of TiO2 shell growth. The highest nonlinearity belongs to the sample synthesized with 100 μlit TiTP. Generally all the prepared Ag@TiO2 core-shells show both saturable and reverse saturable absorption. They exhibit also a considerable nonlinear absorption and nonlinear refractive index ranging from -4.21 × 10-7 to -3.51 × 10-6 which are comparable to the sole Ag and TiO2 nanoparticles.

Engineered magnetic core shell nanoprobes: Synthesis and applications to cancer imaging and therapeutics.

PubMed

Mandal, Samir; Chaudhuri, Keya

2016-02-26

Magnetic core shell nanoparticles are composed of a highly magnetic core material surrounded by a thin shell of desired drug, polymer or metal oxide. These magnetic core shell nanoparticles have a wide range of applications in biomedical research, more specifically in tissue imaging, drug delivery and therapeutics. The present review discusses the up-to-date knowledge on the various procedures for synthesis of magnetic core shell nanoparticles along with their applications in cancer imaging, drug delivery and hyperthermia or cancer therapeutics. Literature in this area shows that magnetic core shell nanoparticle-based imaging, drug targeting and therapy through hyperthermia can potentially be a powerful tool for the advanced diagnosis and treatment of various cancers.

Optical properties of core-shell and multi-shell nanorods

NASA Astrophysics Data System (ADS)

Mokkath, Junais Habeeb; Shehata, Nader

2018-05-01

We report a first-principles time dependent density functional theory study of the optical response modulations in bimetallic core-shell (Na@Al and Al@Na) and multi-shell (Al@Na@Al@Na and Na@Al@Na@Al: concentric shells of Al and Na alternate) nanorods. All of the core-shell and multi-shell configurations display highly enhanced absorption intensity with respect to the pure Al and Na nanorods, showing sensitivity to both composition and chemical ordering. Remarkably large spectral intensity enhancements were found in a couple of core-shell configurations, indicative that optical response averaging based on the individual components can not be considered as true as always in the case of bimetallic core-shell nanorods. We believe that our theoretical results would be useful in promising applications depending on Aluminum-based plasmonic materials such as solar cells and sensors.

Polar wander of an ice shell on Europa

NASA Technical Reports Server (NTRS)

Ojakangas, Gregory W.; Stevenson, David J.

1989-01-01

The present consideration of a hypothesized ice shell around Europa, which is decoupled from the silicate core by a liquid water layer and possesses a spatially varying thermal equilibrium thickness profile, proceeds through the development of equations for variations in the inertia tensor of a body when second-harmonic-degree topography is added to the crustal base. Attention is given to a realistic model in which the shell and ocean are assumed to undergo reorientations as a single entity independently of the core, but subject to viscous dissipation within the shell. Shell friction is in this case noted to preclude polar wander, unless a low conductivity regolith increases the near-surface temperature by a few tens of degrees C; the ice beneath the regolith would then behave viscously on the time-scale of polar wander.

High performance carbon nanotube-Si core-shell wires with a rationally structured core for lithium ion battery anodes.

PubMed

Fan, Yu; Zhang, Qing; Lu, Congxiang; Xiao, Qizhen; Wang, Xinghui; Tay, Beng Kang

2013-02-21

Core-shell Si nanowires are very promising anode materials. Here, we synthesize vertically aligned carbon nanotubes (CNTs) with relatively large diameters and large inter-wire spacing as core wires and demonstrate a CNT-Si core-shell wire composite as a lithium ion battery (LIB) anode. Owing to the rationally engineered core structure, the composite shows good capacity retention and rate performance. The excellent performance is superior to most core-shell nanowires previously reported.

Photonic bandgap of inverse opals prepared from core-shell spheres

PubMed Central

2012-01-01

In this study, we synthesized monodispersed polystyrene (PS)-silica core-shell spheres with various shell thicknesses for the fabrication of photonic crystals. The shell thickness of the spheres was controlled by various additions of tetraethyl orthosilicate during the shell growth process. The shrinkage ratio of the inverse opal photonic crystals prepared from the core-shell spheres was significantly reduced from 14.7% to within 3%. We suspected that the improvement resulted from the confinement of silica shell to the contraction of PS space during calcination. Due to the shell effect, the inverse opals prepared from the core-shell spheres have higher filling fraction and larger wavelength of stop band maximum. PMID:22894600

Core-Shell Structuring of Pure Metallic Aerogels towards Highly Efficient Platinum Utilization for the Oxygen Reduction Reaction.

PubMed

Cai, Bin; Hübner, René; Sasaki, Kotaro; Zhang, Yuanzhe; Su, Dong; Ziegler, Christoph; Vukmirovic, Miomir B; Rellinghaus, Bernd; Adzic, Radoslav R; Eychmüller, Alexander

2018-03-05

The development of core-shell structures remains a fundamental challenge for pure metallic aerogels. Here we report the synthesis of Pd x Au-Pt core-shell aerogels composed of an ultrathin Pt shell and a composition-tunable Pd x Au alloy core. The universality of this strategy ensures the extension of core compositions to Pd transition-metal alloys. The core-shell aerogels exhibited largely improved Pt utilization efficiencies for the oxygen reduction reaction and their activities show a volcano-type relationship as a function of the lattice parameter of the core substrate. The maximum mass and specific activities are 5.25 A mg Pt -1 and 2.53 mA cm -2 , which are 18.7 and 4.1 times higher than those of Pt/C, respectively, demonstrating the superiority of the core-shell metallic aerogels. The proposed core-based activity descriptor provides a new possible strategy for the design of future core-shell electrocatalysts. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Transition-Metal Nitride Core@Noble-Metal Shell Nanoparticles as Highly CO Tolerant Catalysts

DOE PAGES

Garg, Aaron; Milina, Maria; Ball, Madelyn; ...

2017-05-25

Core–shell architectures offer an effective way to tune and enhance the properties of noble-metal catalysts. Herein, we demonstrate the synthesis of Pt shell on titanium tungsten nitride core nanoparticles (Pt/TiWN) by high temperature ammonia nitridation of a parent core–shell carbide material (Pt/TiWC). X-ray photoelectron spectroscopy revealed significant core-level shifts for Pt shells supported on TiWN cores, corresponding to increased stabilization of the Pt valence d-states. The modulation of the electronic structure of the Pt shell by the nitride core translated into enhanced CO tolerance during hydrogen electrooxidation in the presence of CO. In conclusion, the ability to control shell coveragemore » and vary the heterometallic composition of the shell and nitride core opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.« less

Transition-Metal Nitride Core@Noble-Metal Shell Nanoparticles as Highly CO Tolerant Catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garg, Aaron; Milina, Maria; Ball, Madelyn

Core–shell architectures offer an effective way to tune and enhance the properties of noble-metal catalysts. Herein, we demonstrate the synthesis of Pt shell on titanium tungsten nitride core nanoparticles (Pt/TiWN) by high temperature ammonia nitridation of a parent core–shell carbide material (Pt/TiWC). X-ray photoelectron spectroscopy revealed significant core-level shifts for Pt shells supported on TiWN cores, corresponding to increased stabilization of the Pt valence d-states. The modulation of the electronic structure of the Pt shell by the nitride core translated into enhanced CO tolerance during hydrogen electrooxidation in the presence of CO. In conclusion, the ability to control shell coveragemore » and vary the heterometallic composition of the shell and nitride core opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.« less

Comprehensive analyses of core-shell InGaN/GaN single nanowire photodiodes

NASA Astrophysics Data System (ADS)

Zhang, H.; Guan, N.; Piazza, V.; Kapoor, A.; Bougerol, C.; Julien, F. H.; Babichev, A. V.; Cavassilas, N.; Bescond, M.; Michelini, F.; Foldyna, M.; Gautier, E.; Durand, C.; Eymery, J.; Tchernycheva, M.

2017-12-01

Single nitride nanowire core/shell n-p photodetectors are fabricated and analyzed. Nanowires consisting of an n-doped GaN stem, a radial InGaN/GaN multiple quantum well system and a p-doped GaN external shell were grown by catalyst-free metal-organic vapour phase epitaxy on sapphire substrates. Single nanowires were dispersed and the core and the shell regions were contacted with a metal and an ITO deposition, respectively, defined using electron beam lithography. The single wire photodiodes present a response in the visible to UV spectral range under zero external bias. The detector operation speed has been analyzed under different bias conditions. Under zero bias, the  -3 dB cut-off frequency is ~200 Hz for small light modulations. The current generation was modeled using non-equilibrium Green function formalism, which evidenced the importance of phonon scattering for carrier extraction from the quantum wells.

Interfacial effect on the structural and optical properties of pure SnO2 and dual shells (ZnO; SiO2) coated SnO2 core-shell nanospheres for optoelectronic applications

NASA Astrophysics Data System (ADS)

Selvi, N.; Sankar, S.; Dinakaran, K.

2014-12-01

Nanocrystallites of SnO2 core and dual shells (ZnO, SiO2) coated SnO2 core-shell nanospheres were successfully synthesized by co-precipitation method. The as prepared and annealed samples were characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), High resolution transmission electron microscopy (HRTEM) and UV-Vis analysis. XRD pattern confirms the obtained SnO2 core with tetragonal rutile crystalline structure and the shell ZnO with hexagonal structure. FTIR result shows the functional groups present in the samples. The spherical morphology and the formation of the core-shell structures have been confirmed by HRTEM measurements. The UV-Vis showed that band gap is red shifted for as-prepared and the shells coated core-shell samples. From this investigation it can be concluded that the surface modification with different metal and insulating oxides strongly influences the optical properties of the core-shell materials which enhance their potential applications towards optical devices fabrication.

Revealing the core-shell interactions of a giant strain relaxor ferroelectric 0.75Bi1/2Na1/2TiO3-0.25SrTiO3.

PubMed

Liu, Na; Acosta, Matias; Wang, Shuai; Xu, Bai-Xiang; Stark, Robert W; Dietz, Christian

2016-11-14

Lead-free relaxor ferroelectrics that feature a core-shell microstructure provide an excellent electromechanical response. They even have the potential to replace the environmentally hazardous lead-zirconia-titanate (PZT) in large strain actuation applications. Although the dielectric properties of core-shell ceramics have been extensively investigated, their piezoelectric properties are not yet well understood. To unravel the interfacial core-shell interaction, we studied the relaxation behaviour of field-induced ferroelectric domains in 0.75Bi 1/2 Na 1/2 TiO 3 -0.25SrTiO 3 (BNT-25ST), as a typical core-shell bulk material, using a piezoresponse force microscope. We found that after poling, lateral domains emerged at the core-shell interface and propagated to the shell region. Phase field simulations showed that the increased electrical potential beneath the core is responsible for the in-plane domain evolution. Our results imply that the field-induced domains act as pivotal points at the coherent heterophase core-shell interface, reinforcing the phase transition in the non-polar shell and thus promoting the giant strain.

Nanostructured core-shell electrode materials for electrochemical capacitors

NASA Astrophysics Data System (ADS)

Jiang, Long-bo; Yuan, Xing-zhong; Liang, Jie; Zhang, Jin; Wang, Hou; Zeng, Guang-ming

2016-11-01

Core-shell nanostructure represents a unique system for applications in electrochemical energy storage devices. Owing to the unique characteristics featuring high power delivery and long-term cycling stability, electrochemical capacitors (ECs) have emerged as one of the most attractive electrochemical storage systems since they can complement or even replace batteries in the energy storage field, especially when high power delivery or uptake is needed. This review aims to summarize recent progress on core-shell nanostructures for advanced supercapacitor applications in view of their hierarchical architecture which not only create the desired hierarchical porous channels, but also possess higher electrical conductivity and better structural mechanical stability. The core-shell nanostructures include carbon/carbon, carbon/metal oxide, carbon/conducting polymer, metal oxide/metal oxide, metal oxide/conducting polymer, conducting polymer/conducting polymer, and even more complex ternary core-shell nanoparticles. The preparation strategies, electrochemical performances, and structural stabilities of core-shell materials for ECs are summarized. The relationship between core-shell nanostructure and electrochemical performance is discussed in detail. In addition, the challenges and new trends in core-shell nanomaterials development have also been proposed.

Core-shell Au-Pd nanoparticles as cathode catalysts for microbial fuel cell applications

PubMed Central

Yang, Gaixiu; Chen, Dong; Lv, Pengmei; Kong, Xiaoying; Sun, Yongming; Wang, Zhongming; Yuan, Zhenhong; Liu, Hui; Yang, Jun

2016-01-01

Bimetallic nanoparticles with core-shell structures usually display enhanced catalytic properties due to the lattice strain created between the core and shell regions. In this study, we demonstrate the application of bimetallic Au-Pd nanoparticles with an Au core and a thin Pd shell as cathode catalysts in microbial fuel cells, which represent a promising technology for wastewater treatment, while directly generating electrical energy. In specific, in comparison with the hollow structured Pt nanoparticles, a benchmark for the electrocatalysis, the bimetallic core-shell Au-Pd nanoparticles are found to have superior activity and stability for oxygen reduction reaction in a neutral condition due to the strong electronic interaction and lattice strain effect between the Au core and the Pd shell domains. The maximum power density generated in a membraneless single-chamber microbial fuel cell running on wastewater with core-shell Au-Pd as cathode catalysts is ca. 16.0 W m−3 and remains stable over 150 days, clearly illustrating the potential of core-shell nanostructures in the applications of microbial fuel cells. PMID:27734945

Magnetite and magnetite/silver core/shell nanoparticles with diluted magnet-like behavior

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garza-Navarro, Marco; Torres-Castro, Alejandro, E-mail: alejandro.torrescs@uanl.edu.m; Centro de Innovacion, Investigacion y Desarrollo en Ingenieria y Tecnologia, Universidad Autonoma de Nuevo Leon, Apodaca, Nuevo Leon 66600

2010-01-15

In the present work is reported the use of the biopolymer chitosan as template for the preparation of magnetite and magnetite/silver core/shell nanoparticles systems, following a two step procedure of magnetite nanoparticles in situ precipitation and subsequent silver ions reduction. The crystalline and morphological characteristics of both magnetite and magnetite/silver core/shell nanoparticles systems were analyzed by high resolution transmission electron microscopy (HRTEM) and nanobeam diffraction patterns (NBD). The results of these studies corroborate the core/shell morphology and the crystalline structure of the magnetite core and the silver shell. Moreover, magnetization temperature dependent, M(T), measurements show an unusual diluted magnetic behaviormore » attributed to the dilution of the magnetic ordering in the magnetite and magnetite/silver core/shell nanoparticles systems. - Graphical abstract: Biopolymer chitosan was used as stabilization media to synthesize both magnetite and magnetite/silver core/shell nanoparticles. Results of HRTEM and NBD patterns confirm core/shell morphology of the obtained nanoparticles. It was found that the composites show diluted magnet-like behavior.« less

Current advances in precious metal core-shell catalyst design.

PubMed

Wang, Xiaohong; He, Beibei; Hu, Zhiyu; Zeng, Zhigang; Han, Sheng

2014-08-01

Precious metal nanoparticles are commonly used as the main active components of various catalysts. Given their high cost, limited quantity, and easy loss of catalytic activity under severe conditions, precious metals should be used in catalysts at low volumes and be protected from damaging environments. Accordingly, reducing the amount of precious metals without compromising their catalytic performance is difficult, particularly under challenging conditions. As multifunctional materials, core-shell nanoparticles are highly important owing to their wide range of applications in chemistry, physics, biology, and environmental areas. Compared with their single-component counterparts and other composites, core-shell nanoparticles offer a new active interface and a potential synergistic effect between the core and shell, making these materials highly attractive in catalytic application. On one hand, when a precious metal is used as the shell material, the catalytic activity can be greatly improved because of the increased surface area and the closed interfacial interaction between the core and the shell. On the other hand, when a precious metal is applied as the core material, the catalytic stability can be remarkably improved because of the protection conferred by the shell material. Therefore, a reasonable design of the core-shell catalyst for target applications must be developed. We summarize the latest advances in the fabrications, properties, and applications of core-shell nanoparticles in this paper. The current research trends of these core-shell catalysts are also highlighted.

Manipulation of polarization anisotropy in bare InAs and InAs/GaSb core-shell nanowires

NASA Astrophysics Data System (ADS)

Patra, Atanu; Roy, Anushree; Gomes, Umesh Prasad; Zannier, Valentina; Ercolani, Daniele; Sorba, Lucia

2018-04-01

In this article, we compare the excitation wavelength dependence of the polarization anisotropy (ρ) of an internal field induced Raman scattering signal in individual bare InAs and InAs/GaSb core-shell nanowires. The measured value of ρ of the Raman scattering intensity for InAs/GaSb core-shell nanowires has a minimum at ˜500 nm, while for the bare InAs nanowire, the value of ρ monotonically increases over the same range of wavelengths. We have modeled the scattering intensities of both systems by considering the joint role of Raman tensor components and confinement of electromagnetic radiation inside the nanowire at two orthogonal polarization configurations of the electromagnetic radiation. The theoretical results allow us to understand that the observed behavior of ρ is related to the nanowire geometry and to the difference in the wavelength dependence of the dielectric constants of InAs and GaSb. This work shows the possibility of manipulating the polarization anisotropy by selecting suitable diameters and materials for the core and the shell of the nanowire. We also report a six-fold increase in Raman scattering intensity due to the GaSb shell on InAs nanowires.

Vertically aligned P(VDF-TrFE) core-shell structures on flexible pillar arrays

PubMed Central

Choi, Yoon-Young; Yun, Tae Gwang; Qaiser, Nadeem; Paik, Haemin; Roh, Hee Seok; Hong, Jongin; Hong, Seungbum; Han, Seung Min; No, Kwangsoo

2015-01-01

PVDF and P(VDF-TrFE) nano- and micro- structures have been widely used due to their potential applications in several fields, including sensors, actuators, vital sign transducers, and energy harvesters. In this study, we developed vertically aligned P(VDF-TrFE) core-shell structures using high modulus polyurethane acrylate (PUA) pillars as the support structure to maintain the structural integrity. In addition, we were able to improve the piezoelectric effect by 1.85 times from 40 ± 2 to 74 ± 2 pm/V when compared to the thin film counterpart, which contributes to the more efficient current generation under a given stress, by making an effective use of the P(VDF-TrFE) thin top layer as well as the side walls. We attribute the enhancement of piezoelectric effects to the contributions from the shell component and the strain confinement effect, which was supported by our modeling results. We envision that these organic-based P(VDF-TrFE) core-shell structures will be used widely as 3D sensors and power generators because they are optimized for current generations by utilizing all surface areas, including the side walls of core-shell structures. PMID:26040539

Vertically aligned P(VDF-TrFE) core-shell structures on flexible pillar arrays

DOE PAGES

Choi, Yoon-Young; Yun, Tae Gwang; Qaiser, Nadeem; ...

2015-06-04

PVDF and P(VDF-TrFE) nano- and micro- structures are widely used due to their potential applications in several fields, including sensors, actuators, vital sign transducers, and energy harvesters. In this study, we developed vertically aligned P(VDF-TrFE) core-shell structures using high modulus polyurethane acrylate (PUA) pillars as the support structure to maintain the structural integrity. In addition, we were able to improve the piezoelectric effect by 1.85 times from 40 ± 2 to 74 ± 2 pm/V when compared to the thin film counterpart, which contributes to the more efficient current generation under a given stress, by making an effective use ofmore » the P(VDF-TrFE) thin top layer as well as the side walls. We attribute the enhancement of piezoelectric effects to the contributions from the shell component and the strain confinement effect, which was supported by our modeling results. We envision that these organic-based P(VDF-TrFE) core-shell structures will be used widely as 3D sensors and power generators because they are optimized for current generations by utilizing all surface areas, including the side walls of core-shell structures.« less

PbSe-Based Colloidal Core/Shell Heterostructures for Optoelectronic Applications

PubMed Central

Zaiats, Gary; Yanover, Diana; Vaxenburg, Roman; Tilchin, Jenya; Sashchiuk, Aldona; Lifshitz, Efrat

2014-01-01

Lead-based (IV–VI) colloidal quantum dots (QDs) are of widespread scientific and technological interest owing to their size-tunable band-gap energy in the near-infrared optical region. This article reviews the synthesis of PbSe-based heterostructures and their structural and optical investigations at various temperatures. The review focuses on the structures consisting of a PbSe core coated with a PbSexS1–x (0 ≤ x ≤ 1) or CdSe shell. The former-type shells were epitaxially grown on the PbSe core, while the latter-type shells were synthesized using partial cation-exchange. The influence of the QD composition and the ambient conditions, i.e., exposure to oxygen, on the QD optical properties, such as radiative lifetime, Stokes shift, and other temperature-dependent characteristics, was investigated. The study revealed unique properties of core/shell heterostructures of various compositions, which offer the opportunity of fine-tuning the QD electronic structure by changing their architecture. A theoretical model of the QD electronic band structure was developed and correlated with the results of the optical studies. The review also outlines the challenges related to potential applications of colloidal PbSe-based heterostructures. PMID:28788244

Influence of Shell Thickness on the Colloidal Stability of Magnetic Core-Shell Particle Suspensions

PubMed Central

Neville, Frances; Moreno-Atanasio, Roberto

2018-01-01

We present a Discrete Element study of the behavior of magnetic core-shell particles in which the properties of the core and the shell are explicitly defined. Particle cores were considered to be made of pure iron and thus possessed ferromagnetic properties, while particle shells were considered to be made of silica. Core sizes ranged between 0.5 and 4.0 μm with the actual particle size of the core-shell particles in the range between 0.6 and 21 μm. The magnetic cores were considered to have a magnetization of one tenth of the saturation magnetization of iron. This study aimed to understand how the thickness of the shell hinders the formation of particle chains. Chain formation was studied with different shell thicknesses and particle sizes in the presence and absence of an electrical double layer force in order to investigate the effect of surface charge density on the magnetic core-shell particle interactions. For core sizes of 0.5 and 4.0 μm the relative shell thicknesses needed to hinder the aggregation process were approximately 0.4 and 0.6 respectively, indicating that larger core sizes are detrimental to be used in applications in which no flocculation is needed. In addition, the presence of an electrical double layer, for values of surface charge density of less than 20 mC/m2, could stop the contact between particles without hindering their vertical alignment. Only when the shell thickness was considerably larger, was the electrical double layer able to contribute to the full disruption of the magnetic flocculation process. PMID:29922646

Influence of Shell Thickness on the Colloidal Stability of Magnetic Core-Shell Particle Suspensions.

PubMed

Neville, Frances; Moreno-Atanasio, Roberto

2018-01-01

We present a Discrete Element study of the behavior of magnetic core-shell particles in which the properties of the core and the shell are explicitly defined. Particle cores were considered to be made of pure iron and thus possessed ferromagnetic properties, while particle shells were considered to be made of silica. Core sizes ranged between 0.5 and 4.0 μm with the actual particle size of the core-shell particles in the range between 0.6 and 21 μm. The magnetic cores were considered to have a magnetization of one tenth of the saturation magnetization of iron. This study aimed to understand how the thickness of the shell hinders the formation of particle chains. Chain formation was studied with different shell thicknesses and particle sizes in the presence and absence of an electrical double layer force in order to investigate the effect of surface charge density on the magnetic core-shell particle interactions. For core sizes of 0.5 and 4.0 μm the relative shell thicknesses needed to hinder the aggregation process were approximately 0.4 and 0.6 respectively, indicating that larger core sizes are detrimental to be used in applications in which no flocculation is needed. In addition, the presence of an electrical double layer, for values of surface charge density of less than 20 mC/m 2 , could stop the contact between particles without hindering their vertical alignment. Only when the shell thickness was considerably larger, was the electrical double layer able to contribute to the full disruption of the magnetic flocculation process.

Core-shell silk hydrogels with spatially tuned conformations as drug-delivery system.

PubMed

Yan, Le-Ping; Oliveira, Joaquim M; Oliveira, Ana L; Reis, Rui L

2017-11-01

Hydrogels of spatially controlled physicochemical properties are appealing platforms for tissue engineering and drug delivery. In this study, core-shell silk fibroin (SF) hydrogels of spatially controlled conformation were developed. The core-shell structure in the hydrogels was formed by means of soaking the preformed (enzymatically crosslinked) random coil SF hydrogels in methanol. When increasing the methanol treatment time from 1 to 10 min, the thickness of the shell layer can be tuned from about 200 to about 850 μm as measured in wet status. After lyophilization of the rehydrated core-shell hydrogels, the shell layer displayed compact morphology and the core layer presented porous structure, when observed by scanning electron microscopy. The conformation of the hydrogels was evaluated by Fourier transform infrared spectroscopy in wet status. The results revealed that the shell layer possessed dominant β-sheet conformation and the core layer maintained mainly random coil conformation. Enzymatic degradation data showed that the shell layers presented superior stability to the core layer. The mechanical analysis displayed that the compressive modulus of the core-shell hydrogels ranged from about 25 kPa to about 1.1 MPa by increasing the immersion time in methanol. When incorporated with albumin, the core-shell SF hydrogels demonstrated slower and more controllable release profiles compared with the non-treated hydrogel. These core-shell SF hydrogels of highly tuned properties are useful systems as drug-delivery system and may be applied as cartilage substitute. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Study on surface-enhanced Raman scattering efficiency of Ag core-Au shell bimetallic nanoparticles

NASA Astrophysics Data System (ADS)

Dong, Xiao; Gu, Huaimin; Kang, Jian; Yuan, Xiaojuan

2009-08-01

In this article, the relationship between the states of Ag core-Au shell (core-shell) nanoparticles (NP) and the intensity of Raman scattering of analytes dissolved in the water and adsorbed on the NP was studied. The core-shell NP were synthesised by coating Au layers over Ag seeds by the method of "seed-growth". To highlight the advantage of the core-shell NP, Ag colloid and Au colloid were chosen for contrasting. The analyte that were chosen for this testing were methylene blue (MB) for the reason that MB has very strong signal in surface-enhanced Raman scattering (SERS). The SERS activity of optimalizing states of Ag and Au colloids were compared with that of core-shell NP when MB was used as analyte. In this study, sodium chloride, sodium sulfate and sodium nitrate were used as aggregating agents for Ag, Au colloids and core-shell NP, because anions have a strong influence on the SERS efficiency and the stability of colloids. The results indicate that core-shell NP can obviously enhance the SERS of MB. The aim of this study is to prove that compared with the metal colloid, the core-shell NP is a high efficiency SERS active substrate.

Development of magnetic luminescent core/shell nanocomplex particles with fluorescence using Rhodamine 6G

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Hee Uk; Song, Yoon Seok; Park, Chulhwan

2012-12-15

Graphical abstract: Display Omitted Highlights: ► A simple method was developed to synthesize Co-B/SiO{sub 2}/dye/SiO{sub 2} composite particles. ► The magnetic particle shows that highly luminescent and core/shell particles are formed. ► Such core/shell particles can be easily suspended in water. ► The magnetic particles could detect fluorescence for the application of biosensor. -- Abstract: A simple and reproducible method was developed to synthesize a novel class of Co-B/SiO{sub 2}/dye/SiO{sub 2} composite core/shell particles. Using a single cobalt core, Rhodamine 6G of organic dye molecules was entrapped in a silica shell, resulting in core/shell particles of ∼200 nm diameter. Analysesmore » using a variety of techniques such as transmission electron microscopy, X-ray photoelectron spectroscopy, vibration sample magnetometry, confocal laser scanning microscopy, and fluorescence intensity demonstrated that dye molecules were trapped inside the core/shell particles. A photoluminescence investigation showed that highly luminescent and photostable core/shell particles were formed. Such core/shell particles can be easily suspended in water. The synthesized magnetic particles could be used to detect fluorescence on glass substrate arrays for bioassay and biosensor applications.« less

Effects of quantum confinement and shape on band gap of core/shell quantum dots and nanowires

NASA Astrophysics Data System (ADS)

Gao, Faming

2011-05-01

A quantum confinement model for nanocrystals developed is extended to study for the optical gap shifts in core/shell quantum dots and nanowires. The chemical bond properties and gap shifts in the InP/ZnS, CdSe/CdS, CdSe/ZnS, and CdTe/ZnS core/shell quantum dots are calculated in detail. The calculated band gaps are in excellent agreement with experimental values. The effects of structural taping and twinning on quantum confinement of InP and Si nanowires are elucidated. It is found theoretically that a competition between the positive Kubo energy-gap shift and the negative surface energy shift plays the crucial role in the optical gaps of these nanosystems.

Fabrication of Fe{sub 3}O{sub 4}@CuO core-shell from MOF based materials and its antibacterial activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rajabi, S.K.; Sohrabnezhad, Sh., E-mail: sohrabnezhad@guilan.ac.ir; Ghafourian, S.

Magnetic Fe{sub 3}O{sub 4}@CuO nanocomposite with a core/shell structure was successfully synthesized via direct calcinations of magnetic Fe{sub 3}O{sub 4}@HKUST-1 in air atmosphere. The morphology, structure, magnetic and porous properties of the as-synthesized nano composites were characterized by using scanning electron microscope (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), and vibration sample magnetometer (VSM). The results showed that the nanocomposite material included a Fe{sub 3}O{sub 4} core and a CuO shell. The Fe{sub 3}O{sub 4}@CuO core-shell can be separated easily from the medium by a small magnet. The antibacterial activity of Fe{sub 3}O{sub 4}-CuO core-shell was investigated againstmore » gram-positive and gram-negative bacteria. A new mechanism was proposed for inactivation of bacteria over the prepared sample. It was demonstrated that the core-shell exhibit recyclable antibacterial activity, acting as an ideal long-acting antibacterial agent. - Graphical abstract: Fe{sub 3}O{sub 4}@CuO core-shell release of copper ions. These Cu{sup 2+} ions were responsible for the exhibited antibacterial activity. - Highlights: • The Fe{sub 3}O{sub 4}@CuO core-shell was prepared by MOF method. • This is the first study of antibacterial activity of core-shell consist of CuO and Fe{sub 3}O{sub 4}. • The core-shell can be reused effectively. • Core-shell was separated from the reaction solution by external magnetic field.« less

Chemical insights into the roles of nanowire cores on the growth and supercapacitor performances of Ni-Co-O/Ni(OH)2 core/shell electrodes

PubMed Central

Yin, Xuesong; Tang, Chunhua; Zhang, Liuyang; Yu, Zhi Gen; Gong, Hao

2016-01-01

Nanostructured core/shell electrodes have been experimentally demonstrated promising for high-performance electrochemical energy storage devices. However, chemical insights into the significant roles of nanowire cores on the growth of shells and their supercapacitor behaviors still remain as a research shortfall. In this work, by substituting 1/3 cobalt in the Co3O4 nanowire core with nickel, a 61% enhancement of the specific mass-loading of the Ni(OH)2 shell, a tremendous 93% increase of the volumetric capacitance and a superior cyclability were achieved in a novel NiCo2O4/Ni(OH)2 core/shell electrode in contrast to a Co3O4/Ni(OH)2 one. A comparative study suggested that not only the growth of Ni(OH)2 shells but also the contribution of cores were attributed to the overall performances. Importantly, their chemical origins were revealed through a theoretical simulation of the core/shell interfacial energy changes. Besides, asymmetric supercapacitor devices and applications were also explored. The scientific clues and practical potentials obtained in this work are helpful for the design and analysis of alternative core/shell electrode materials. PMID:26857606

Chemical insights into the roles of nanowire cores on the growth and supercapacitor performances of Ni-Co-O/Ni(OH)₂ core/shell electrodes.

PubMed

Yin, Xuesong; Tang, Chunhua; Zhang, Liuyang; Yu, Zhi Gen; Gong, Hao

2016-02-09

Nanostructured core/shell electrodes have been experimentally demonstrated promising for high-performance electrochemical energy storage devices. However, chemical insights into the significant roles of nanowire cores on the growth of shells and their supercapacitor behaviors still remain as a research shortfall. In this work, by substituting 1/3 cobalt in the Co3O4 nanowire core with nickel, a 61% enhancement of the specific mass-loading of the Ni(OH)2 shell, a tremendous 93% increase of the volumetric capacitance and a superior cyclability were achieved in a novel NiCo2O4/Ni(OH)2 core/shell electrode in contrast to a Co3O4/Ni(OH)2 one. A comparative study suggested that not only the growth of Ni(OH)2 shells but also the contribution of cores were attributed to the overall performances. Importantly, their chemical origins were revealed through a theoretical simulation of the core/shell interfacial energy changes. Besides, asymmetric supercapacitor devices and applications were also explored. The scientific clues and practical potentials obtained in this work are helpful for the design and analysis of alternative core/shell electrode materials.

Temperature dependent electron delocalization in CdSe/CdS type-I core-shell systems: An insight from scanning tunneling spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kundu, Biswajit; Chakrabarti, Sudipto; Pal, Amlan J., E-mail: sspajp@iacs.res.in

2016-03-14

Core-shell nanocrystals having a type-I band-alignment confine charge carriers to the core. In this work, we choose CdSe/CdS core-shell nano-heterostructures that evidence confinement of holes only. Such a selective confinement occurs in the core-shell nanocrystals due to a low energy-offset of conduction band (CB) edges resulting in delocalization of electrons and thus a decrease in the conduction band-edge. Since the delocalization occurs through a thermal assistance, we study temperature dependence of selective delocalization process through scanning tunneling spectroscopy. From the density of states (DOS), we observe that the electrons are confined to the core at low temperatures. Above a certainmore » temperature, they become delocalized up to the shell leading to a decrease in the CB of the core-shell system due to widening of quantum confinement effect. With holes remaining confined to the core due to a large offset in the valence band (VB), we record the topography of the core-shell nanocrystals by probing their CB and VB edges separately. The topographies recorded at different temperatures representing wave-functions of electrons and holes corresponded to the results obtained from the DOS spectra. The results evidence temperature-dependent wave-function delocalization of one-type of carriers up to the shell layer in core-shell nano-heterostructures.« less

Core-shell microparticles for protein sequestration and controlled release of a protein-laden core.

PubMed

Rinker, Torri E; Philbrick, Brandon D; Temenoff, Johnna S

2017-07-01

Development of multifunctional biomaterials that sequester, isolate, and redeliver cell-secreted proteins at a specific timepoint may be required to achieve the level of temporal control needed to more fully regulate tissue regeneration and repair. In response, we fabricated core-shell heparin-poly(ethylene-glycol) (PEG) microparticles (MPs) with a degradable PEG-based shell that can temporally control delivery of protein-laden heparin MPs. Core-shell MPs were fabricated via a re-emulsification technique and the number of heparin MPs per PEG-based shell could be tuned by varying the mass of heparin MPs in the precursor PEG phase. When heparin MPs were loaded with bone morphogenetic protein-2 (BMP-2) and then encapsulated into core-shell MPs, degradable core-shell MPs initiated similar C2C12 cell alkaline phosphatase (ALP) activity as the soluble control, while non-degradable core-shell MPs initiated a significantly lower response (85+19% vs. 9.0+4.8% of the soluble control, respectively). Similarly, when degradable core-shell MPs were formed and then loaded with BMP-2, they induced a ∼7-fold higher C2C12 ALP activity than the soluble control. As C2C12 ALP activity was enhanced by BMP-2, these studies indicated that degradable core-shell MPs were able to deliver a bioactive, BMP-2-laden heparin MP core. Overall, these dynamic core-shell MPs have the potential to sequester, isolate, and then redeliver proteins attached to a heparin core to initiate a cell response, which could be of great benefit to tissue regeneration applications requiring tight temporal control over protein presentation. Tissue repair requires temporally controlled presentation of potent proteins. Recently, biomaterial-mediated binding (sequestration) of cell-secreted proteins has emerged as a strategy to harness the regenerative potential of naturally produced proteins, but this strategy currently only allows immediate amplification and re-delivery of these signals. The multifunctional, dynamic core-shell heparin-PEG microparticles presented here overcome this limitation by sequestering proteins through a PEG-based shell onto a protein-protective heparin core, temporarily isolating bound proteins from the cellular microenvironment, and re-delivering proteins only after degradation of the PEG-based shell. Thus, these core-shell microparticles have potential to be a novel tool to harness and isolate proteins produced in the cellular environment and then control when proteins are re-introduced for the most effective tissue regeneration and repair. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Biomimetic synthesis of raspberry-like hybrid polymer-silica core-shell nanoparticles by templating colloidal particles with hairy polyamine shell.

PubMed

Pi, Mengwei; Yang, Tingting; Yuan, Jianjun; Fujii, Syuji; Kakigi, Yuichi; Nakamura, Yoshinobu; Cheng, Shiyuan

2010-07-01

The nanoparticles composed of polystyrene core and poly[2-(diethylamino)ethyl methacrylate] (PDEA) hairy shell were used as colloidal templates for in situ silica mineralization, allowing the well-controlled synthesis of hybrid silica core-shell nanoparticles with raspberry-like morphology and hollow silica nanoparticles by subsequent calcination. Silica deposition was performed by simply stirring a mixture of the polymeric core-shell particles in isopropanol, tetramethyl orthosilicate (TMOS) and water at 25 degrees C for 2.5h. No experimental evidence was found for nontemplated silica formation, which indicated that silica deposition occurred exclusively in the PDEA shell and formed PDEA-silica hybrid shell. The resulting hybrid silica core-shell particles were characterized by transmission electron microscopy (TEM), thermogravimetry, aqueous electrophoresis, and X-ray photoelectron spectroscopy. TEM studies indicated that the hybrid particles have well-defined core-shell structure with raspberry morphology after silica deposition. We found that the surface nanostructure of hybrid nanoparticles and the composition distribution of PDEA-silica hybrid shell could be well controlled by adjusting the silicification conditions. These new hybrid core-shell nanoparticles and hollow silica nanoparticles would have potential applications for high-performance coatings, encapsulation and delivery of active organic molecules. 2010 Elsevier B.V. All rights reserved.

Bandgap engineered reverse type-I CdTe/InP/ZnS core-shell nanocrystals for the near-infrared.

PubMed

Kim, Sunghoon; Shim, Wooyoung; Seo, Heonjin; Hyun Bae, Je; Sung, Jaeyoung; Choi, Seung Hong; Moon, Woo Kyung; Lee, Gwang; Lee, Bunyeoul; Kim, Sang-Wook

2009-03-14

New quantum dots were fabricated with a core/shell/shell structure consisting of CdTe core/InP shell/ZnS shell of which the InP shell causes a red-shift to the NIR region and the ZnS shell imparts photo-stability; toxicity tests on mammalian cells and NIR imaging of a mouse highlight their potential applications in biomedical imaging.

Ab initio many-body perturbation theory and no-core shell model

NASA Astrophysics Data System (ADS)

Hu, B. S.; Wu, Q.; Xu, F. R.

2017-10-01

In many-body perturbation theory (MBPT) we always introduce a parameter N shell to measure the maximal allowed major harmonic-oscillator (HO) shells for the single-particle basis, while the no-core shell model (NCSM) uses N maxℏΩ HO excitation truncation above the lowest HO configuration for the many-body basis. It is worth comparing the two different methods. Starting from “bare” and Okubo-Lee-Suzuki renormalized modern nucleon-nucleon interactions, NNLOopt and JISP16, we show that MBPT within Hartree-Fock bases is in reasonable agreement with NCSM within harmonic oscillator bases for 4He and 16O in “close” model space. In addition, we compare the results using “bare” force with the Okubo-Lee-Suzuki renormalized force. Supported by National Key Basic Research Program of China (2013CB834402), National Natural Science Foundation of China (11235001, 11320101004, 11575007) and the CUSTIPEN (China-U.S. Theory Institute for Physics with Exotic Nuclei) funded by the U.S. Department of Energy, Office of Science (DE-SC0009971)

Effect of ZnO core electrodeposition conditions on electrochemical and photocatalytic properties of polypyrrole-graphene oxide shelled nanoarrays

NASA Astrophysics Data System (ADS)

Pruna, A.; Shao, Q.; Kamruzzaman, M.; Li, Y. Y.; Zapien, J. A.; Pullini, D.; Busquets Mataix, D.; Ruotolo, A.

2017-01-01

Novel hybrid core-shell nanoarchitectures were fabricated by a simple two-step electrochemical approach: first ZnO nanorod core was electrodeposited from Zn(NO3)2 solution; further, the core nanoarray was coated with a shell based on polypyrrole hybridized with graphene oxide by electropolymerization. The properties of the core/shell nanoarchitectures were studied as a function of the core properties induced by electrodeposition parameters. The ZnO nanostructures showed improved crystallinity and c-axis preferred orientation with increasing cathodic deposition potential while the increased deposition duration resulted in a morphology transition from nanorod to pyramidal shape. The electrochemical activity of the core/shell arrays was found to increase with the deposition potential of ZnO core but decreased when morphology changed from nanorod to pyramid shape. The photocatalytic results showed improved activity for the core/hybrid shell nanoarrays with respect to ZnO and ZnO/PPy ones. The degradation rate for methylene blue decreased with prolonged deposition duration of the core. The obtained results highlight the importance of electrochemical tuning of ZnO-based core/shell nanoarrays for improved performance in electrochemical and photocatalytic applications.

Bubble nucleation and migration in a lead-iron hydr(oxide) core-shell nanoparticle

DOE PAGES

Niu, Kaiyang; Frolov, Timofey; Xin, Huolin L.; ...

2015-10-05

Iron hydroxide is found in a wide range of contexts ranging from biominerals to steel corrosion, and it can transform to anhydrous oxide via releasing O 2 gas and H 2O. However, it is not well understood how gases transport through a crystal lattice. Here, we present in situ observation of the nucleation and migration of gas bubbles in iron (hydr)oxide using transmission electron microscopy. We create Pb–FeOOH model core–shell nanoparticles in a liquid cell. Under electron irradiation, iron hydroxide transforms to iron oxide, during which bubbles are generated, and they migrate through the shell to the nanoparticle surface. Geometricmore » phase analysis of the shell lattice shows an inhomogeneous stain field at the bubbles. In conclusion, our modeling suggests that the elastic interaction between the core and the bubble provides a driving force for bubble migration.« less

Exciton in a spherical core/shell nanostructure: Influence of surface ligand

NASA Astrophysics Data System (ADS)

Anitha, B.; Nithiananthi, P.

2018-04-01

Studies on exciton in an inverted type I spherical GaAs/Al0.3Ga0.7As core/shell nanostructure (CSN) are made using variational method. Dielectric constant and effective mass mismatches of the core and shell materials are considered. The effect of core and the shell dimensions on the exciton binding energy (BE) are analyzed for different shell (Rs) and core radii (Rc). It is observed that with the core and the shell inducement, significant change in BE can be achieved. In addition, the influence of ligand enclosureon the BE as a function of shell thickness (ST) is reviewed. The result exhibits that the presence of ligand considerably affects the BE. Further the transmission probability of exciton for various Rc and Rs are reported. The notable changes are compared and examined with and without ligand inclusion.

Growth of InAs/InP core-shell nanowires with various pure crystal structures.

PubMed

Gorji Ghalamestani, Sepideh; Heurlin, Magnus; Wernersson, Lars-Erik; Lehmann, Sebastian; Dick, Kimberly A

2012-07-20

We have studied the epitaxial growth of an InP shell on various pure InAs core nanowire crystal structures by metal-organic vapor phase epitaxy. The InP shell is grown on wurtzite (WZ), zinc-blende (ZB), and {111}- and {110}-type faceted ZB twin-plane superlattice (TSL) structures by tuning the InP shell growth parameters and controlling the shell thickness. The growth results, particularly on the WZ nanowires, show that homogeneous InP shell growth is promoted at relatively high temperatures (∼500 °C), but that the InAs nanowires decompose under the applied conditions. In order to protect the InAs core nanowires from decomposition, a short protective InP segment is first grown axially at lower temperatures (420-460 °C), before commencing the radial growth at a higher temperature. Further studies revealed that the InP radial growth rate is significantly higher on the ZB and TSL nanowires compared to WZ counterparts, and shows a strong anisotropy in polar directions. As a result, thin shells were obtained during low temperature InP growth on ZB structures, while a higher temperature was used to obtain uniform thick shells. In addition, a schematic growth model is suggested to explain the basic processes occurring during the shell growth on the TSL crystal structures.

Shell effect on the electron and hole reorganization energy of core-shell II-VI nanoclusters

NASA Astrophysics Data System (ADS)

Cui, Xianhui; Wang, Xinqin; Yang, Fang; Cui, Yingqi; Yang, Mingli

2017-09-01

Density functional theory calculations were performed to study the effect of shell encapsulation on the geometrical and electronic properties of pure and hybrid core-shell CdSe nanoclusters. The CdSe cores are distorted by the shells, and the shells exhibit distinct surface activity from the cores, which leads to remarkable changes in their electron transition behaviors. Although the electron and hole reorganization energies, which are related to the formation and recombination of electron-hole pairs, vary in a complicated way, their itemized contributions, potentials of electron extraction, ionization and affinity, and hole extraction (HEP), are dependent on the cluster size, shell composition and/or solvent. Our calculations suggest that the behaviors of charge carriers, free electrons and holes, in the semiconductor core-shell nanoclusters can be modulated by selecting appropriate cluster size and controlling the chemical composition of the shells.

Photophysical Properties of II-VI Semiconductor Nanocrystals

NASA Astrophysics Data System (ADS)

Gong, Ke

As it is well known, semiconductor nanocrystals (also called quantum dots, QDs) are being actively pursued for use in many different types of luminescent optical materials. These materials include the active media for luminescence downconversion in artificial lighting, lasers, luminescent solar concentrators and many other applications. Chapter 1 gives general introduction of QDs, which describe the basic physical properties and optical properties. Based on the experimental spectroscopic study, a semiquantitative method-effective mass model is employed to give theoretical prediction and guide. The following chapters will talks about several topics respectively. A predictive understanding of the radiative lifetimes is therefore a starting point for the understanding of the use of QDs for these applications. Absorption intensities and radiative lifetimes are fundamental properties of any luminescent material. Meantime, achievement of high efficiency with high working temperature and heterostructure fabrication with manipulation of lattice strain are not easy and need systematic investigation. To make accurate connections between extinction coefficients and radiative recombination rates, chapter 2 will consider three closely related aspects of the size dependent spectroscopy of II-VI QDs. First, it will consider the existing literature on cadmium selenide (CdSe) QD absorption spectra and extinction coefficients. From these results and fine structure considerations Boltzmann weighted radiative lifetimes are calculated. These lifetimes are compared to values measured on very high quality CdSe and CdSe coated with zinc selenide (ZnSe) shells. Second, analogous literature data are analyzed for cadmium telluride (CdTe) nanocrystals and compared to lifetimes measured for very high quality QDs. Furthermore, studies of the absorption and excitation spectra and measured radiative lifetimes for CdTe/CdSe Type-II core/shell QDs are reported. These results are also analyzed in terms of a Boltzmann population of exciton sublevels and calculated electron and hole wave functions. Much of the absorption data and fine structure calculations are already in the literature. These results are combined with new measurements of radiative lifetimes and electron-hole overlap calculations to produce an integrated picture of the II-VI QD spectroscopic fundamentals. Finally, we adopt recent synthetic advances to make very monodisperse zincblende CdSe/CdS quantum dots having near-unity photoluminescence quantum yields (PLQYs). Due the absence of nonradiative decay pathways, accurate values of the radiative lifetimes can be obtained from time resolved PL measurements. Radiative lifetimes can also be obtained from the Einstein relations, using the static absorption spectra and the relative thermal populations in the angular momentum sublevels. One of the inputs into these calculations is the shell thickness, and it is useful to be able to determine shell thickness from spectroscopic measurements. We use an empirically corrected effective mass model to produce a "map" of exciton wavelength as a function of core size and shell thickness. These calculations use an elastic continuum model and the known lattice and elastic constants to include the effect of lattice strain on the band gap energy. Radiative lifetimes calculated both experimentally and theoretically are checked and the size dependence is compared to previous studied Type-I, II and single component particles. However, it is not enough to just understanding these basic photophysics of absorption and emission. The emission intensities (related to QYs) also change with changes of the temperature. The temperature dependent PLs of II-VI QDs is extensively studied, but most of this work is at low temperatures. Temperatures well above ambient are of interest to lighting applications and in this regime both the reversible and irreversible loss of quantum yield (thermal quenching) are serious impediments to the implementation of QDs in commercial devices. Chapter 3 will elucidate the mechanism of static thermal quenching, in which the reduction of QYs does not affect the PL decay kinetics, on CdSe, CdTe and CdSe/ZnSe QDs as a function of particle sizes/shapes, surface composition and surface ligands. Through systematic experiments, this part of the dissertation discusses several possible mechanisms (e.g. structural, activated excited state, and electronic charging) and examines which the dominant cause for loss of QY at high temperature is. The more practical step is to develop the synthetic method of highly luminescent and stable core/shell QDs with minimum thermal quenching, which greatly enhance the energy efficiency of light emitting and photovoltaic devices. As the nonradiative Auger processed are induced by surface charging described in chapter 3, static and time-resolved fluorescence and high and low power transient absorption results on CdSe/CdS and CdSe/ZnSe core/shell particles are presented in chapter 4. Two CdS shell thicknesses were examined and all of the particles had either octadecylamine (ODA) and tributylphosphine (TBP) or just ODA ligands. The results can be understood in terms of a mechanism in which there is a thermal equilibrium between electrons being in the valence band or in chalcogenide localized surface states. Thermal promotion of a valence band electron to a surface state leaves the particle core positively charged. Photon absorption when the particle is in this state results in a positive trion, which undergoes a fast Auger recombination, making the particle nonluminescent. A lack of TBP ligands results in more empty surface orbitals and therefore shifts the equilibrium toward surface trapped electrons and hence trion formation. Low- and high-power transient absorption measurements give the trion and biexciton lifetimes and the ratio of the trion to biexciton Auger lifetimes are examined and compared to the degeneracies of Auger pathways. We also study the shell thickness and composition dependence of Auger times, which is compared to the scaling factors of effective volume and electron-hole overlap considerations. Core/shell QDs often exhibit much higher luminescence quantum yields (QYs), more stability, and are depicted as having a nearly spherical core and a shell of very nearly uniform thickness, which results in a very simple picture of surface passivation. The uniformity of the shell is crucial in obtaining QDs with well passivated surfaces. However, transmission electron microscope (TEM) images disprove the ideal situation. Defects and thickness inhomogeneity in shell materials are treated qualitatively as an analog to film thickness inhomogeneity in epitaxially grown thin films. More quantitatively, the extent to which the shell thickness of core/shell particles is constant can be determined by time-resolved PL studies that measure the dynamics of hole tunneling to acceptors that are adsorbed on the shell surface due that tunneling rates varies strongly with core-acceptor separation. Careful analysis of the hole transfer kinetics reveals the extent of shell thickness inhomogeneity, however, it may be complicated by the distribution of numbers of adsorbed acceptors. All the considerations can be incorporated into a model we establish in Chapter 5for the distribution of measured hole tunneling rates. From this analysis the distribution of shell thicknesses can be extracted from the luminescence kinetic results. This approach is therefore a sensitive measure of the distribution of tunneling distances. Thus, any defects or structural irregularities that allow the hole acceptors to adsorb closer to the particle core increases the hole tunneling rate and can be detected and quantified. A quantitative treatment of the lattice strain energy in determining the shell morphology of CdSe/CdS core/shell nanoparticles is presented in chapter 5. We use the inhomogeneity in hole tunneling rates through the shell to adsorbed hole acceptors to quantify the extent of shell thickness inhomogeneity. The results can be understood in terms of a model based on elastic continuum calculations, which indicate that the lattice strain energy depends on both core size and shell thickness. This model assumes thermodynamic equilibrium, i.e., that the shell morphology corresponds to a minimum total (lattice strain plus surface) energy. Comparison with the experimental results indicates that CdSe/CdS nanoparticles undergo an abrupt transition from smooth to rough shells when the total lattice strain energy exceeds about 27eV or the strain energy density exceeds 0.59 eV/nm2. The predictions of this model are not followed for CdSe/CdS nanoparticles when the shell is deposited at very low temperature and therefore equilibrium is not established. The effects of lattice strain on the spectroscopy and photoluminescence quantum yields of zincblende CdSe/CdS core/shell quantum dots are examined. The quantum yields are measured as a function of core size and shell thickness. High quantum yields are achieved as long as the lattice strain energy density is below ~0.85 eV/nm2, which is considerably greater than the limiting value of 0.59 eV/nm2 for thermodynamicstability of a smooth, defect free shell, as previously reported in chapter 5. Thus, core/shell quantum dots having strain energy densities between 0.59 and 0.85 eV/nm2 can have very high PL QYs, but are metastable with respect to surface defect formation. Such metastable core/shell QDs can be produced by shell deposition at comparatively low temperatures (< 140 °C). Annealing of these particles causes partial loss of core pressure, and a red shift of the spectrum.

Material with core-shell structure

DOEpatents

Luhrs, Claudia [Rio Rancho, NM; Richard, Monique N [Ann Arbor, MI; Dehne, Aaron [Maumee, OH; Phillips, Jonathan [Rio Rancho, NM; Stamm, Kimber L [Ann Arbor, MI; Fanson, Paul T [Brighton, MI

2011-11-15

Disclosed is a material having a composite particle, the composite particle including an outer shell and a core. The core is made from a lithium alloying material and the outer shell has an inner volume that is greater in size than the core of the lithium alloying material. In some instances, the outer mean diameter of the outer shell is less than 500 nanometers and the core occupies between 5 and 99% of the inner volume. In addition, the outer shell can have an average wall thickness of less than 100 nanometers.

Glucose Sensors Based on Core@Shell Magnetic Nanomaterials and Their Application in Diabetes Management: A Review.

PubMed

Liu, Lin; Lv, Hongying; Teng, Zhenyuan; Wang, Chengyin; Wang, Guoxiu

2015-01-01

This review presents a comprehensive attempt to conclude and discuss various glucose biosensors based on core@shell magnetic nanomaterials. Owing to good biocompatibility and stability, the core@shell magnetic nanomaterials have found widespread applications in many fields and draw extensive attention. Most magnetic nanoparticles possess an intrinsic enzyme mimetic activity like natural peroxidases, which invests magnetic nanomaterials with great potential in the construction of glucose sensors. We summarize the synthesis of core@shell magnetic nanomaterials, fundamental theory of glucose sensor and the advances in glucose sensors based on core@shell magnetic nanomaterials. The aim of the review is to provide an overview of the exploitation of the core@shell magnetic nanomaterials for glucose sensors construction.

Differential Dopamine Release Dynamics in the Nucleus Accumbens Core and Shell Reveal Complementary Signals for Error Prediction and Incentive Motivation

PubMed Central

Cacciapaglia, Fabio; Wightman, R. Mark; Carelli, Regina M.

2015-01-01

Mesolimbic dopamine (DA) is phasically released during appetitive behaviors, though there is substantive disagreement about the specific purpose of these DA signals. For example, prediction error (PE) models suggest a role of learning, while incentive salience (IS) models argue that the DA signal imbues stimuli with value and thereby stimulates motivated behavior. However, within the nucleus accumbens (NAc) patterns of DA release can strikingly differ between subregions, and as such, it is possible that these patterns differentially contribute to aspects of PE and IS. To assess this, we measured DA release in subregions of the NAc during a behavioral task that spatiotemporally separated sequential goal-directed stimuli. Electrochemical methods were used to measure subsecond NAc dopamine release in the core and shell during a well learned instrumental chain schedule in which rats were trained to press one lever (seeking; SL) to gain access to a second lever (taking; TL) linked with food delivery, and again during extinction. In the core, phasic DA release was greatest following initial SL presentation, but minimal for the subsequent TL and reward events. In contrast, phasic shell DA showed robust release at all task events. Signaling decreased between the beginning and end of sessions in the shell, but not core. During extinction, peak DA release in the core showed a graded decrease for the SL and pauses in release during omitted expected rewards, whereas shell DA release decreased predominantly during the TL. These release dynamics suggest parallel DA signals capable of supporting distinct theories of appetitive behavior. SIGNIFICANCE STATEMENT Dopamine signaling in the brain is important for a variety of cognitive functions, such as learning and motivation. Typically, it is assumed that a single dopamine signal is sufficient to support these cognitive functions, though competing theories disagree on how dopamine contributes to reward-based behaviors. Here, we have found that real-time dopamine release within the nucleus accumbens (a primary target of midbrain dopamine neurons) strikingly varies between core and shell subregions. In the core, dopamine dynamics are consistent with learning-based theories (such as reward prediction error) whereas in the shell, dopamine is consistent with motivation-based theories (e.g., incentive salience). These findings demonstrate that dopamine plays multiple and complementary roles based on discrete circuits that help animals optimize rewarding behaviors. PMID:26290234

Measurement of the shell decompression in direct-drive inertial-confinement-fusion implosions

DOE PAGES

Michel, D. T.; Hu, S. X.; Davis, A. K.; ...

2017-05-10

Measurement of the effect of adiabat (α) on the shell thickness were performed in direct-drive implosions. When reducing the adiabat of the shell from α = 6 to α = 4:5, the shell thickness was measured to decrease from 75 μm to 60 μm, but when decreasing the adiabat further (α = 1:8), the shell thickness was measured to increase to 75 μm. The measured shell thickness, shell trajectories, neutron bang time, and neutron yield were reproduced by two dimensional simulations that include laser imprint, nonlocal thermal transport, cross-beam energy transfer, and first-principles equation-of-state models. The minimum core size wasmore » measured to decrease from 40 μm to 30 μm, consistent with the reduction of the adiabat from α = 6 to α = 1:8. Simulations that neglected imprint reproduced the measured core size of the entire adiabat scan, but signi cantly underestimate the shell thickness for adiabat below ~3. These results show that the decompression of the shell measured for low-adiabat implosions was a result of laser imprint.« less

Measurement of the shell decompression in direct-drive inertial-confinement-fusion implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michel, D. T.; Hu, S. X.; Davis, A. K.

Measurement of the effect of adiabat (α) on the shell thickness were performed in direct-drive implosions. When reducing the adiabat of the shell from α = 6 to α = 4:5, the shell thickness was measured to decrease from 75 μm to 60 μm, but when decreasing the adiabat further (α = 1:8), the shell thickness was measured to increase to 75 μm. The measured shell thickness, shell trajectories, neutron bang time, and neutron yield were reproduced by two dimensional simulations that include laser imprint, nonlocal thermal transport, cross-beam energy transfer, and first-principles equation-of-state models. The minimum core size wasmore » measured to decrease from 40 μm to 30 μm, consistent with the reduction of the adiabat from α = 6 to α = 1:8. Simulations that neglected imprint reproduced the measured core size of the entire adiabat scan, but signi cantly underestimate the shell thickness for adiabat below ~3. These results show that the decompression of the shell measured for low-adiabat implosions was a result of laser imprint.« less

Ni@Ru and NiCo@Ru Core-Shell Hexagonal Nanosandwiches with a Compositionally Tunable Core and a Regioselectively Grown Shell.

PubMed

Hwang, Hyeyoun; Kwon, Taehyun; Kim, Ho Young; Park, Jongsik; Oh, Aram; Kim, Byeongyoon; Baik, Hionsuck; Joo, Sang Hoon; Lee, Kwangyeol

2018-01-01

The development of highly active electrocatalysts is crucial for the advancement of renewable energy conversion devices. The design of core-shell nanoparticle catalysts represents a promising approach to boost catalytic activity as well as save the use of expensive precious metals. Here, a simple, one-step synthetic route is reported to prepare hexagonal nanosandwich-shaped Ni@Ru core-shell nanoparticles (Ni@Ru HNS), in which Ru shell layers are overgrown in a regioselective manner on the top and bottom, and around the center section of a hexagonal Ni nanoplate core. Notably, the synthesis can be extended to NiCo@Ru core-shell nanoparticles with tunable core compositions (Ni 3 Co x @Ru HNS). Core-shell HNS structures show superior electrocatalytic activity for the oxygen evolution reaction (OER) to a commercial RuO 2 black catalyst, with their OER activity being dependent on their core compositions. The observed trend in OER activity is correlated to the population of Ru oxide (Ru 4+ ) species, which can be modulated by the core compositions. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electronic and Optical Properties of Core/Shell Pb16X16/Cd52X52 (X =S, Se, Te) Quantum Dots

NASA Astrophysics Data System (ADS)

Tamukong, Patrick; Mayo, Michael; Kilina, Svetlana

2015-03-01

The electronic and optoelectronic properties of semiconductor quantum dots (QDs) are mediated by surface defects due to the presence of dangling bonds producing trap states within the HOMO-LUMO energy gap, and contributing to fluorescence quenching. Surface capping ligands are generally used to alleviate this problem and increase the quantum yields of QDs. An alternative way is to synthesize core-shell QD structures; i.e., a QD core with a shell of another semiconductor material. We have investigated the effects of Cd52X52 shells on the photoexcited dynamics of Pb16X16 (X =S, Se, Te) QDs. The thin (~ 0.50 nm) shells were found to result largely in type I core/shell structures and a blue shift of the absorption spectra. Our studies revealed fairly strong core-shell hybridization in the electronic states close to the conduction band (CB) edge for Pb16S16andPb16Se16 cores, whereas for the Pb16Te16 core, such CB states were largely shell-like in nature. Nonadiabatic DFT-based dynamics, coupled with the surface hopping method, was used to study the effects of the core and shell compositions on energy relaxation rates in these systems.

The effects of the chemical composition and strain on the electronic properties of GaSb/InAs core-shell nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ning, Feng; Wang, Dan; Tang, Li-Ming, E-mail: lmtang@hnu.edu.cn

2014-09-07

The effects of the chemical composition and strain on the electronic properties of [111] zinc-blende (ZB) and [0001] wurtzite (WZ) GaSb/InAs core-shell nanowires (NWs) with different core diameters and shell thicknesses are studied using first-principles methods. The band structures of the [111] ZB GaSb/InAs core-shell NWs underwent a noticeable type-I/II band alignment transition, associated with a direct-to-indirect band gap transition under a compressive uniaxial strain. The band structures of the [0001] WZ GaSb/InAs core-shell NWs preserved the direct band gap under either compressive or tensile uniaxial strains. In addition, the band gaps and the effective masses of the carriers couldmore » be tuned by their composition. For the core-shell NWs with a fixed GaSb-core size, the band gaps decreased linearly with an increasing InAs-shell thickness, caused by the significant downshift of the conduction bands. For the [111] ZB GaSb/InAs core-shell NWs, the calculated effective masses indicated that the transport properties could be changed from hole-dominated conduction to electron-dominated conduction by changing the InAs-shell thickness.« less

Magnetic spherical cores partly coated with periodic mesoporous organosilica single crystals.

PubMed

Li, Jing; Wei, Yong; Li, Wei; Deng, Yonghui; Zhao, Dongyuan

2012-03-07

Core-shell structured materials are of special significance in various applications. Until now, most reported core-shell structures have polycrystalline or amorphous coatings as their shell layers, with popular morphologies of microspheres or quasi-spheres. However, the single crystals, either mesoscale or atomic ones, are still rarely reported as shell layers. If single crystals can be coated on core materials, it would result in a range of new type core-shell structures with various morphologies, and probably more potential applications. In this work, we demonstrate that periodic mesoporous organosilica (PMO) single crystals can partly grow on magnetic microspheres to form incomplete Fe(3)O(4)@nSiO(2)@PMO core-shell materials in aqueous solution, which indeed is the first illustration that mesoporous single-crystal materials can be used as shell layers for preparation of core-shell materials. The achieved materials have advantages of high specific surface areas, good magnetic responses, embedded functional groups and cubic mesopore channels, which might provide them with various application conveniences. We suppose the partial growth is largely decided by the competition between growing tendency of single crystals and the resistances to this tendency. In principle, other single crystals, including a range of atomic single crystals, such as zeolites, are able to be developed into such core-shell structures.

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

DOE PAGES

Hansen, Stephanie B.; Harding, Eric C.; Knapp, Patrick F.; ...

2018-03-07

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. In this work, we show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated bymore » the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Lastly, analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 10 24 e/cm 3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.« less

Spontaneous formation of GaN/AlN core-shell nanowires on sapphire by hydride vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Trassoudaine, Agnès; Roche, Elissa; Bougerol, Catherine; André, Yamina; Avit, Geoffrey; Monier, Guillaume; Ramdani, Mohammed Réda; Gil, Evelyne; Castelluci, Dominique; Dubrovskii, Vladimir G.

2016-11-01

Spontaneous GaN/AlN core-shell nanowires with high crystal quality were synthesized on sapphire substrates by vapor-liquid-solid hydride vapor phase epitaxy (VLS-HVPE) without any voluntary aluminum source. Deposition of aluminum is difficult to achieve in this growth technique which uses metal-chloride gaseous precursors: the strong interaction between the AlCl gaseous molecules and the quartz reactor yields a huge parasitic nucleation on the walls of the reactor upstream the substrate. We open up an innovative method to produce GaN/AlN structures by HVPE, thanks to aluminum etching from the sapphire substrate followed by redeposition onto the sidewalls of the GaN core. The paper presents the structural characterization of GaN/AlN core-shell nanowires, speculates on the growth mechanism and discusses a model which describes this unexpected behavior.

Profound Interfacial Effects in CoFe2O4/Fe3O4 and Fe3O4/CoFe2O4 Core/Shell Nanoparticles

NASA Astrophysics Data System (ADS)

Polishchuk, Dmytro; Nedelko, Natalia; Solopan, Sergii; Ślawska-Waniewska, Anna; Zamorskyi, Vladyslav; Tovstolytkin, Alexandr; Belous, Anatolii

2018-03-01

Two sets of core/shell magnetic nanoparticles, CoFe2O4/Fe3O4 and Fe3O4/CoFe2O4, with a fixed diameter of the core ( 4.1 and 6.3 nm for the former and latter sets, respectively) and thickness of shells up to 2.5 nm were synthesized from metal chlorides in a diethylene glycol solution. The nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, and magnetic measurements. The analysis of the results of magnetic measurements shows that coating of magnetic nanoparticles with the shells results in two simultaneous effects: first, it modifies the parameters of the core-shell interface, and second, it makes the particles acquire combined features of the core and the shell. The first effect becomes especially prominent when the parameters of core and shell strongly differ from each other. The results obtained are useful for optimizing and tailoring the parameters of core/shell spinel ferrite magnetic nanoparticles for their use in various technological and biomedical applications.

Room-temperature ferromagnetic Cr-doped Ge/GeOx core-shell nanowires.

PubMed

Katkar, Amar S; Gupta, Shobhnath P; Seikh, Md Motin; Chen, Lih-Juann; Walke, Pravin S

2018-06-08

The Cr-doped tunable thickness core-shell Ge/GeO x nanowires (NWs) were synthesized and characterized using x-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy and magnetization studies. The shell thickness increases with the increase in synthesis temperature. The presence of metallic Cr and Cr 3+ in core-shell structure was confirmed from XPS study. The magnetic property is highly sensitive to the core-shell thickness and intriguing room temperature ferromagnetism is realized only in core-shell NWs. The magnetization decreases with an increase in shell thickness and practically ceases to exist when there is no core. These NWs show remarkably high Curie temperature (T C  > 300 K) with the dominating values of its magnetic remanence (M R ) and coercivity (H C ) compared to germanium dilute magnetic semiconductor nanomaterials. We believe that our finding on these Cr-doped Ge/GeO X core-shell NWs has the potential to be used as a hard magnet for future spintronic devices, owing to their higher characteristic values of ferromagnetic ordering.

Graded core/shell semiconductor nanorods and nanorod barcodes

DOEpatents

Alivisatos, A. Paul; Scher, Erik C.; Manna, Liberato

2010-12-14

Graded core/shell semiconductor nanorods and shaped nanorods are disclosed comprising Group II-VI, Group III-V and Group IV semiconductors and methods of making the same. Also disclosed are nanorod barcodes using core/shell nanorods where the core is a semiconductor or metal material, and with or without a shell. Methods of labeling analytes using the nanorod barcodes are also disclosed.

Graded core/shell semiconductor nanorods and nanorod barcodes

DOEpatents

Alivisatos, A. Paul; Scher, Erik C.; Manna, Liberato

2013-03-26

Graded core/shell semiconductor nanorods and shapped nanorods are disclosed comprising Group II-VI, Group III-V and Group IV semiconductors and methods of making the same. Also disclosed are nanorod barcodes using core/shell nanorods where the core is a semiconductor or metal material, and with or without a shell. Methods of labeling analytes using the nanorod barcodes are also disclosed.

Enhancing oxidative stability in heated oils using core/shell structures of collagen and α-tocopherol complex.

PubMed

Gim, Seo Yeong; Hong, Seungmi; Kim, Jisu; Kwon, YongJun; Kim, Mi-Ja; Kim, GeunHyung; Lee, JaeHwan

2017-11-15

In this study, collagen mesh structure was prepared by carrying α-tocopherol in the form of core/shell complex. Antioxidant properties of α-tocopherol loaded carriers were tested in moisture added bulk oils at 140°C. From one gram of collagen core/shell complex, 138mg α-tocopherol was released in medium chain triacylglycerol (MCT). α-Tocopherol was substantially protected against heat treatment when α-tocopherol was complexed in collagen core/shell. Oxidative stability in bulk oil was significantly enhanced by added collagen mesh structure or collagen core/shell complex with α-tocopherol compared to that in control bulk oils (p<0.05), although no significant difference was observed between oils containing collagen mesh structure and collagen core/shell with α-tocopherol (p>0.05). Results of DPPH loss in methanol demonstrated that collagen core/shell with α-tocopherol had significantly (p<0.05) higher antioxidant properties than collagen mesh structure up to a certain period. Therefore, collagen core/shell complex is a promising way to enhance the stability of α-tocopherol and oxidative stability in oil-rich foods prepared at high temperature. Copyright © 2017 Elsevier Ltd. All rights reserved.

Study of the effect of varying core diameter, shell thickness and strain velocity on the tensile properties of single crystals of Cu-Ag core-shell nanowire using molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Sarkar, Jit; Das, D. K.

2018-01-01

Core-shell type nanostructures show exceptional properties due to their unique structure having a central solid core of one type and an outer thin shell of another type which draw immense attention among researchers. In this study, molecular dynamics simulations are carried out on single crystals of copper-silver core-shell nanowires having wire diameter ranging from 9 to 30 nm with varying core diameter, shell thickness, and strain velocity. The tensile properties like yield strength, ultimate tensile strength, and Young's modulus are studied and correlated by varying one parameter at a time and keeping the other two parameters constant. The results obtained for a fixed wire size and different strain velocities were extrapolated to calculate the tensile properties like yield strength and Young's modulus at standard strain rate of 1 mm/min. The results show ultra-high tensile properties of copper-silver core-shell nanowires, several times than that of bulk copper and silver. These copper-silver core-shell nanowires can be used as a reinforcing agent in bulk metal matrix for developing ultra-high strength nanocomposites.

Mean-field and linear regime approach to magnetic hyperthermia of core-shell nanoparticles: can tiny nanostructures fight cancer?

PubMed

Carrião, Marcus S; Bakuzis, Andris F

2016-04-21

The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. Here, a magnetic hyperthermia model for core-shell nanoparticles is developed. The theoretical calculation, different from previous models, highlights the importance of heterogeneity by identifying the role of surface and core spins on nanoparticle heat generation. We found that the most efficient nanoparticles should be obtained by selecting materials to reduce the surface to core damping factor ratio, increasing the interface exchange parameter and tuning the surface to core anisotropy ratio for each material combination. From our results we propose a novel heat-based hyperthermia strategy with the focus on improving the heating efficiency of small sized nanoparticles instead of larger ones. This approach might have important implications for cancer treatment and could help improving clinical efficacy.

Fractal dimension study of polaron effects in cylindrical GaAs/Al x Ga1- x As core-shell nanowires

NASA Astrophysics Data System (ADS)

Sun, Hui; Li, Hua; Tian, Qiang

2018-04-01

Polaron effects in cylindrical GaAs/Al x Ga1- x As core-shell nanowires are studied by applying the fractal dimension method. In this paper, the polaron properties of GaAs/Al x Ga1- x As core-shell nanowires with different core radii and aluminum concentrations are discussed. The polaron binding energy, polaron mass shift, and fractal dimension parameter are numerically determined as functions of shell width. The calculation results reveal that the binding energy and mass shift of the polaron first increase and then decrease as the shell width increases. A maximum value appears at a certain shell width for different aluminum concentrations and a given core radius. By using the fractal dimension method, polaron problems in cylindrical GaAs/Al x Ga1- x As core-shell nanowires are solved in a simple manner that avoids complex and lengthy calculations.

Dendritic core-shell nickel-iron-copper metal/metal oxide electrode for efficient electrocatalytic water oxidation.

PubMed

Zhang, Peili; Li, Lin; Nordlund, Dennis; Chen, Hong; Fan, Lizhou; Zhang, Biaobiao; Sheng, Xia; Daniel, Quentin; Sun, Licheng

2018-01-26

Electrochemical water splitting requires efficient water oxidation catalysts to accelerate the sluggish kinetics of water oxidation reaction. Here, we report a promisingly dendritic core-shell nickel-iron-copper metal/metal oxide electrode, prepared via dealloying with an electrodeposited nickel-iron-copper alloy as a precursor, as the catalyst for water oxidation. The as-prepared core-shell nickel-iron-copper electrode is characterized with porous oxide shells and metallic cores. This tri-metal-based core-shell nickel-iron-copper electrode exhibits a remarkable activity toward water oxidation in alkaline medium with an overpotential of only 180 mV at a current density of 10 mA cm -2 . The core-shell NiFeCu electrode exhibits pH-dependent oxygen evolution reaction activity on the reversible hydrogen electrode scale, suggesting that non-concerted proton-electron transfers participate in catalyzing the oxygen evolution reaction. To the best of our knowledge, the as-fabricated core-shell nickel-iron-copper is one of the most promising oxygen evolution catalysts.

Investigation of mechanical properties and deformation behavior of single-crystal Al-Cu core-shell nanowire generated using non-equilibrium molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Sarkar, Jit

2018-06-01

Molecular dynamics (MD) simulation studies were carried out to generate a cylindrical single-crystal Al-Cu core-shell nanowire and its mechanical properties like yield strength and Young's modulus were evaluated in comparison to a solid aluminum nanowire and hollow copper nanowire which combines to constitute the core-shell structure respectively. The deformation behavior due to changes in the number of Wigner-Seitz defects and dislocations during the entire tensile deformation process was thoroughly studied for the Al-Cu core-shell nanowire. The single-crystal Al-Cu core-shell nanowire shows much higher yield strength and Young's modulus in comparison to the solid aluminum core and hollow copper shell nanowire due to tangling of dislocations caused by lattice mismatch between aluminum and copper. Thus, the Al-Cu core-shell nanowire can be reinforced in different bulk matrix to develop new type of light-weight nanocomposite materials with greatly enhanced material properties.

Folic acid-functionalized magnetic ZnFe2O4 hollow microsphere core/mesoporous silica shell composite particles: synthesis and application in drug release.

PubMed

Yang, Dandan; Wei, Kaiwei; Liu, Qi; Yang, Yong; Guo, Xue; Rong, Hongren; Cheng, Mei-Ling; Wang, Guoxiu

2013-07-01

A drug delivery system was designed by deliberately combining the useful functions into one entity, which was composed of magnetic ZnFe2O4 hollow microsphere as the core, and mesoporous silica with folic acid molecules as the outer shell. Amine groups coated magnetic ZnFe2O4 hollow microsphere core/mesoporous silica shell (MZHM-MSS-NH2) composite particles were first synthesized by a one-pot direct co-condensation method. Subsequently a novel kind of folic acid-functionalized magnetic ZnFe2O4 hollow microsphere core/mesoporous silica shell (MZHM-MSS-NHFA) composite particles were synthesized by conjugating folic acid as targeted molecule to MZHM-MSS-NH2. Ibuprofen, a well-known antiphlogistic drug, was used as a model drug to assess the loading and releasing behavior of the composite microspheres. The results show that the MZHM-MSS-NHFA system has the higher capacity of drug storage and good sustained drug-release property. Copyright © 2013 Elsevier B.V. All rights reserved.

Isostructural solid-solid phase transition in monolayers of soft core-shell particles at fluid interfaces: structure and mechanics.

PubMed

Rey, Marcel; Fernández-Rodríguez, Miguel Ángel; Steinacher, Mathias; Scheidegger, Laura; Geisel, Karen; Richtering, Walter; Squires, Todd M; Isa, Lucio

2016-04-21

We have studied the complete two-dimensional phase diagram of a core-shell microgel-laden fluid interface by synchronizing its compression with the deposition of the interfacial monolayer. Applying a new protocol, different positions on the substrate correspond to different values of the monolayer surface pressure and specific area. Analyzing the microstructure of the deposited monolayers, we discovered an isostructural solid-solid phase transition between two crystalline phases with the same hexagonal symmetry, but with two different lattice constants. The two phases corresponded to shell-shell and core-core inter-particle contacts, respectively; with increasing surface pressure the former mechanically failed enabling the particle cores to come into contact. In the phase-transition region, clusters of particles in core-core contacts nucleate, melting the surrounding shell-shell crystal, until the whole monolayer moves into the second phase. We furthermore measured the interfacial rheology of the monolayers as a function of the surface pressure using an interfacial microdisk rheometer. The interfaces always showed a strong elastic response, with a dip in the shear elastic modulus in correspondence with the melting of the shell-shell phase, followed by a steep increase upon the formation of a percolating network of the core-core contacts. These results demonstrate that the core-shell nature of the particles leads to a rich mechanical and structural behavior that can be externally tuned by compressing the interface, indicating new routes for applications, e.g. in surface patterning or emulsion stabilization.

Exciton dynamics in GaAs/(Al,Ga)As core-shell nanowires with shell quantum dots

NASA Astrophysics Data System (ADS)

Corfdir, Pierre; Küpers, Hanno; Lewis, Ryan B.; Flissikowski, Timur; Grahn, Holger T.; Geelhaar, Lutz; Brandt, Oliver

2016-10-01

We study the dynamics of excitons in GaAs/(Al,Ga)As core-shell nanowires by continuous-wave and time-resolved photoluminescence and photoluminescence excitation spectroscopy. Strong Al segregation in the shell of the nanowires leads to the formation of Ga-rich inclusions acting as quantum dots. At 10 K, intense light emission associated with these shell quantum dots is observed. The average radiative lifetime of excitons confined in the shell quantum dots is 1.7 ns. We show that excitons may tunnel toward adjacent shell quantum dots and nonradiative point defects. We investigate the changes in the dynamics of charge carriers in the shell with increasing temperature, with particular emphasis on the transfer of carriers from the shell to the core of the nanowires. We finally discuss the implications of carrier localization in the (Al,Ga)As shell for fundamental studies and optoelectronic applications based on core-shell III-As nanowires.

Gold decorated NaYF4:Yb,Er/NaYF4/silica (core/shell/shell) upconversion nanoparticles for photothermal destruction of BE(2)-C neuroblastoma cells

NASA Astrophysics Data System (ADS)

Qian, Li Peng; Zhou, Li Han; Too, Heng-Phon; Chow, Gan-Moog

2011-02-01

Gold decorated NaYF4:Yb,Er/NaYF4/silica (core/shell/shell) upconversion (UC) nanoparticles ( 70-80 nm) were synthesized using tetraethyl orthosilicate and chloroauric acid in a one-step reverse microemulsion method. Gold nanoparticles ( 6 nm) were deposited on the surface of silica shell of these core/shell/shell nanoparticles. The total upconversion emission intensity (green, red, and blue) of the core/shell/shell nanoparticles decreased by 31% after Au was deposited on the surface of silica shell. The upconverted green light was coupled with the surface plasmon of Au leading to rapid heat conversion. These UC/silica/Au nanoparticles were very efficient to destroy BE(2)-C cancer cells and showed strong potential in photothermal therapy.

A Solar Model with g-Modes

NASA Technical Reports Server (NTRS)

Wolff, Charles L.; Niemann, Hasso (Technical Monitor)

2002-01-01

Good evidence is assembled showing that the Suit's core arid surface vary on time scales from a month to a decade arid that a number of scales are similar. The most plausible source for numerous long time scales and periodicities is long-lived global oscillations. This suggests g-modes (oscillations restored mainly by buoyancy) because they particularly affect the core and base of the convective envelope, which then indirectly modulates the surface. Also, standing g-modes have rotational properties that match many observed periodicities. But the standard solar model (SSM) has a static core and excites few if any g-modes. making new interior structures worth exploring. The model outlined here assumes two well mixed shells near 0.18 and 0.68 R, (13 = solar radius) where sound speed data shows sharp deviations from the SSM. Mixing is sustained by flows driven by the oscillations. The shells form a cavity that excludes g-modes from their main damping region below 0.1 R, assisting their net excitation and increasing their oscillation periods by at least a factor of two and probably much more. In terms of the solar luminosity L, the modes transport up through the cavity a power approx. 0.004 L as a lower limit and 0.11 L as all upper limit. The modes dissipate energy in the outer shell and cool the inner shell, asymmetrically in each case, and this stimulates occasional convective events whose response time is typically 0.8 years longer near the inner shell. Such events cool the core and reduce neutrino flux while heating the envelope and increasing solar activity. This gives a physical basis for a well mixed Sun with low neutrino flux and basis for the observed anticorrelation and lag of neutrino behind surface activity.

Luminescence and efficiency optimization of InGaN/GaN core-shell nanowire LEDs by numerical modelling

NASA Astrophysics Data System (ADS)

Römer, Friedhard; Deppner, Marcus; Andreev, Zhelio; Kölper, Christopher; Sabathil, Matthias; Strassburg, Martin; Ledig, Johannes; Li, Shunfeng; Waag, Andreas; Witzigmann, Bernd

2012-02-01

We present a computational study on the anisotropic luminescence and the efficiency of a core-shell type nanowire LED based on GaN with InGaN active quantum wells. The physical simulator used for analyzing this device integrates a multidimensional drift-diffusion transport solver and a k . p Schrödinger problem solver for quantization effects and luminescence. The solution of both problems is coupled to achieve self-consistency. Using this solver we investigate the effect of dimensions, design of quantum wells, and current injection on the efficiency and luminescence of the core-shell nanowire LED. The anisotropy of the luminescence and re-absorption is analyzed with respect to the external efficiency of the LED. From the results we derive strategies for design optimization.

Graded core/shell semiconductor nanorods and nanorod barcodes

DOEpatents

Alivisatos, A Paul [Oakland, CA; Scher, Erik C [San Francisco, CA; Manna, Liberato [Palo Del Collie, IT

2009-05-19

Disclosed herein is a graded core/shell semiconductor nanorod having at least a first segment of a core of a Group II-VI, Group III-V or a Group IV semiconductor, a graded shell overlying the core, wherein the graded shell comprises at least two monolayers, wherein the at least two monolayers each independently comprise a Group II-VI, Group III-V or a Group IV semiconductor.

Strain distribution of confined Ge/GeO2 core/shell nanoparticles engineered by growth environments

NASA Astrophysics Data System (ADS)

Wei, Wenyan; Yuan, Cailei; Luo, Xingfang; Yu, Ting; Wang, Gongping

2016-02-01

The strain distributions of Ge/GeO2 core/shell nanoparticles confined in different host matrix grown by surface oxidation are investigated. The simulated results by finite element method demonstrated that the strains of the Ge core and the GeO2 shell strongly depend on the growth environments of the nanoparticles. Moreover, it can be found that there is a transformation of the strain on Ge core from tensile to compressive strain during the growth of Ge/GeO2 core/shell nanoparticles. And, the transformation of the strain is closely related with the Young's modulus of surrounding materials of Ge/GeO2 core/shell nanoparticles.

The diamagnetic susceptibility of a donor in a semiconductor core shell quantum dot

NASA Astrophysics Data System (ADS)

Sudharshan, M. S.; Subhash, P.; Shaik, Nagoor Babu; Kalpana, P.; Jayakumar, K.; Reuben, A. Merwyn Jasper D.

2015-06-01

The effect of Aluminium concentration, shell thickness and size of the core shell Quantum Dot on the Diamagnetic Susceptibility of a donor in the Core Shell Quantum Dot is calculated in the effective mass approximation using the variational method. The results are presented and discussed.

Gamow-Teller Strength Distributions for pf-shell Nuclei and its Implications in Astrophysics

NASA Astrophysics Data System (ADS)

Rahman, M.-U.; Nabi, J.-U.

2009-08-01

The {pf}-shell nuclei are present in abundance in the pre-supernova and supernova phases and these nuclei are considered to play an important role in the dynamics of core collapse supernovae. The B(GT) values are calculated for the {pf}-shell nuclei 55Co and 57Zn using the pn-QRPA theory. The calculated B(GT) strengths have differences with earlier reported shell model calculations, however, the results are in good agreement with the experimental data. These B(GT) strengths are used in the calculations of weak decay rates which play a decisive role in the core-collapse supernovae dynamics and nucleosynthesis. Unlike previous calculations the so-called Brink's hypothesis is not assumed in the present calculation which leads to a more realistic estimate of weak decay rates. The electron capture rates are calculated over wide grid of temperature ({0.01} × 109 - 30 × 109 K) and density (10-1011 g-cm-3). Our rates are enhanced compared to the reported shell model rates. This enhancement is attributed partly to the liberty of selecting a huge model space, allowing consideration of many more excited states in the present electron capture rates calculations.

Structure and magnetic properties of chromium doped cobalt molybdenum nitrides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guskos, Niko; Żołnierkiewicz, Grzegorz; Typek, Janusz

Four nanocomposites containing mixed phases of Co{sub 3}Mo{sub 3}N and Co{sub 2}Mo{sub 3}N doped with chromium have been prepared. A linear fit is found for relation between Co{sub 2}Mo{sub 3}N and chromium concentrations. The magnetization in ZFC and FC modes at different temperatures (2–300 K) and in applied magnetic fields (up to 70 kOe) have been investigated. It has been detected that many magnetic characteristics of the studied four nanocomposites correlate not with the chromium concentration but with nanocrystallite sizes. The obtained results were interpreted in terms of magnetic core-shell model of a nanoparticle involving paramagnetic core with two magneticmore » sublattices and a ferromagnetic shell related to chromium doping. - Highlights: • A new chromium doped mixed Co-Mn-N nanocomposites were synthesized. • Surface ferromagnetism was detected in a wide temperature range. • Core-shell model was applied to explain nanocomposites magnetism.« less

Long-period seismology on Europa: 1. Physically consistent interior models

NASA Astrophysics Data System (ADS)

Cammarano, F.; Lekic, V.; Manga, M.; Panning, M.; Romanowicz, B.

2006-12-01

In order to examine the potential of seismology to determine the interior structure and properties of Europa, it is essential to calculate seismic velocities and attenuation for the range of plausible interiors. We calculate a range of models for the physical structure of Europa, as constrained by the satellite's composition, mass, and moment of inertia. We assume a water-ice shell, a pyrolitic or a chondritic mantle, and a core composed of pure iron or iron plus 20 weight percent of sulfur. We consider two extreme mantle thermal states: hot and cold. Given a temperature and composition, we determine density, seismic velocities, and attenuation using thermodynamical models. While anelastic effects will be negligible in a cold mantle and the brittle part of the ice shell, strong dispersion and dissipation are expected in a hot convective mantle and the bulk of the ice shell. There is a strong relationship between different thermal structures and compositions. The ``hot'' mantle may maintain temperatures consistent with a liquid core made of iron plus light elements. For the ``cold scenarios,'' the possibility of a solid iron core cannot be excluded, and it may even be favored. The depths of the ocean and core-mantle boundary are determined with high precision, 10 km and 40 km, respectively, once we assume a composition and thermal structure. Furthermore, the depth of the ocean is relatively insensitive (4 km) to the core composition used.

NaF-loaded core-shell PAN-PMMA nanofibers as reinforcements for Bis-GMA/TEGDMA restorative resins.

PubMed

Cheng, Liyuan; Zhou, Xuegang; Zhong, Hong; Deng, Xuliang; Cai, Qing; Yang, Xiaoping

2014-01-01

A kind of core-shell nanofibers containing sodium fluoride (NaF) was produced and used as reinforcing materials for dimethacrylate-based dental restorative resins in this study. The core-shell nanofibers were prepared by coaxial-electrospinning with polyacrylonitrile (PAN) and poly(methyl methacrylate) (PMMA) solutions as core and shell fluids, respectively. The produced PAN-PMMA nanofibers varied in fiber diameter and the thickness of PMMA shell depending on electrospinning parameters. NaF-loaded nanofibers were obtained by incorporating NaF nanocrystals into the core fluid at two loadings (0.8 or 1.0wt.%). Embedment of NaF nanocrystals into the PAN core did not damage the core-shell structure. The addition of PAN-PMMA nanofibers into Bis-GMA/TEGDMA clearly showed the reinforcement due to the good interfacial adhesion between fibers and resin. The flexural strength (Fs) and flexural modulus (Ey) of the composites decreased slightly as the thickness of PMMA shell increasing. Sustained fluoride releases with minor initial burst release were achieved from NaF-loaded core-shell nanofibers and the corresponding composites, which was quite different from the case of embedding NaF nanocrystals into the dental resin directly. The study demonstrated that NaF-loaded PAN-PMMA core-shell nanofibers were not only able to improve the mechanical properties of restorative resin, but also able to provide sustained fluoride release to help in preventing secondary caries. © 2013.

Development of hydrogel TentaGel shell-core beads for ultrahigh throughput solution-phase screening of encoded OBOC combinatorial small molecule libraries.

PubMed

Baek, Hyoung Gee; Liu, Ruiwu; Lam, Kit S

2009-01-01

The one-bead one-compound (OBOC) combinatorial library method enables the rapid generation and screening of millions of discrete chemical compounds on beads. Most of the OBOC screening methods require the library compounds to remain tethered to the bead during screening process. Methods have also been developed to release library compounds from immobilized beads for in situ solution phase or "lawn" assays. However, this latter approach, while extremely powerful, is severely limited by the lack of suitable solid supports for such assays. Here, we report on the development of a novel hydrogel TentaGel shell-core (HTSC) bead in which hydrogel is grafted onto the polystyrene-based TentaGel (TG) bead as an outer shell (5-80 mum thick) via free radical surface-initiated polymerization. This novel shell-core bilayer resin enables the preparation of encoded OBOC combinatorial small molecule libraries, such that the library compounds reside on the highly hydrophilic outer layer and the coding tags reside in the polystyrene-based TG core. Using fluorescein as a model small molecule compound, we have demonstrated that fluorescein molecules that have been linked covalently to the hydrogel shell via a disulfide bond could readily diffuse out of the hydrogel layer into the bead surrounding after reduction with dithiothreitol. In contrast, under identical condition, the released fluorescein molecules remained bound to unmodified TG bead. We have prepared an encoded OBOC small molecule library on the novel shell-core beads and demonstrated that the beads can be readily decoded.

The Magnetic Dichotomy of the Galilean Satellites Europa and Ganymede

NASA Astrophysics Data System (ADS)

Breuer, D.; Hussmann, H.; Spohn, T.

2006-12-01

A major discovery of the Galileo mission was the detection of Ganymede's self-generated magnetic field. The magnetic field also proves beyond doubt that Ganymede is fully differentiated into an iron-rich core, a silicate mantle, and an outer ice shell that most likely also contains an ocean. It is widely believed that Europa has a similar structure although the absence of a self-sustained magnetic field makes the case for a core in Europa less compelling. Since Callisto's moment-of-inertia factor suggests an undifferentiated satellite and since the absence of a magnetic of Io is best explained by tidal heating in the mantle blocking the heat flow from the core (Wienbruch and Spohn, 1995), Europa and Ganymede form a magnetic dichotomy in the Jovian system. We have used stagnant lid models of convection in the two icy satellites to calculate thermal history models with core cooling and have allowed for inner core growth through freezing. The models have stagnant lid convection or conduction in the outer ice shells (depending on material parameters), isothermal oceans, and, in the case of Ganymede, stagnant-lid convection in the ice shell underneath the ocean and above the rock mantle. For Europa the ocean interfaces with the rock mantle. We assume iron cores that start fully molten for both satellites, the radii of which were taken from Sohl et al. (2002). These models suggest that Europa has a few 100 km smaller core and thinner mantle and a substantially thinner ice shell. All but interior structure parameters equal, we find that core convection and hence dynamo action is more likely for Europa than for Ganymede. The reason are mainly the larger core and the thicker mantle. Accepting core convection in Ganymede, the question than poses itself of how to explain the absence of core convection in Europa. We find and will discuss the following possibilities: 1) Europa has no iron core. This is consistent with the observation but leaves the question why Ganymede should have fully differentiated while Europa did not. 2) A higher concentration of light elements in Europa's core. Taking Sulfur as a point in case, Europa may have more sulfur, in which case more cooling would be required to freeze the core, or may even be on the FeS rich side of the eutectic, in which case chemical convection could be less efficient in Europa. 3) Tidal heating. We find that a few times the present-day radiogenic heating rate would be required to possibly frustrate dynamo action. This much tidal heat is consistent with the models of Hussmann et al. (2002) Hussmann, H. et al., 2002. Icarus, 156, 143-151; Sohl, F. et al., 2002, Icarus, 157,104-119; Wienbruch, U. and T. Spohn, 1995, PSS, 43, 1045-1057

Large-area super-resolution optical imaging by using core-shell microfibers

NASA Astrophysics Data System (ADS)

Liu, Cheng-Yang; Lo, Wei-Chieh

2017-09-01

We first numerically and experimentally report large-area super-resolution optical imaging achieved by using core-shell microfibers. The particular spatial electromagnetic waves for different core-shell microfibers are studied by using finite-difference time-domain and ray tracing calculations. The focusing properties of photonic nanojets are evaluated in terms of intensity profile and full width at half-maximum along propagation and transversal directions. In experiment, the general optical fiber is chemically etched down to 6 μm diameter and coated with different metallic thin films by using glancing angle deposition. The direct imaging of photonic nanojets for different core-shell microfibers is performed with a scanning optical microscope system. We show that the intensity distribution of a photonic nanojet is highly related to the metallic shell due to the surface plasmon polaritons. Furthermore, large-area super-resolution optical imaging is performed by using different core-shell microfibers placed over the nano-scale grating with 150 nm line width. The core-shell microfiber-assisted imaging is achieved with super-resolution and hundreds of times the field-of-view in contrast to microspheres. The possible applications of these core-shell optical microfibers include real-time large-area micro-fluidics and nano-structure inspections.

A colorimetric assay for measuring iodide using Au@Ag core-shell nanoparticles coupled with Cu(2+).

PubMed

Zeng, Jingbin; Cao, Yingying; Lu, Chun-Hua; Wang, Xu-Dong; Wang, Qianru; Wen, Cong-Ying; Qu, Jian-Bo; Yuan, Cunguang; Yan, Zi-Feng; Chen, Xi

2015-09-03

Au@Ag core-shell nanoparticles (NPs) were synthesized and coupled with copper ion (Cu(2+)) for the colorimetric sensing of iodide ion (I(-)). This assay relies on the fact that the absorption spectra and the color of metallic core-shell NPs are sensitive to their chemical ingredient and dimensional core-to-shell ratio. When I(-) was added to the Au@Ag core-shell NPs-Cu(2+) system/solution, Cu(2+) can oxidize I(-) into iodine (I2), which can further oxidize silver shells to form silver iodide (AgI). The generated Au@AgI core-shell NPs led to color changes from yellow to purple, which was utilized for the colorimetric sensing of I(-). The assay only took 10 min with a lowest detectable concentration of 0.5 μM, and it exhibited excellent selectivity for I(-) over other common anions tested. Furthermore, Au@Ag core-shell NPs-Cu(2+) was embedded into agarose gels as inexpensive and portable "test strips", which were successfully used for the semi-quantitation of I(-) in dried kelps. Copyright © 2015 Elsevier B.V. All rights reserved.

Ultrafast light matter interaction in CdSe/ZnS core-shell quantum dots

NASA Astrophysics Data System (ADS)

Yadav, Rajesh Kumar; Sharma, Rituraj; Mondal, Anirban; Adarsh, K. V.

2018-04-01

Core-shell quantum dot are imperative for carrier (electron and holes) confinement in core/shell, which provides a stage to explore the linear and nonlinear optical phenomena at the nanoscalelimit. Here we present a comprehensive study of ultrafast excitation dynamics and nonlinear optical absorption of CdSe/ZnS core shell quantum dot with the help of ultrafast spectroscopy. Pump-probe and time-resolved measurements revealed the drop of trapping at CdSe surface due to the presence of the ZnS shell, which makes more efficient photoluminescence. We have carried out femtosecond transient absorption studies of the CdSe/ZnS core-shell quantum dot by irradiation with 400 nm laser light, monitoring the transients in the visible region. The optical nonlinearity of the core-shell quantum dot studied by using the Z-scan technique with 120 fs pulses at the wavelengths of 800 nm. The value of two photon absorption coefficients (β) of core-shell QDs extracted as80cm/GW, and it shows excellent benchmark for the optical limiting onset of 2.5GW/cm2 with the low limiting differential transmittance of 0.10, that is an order of magnitude better than graphene based materials.

Fabrication of Ni@Ti core-shell nanoparticles by modified gas aggregation source

NASA Astrophysics Data System (ADS)

Hanuš, J.; Vaidulych, M.; Kylián, O.; Choukourov, A.; Kousal, J.; Khalakhan, I.; Cieslar, M.; Solař, P.; Biederman, H.

2017-11-01

Ni@Ti core-shell nanoparticles were prepared by a vacuum based method using the gas aggregation source (GAS) of nanoparticles. Ni nanoparticles fabricated in the GAS were afterwards coated by a Ti shell. The Ti shell was deposited by means of magnetron sputtering. The Ni nanoparticles were decelerated in the vicinity of the magnetron to the Ar drift velocity in the second deposition chamber. X-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy analysis of the nanoparticles showed the core-shell structure. It was shown that the thickness of the shell can be easily tuned by the process parameters with a maximum achieved thickness of the Ti shell ~2.5 nm. The core-shell structure was confirmed by the STEM analysis of the particles.

3D Study of the Morphology and Dynamics of Zeolite Nucleation.

PubMed

Melinte, Georgian; Georgieva, Veselina; Springuel-Huet, Marie-Anne; Nossov, Andreï; Ersen, Ovidiu; Guenneau, Flavien; Gedeon, Antoine; Palčić, Ana; Bozhilov, Krassimir N; Pham-Huu, Cuong; Qiu, Shilun; Mintova, Svetlana; Valtchev, Valentin

2015-12-07

The principle aspects and constraints of the dynamics and kinetics of zeolite nucleation in hydrogel systems are analyzed on the basis of a model Na-rich aluminosilicate system. A detailed time-series EMT-type zeolite crystallization study in the model hydrogel system was performed to elucidate the topological and temporal aspects of zeolite nucleation. A comprehensive set of analytical tools and methods was employed to analyze the gel evolution and complement the primary methods of transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR) spectroscopy. TEM tomography reveals that the initial gel particles exhibit a core-shell structure. Zeolite nucleation is topologically limited to this shell structure and the kinetics of nucleation is controlled by the shell integrity. The induction period extends to the moment when the shell is consumed and the bulk solution can react with the core of the gel particles. These new findings, in particular the importance of the gel particle shell in zeolite nucleation, can be used to control the growth process and properties of zeolites formed in hydrogels. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetic field directed assembly of superstructures of ferrite-ferroelectric core-shell nanoparticles and studies on magneto-electric interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Srinivasan, G., E-mail: srinivas@oakland.edu; Sreenivasulu, G.; Benoit, Crystal

2015-05-07

Composites of ferromagnetic and ferroelectric are of interest for studies on mechanical strain mediated magneto-electric (ME) interactions and for useful technologies. Here, we report on magnetic-field-assisted-assembly of barium titanate (BTO)-nickel ferrite (NFO) core-shell particles into linear chains and 2D/3D arrays and measurements of ME effects in such assemblies. First, we synthesized the core-shell nano-particles with 50–600 nm BTO and 10–200 nm NFO by chemical self-assembly by coating the ferroic particles with complementary coupling groups and allowing them to self-assemble in the presence of a catalyst via the “click” reaction. The core-shell structure was confirmed with electron microscopy and scanning probe microscopy. Wemore » obtained superstructure of the core-shell particles by subjecting them to a magnetic field gradient that exerts an attractive force on the particles and align them toward the regions of high field strengths. At low particle concentration, linear chains were formed and they evolved into 2D and 3D arrays at high particle concentrations. Magnetoelectric characterization on unassembled films and assembled arrays has been performed through measurements of low-frequency ME voltage coefficient (MEVC) by subjecting the sample to a bias magnetic field and an ac magnetic field. The MEVC is higher for field-assembled samples than for unassembled films and is found to be sensitive to field orientation with a higher MEVC for magnetic fields parallel to the array direction than for magnetic fields perpendicular to the array. A maximum MEVC of 20 mV/cm Oe, one of the highest reported for any bulk nanocomposite, is measured across the array thickness. A model is provided for ME coupling in the superstructures of BTO-NFO particulate composites. First, we estimated the MEVC for a free-standing BTO-NFO core-shell particle and then extended the model to include an array of linear chains of the particles. The theoretical estimates are in qualitative agreement with the data.« less

Magnetic field directed assembly of superstructures of ferrite-ferroelectric core-shell nanoparticles and studies on magneto-electric interactions

NASA Astrophysics Data System (ADS)

Srinivasan, G.; Sreenivasulu, G.; Benoit, Crystal; Petrov, V. M.; Chavez, F.

2015-05-01

Composites of ferromagnetic and ferroelectric are of interest for studies on mechanical strain mediated magneto-electric (ME) interactions and for useful technologies. Here, we report on magnetic-field-assisted-assembly of barium titanate (BTO)-nickel ferrite (NFO) core-shell particles into linear chains and 2D/3D arrays and measurements of ME effects in such assemblies. First, we synthesized the core-shell nano-particles with 50-600 nm BTO and 10-200 nm NFO by chemical self-assembly by coating the ferroic particles with complementary coupling groups and allowing them to self-assemble in the presence of a catalyst via the "click" reaction. The core-shell structure was confirmed with electron microscopy and scanning probe microscopy. We obtained superstructure of the core-shell particles by subjecting them to a magnetic field gradient that exerts an attractive force on the particles and align them toward the regions of high field strengths. At low particle concentration, linear chains were formed and they evolved into 2D and 3D arrays at high particle concentrations. Magnetoelectric characterization on unassembled films and assembled arrays has been performed through measurements of low-frequency ME voltage coefficient (MEVC) by subjecting the sample to a bias magnetic field and an ac magnetic field. The MEVC is higher for field-assembled samples than for unassembled films and is found to be sensitive to field orientation with a higher MEVC for magnetic fields parallel to the array direction than for magnetic fields perpendicular to the array. A maximum MEVC of 20 mV/cm Oe, one of the highest reported for any bulk nanocomposite, is measured across the array thickness. A model is provided for ME coupling in the superstructures of BTO-NFO particulate composites. First, we estimated the MEVC for a free-standing BTO-NFO core-shell particle and then extended the model to include an array of linear chains of the particles. The theoretical estimates are in qualitative agreement with the data.

Interface engineered ferrite@ferroelectric core-shell nanostructures: A facile approach to impart superior magneto-electric coupling

NASA Astrophysics Data System (ADS)

Abraham, Ann Rose; Raneesh, B.; Das, Dipankar; Oluwafemi, Oluwatobi Samuel; Thomas, Sabu; Kalarikkal, Nandakumar

2018-04-01

The electric field control of magnetism in multiferroics is attractive for the realization of ultra-fast and miniaturized low power device applications like nonvolatile memories. Room temperature hybrid multiferroic heterostructures with core-shell (0-0) architecture (ferrite core and ferroelectric shell) were developed via a two-step method. High-Resolution Transmission Electron Microscopy (HRTEM) images confirm the core-shell structure. The temperature dependant magnetization measurements and Mossbauer spectra reveal superparamagnetic nature of the core-shell sample. The ferroelectric hysteresis loops reveal leaky nature of the samples. The results indicate the promising applications of the samples for magneto-electric memories and spintronics.

Size-Dependent Specific Surface Area of Nanoporous Film Assembled by Core-Shell Iron Nanoclusters

DOE PAGES

Antony, Jiji; Nutting, Joseph; Baer, Donald R.; ...

2006-01-01

Nmore » anoporous films of core-shell iron nanoclusters have improved possibilities for remediation, chemical reactivity rate, and environmentally favorable reaction pathways. Conventional methods often have difficulties to yield stable monodispersed core-shell nanoparticles. We produced core-shell nanoclusters by a cluster source that utilizes combination of Fe target sputtering along with gas aggregations in an inert atmosphere at 7 ∘ C . Sizes of core-shell iron-iron oxide nanoclusters are observed with transmission electron microscopy (TEM). The specific surface areas of the porous films obtained from Brunauer-Emmett-Teller (BET) process are size-dependent and compared with the calculated data.« less

Hierarchical Mesoporous Organosilica-Silica Core-Shell Nanoparticles Capable of Controlled Fungicide Release.

PubMed

Luo, Leilei; Liang, Yucang; Erichsen, Egil Severin; Anwander, Reiner

2018-05-17

A new class of hierarchically structured mesoporous silica core-shell nanoparticles (HSMSCSNs) with a periodic mesoporous organosilica (PMO) core and a mesoporous silica (MS) shell is reported. The applied one-pot, two-step strategy allows rational control over the core/shell chemical composition, topology, and pore/particle size, simply by adjusting the reaction conditions in the presence of cetyltrimethylammonium bromide (CTAB) as structure-directing agent under basic conditions. The spherical, ethylene- or methylene-bridged PMO cores feature hexagonal (p6mm) or cage-like cubic symmetry (Pm3‾ n) depending on the organosilica precursor. The hexagonal MS shell was obtained by n-hexane-induced controlled hydrolysis of TEOS followed by directional co-assembly/condensation of silicate/CTAB composites at the PMO cores. The HSMSCSNs feature a hierarchical pore structure with pore diameters of about 2.7 and 5.6 nm in the core and shell domains, respectively. The core sizes and shell thicknesses are adjustable in the ranges of 90-275 and 15-50 nm, respectively, and the surface areas (max. 1300 m 2  g -1 ) and pore volumes (max. 1.83 cm 3  g -1 ) are among the highest reported for core-shell nanoparticles. The adsorption and controlled release of the fungicide propiconazole by the HSMSCSNs showed a three-stage release profile. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hypersonic vibrations of Ag@SiO2 (cubic core)-shell nanospheres.

PubMed

Sun, Jing Ya; Wang, Zhi Kui; Lim, Hock Siah; Ng, Ser Choon; Kuok, Meng Hau; Tran, Toan Trong; Lu, Xianmao

2010-12-28

The intriguing optical and catalytic properties of metal-silica core-shell nanoparticles, inherited from their plasmonic metallic cores together with the rich surface chemistry and increased stability offered by their silica shells, have enabled a wide variety of applications. In this work, we investigate the confined vibrational modes of a series of monodisperse Ag@SiO(2) (cubic core)-shell nanospheres synthesized using a modified Stöber sol-gel method. The particle-size dependence of their mode frequencies has been mapped by Brillouin light scattering, a powerful tool for probing hypersonic vibrations. Unlike the larger particles, the observed spheroidal-like mode frequencies of the smaller ones do not scale with inverse diameter. Interestingly, the onset of the deviation from this linearity occurs at a smaller particle size for higher-energy modes than for lower-energy ones. Finite element simulations show that the mode displacement profiles of the Ag@SiO(2) core-shells closely resemble those of a homogeneous SiO(2) sphere. Simulations have also been performed to ascertain the effects that the core shape and the relative hardness of the core and shell materials have on the vibrations of the core-shell as a whole. As the vibrational modes of a particle have a bearing on its thermal and mechanical properties, the findings would be of value in designing core-shell nanostructures with customized thermal and mechanical characteristics.

Gold/silver core-shell 20 nm nanoparticles extracted from citrate solution examined by XPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Engelhard, Mark H.; Smith, Jordan N.; Baer, Donald R.

Silver nanoparticles of many types are widely used in consumer and medical products. The surface chemistry of particles and the coatings that form during synthesis or use in many types of media can significantly impact the behaviors of particles including dissolution, transformation and biological or environmental impact. Consequently it is useful to be able to extract information about the thickness of surface coatings and other attributes of nanoparticles produced in a variety of ways. It has been demonstrated that X-ray Photoelectron Spectroscopy (XPS) can be reliably used to determine the thickness of organic and other nanoparticles coatings and shells. However,more » care is required to produce reliable and consistent information. Here we report the XPS spectra from gold/silver core-shell nanoparticles of nominal size 20 nm removed from a citrate saturated solution after one and two washing cycles. The Simulation of Electron Spectra for Surface Analysis (SESSA) program had been used to model peak amplitudes to obtain information on citrate coatings that remain after washing and demonstrate the presence of the gold core. This data is provided so that others can compare use of SESSA or other modeling approaches to quantify the nature of coatings to those already published and to explore the impacts particle non-uniformities on XPS signals from core-shell nanoparticles.« less

Facet-Dependent Deposition of Highly Strained Alloyed Shells on Intermetallic Nanoparticles for Enhanced Electrocatalysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Chenyu; Sang, Xiahan; Gamler, Jocelyn T. L.

Compressive surface strains can enhance the performance of platinum-based core@shell electrocatalysts for the oxygen reduction reaction (ORR). Bimetallic core@shell nanoparticles (NPs) are widely studied nanocatalysts but often have limited lattice mismatch and surface compositions; investigations of core@shell NPs with greater compositional complexity and lattice misfit are in their infancy. Here, a new class of multimetallic NPs composed of intermetallic cores and random alloy shells is reported. Specifically, face-centered cubic (fcc) Pt- Cu random alloy shells were deposited non-epitaxially on PdCu B2 intermetallic seeds, giving rise to faceted core@shell NPs with highly strained surfaces. In fact, high resolution transmission electron microscopymore » (HRTEM) revealed orientation-dependent surface strains, where the compressive strains were minimal on Pt-Cu {111} facets but greater on {200} facets. These core@shell NPs provide higher specific and mass activities for the ORR when compared to conventional Pt-Cu NPs. Moreover, these intermetallic@random alloy NPs displayed high endurance, undergoing 10,000 cycles with only a slight decay in activity and no apparent structural changes.« less

Core-shell TiO2@ZnO nanorods for efficient ultraviolet photodetection

NASA Astrophysics Data System (ADS)

Panigrahi, Shrabani; Basak, Durga

2011-05-01

Core-shell TiO2@ZnO nanorods (NRs) have been fabricated by a simple two step method: growth of ZnO NRs' array by an aqueous chemical technique and then coating of the NRs with a solution of titanium isopropoxide [Ti(OC3H7)4] followed by a heating step to form the shell. The core-shell nanocomposites are composed of single-crystalline ZnO NRs, coated with a thin TiO2 shell layer obtained by varying the number of coatings (one, three and five times). The ultraviolet (UV) emission intensity of the nanocomposite is largely quenched due to an efficient electron-hole separation reducing the band-to-band recombinations. The UV photoconductivity of the core-shell structure with three times TiO2 coating has been largely enhanced due to photoelectron transfer between the core and the shell. The UV photosensitivity of the nanocomposite becomes four times larger while the photocurrent decay during steady UV illumination has been decreased almost by 7 times compared to the as-grown ZnO NRs indicating high efficiency of these core-shell structures as UV sensors.

Facet-Dependent Deposition of Highly Strained Alloyed Shells on Intermetallic Nanoparticles for Enhanced Electrocatalysis

DOE PAGES

Wang, Chenyu; Sang, Xiahan; Gamler, Jocelyn T. L.; ...

2017-08-25

Compressive surface strains can enhance the performance of platinum-based core@shell electrocatalysts for the oxygen reduction reaction (ORR). Bimetallic core@shell nanoparticles (NPs) are widely studied nanocatalysts but often have limited lattice mismatch and surface compositions; investigations of core@shell NPs with greater compositional complexity and lattice misfit are in their infancy. Here, a new class of multimetallic NPs composed of intermetallic cores and random alloy shells is reported. Specifically, face-centered cubic (fcc) Pt- Cu random alloy shells were deposited non-epitaxially on PdCu B2 intermetallic seeds, giving rise to faceted core@shell NPs with highly strained surfaces. In fact, high resolution transmission electron microscopymore » (HRTEM) revealed orientation-dependent surface strains, where the compressive strains were minimal on Pt-Cu {111} facets but greater on {200} facets. These core@shell NPs provide higher specific and mass activities for the ORR when compared to conventional Pt-Cu NPs. Moreover, these intermetallic@random alloy NPs displayed high endurance, undergoing 10,000 cycles with only a slight decay in activity and no apparent structural changes.« less

LaF3 core/shell nanoparticles for subcutaneous heating and thermal sensing in the second biological-window

NASA Astrophysics Data System (ADS)

Ximendes, Erving Clayton; Rocha, Uéslen; Kumar, Kagola Upendra; Jacinto, Carlos; Jaque, Daniel

2016-06-01

We report on Ytterbium and Neodymium codoped LaF3 core/shell nanoparticles capable of simultaneous heating and thermal sensing under single beam infrared laser excitation. Efficient light-to-heat conversion is produced at the Neodymium highly doped shell due to non-radiative de-excitations. Thermal sensing is provided by the temperature dependent Nd3+ → Yb3+ energy transfer processes taking place at the core/shell interface. The potential application of these core/shell multifunctional nanoparticles for controlled photothermal subcutaneous treatments is also demonstrated.

X-rays from Eta Carinae

NASA Technical Reports Server (NTRS)

Chlebowski, T.; Seward, F. D.; Swank, J.; Szymkowiak, A.

1984-01-01

X-ray observations of Eta Car obtained with the high-resolution imager and solid-state spectrometer of the Einstein observatory are reported and interpreted in terms of a two-shell model. A soft component with temperature 5 million K is located in the expanding outer shell, and the hard core component with temperature 80 million K is attributed to the interaction of a high-velocity stellar wind from the massive central object with the inner edge of a dust shell. Model calculations based on comparison with optical and IR data permit estimation of the mass of the outer shell (0.004 solar mass), the mass of the dust shell (3 solar mass), and the total shell expansion energy (less than 2 x 10 to the 49th ergs).

Inorganic/organic nanocomposites: Reaching a high filler content without increasing viscosity using core-shell structured nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benhadjala, W., E-mail: warda.benhadjala@cea.fr; CEA, LETI, Minatec Campus, 38000 Grenoble; Gravoueille, M.

2015-11-23

Extensive research is being conducted on the development of inorganic/organic nanocomposites for a wide variety of applications in microelectronics, biotechnologies, photonics, adhesives, or optical coatings. High filler contents are usually required to fully optimize the nanocomposites properties. However, numerous studies demonstrated that traditional composite viscosity increases with increasing the filler concentration reducing therefore significantly the material processability. In this work, we synthesized inorganic/organic core-shell nanocomposites with different shell thicknesses. By reducing the shell thickness while maintaining a constant core size, the nanoparticle molecular mass decreases but the nanocomposite filler fraction is correlatively increased. We performed viscosity measurements, which clearly highlightedmore » that intrinsic viscosity of hybrid nanoparticles decreases as the molecular mass decreases, and thus, as the filler fraction increases, as opposed to Einstein predictions about the viscosity of traditional inorganic/polymer two-phase mixtures. This exceptional behavior, modeled by Mark-Houwink-Sakurada equation, proves to be a significant breakthrough for the development of industrializable nanocomposites with high filler contents.« less

Synthesis and optical properties of core-multi-shell CdSe/CdS/ZnS quantum dots: Surface modifications

NASA Astrophysics Data System (ADS)

Ratnesh, R. K.; Mehata, Mohan Singh

2017-02-01

We report two port synthesis of CdSe/CdS/ZnS core-multi-shell quantum dots (Q-dots) and their structural properties. The multi-shell structures of Q-dots were developed by using successive ionic layer adsorption and reaction (SILAR) technique. The obtained Q-dots show high crystallinity with the step-wise adjustment of lattice parameters in the radial direction. The size of the core and core-shell Q-dots estimated by transmission electron microscopy images and absorption spectra is about 3.4 and 5.3 nm, respectively. The water soluble Q-dots (scheme-1) were prepared by using ligand exchange method, and the effect of pH was discussed regarding the variation of quantum yield (QY). The decrease of a lifetime of core-multi-shell Q-dots with respect to core CdSe indicates that the shell growth may be tuned by the lifetimes. Thus, the study clearly demonstrates that the core-shell approach can be used to substantially improve the optical properties of Q-dots desired for various applications.

Dendritic core-shell nickel-iron-copper metal/metal oxide electrode for efficient electrocatalytic water oxidation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Peili; Li, Lin; Nordlund, Dennis

Electrochemical water splitting requires efficient water oxidation catalysts to accelerate the sluggish kinetics of water oxidation reaction. Here in this paper, we report a promisingly dendritic core-shell nickel-iron-copper metal/metal oxide electrode, prepared via dealloying with an electrodeposited nickel-iron-copper alloy as a precursor, as the catalyst for water oxidation. The as-prepared core-shell nickel-iron-copper electrode is characterized with porous oxide shells and metallic cores. This tri-metal-based core-shell nickel-iron-copper electrode exhibits a remarkable activity toward water oxidation in alkaline medium with an overpotential of only 180 mV at a current density of 10 mA cm -2. The core-shell NiFeCu electrode exhibits pH-dependent oxygenmore » evolution reaction activity on the reversible hydrogen electrode scale, suggesting that non-concerted proton-electron transfers participate in catalyzing the oxygen evolution reaction. To the best of our knowledge, the as-fabricated core-shell nickel-iron-copper is one of the most promising oxygen evolution catalysts.« less

Construction of self-supported porous TiO2/NiO core/shell nanorod arrays for electrochemical capacitor application

NASA Astrophysics Data System (ADS)

Wu, J. B.; Guo, R. Q.; Huang, X. H.; Lin, Y.

2013-12-01

High-quality metal oxides hetero-structured nanoarrays have been receiving great attention in electrochemical energy storage application. Self-supported TiO2/NiO core/shell nanorod arrays are prepared on carbon cloth via the combination of hydrothermal synthesis and electro-deposition methods. The obtained core/shell nanorods consist of nanorod core and interconnected nanoflake shell, as well as hierarchical porosity. As cathode materials for pseudo-capacitors, the TiO2/NiO core/shell nanorod arrays display impressive electrochemical performances with both high capacitance of 611 F g-1 at 2 A g-1, and pretty good cycling stability with a retention of 89% after 5000 cycles. Besides, as compared to the single NiO nanoflake arrays on carbon cloth, the TiO2/NiO core/shell nanorod arrays exhibit much better electrochemical properties with higher capacitance, better electrochemical activity and cycling life. This enhanced performance is mainly due to the core/shell nanorods architecture offering fast ion/electron transfer and sufficient contact between active materials and electrolyte.

Degradation of Si/Ge core/shell nanowire heterostructures during lithiation and delithiation at 0.8 and 20 A g-1.

PubMed

Kim, Dongheun; Li, Nan; Sheehan, Chris J; Yoo, Jinkyoung

2018-04-26

Si/Ge core/shell nanowire heterostructures have been expected to provide high energy and power densities for lithium ion battery anodes due to the large capacity of Si and the high electrical and ionic conductivities of Ge. Although the battery anode performances of Si/Ge core/shell nanowire heterostructures have been characterized, the degradation of Si/Ge core/shell nanowire heterostructures has not been thoroughly investigated. Here we report the compositional and structural changes of the Si/Ge core/shell nanowire heterostructure over cycling of lithiation and delithiation at different charging rates. The Si/Ge core/shell nanowire heterostructure holds the core and shell structure at a charging rate of 0.8 A g-1 up to 50 cycles. On the other hand, compositional intermixing and loss of Si occur at a charging rate of 20 A g-1 within 50 cycles. The operation condition-dependent degradation provides a new aspect of materials research for the development of high performance lithium ion battery anodes with a long cycle life.

Dendritic core-shell nickel-iron-copper metal/metal oxide electrode for efficient electrocatalytic water oxidation

DOE PAGES

Zhang, Peili; Li, Lin; Nordlund, Dennis; ...

2018-01-26

Electrochemical water splitting requires efficient water oxidation catalysts to accelerate the sluggish kinetics of water oxidation reaction. Here in this paper, we report a promisingly dendritic core-shell nickel-iron-copper metal/metal oxide electrode, prepared via dealloying with an electrodeposited nickel-iron-copper alloy as a precursor, as the catalyst for water oxidation. The as-prepared core-shell nickel-iron-copper electrode is characterized with porous oxide shells and metallic cores. This tri-metal-based core-shell nickel-iron-copper electrode exhibits a remarkable activity toward water oxidation in alkaline medium with an overpotential of only 180 mV at a current density of 10 mA cm -2. The core-shell NiFeCu electrode exhibits pH-dependent oxygenmore » evolution reaction activity on the reversible hydrogen electrode scale, suggesting that non-concerted proton-electron transfers participate in catalyzing the oxygen evolution reaction. To the best of our knowledge, the as-fabricated core-shell nickel-iron-copper is one of the most promising oxygen evolution catalysts.« less

Shell-corona microgels from double interpenetrating networks.

PubMed

Rudyak, Vladimir Yu; Gavrilov, Alexey A; Kozhunova, Elena Yu; Chertovich, Alexander V

2018-04-18

Polymer microgels with a dense outer shell offer outstanding features as universal carriers for different guest molecules. In this paper, microgels formed by an interpenetrating network comprised of collapsed and swollen subnetworks are investigated using dissipative particle dynamics (DPD) computer simulations, and it is found that such systems can form classical core-corona structures, shell-corona structures, and core-shell-corona structures, depending on the subchain length and molecular mass of the system. The core-corona structures consisting of a dense core and soft corona are formed at small microgel sizes when the subnetworks are able to effectively separate in space. The most interesting shell-corona structures consist of a soft cavity in a dense shell surrounded with a loose corona, and are found at intermediate gel sizes; the area of their existence depends on the subchain length and the corresponding mesh size. At larger molecular masses the collapsing network forms additional cores inside the soft cavity, leading to the core-shell-corona structure.

Synthesis and gas sensing properties of α-Fe(2)O(3)@ZnO core-shell nanospindles.

PubMed

Zhang, Jun; Liu, Xianghong; Wang, Liwei; Yang, Taili; Guo, Xianzhi; Wu, Shihua; Wang, Shurong; Zhang, Shoumin

2011-05-06

α-Fe(2)O(3)@ZnO core-shell nanospindles were synthesized via a two-step hydrothermal approach, and characterized by means of SEM/TEM/XRD/XPS. The ZnO shell coated on the nanospindles has a thickness of 10-15 nm. Considering that both α-Fe(2)O(3) and ZnO are good sensing materials, we have investigated the gas sensing performances of the core-shell nanocomposite using ethanol as the main probe gas. It is interesting to find that the gas sensor properties of the core-shell nanospindles are significantly enhanced compared with pristine α-Fe(2)O(3). The enhanced sensor properties are attributed to the unique core-shell nanostructure. The detailed sensing mechanism is discussed with respect to the energy band structure and the electron depletion theory. The core-shell nanostructure reported in this work provides a new path to fabricate highly sensitive materials for gas sensing applications.

Platinum-coated non-noble metal-noble metal core-shell electrocatalysts

DOEpatents

Adzic, Radoslav; Zhang, Junliang; Mo, Yibo; Vukmirovic, Miomir

2015-04-14

Core-shell particles encapsulated by a thin film of a catalytically active metal are described. The particles are preferably nanoparticles comprising a non-noble core with a noble metal shell which preferably do not include Pt. The non-noble metal-noble metal core-shell nanoparticles are encapsulated by a catalytically active metal which is preferably Pt. The core-shell nanoparticles are preferably formed by prolonged elevated-temperature annealing of nanoparticle alloys in an inert environment. This causes the noble metal component to surface segregate and form an atomically thin shell. The Pt overlayer is formed by a process involving the underpotential deposition of a monolayer of a non-noble metal followed by immersion in a solution comprising a Pt salt. A thin Pt layer forms via the galvanic displacement of non-noble surface atoms by more noble Pt atoms in the salt. The overall process is a robust and cost-efficient method for forming Pt-coated non-noble metal-noble metal core-shell nanoparticles.

Boron-based nanostructures: Synthesis, functionalization, and characterization

NASA Astrophysics Data System (ADS)

Bedasso, Eyrusalam Kifyalew

Boron-based nanostructures have not been explored in detail; however, these structures have the potential to revolutionize many fields including electronics and biomedicine. The research discussed in this dissertation focuses on synthesis, functionalization, and characterization of boron-based zero-dimensional nanostructures (core/shell and nanoparticles) and one-dimensional nanostructures (nanorods). The first project investigates the synthesis and functionalization of boron-based core/shell nanoparticles. Two boron-containing core/shell nanoparticles, namely boron/iron oxide and boron/silica, were synthesized. Initially, boron nanoparticles with a diameter between 10-100 nm were prepared by decomposition of nido-decaborane (B10H14) followed by formation of a core/shell structure. The core/shell structures were prepared using the appropriate precursor, iron source and silica source, for the shell in the presence of boron nanoparticles. The formation of core/shell nanostructures was confirmed using high resolution TEM. Then, the core/shell nanoparticles underwent a surface modification. Boron/iron oxide core/shell nanoparticles were functionalized with oleic acid, citric acid, amine-terminated polyethylene glycol, folic acid, and dopamine, and boron/silica core/shell nanoparticles were modified with 3-(amino propyl) triethoxy silane, 3-(2-aminoethyleamino)propyltrimethoxysilane), citric acid, folic acid, amine-terminated polyethylene glycol, and O-(2-Carboxyethyl)polyethylene glycol. A UV-Vis and ATR-FTIR analysis established the success of surface modification. The cytotoxicity of water-soluble core/shell nanoparticles was studied in triple negative breast cancer cell line MDA-MB-231 and the result showed the compounds are not toxic. The second project highlights optimization of reaction conditions for the synthesis of boron nanorods. This synthesis, done via reduction of boron oxide with molten lithium, was studied to produce boron nanorods without any contamination and with a uniform size distribution. Various reaction parameters such as temperature, reaction time, and sonication were altered to find the optimal reaction conditions. Once these conditions were determined, boron nanorods were produced then functionalized with amine-terminated polyethylene glycol.

High performance of PbSe/PbS core/shell quantum dot heterojunction solar cells: short circuit current enhancement without the loss of open circuit voltage by shell thickness control.

PubMed

Choi, Hyekyoung; Song, Jung Hoon; Jang, Jihoon; Mai, Xuan Dung; Kim, Sungwoo; Jeong, Sohee

2015-11-07

We fabricated heterojunction solar cells with PbSe/PbS core shell quantum dots and studied the precisely controlled PbS shell thickness dependency in terms of optical properties, electronic structure, and solar cell performances. When the PbS shell thickness increases, the short circuit current density (JSC) increases from 6.4 to 11.8 mA cm(-2) and the fill factor (FF) enhances from 30 to 49% while the open circuit voltage (VOC) remains unchanged at 0.46 V even with the decreased effective band gap. We found that the Fermi level and the valence band maximum level remain unchanged in both the PbSe core and PbSe/PbS core/shell with a less than 1 nm thick PbS shell as probed via ultraviolet photoelectron spectroscopy (UPS). The PbS shell reduces their surface trap density as confirmed by relative quantum yield measurements. Consequently, PbS shell formation on the PbSe core mitigates the trade-off relationship between the open circuit voltage and the short circuit current density. Finally, under the optimized conditions, the PbSe core with a 0.9 nm thick shell yielded a power conversion efficiency of 6.5% under AM 1.5.

Hydrophilic-Core Microcapsules and Their Formation

NASA Technical Reports Server (NTRS)

Calle, Luz M. (Inventor); Li, Wenyan (Inventor); Buhrow, Jerry W. (Inventor); Jolley, Scott T. (Inventor)

2016-01-01

Hydrophilic-core microcapsules and methods of their formation are provided. A hydrophilic-core microcapsule may include a shell that encapsulates water with the core substance dissolved or dispersed therein. The hydrophilic-core microcapsules may be formed from an emulsion having hydrophilic-phase droplets dispersed in a hydrophobic phase, with shell-forming compound contained in the hydrophilic phase or the hydrophobic phase and the core substance contained in the hydrophilic phase. The shells of the microcapsules may be capable of being broken down in response to being contacted by an alkali, e.g., produced during corrosion, contacting the shell.

Hydrophobic-Core Microcapsules and Their Formation

NASA Technical Reports Server (NTRS)

Buhrow, Jerry W. (Inventor); Li, Wenyan (Inventor); Jolley, Scott T. (Inventor); Calle, Luz M. (Inventor)

2016-01-01

Hydrophobic-core microcapsules and methods of their formation are provided. A hydrophobic-core microcapsule may include a shell that encapsulates a hydrophobic substance with a core substance, such as dye, corrosion indicator, corrosion inhibitor, and/or healing agent, dissolved or dispersed therein. The hydrophobic-core microcapsules may be formed from an emulsion having hydrophobic-phase droplets, e.g., containing the core substance and shell-forming compound, dispersed in a hydrophilic phase. The shells of the microcapsules may be capable of being broken down in response to being contacted by an alkali, e.g., produced during corrosion, contacting the shell.

Ultrasonic approach to the synthesis of HMX@TATB core-shell microparticles with improved mechanical sensitivity.

PubMed

Huang, Bing; Hao, Xiaofei; Zhang, Haobin; Yang, Zhijian; Ma, Zhigang; Li, Hongzhen; Nie, Fude; Huang, Hui

2014-07-01

To improve the safety of sensitive explosive HMX while maintaining explosion performance, a moderately powerful but insensitive explosive TATB was used to coat HMX microparticles via a facile ultrasonic method. By using Estane as surface modifier and nano-sized TATB as the shell layer, the HMX@TATB core-shell microparticles with a monodisperse size and compact shell structure were successfully constructed. Both scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) results confirmed the formation of perfect core-shell structured composites. Based on a systematic and comparative study of the effect of experimental conditions, a possible formation mechanism of core-shell structure was proposed in detail. Moreover, the perfect core-shell HMX@TATB microparticles exhibited a unique thermal behavior and significantly improved mechanical sensitivity compared with that of the physical mixture. Copyright © 2014 Elsevier B.V. All rights reserved.

The radiative decays of excited states of transition elements located inside and near core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Pukhov, Konstantin K.

2017-12-01

Here we discuss the radiative decays of excited states of transition elements located inside and outside of the subwavelength core-shell nanoparticles embedded in dielectric medium. Based on the quantum mechanics and quantum electrodynamics, the general analytical expressions are derived for the probability of the spontaneous transitions in the luminescent centers (emitter) inside and outside the subwavelength core-shell nanoparticle. Obtained expressions holds for arbitrary orientation of the dipole moment and the principal axes of the quadrupole moment of the emitter with respect to the radius-vector r connecting the center of the emitter with the center of the nanoparticle. They have simple form and show how the spontaneous emission in core-shell NPs can be controlled and engineered due to the dependence of the emission rates on core-shell sizes, radius-vector r and permittivities of the surrounding medium, shell, and core.

Core/shell face-centered tetragonal FePd/Pd nanoparticles as an efficient non-Pt catalyst for the oxygen reduction reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu

We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe 3O 4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO 4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly,more » our study offers a general approach to enhance Pd catalysis in acid for ORB.« less

Process to make core-shell structured nanoparticles

DOEpatents

Luhrs, Claudia; Phillips, Jonathan; Richard, Monique N

2014-01-07

Disclosed is a process for making a composite material that contains core-shell structured nanoparticles. The process includes providing a precursor in the form of a powder a liquid and/or a vapor of a liquid that contains a core material and a shell material, and suspending the precursor in an aerosol gas to produce an aerosol containing the precursor. In addition, the process includes providing a plasma that has a hot zone and passing the aerosol through the hot zone of the plasma. As the aerosol passes through the hot zone of the plasma, at least part of the core material and at least part of the shell material in the aerosol is vaporized. Vapor that contains the core material and the shell material that has been vaporized is removed from the hot zone of the plasma and allowed to condense into core-shell structured nanoparticles.

Core/shell face-centered tetragonal FePd/Pd nanoparticles as an efficient non-Pt catalyst for the oxygen reduction reaction

DOE PAGES

Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu; ...

2015-10-04

We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe 3O 4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO 4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly,more » our study offers a general approach to enhance Pd catalysis in acid for ORB.« less

Enhance the photoluminescence and radioluminescence of La2Zr2O7:Eu3+ core nanoparticles by coating with a thin Y2O3 shell

NASA Astrophysics Data System (ADS)

Pokhrel, Madhab; Burger, Arnold; Groza, Michael; Mao, Yuanbing

2017-06-01

We report the generation of La2Zr2O7:5%Eu3+@Y2O3 (LZO5E@YO) core@shell crystalline inorganic-inorganic heterogeneous nanoparticles (NPs). The Y2O3 (YO) shell coating process based on a chemical sol-gel method led to the growth of a thin YO shell on the ordered pyrochlore La2Zr2O7:5%Eu3+ (LZO5E) core NPs. Photoluminescence (PL) analyses demonstrated a blue shift of 15 nm on charge transfer (CT) excitation band of the core@shell NPs from that of the core NPs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) along x-ray diffraction (XRD), Fourier-transform Infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) studies confirmed the formation of the thin YO layer over the LZO5E core NPs. The PL intensity of the LZO5E@YO core@shell NPs was enhanced by three fold compared to that of the LZO5E core NPs, and higher quantum yield (QY) was observed for the former compared to the original NPs by more than 70%. Higher radioluminescence (RL) emission was also observed for the core@shell NPs compared to the core NPs. Our ability of obtaining near-perfect core@shell heterostructure with enhanced luminescence performance opens the door for the development of efficient La2Zr2O7:5%Eu3+@Y2O3 NPs for both optical and x-ray scintillation applications.

Structural and optical properties of ZnSe:Eu/ZnS quantum dots depending on interfacial residual europium

NASA Astrophysics Data System (ADS)

Park, Ji Young; Lee, Chan Gi; Seo, Han Wook; Jeong, Da-Woon; Kim, Min Young; Kim, Woo-Byoung; Kim, Bum Sung

2018-01-01

A multimodal emitter comprising of ZnSe:Eu/ZnS (core/shell) quantum dots (QDs) by adding a ZnS precursor in situ during synthesis. ZnSe/Eu2+/Eu3+/ZnS actives both core and core/shell. QDs prepared with the ZnS precursor displayed a luminescence intensity three times that of ZnSe QDs due to the passivation effect of the Shell. While the core QDs display the 450-550 nm emission of Eu2+ (4F65D1 → 4F7), the core/shell system showed no Eu2+ emission but only the sharp peaks in the red at 579, 592, 615, 651, and 700 nm due to the electronic transitions of 5D0 → 7Fn (n = 0-4) depending on leisurely decreased with increased reaction time. These results are in agreement with Eu 3d spectra of XPS analysis results. Microscopic analyses show that the core and core/shell QDs both have a zinc blende structure, and their respective sizes were about 3.19 and 3.44 nm. The lattice constant in the central portion of the core/shell QDs are around d111 = 3.13 Å, which is between the outside and inside ring patterns (d111 = 3.27 and 3.07 Å, respectively). This shows the effective over-capping of shell onto the core QDs. The core/shell structure may contain Eu2O3 bonding the over-coated ZnS surface on the Eu3+-doped ZnSe core.

A versatile cooperative template-directed coating method to construct uniform microporous carbon shells for multifunctional core-shell nanocomposites.

PubMed

Guan, Buyuan; Wang, Xue; Xiao, Yu; Liu, Yunling; Huo, Qisheng

2013-03-21

A very simple cooperative template-directed coating method is developed for the preparation of core-shell, hollow, and yolk-shell microporous carbon nanocomposites. Particularly, the cationic surfactant C16TMA(+)·Br(-) used in the coating procedure improves the core dispersion in the reaction media and serves as the soft template for mesostructured resorcinol-formaldehyde resin formation, which results in the uniform polymer and microporous carbon shell coating on most functional cores with different surface properties. The core diameter and the shell thickness of the nanocomposites can be precisely tailored. This approach is highly reproducible and scalable. Several grams of polymer and carbon nanocomposites can be easily prepared by a facile one-pot reaction. The Au@hydrophobic microporous carbon yolk-shell catalyst favors the reduction of more hydrophobic nitrobenzene than hydrophilic 4-nitrophenol by sodium borohydride, which makes this type of catalyst@carbon yolk-shell composites promising nanomaterials as selective catalysts for hydrophobic reactants.

Carbon-silicon core-shell nanowires as high capacity electrode for lithium ion batteries.

PubMed

Cui, Li-Feng; Yang, Yuan; Hsu, Ching-Mei; Cui, Yi

2009-09-01

We introduce a novel design of carbon-silicon core-shell nanowires for high power and long life lithium battery electrodes. Amorphous silicon was coated onto carbon nanofibers to form a core-shell structure and the resulted core-shell nanowires showed great performance as anode material. Since carbon has a much smaller capacity compared to silicon, the carbon core experiences less structural stress or damage during lithium cycling and can function as a mechanical support and an efficient electron conducting pathway. These nanowires have a high charge storage capacity of approximately 2000 mAh/g and good cycling life. They also have a high Coulmbic efficiency of 90% for the first cycle and 98-99.6% for the following cycles. A full cell composed of LiCoO(2) cathode and carbon-silicon core-shell nanowire anode is also demonstrated. Significantly, using these core-shell nanowires we have obtained high mass loading and an area capacity of approximately 4 mAh/cm(2), which is comparable to commercial battery values.

Core-shell polymer nanoparticles for prevention of GSH drug detoxification and cisplatin delivery to breast cancer cells

NASA Astrophysics Data System (ADS)

Surnar, Bapurao; Sharma, Kavita; Jayakannan, Manickam

2015-10-01

Platinum drug delivery against the detoxification of cytoplasmic thiols is urgently required for achieving efficacy in breast cancer treatment that is over expressed by glutathione (GSH, thiol-oligopeptide). GSH-resistant polymer-cisplatin core-shell nanoparticles were custom designed based on biodegradable carboxylic functional polycaprolactone (PCL)-block-poly(ethylene glycol) diblock copolymers. The core of the nanoparticle was fixed as 100 carboxylic units and the shell part was varied using various molecular weight poly(ethylene glycol) monomethyl ethers (MW of PEGs = 100-5000 g mol-1) as initiator in the ring-opening polymerization. The complexation of cisplatin aquo species with the diblocks produced core-shell nanoparticles of 75 nm core with precise size control the particles up to 190 nm. The core-shell nanoparticles were found to be stable in saline solution and PBS and they exhibited enhanced stability with increase in the PEG shell thickness at the periphery. The hydrophobic PCL layer on the periphery of the cisplatin core behaved as a protecting layer against the cytoplasmic thiol residues (GSH and cysteine) and exhibited <5% of drug detoxification. In vitro drug-release studies revealed that the core-shell nanoparticles were ruptured upon exposure to lysosomal enzymes like esterase at the intracellular compartments. Cytotoxicity studies were performed both in normal wild-type mouse embryonic fibroblast cells (Wt-MEFs), and breast cancer (MCF-7) and cervical cancer (HeLa) cell lines. Free cisplatin and polymer drug core-shell nanoparticles showed similar cytotoxicity effects in the HeLa cells. In MCF-7 cells, the free cisplatin drug exhibited 50% cell death whereas complete cell death (100%) was accomplished by the polymer-cisplatin core-shell nanoparticles. Confocal microscopic images confirmed that the core-shell nanoparticles were taken up by the MCF-7 and HeLa cells and they were accumulated both at the cytoplasm as well at peri-nuclear environments. The present investigation lays a new foundation for the polymer-based core-shell nanoparticles approach for overcoming detoxification in platinum drugs for the treatment of GSH over-expressed breast cancer cells.Platinum drug delivery against the detoxification of cytoplasmic thiols is urgently required for achieving efficacy in breast cancer treatment that is over expressed by glutathione (GSH, thiol-oligopeptide). GSH-resistant polymer-cisplatin core-shell nanoparticles were custom designed based on biodegradable carboxylic functional polycaprolactone (PCL)-block-poly(ethylene glycol) diblock copolymers. The core of the nanoparticle was fixed as 100 carboxylic units and the shell part was varied using various molecular weight poly(ethylene glycol) monomethyl ethers (MW of PEGs = 100-5000 g mol-1) as initiator in the ring-opening polymerization. The complexation of cisplatin aquo species with the diblocks produced core-shell nanoparticles of 75 nm core with precise size control the particles up to 190 nm. The core-shell nanoparticles were found to be stable in saline solution and PBS and they exhibited enhanced stability with increase in the PEG shell thickness at the periphery. The hydrophobic PCL layer on the periphery of the cisplatin core behaved as a protecting layer against the cytoplasmic thiol residues (GSH and cysteine) and exhibited <5% of drug detoxification. In vitro drug-release studies revealed that the core-shell nanoparticles were ruptured upon exposure to lysosomal enzymes like esterase at the intracellular compartments. Cytotoxicity studies were performed both in normal wild-type mouse embryonic fibroblast cells (Wt-MEFs), and breast cancer (MCF-7) and cervical cancer (HeLa) cell lines. Free cisplatin and polymer drug core-shell nanoparticles showed similar cytotoxicity effects in the HeLa cells. In MCF-7 cells, the free cisplatin drug exhibited 50% cell death whereas complete cell death (100%) was accomplished by the polymer-cisplatin core-shell nanoparticles. Confocal microscopic images confirmed that the core-shell nanoparticles were taken up by the MCF-7 and HeLa cells and they were accumulated both at the cytoplasm as well at peri-nuclear environments. The present investigation lays a new foundation for the polymer-based core-shell nanoparticles approach for overcoming detoxification in platinum drugs for the treatment of GSH over-expressed breast cancer cells. Electronic supplementary information (ESI) available: TGA profile and DSC thermogram of all polymers, DLS data, AFM image, 1H-NMR, 13C-NMR, and MALDI spectra of all polymers and monomers. See DOI: 10.1039/c5nr04963f

Fermi energy dependence of the optical emission in core/shell InAs nanowire homostructures

NASA Astrophysics Data System (ADS)

Möller, M.; Oliveira, D. S.; Sahoo, P. K.; Cotta, M. A.; Iikawa, F.; Motisuke, P.; Molina-Sánchez, A.; de Lima, M. M., Jr.; García-Cristóbal, A.; Cantarero, A.

2017-07-01

InAs nanowires grown by vapor-liquid-solid (VLS) method are investigated by photoluminescence. We observe that the Fermi energy of all samples is reduced by ˜20 meV when the size of the Au nanoparticle used for catalysis is increased from 5 to 20 nm. Additional capping with a thin InP shell enhances the optical emission and does not affect the Fermi energy. The unexpected behavior of the Fermi energy is attributed to the differences in the residual donor (likely carbon) incorporation in the axial (low) and lateral (high incorporation) growth in the VLS and vapor-solid (VS) methods, respectively. The different impurity incorporation rate in these two regions leads to a core/shell InAs homostructure. In this case, the minority carriers (holes) diffuse to the core due to the built-in electric field created by the radial impurity distribution. As a result, the optical emission is dominated by the core region rather than by the more heavily doped InAs shell. Thus, the photoluminescence spectra and the Fermi energy become sensitive to the core diameter. These results are corroborated by a theoretical model using a self-consistent method to calculate the radial carrier distribution and Fermi energy for distinct diameters of Au nanoparticles.

Tunable plasmon resonance and enhanced second harmonic generation and upconverted fluorescence of hemispheric-like silver core/shell islands

NASA Astrophysics Data System (ADS)

Ding, Si-Jing; Nan, Fan; Yang, Da-Jie; Zhong, Yu-Ting; Hao, Zhong-Hua; Wang, Qu-Quan

2015-09-01

We investigate tunable plasmon resonance and enhanced second harmonic generation (SHG) and up-converted fluorescence (UCF) of the hemispheric-like silver core/shell islands. The Ag, Ag/Ag2O, and Ag/Ag2O/Ag island films are prepared by using a sputtering technique. The SHG and UCF of the Ag/Ag2O/Ag core/shell islands near the percolating regime is enhanced 2.34 and 3.94 times compared to the sum of two individual counterparts of Ag/Ag2O core/shell and Ag shell islands. The ratio of SHG intensity induced by p- and s-polarization is 0.86 for the initial Ag islands and increase to 1.61 for the Ag/Ag2O/Ag core/shell samples. The tunable intensity ratio of SHG to UCF of the Ag islands treated by thermal and laser annealing processes is also observed. The physical mechanism of the enhanced SHG and UCF in the Ag/Ag2O/Ag core/shell islands is discussed. Our observations provide a new approach to fabricate plasmon-enhanced optical nonlinear nanodevices with tunable SHG and UCF.We investigate tunable plasmon resonance and enhanced second harmonic generation (SHG) and up-converted fluorescence (UCF) of the hemispheric-like silver core/shell islands. The Ag, Ag/Ag2O, and Ag/Ag2O/Ag island films are prepared by using a sputtering technique. The SHG and UCF of the Ag/Ag2O/Ag core/shell islands near the percolating regime is enhanced 2.34 and 3.94 times compared to the sum of two individual counterparts of Ag/Ag2O core/shell and Ag shell islands. The ratio of SHG intensity induced by p- and s-polarization is 0.86 for the initial Ag islands and increase to 1.61 for the Ag/Ag2O/Ag core/shell samples. The tunable intensity ratio of SHG to UCF of the Ag islands treated by thermal and laser annealing processes is also observed. The physical mechanism of the enhanced SHG and UCF in the Ag/Ag2O/Ag core/shell islands is discussed. Our observations provide a new approach to fabricate plasmon-enhanced optical nonlinear nanodevices with tunable SHG and UCF. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03627e

Geometric screening of core/shell hydrogel microcapsules using a tapered microchannel with interdigitated electrodes.

PubMed

Niu, Ye; Qi, Lin; Zhang, Fen; Zhao, Yi

2018-07-30

Core/shell hydrogel microcapsules attract increasing research attention due to their potentials in tissue engineering, food engineering, and drug delivery. Current approaches for generating core/shell hydrogel microcapsules suffer from large geometric variations. Geometrically defective core/shell microcapsules need to be removed before further use. High-throughput geometric characterization of such core/shell microcapsules is therefore necessary. In this work, a continuous-flow device was developed to measure the geometric properties of microcapsules with a hydrogel shell and an aqueous core. The microcapsules were pumped through a tapered microchannel patterned with an array of interdigitated microelectrodes. The geometric parameters (the shell thickness and the diameter) were derived from the displacement profiles of the microcapsules. The results show that this approach can successfully distinguish all unencapsulated microparticles. The geometric properties of core/shell microcapsules can be determined with high accuracy. The efficacy of this method was demonstrated through a drug releasing experiment where the optimization of the electrospray process based on geometric screening can lead to controlled and extended drug releasing profiles. This method does not require high-speed optical systems, simplifying the system configuration and making it an indeed miniaturized device. The throughput of up to 584 microcapsules per minute was achieved. This study provides a powerful tool for screening core/shell hydrogel microcapsules and is expected to facilitate the applications of these microcapsules in various fields. Copyright © 2018 Elsevier B.V. All rights reserved.

Enhanced Ethanol Gas Sensing Properties of SnO2-Core/ZnO-Shell Nanostructures

PubMed Central

Tharsika, T.; Haseeb, A. S. M. A.; Akbar, Sheikh A.; Sabri, Mohd Faizul Mohd; Hoong, Wong Yew

2014-01-01

An inexpensive single-step carbon-assisted thermal evaporation method for the growth of SnO2-core/ZnO-shell nanostructures is described, and the ethanol sensing properties are presented. The structure and phases of the grown nanostructures are investigated by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. XRD analysis indicates that the core-shell nanostructures have good crystallinity. At a lower growth duration of 15 min, only SnO2 nanowires with a rectangular cross-section are observed, while the ZnO shell is observed when the growth time is increased to 30 min. Core-shell hierarchical nanostructures are present for a growth time exceeding 60 min. The growth mechanism for SnO2-core/ZnO-shell nanowires and hierarchical nanostructures are also discussed. The sensitivity of the synthesized SnO2-core/ZnO-shell nanostructures towards ethanol sensing is investigated. Results show that the SnO2-core/ZnO-shell nanostructures deposited at 90 min exhibit enhanced sensitivity to ethanol. The sensitivity of SnO2-core/ZnO-shell nanostructures towards 20 ppm ethanol gas at 400 °C is about ∼5-times that of SnO2 nanowires. This improvement in ethanol gas response is attributed to high active sensing sites and the synergistic effect of the encapsulation of SnO2 by ZnO nanostructures. PMID:25116903

Preparation and characterization of SiO2-coated submicron-sized L10 Fe-Pt particles

NASA Astrophysics Data System (ADS)

Hayashi, Yoshiaki; Ogawa, Tomoyuki; Ishiyama, Kazushi

2018-05-01

The development of magnets with higher performance is attracting increasing interest. The optimization of their microstructure is essential to enhance their properties, and a microstructure comprising magnetically isolated hard magnetic grains of a single-domain size has been proposed as an ideal structure for enhancing the coercivity of magnets. To obtain magnets with an ideal structure, we consider the fabrication of magnets by an approach based on core/shell nanoparticles with a hard magnetic core and a non-magnetic shell. In this study, to obtain particles for our proposed approach, we attempted to fabricate L10 Fe-Pt/SiO2-core/shell particles with submicron-sized cores less than the critical single-domain size. The fabrication of such core/shell particles was confirmed from morphology observations and XRD analysis of the particles. Although the formation of more desirable core/shell particles with submicron-sized single-crystal cores in the single-domain size range was not achieved, the fabricated core/shell particles showed a high coercivity of 25 kOe.

Differential Dopamine Release Dynamics in the Nucleus Accumbens Core and Shell Reveal Complementary Signals for Error Prediction and Incentive Motivation.

PubMed

Saddoris, Michael P; Cacciapaglia, Fabio; Wightman, R Mark; Carelli, Regina M

2015-08-19

Mesolimbic dopamine (DA) is phasically released during appetitive behaviors, though there is substantive disagreement about the specific purpose of these DA signals. For example, prediction error (PE) models suggest a role of learning, while incentive salience (IS) models argue that the DA signal imbues stimuli with value and thereby stimulates motivated behavior. However, within the nucleus accumbens (NAc) patterns of DA release can strikingly differ between subregions, and as such, it is possible that these patterns differentially contribute to aspects of PE and IS. To assess this, we measured DA release in subregions of the NAc during a behavioral task that spatiotemporally separated sequential goal-directed stimuli. Electrochemical methods were used to measure subsecond NAc dopamine release in the core and shell during a well learned instrumental chain schedule in which rats were trained to press one lever (seeking; SL) to gain access to a second lever (taking; TL) linked with food delivery, and again during extinction. In the core, phasic DA release was greatest following initial SL presentation, but minimal for the subsequent TL and reward events. In contrast, phasic shell DA showed robust release at all task events. Signaling decreased between the beginning and end of sessions in the shell, but not core. During extinction, peak DA release in the core showed a graded decrease for the SL and pauses in release during omitted expected rewards, whereas shell DA release decreased predominantly during the TL. These release dynamics suggest parallel DA signals capable of supporting distinct theories of appetitive behavior. Dopamine signaling in the brain is important for a variety of cognitive functions, such as learning and motivation. Typically, it is assumed that a single dopamine signal is sufficient to support these cognitive functions, though competing theories disagree on how dopamine contributes to reward-based behaviors. Here, we have found that real-time dopamine release within the nucleus accumbens (a primary target of midbrain dopamine neurons) strikingly varies between core and shell subregions. In the core, dopamine dynamics are consistent with learning-based theories (such as reward prediction error) whereas in the shell, dopamine is consistent with motivation-based theories (e.g., incentive salience). These findings demonstrate that dopamine plays multiple and complementary roles based on discrete circuits that help animals optimize rewarding behaviors. Copyright © 2015 the authors 0270-6474/15/3511572-11$15.00/0.

Stability of a Bifunctional Cu-Based Core@Zeolite Shell Catalyst for Dimethyl Ether Synthesis Under Redox Conditions Studied by Environmental Transmission Electron Microscopy and In Situ X-Ray Ptychography.

PubMed

Baier, Sina; Damsgaard, Christian D; Klumpp, Michael; Reinhardt, Juliane; Sheppard, Thomas; Balogh, Zoltan; Kasama, Takeshi; Benzi, Federico; Wagner, Jakob B; Schwieger, Wilhelm; Schroer, Christian G; Grunwaldt, Jan-Dierk

2017-06-01

When using bifunctional core@shell catalysts, the stability of both the shell and core-shell interface is crucial for catalytic applications. In the present study, we elucidate the stability of a CuO/ZnO/Al2O3@ZSM-5 core@shell material, used for one-stage synthesis of dimethyl ether from synthesis gas. The catalyst stability was studied in a hierarchical manner by complementary environmental transmission electron microscopy (ETEM), scanning electron microscopy (SEM) and in situ hard X-ray ptychography with a specially designed in situ cell. Both reductive activation and reoxidation were applied. The core-shell interface was found to be stable during reducing and oxidizing treatment at 250°C as observed by ETEM and in situ X-ray ptychography, although strong changes occurred in the core on a 10 nm scale due to the reduction of copper oxide to metallic copper particles. At 350°C, in situ X-ray ptychography indicated the occurrence of structural changes also on the µm scale, i.e. the core material and parts of the shell undergo restructuring. Nevertheless, the crucial core-shell interface required for full bifunctionality appeared to remain stable. This study demonstrates the potential of these correlative in situ microscopy techniques for hierarchically designed catalysts.

Preparation, process optimization and characterization of core-shell polyurethane/chitosan nanofibers as a potential platform for bioactive scaffolds.

PubMed

Maleknia, Laleh; Dilamian, Mandana; Pilehrood, Mohammad Kazemi; Sadeghi-Aliabadi, Hojjat; Hekmati, Amir Houshang

2018-06-01

In this paper, polyurethane (PU), chitosan (Cs)/polyethylene oxide (PEO), and core-shell PU/Cs nanofibers were produced at the optimal processing conditions using electrospinning technique. Several methods including SEM, TEM, FTIR, XRD, DSC, TGA and image analysis were utilized to characterize these nanofibrous structures. SEM images exhibited that the core-shell PU/Cs nanofibers were spun without any structural imperfections at the optimized processing conditions. TEM image confirmed the PU/Cs core-shell nanofibers were formed apparently. It that seems the inclusion of Cs/PEO to the shell, did not induce the significant variations in the crystallinity in the core-shell nanofibers. DSC analysis showed that the inclusion of Cs/PEO led to the glass temperature of the composition increased significantly compared to those of neat PU nanofibers. The thermal degradation of core-shell PU/Cs was similar to PU nanofibers degradation due to the higher PU concentration compared to other components. It was hypothesized that the core-shell PU/Cs nanofibers can be used as a potential platform for the bioactive scaffolds in tissue engineering. Further biological tests should be conducted to evaluate this platform as a three dimensional scaffold with the capabilities of releasing the bioactive molecules in a sustained manner.

Drastic difference between hole and electron injection through the gradient shell of CdxSeyZn1-xS1-y quantum dots.

PubMed

Abdellah, Mohamed; Poulsen, Felipe; Zhu, Qiushi; Zhu, Nan; Žídek, Karel; Chábera, Pavel; Corti, Annamaria; Hansen, Thorsten; Chi, Qijin; Canton, Sophie E; Zheng, Kaibo; Pullerits, Tõnu

2017-08-31

Ultrafast fluorescence spectroscopy was used to investigate the hole injection in Cd x Se y Zn 1-x S 1-y gradient core-shell quantum dot (CSQD) sensitized p-type NiO photocathodes. A series of CSQDs with a wide range of shell thicknesses was studied. Complementary photoelectrochemical cell measurements were carried out to confirm that the hole injection from the active core through the gradient shell to NiO takes place. The hole injection from the valence band of the QDs to NiO depends much less on the shell thickness when compared to the corresponding electron injection to n-type semiconductor (ZnO). We simulate the charge carrier tunneling through the potential barrier due to the gradient shell by numerically solving the Schrödinger equation. The details of the band alignment determining the potential barrier are obtained from X-ray spectroscopy measurements. The observed drastic differences between the hole and electron injection are consistent with a model where the hole effective mass decreases, while the gradient shell thickness increases.

NO2 Gas Sensing Properties of Multiple Networked ZnGa2O4 Nanorods Coated with TiO2.

PubMed

An, Soyeon; Park, Sunghoon; Ko, Hyunsung; Jin, Changhyun; Lee, Chongmu

2015-01-01

The NO2 gas sensing properties of ZnGa2O4-TiO2 heterostructure nanorods was examined. ZnGa2O4-core/TiO2-shell nanorods were fabricated by the thermal evaporation of a mixture of Zn and GaN powders and the sputter deposition of TiO2. Multiple networked ZnGa2O4-core/TiO2-shell nanorod sensors showed the response of 876% at 10 ppm NO2 at 300 degrees C. This response value at 10 ppm NO2 is approximately 4 times larger than that of bare ZnGa2O4 nanorod sensors. The response values obtained by the ZnGa2O4-core/TiO2-shell nanorods in this study are more than 13 times higher than those obtained previously by the SnO2-core/ZnO-shell nanofibers at 5% NO2. The significant enhancement in the response of ZnGa2O4 nanorods to NO2 gas by coating them with TiO2 can be explained based on the space-charge model.

Paclitaxel loaded folic acid targeted nanoparticles of mixed lipid-shell and polymer-core: in vitro and in vivo evaluation.

PubMed

Zhao, Peiqi; Wang, Hanjie; Yu, Man; Liao, Zhenyu; Wang, Xianhuo; Zhang, Fei; Ji, Wei; Wu, Bing; Han, Jinghua; Zhang, Haichang; Wang, Huaqing; Chang, Jin; Niu, Ruifang

2012-06-01

A functional drug carrier comprised of folic acid modified lipid-shell and polymer-core nanoparticles (FLPNPs) including poly(D,L-lactide-co-glycolide) (PLGA) core, PEGylated octadecyl-quaternized lysine modified chitosan (PEG-OQLCS) as lipid-shell, folic acid as targeting ligand and cholesterol was prepared and evaluated for targeted delivery of paclitaxel (PTX). Confocal microscopy analysis confirmed the coating of the lipid-shell on the polymer-core. Physicochemical characterizations of FLPNPs, such as particle size, zeta potential, morphology, encapsulation efficiency, and in vitro PTX release, were also evaluated. The internalization efficiency and targeting ability of FLPNPs were demonstrated by flow cytometry and confocal microscopy. PTX loaded FLPNPs showed a significantly higher cytotoxicity than the commercial PTX formulation (Taxol®). The intravenous administration of PTX encapsulated FLPNPs led to tumor regression and improvement of animal survival in a murine model, compared with that observed with Taxol® and biodistribution study showed that PTX concentration in tumor for PTX encapsulated FLPNPs was higher than other PTX formulations. Our data indicate that PTX loaded FLPNPs are a promising nano-sized drug formulation for cancer therapy. Copyright © 2012 Elsevier B.V. All rights reserved.

Enzyme immobilization in novel alginate-chitosan core-shell microcapsules.

PubMed

Taqieddin, Ehab; Amiji, Mansoor

2004-05-01

Alginate-chitosan core-shell microcapsules were prepared in order to develop a biocompatible matrix for enzyme immobilization, where the protein is retained either in a liquid or solid core and the shell allows permeability control over substrates and products. The permeability coefficients of different molecular weight compounds (vitamin B2, vitamin B12, and myoglobin) were determined through sodium tripolyphosphate (Na-TPP)-crosslinked chitosan membrane. The microcapsule core was formed by crosslinking sodium alginate with either calcium or barium ions. The crosslinked alginate core was uniformly coated with a chitosan layer and crosslinked with Na-TPP. In the case of calcium alginate, the phosphate ions of Na-TPP were able to extract the calcium ions from alginate and liquefy the core. A model enzyme, beta-galactosidase, was immobilized in the alginate core and the catalytic activity was measured with o-nitrophenyl-beta-D-galactopyranoside (ONPG). Change in the activity of free and immobilized enzyme was determined at three different temperatures. Na-TPP crosslinked chitosan membranes were found to be permeable to solutes of up to 17,000Da molecular weight. The enzyme loading efficiency was higher in the barium alginate core (100%) as compared to the calcium alginate core (60%). The rate of ONPG conversion to o-nitrophenol was faster in the case of calcium alginate-chitosan microcapsules as compared to barium alginate-chitosan microcapsules. Barium alginate-chitosan microcapsules, however, did improve the stability of the enzyme at 37 degrees C relative to calcium alginate-chitosan microcapsules or free enzyme. This study illustrates a new method of enzyme immobilization for biotechnology applications using liquid or solid core and shell microcapsule technology.

Time-resolved photoluminescence study of CdSe/CdMnS/CdS core/multi-shell nanoplatelets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murphy, J. R.; Department of Physics, State University of New York, University at Buffalo, Buffalo, New York 14260; Delikanli, S.

2016-06-13

We used photoluminescence spectroscopy to resolve two emission features in CdSe/CdMnS/CdS and CdSe/CdS core/multi-shell nanoplatelet heterostructures. The photoluminescence from the magnetic sample has a positive circular polarization with a maximum centered at the position of the lower energy feature. The higher energy feature has a corresponding signature in the absorption spectrum; this is not the case for the low-energy feature. We have also studied the temporal evolution of these features using a pulsed-excitation/time-resolved photoluminescence technique to investigate their corresponding recombination channels. A model was used to analyze the temporal dynamics of the photoluminescence which yielded two distinct timescales associated withmore » these recombination channels. The above results indicate that the low-energy feature is associated with recombination of electrons with holes localized at the core/shell interfaces; the high-energy feature, on the other hand, is excitonic in nature with the holes confined within the CdSe cores.« less

InP/ZnS as a safer alternative to CdSe/ZnS core/shell quantum dots: in vitro and in vivo toxicity assessment

NASA Astrophysics Data System (ADS)

Brunetti, Virgilio; Chibli, Hicham; Fiammengo, Roberto; Galeone, Antonio; Malvindi, Maria Ada; Vecchio, Giuseppe; Cingolani, Roberto; Nadeau, Jay L.; Pompa, Pier Paolo

2012-12-01

We show that water soluble InP/ZnS core/shell QDs are a safer alternative to CdSe/ZnS QDs for biological applications, by comparing their toxicity in vitro (cell culture) and in vivo (animal model Drosophila). By choosing QDs with comparable physical and chemical properties, we find that cellular uptake and localization are practically identical for these two nanomaterials. Toxicity of CdSe/ZnS QDs appears to be related to the release of poisonous Cd2+ ions and indeed we show that there is leaching of Cd2+ ions from the particle core despite the two-layer ZnS shell. Since an almost identical amount of In(iii) ions is observed to leach from the core of InP/ZnS QDs, their very low toxicity as revealed in this study hints at a much lower intrinsic toxicity of indium compared to cadmium.

InP/ZnS as a safer alternative to CdSe/ZnS core/shell quantum dots: in vitro and in vivo toxicity assessment.

PubMed

Brunetti, Virgilio; Chibli, Hicham; Fiammengo, Roberto; Galeone, Antonio; Malvindi, Maria Ada; Vecchio, Giuseppe; Cingolani, Roberto; Nadeau, Jay L; Pompa, Pier Paolo

2013-01-07

We show that water soluble InP/ZnS core/shell QDs are a safer alternative to CdSe/ZnS QDs for biological applications, by comparing their toxicity in vitro (cell culture) and in vivo (animal model Drosophila). By choosing QDs with comparable physical and chemical properties, we find that cellular uptake and localization are practically identical for these two nanomaterials. Toxicity of CdSe/ZnS QDs appears to be related to the release of poisonous Cd(2+) ions and indeed we show that there is leaching of Cd(2+) ions from the particle core despite the two-layer ZnS shell. Since an almost identical amount of In(III) ions is observed to leach from the core of InP/ZnS QDs, their very low toxicity as revealed in this study hints at a much lower intrinsic toxicity of indium compared to cadmium.

Enhanced linear photonic nanojet generated by core-shell optical microfibers

NASA Astrophysics Data System (ADS)

Liu, Cheng-Yang; Yen, Tzu-Ping; Chen, Chien-Wen

2017-05-01

The generation of linear photonic nanojet using core-shell optical microfiber is demonstrated numerically and experimentally in the visible light region. The power flow patterns for the core-shell optical microfiber are calculated by using the finite-difference time-domain method. The focusing properties of linear photonic nanojet are evaluated in terms of length and width along propagation and transversal directions. In experiment, the silica optical fiber is etched chemically down to 6 μm diameter and coated with metallic thin film by using glancing angle deposition. We show that the linear photonic nanojet is enhanced clearly by metallic shell due to surface plasmon polaritons. The large-area superresolution imaging can be performed by using a core-shell optical microfiber in the far-field system. The potential applications of this core-shell optical microfiber include micro-fluidics and nano-structure measurements.

Core-shell TiO2@ZnO nanorods for efficient ultraviolet photodetection.

PubMed

Panigrahi, Shrabani; Basak, Durga

2011-05-01

Core-shell TiO(2)@ZnO nanorods (NRs) have been fabricated by a simple two step method: growth of ZnO NRs' array by an aqueous chemical technique and then coating of the NRs with a solution of titanium isopropoxide [Ti(OC(3)H(7))(4)] followed by a heating step to form the shell. The core-shell nanocomposites are composed of single-crystalline ZnO NRs, coated with a thin TiO(2) shell layer obtained by varying the number of coatings (one, three and five times). The ultraviolet (UV) emission intensity of the nanocomposite is largely quenched due to an efficient electron-hole separation reducing the band-to-band recombinations. The UV photoconductivity of the core-shell structure with three times TiO(2) coating has been largely enhanced due to photoelectron transfer between the core and the shell. The UV photosensitivity of the nanocomposite becomes four times larger while the photocurrent decay during steady UV illumination has been decreased almost by 7 times compared to the as-grown ZnO NRs indicating high efficiency of these core-shell structures as UV sensors. © The Royal Society of Chemistry 2011

Novel chiral core-shell silica microspheres with trans-(1R,2R)-diaminocyclohexane bridged in the mesoporous shell: synthesis, characterization and application in high performance liquid chromatography.

PubMed

Wu, Xiabing; You, Linjun; Di, Bin; Hao, Weiqiang; Su, Mengxiang; Gu, Yu; Shen, Lingling

2013-07-19

Novel chiral core-shell silica microspheres with trans-(1R,2R)-diaminocyclohexane (DACH) moiety bridged in the mesoporous shell were synthesized using layer-by-layer method. The chiral mesoporous shell around the nonporous silica core was formed by the co-condensation of N,N'-bis-[(triethoxysilyl)propyl]-trans-(1R,2R)-bis-(ureido)-cyclohexane (DACH-BS) and tetraethoxysilane (TEOS) using octadecyltrimethylammonium chloride (C18TMACl) and triblock poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) copolymer (P123) as the templates. The functionalized core-shell silica microspheres were characterized and tested as chiral stationary phases for high performance liquid chromatography (HPLC). R/S-1,1'-bi-2,2'-naphthol, R/S-6,6'-dibromo-1,1'-bi-2-naphthol and R/S-1,1'-bi-2,2'-phenanthrol were enantioseparated rapidly on the column packed with the DACH core-shell silica particles. Moreover, the column packed with core-shell particles exhibited better performance than the column packed with the DACH functionalized periodic mesoporous organosilicas. Copyright © 2013 Elsevier B.V. All rights reserved.

Reconfigurable Polymer Shells on Shape-Anisotropic Gold Nanoparticle Cores.

PubMed

Kim, Juyeong; Song, Xiaohui; Kim, Ahyoung; Luo, Binbin; Smith, John W; Ou, Zihao; Wu, Zixuan; Chen, Qian

2018-05-03

Reconfigurable hybrid nanoparticles made by decorating flexible polymer shells on rigid inorganic nanoparticle cores can provide a unique means to build stimuli-responsive functional materials. The polymer shell reconfiguration has been expected to depend on the local core shape details, but limited systematic investigations have been undertaken. Here, two literature methods are adapted to coat either thiol-terminated polystyrene (PS) or polystyrene-poly(acrylic acid) (PS-b-PAA) shells onto a series of anisotropic gold nanoparticles of shapes not studied previously, including octahedron, concave cube, and bipyramid. These core shapes are complex, rendering shell contours with nanoscale details (e.g., local surface curvature, shell thickness) that are imaged and analyzed quantitatively using the authors' customized analysis codes. It is found that the hybrid nanoparticles based on the chosen core shapes, when coated with the above two polymer shells, exhibit distinct shell segregations upon a variation in solvent polarity or temperature. It is demonstrated for the PS-b-PAA-coated hybrid nanoparticles, the shell segregation is maintained even after a further decoration of the shell periphery with gold seeds; these seeds can potentially facilitate subsequent deposition of other nanostructures to enrich structural and functional diversity. These synthesis, imaging, and analysis methods for the hybrid nanoparticles of anisotropically shaped cores can potentially aid in their predictive design for materials reconfigurable from the bottom up. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Epitaxial Growth of Lattice-Mismatched Core-Shell TiO2 @MoS2 for Enhanced Lithium-Ion Storage.

PubMed

Dai, Rui; Zhang, Anqi; Pan, Zhichang; Al-Enizi, Abdullah M; Elzatahry, Ahmed A; Hu, Linfeng; Zheng, Gengfeng

2016-05-01

Core-shell structured nanohybrids are currently of significant interest due to their synergetic properties and enhanced performances. However, the restriction of lattice mismatch remains a severe obstacle for heterogrowth of various core-shells with two distinct crystal structures. Herein, a controlled synthesis of lattice-mismatched core-shell TiO2 @MoS2 nano-onion heterostructures is successfully developed, using unilamellar Ti0.87 O2 nanosheets as the starting material and the subsequent epitaxial growth of MoS2 on TiO2 . The formation of these core-shell nano-onions is attributed to an amorphous layer-induced heterogrowth mechanism. The number of MoS2 layers can be well tuned from few to over ten layers, enabling layer-dependent synergistic effects. The core-shell TiO2 @MoS2 nano-onion heterostructures exhibit significantly enhanced energy storage performance as lithium-ion battery anodes. The approach has also been extended to other lattice-mismatched systems such as TiO2 @MoSe2 , thus suggesting a new strategy for the growth of well-designed lattice-mismatched core-shell structures. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

One-by-one imprinting in two eccentric layers of hollow core-shells: Sequential electroanalysis of anti-HIV drugs.

PubMed

Singh, Kislay; Jaiswal, Swadha; Singh, Richa; Fatma, Sana; Prasad, Bhim Bali

2018-07-15

Double layered one-by-one imprinted hollow core-shells@ pencil graphite electrode was fabricated for sequential sensing of anti-HIV drugs. For this, two eccentric layers were developed on the surface of vinylated silica nanospheres to obtain double layered one-by-one imprinted solid core-shells. This yielded hollow core-shells on treatment with hydrofluoric acid. The modified hollow core-shells (single layered dual imprinted) evolved competitive diffusion of probe/analyte molecules. However, the corresponding double layered one-by-one imprinted hollow core-shells (outer layer imprinted with Zidovudine, and inner layer with Lamivudine) were found relatively better owing to their bilateral diffusions into molecular cavities, without any competition. The entire work is based on differential pulse anodic stripping voltammetry at double layered one-by-one imprinted hollow core-shells. This resulted in indirect detection of electro inactive targets with limits of detection as low as 0.91 and 0.12 (aqueous sample), 0.94 and 0.13 (blood serum), and 0.99 and 0.20 ng mL -1 (pharmaceutics) for lamivudine and zidovudine, respectively in anti-HIV drug combination. Copyright © 2018 Elsevier B.V. All rights reserved.

Scalable Super-Resolution Synthesis of Core-Vest Composites Assisted by Surface Plasmons.

PubMed

Montazeri, A O; Kim, Y; Fang, Y S; Soheilinia, N; Zaghi, G; Clark, J K; Maboudian, R; Kherani, N P; Carraro, C

2018-02-15

The behavior of composite nanostructures depends on both size and elemental composition. Accordingly, concurrent control of size, shape, and composition of nanoparticles is key to tuning their functionality. In typical core-shell nanoparticles, the high degree of symmetry during shell formation results in fully encapsulated cores with severed access to the surroundings. We commingle light parameters (wavelength, intensity, and pulse duration) with the physical properties of nanoparticles (size, shape, and composition) to form hitherto unrealized core-vest composite nanostructures (CVNs). Unlike typical core-shells, the plasmonic core of the resulting CVNs selectively maintains physical access to its surrounding. Tunable variations in local temperature profiles ≳50 °C are plasmonically induced over starburst-shaped nanoparticles as small as 50-100 nm. These temperature variations result in CVNs where the shell coverage mirrors the temperature variations. The precision thus offered individually tailors access pathways of the core and the shell.

Crystal Structure of Faradaurate-279: Au279(SPh-tBu)84 Plasmonic Nanocrystal Molecules.

PubMed

Sakthivel, Naga Arjun; Theivendran, Shevanuja; Ganeshraj, Vigneshraja; Oliver, Allen G; Dass, Amala

2017-11-01

We report the discovery of an unprecedentedly large, 2.2 nm diameter, thiolate protected gold nanocrystal characterized by single crystal X-ray crystallography (sc-XRD), Au 279 (SPh-tBu) 84 named Faradaurate-279 (F-279) in honor of Michael Faraday's (1857) pioneering work on nanoparticles. F-279 nanocrystal has a core-shell structure containing a truncated octahedral core with bulk face-centered cubic-like arrangement, yet a nanomolecule with a precise number of metal atoms and thiolate ligands. The Au 279 S 84 geometry was established from a low-temperature 120 K sc-XRD study at 0.90 Å resolution. The atom counts in core-shell structure of Au 279 follows the mathematical formula for magic number shells: Au@Au 12 @Au 42 @Au 92 @Au 54 , which is further protected by a final shell of Au 48 . Au 249 core is protected by three types of staple motifs, namely: 30 bridging, 18 monomeric, and 6 dimeric staple motifs. Despite the presence of such diverse staple motifs, Au 279 S 84 structure has a chiral pseudo-D 3 symmetry. The core-shell structure can be viewed as nested, concentric polyhedra, containing a total of five forms of Archimedean solids. A comparison between the Au 279 and Au 309 cuboctahedral superatom model in shell-wise growth is illustrated. F-279 can be synthesized and isolated in high purity in milligram quantities using size exclusion chromatography, as evidenced by mass spectrometry. Electrospray ionization-mass spectrometry independently verifies the X-ray diffraction study based heavy atoms formula, Au 279 S 84 , and establishes the molecular formula with the complete ligands, namely, Au 279 (SPh-tBu) 84 . It is also the smallest gold nanocrystal to exhibit metallic behavior, with a surface plasmon resonance band around 510 nm.

Synthesis, Characterization, and In Vivo Efficacy of Shell Cross-Linked Nanoparticle Formulations Carrying Silver Antimicrobials as Aerosolized Therapeutics

PubMed Central

2014-01-01

The use of nebulizable, nanoparticle-based antimicrobial delivery systems can improve efficacy and reduce toxicity for treatment of multi-drug-resistant bacteria in the chronically infected lungs of cystic fibrosis patients. Nanoparticle vehicles are particularly useful for applying broad-spectrum silver-based antimicrobials, for instance, to improve the residence time of small-molecule silver carbene complexes (SCCs) within the lung. Therefore, we have synthesized multifunctional, shell cross-linked knedel-like polymeric nanoparticles (SCK NPs) and capitalized on the ability to independently load the shell and core with silver-based antimicrobial agents. We formulated three silver-loaded variants of SCK NPs: shell-loaded with silver cations, core-loaded with SCC10, and combined loading of shell silver cations and core SCC10. All three formulations provided a sustained delivery of silver over the course of at least 2–4 days. The two SCK NP formulations with SCC10 loaded in the core each exhibited excellent antimicrobial activity and efficacy in vivo in a mouse model of Pseudomonas aeruginosa pneumonia. SCK NPs with shell silver cation-load only, while efficacious in vitro, failed to demonstrate efficacy in vivo. However, a single dose of core SCC10-loaded SCK NPs (0.74 ± 0.16 mg Ag) provided a 28% survival advantage over sham treatment, and administration of two doses (0.88 mg Ag) improved survival to 60%. In contrast, a total of 14.5 mg of Ag+ delivered over 5 doses at 12 h intervals was necessary to achieve a 60% survival advantage with a free-drug (SCC1) formulation. Thus, SCK NPs show promise for clinical impact by greatly reducing antimicrobial dosage and dosing frequency, which could minimize toxicity and improve patient adherence. PMID:23718195

Towards better light harvesting capability for DSSC (dye sensitized solar cells) through addition of Au@SiO2 core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Fadhilah, Nur; Alhadi, Emha Riyadhul Jinan; Risanti, Doty Dewi

2018-04-01

The Au nanoparticles as core can increase the light harvesting due to the strong near-field effect LSPR (Localized Surface Plasmon Resonance), effectively minimized the electron recombination process and also can improve the optical absorption of the dye sensitized. Au@SiO2 core-shell nanoparticles were prepared using SiO2 extracted from Sidoarjo mud volcano. In this work investigated the influence of pH solution and silica shell volume fraction in Au@SiO2 nanoparticles core-shell structure on DSSC loaded with Ru-based dye. From XRD characterization it was found that core-shell contains SiO2, Au, γAl2O3 and traces NaCl. UV-Vis absorption spectra of core-shell showed the position of the surface plasmon AuNP band in the range of 500-600 nm. The Au@SiO2 core-shell with volume fraction of 30ml silica has the highest peak absorbance. The enhanced light absorption is primarily attributed to the LSPR effect of the Au core. Our results on incident photon-to-current conversion efficiency indicates that the presence of SiO2 depending on its volume fraction tends to shift to longer wavelength.

Optical phonon modes of III-V nanoparticles and indium phosphide/II-VI core-shell nanoparticles: A Raman and infrared study

NASA Astrophysics Data System (ADS)

Manciu, Felicia Speranta

The prospects for realizing efficient nanoparticle light emitters in the visible/near IR for communications and bio-medical applications have benefited from progress in chemical fabrication of nanoparticles. III-V semiconductor nanopaticles such as GaP and InP are promising materials for the development of "blue" and "green" emitters, respectively, due to their large effective bandgaps. Enhanced emission efficiency has been achieved for core-shell nanoparticles, since inorganic shell materials increase electronic tunability and may decrease surface defects that often occur for nanoparticles capped with organic molecules. Also, the emission wavelength of InP nanoparticle cores can be tuned from green to red by changing the shell material in InP/II-VI core-shell nanoparticles. Investigations of phonon modes in nanocrystals are of both fundamental and applied interest. In the former case the optical phonon modes, such as surface/interface modes, are dependent on the nanoparticle dimensions, and also can provide information about dynamical properties of the nanoparticles and test the validity of various theoretical approaches. In the latter case the vibronic properties of nanoparticle emitters are controlled by confined phonons and modifications of the electron-phonon interaction by the confinement. Thus, the objective of the present thesis is the detailed study of the phonon modes of III-V nanoparticles (GaP and InP) and InP/II-VI core-shell nanoparticles by IR absorption and Raman scattering spectroscopies, and an elucidation of their complex vibrational properties. With the exception of three samples (two GaP and one InP), all samples were synthesized by a novel colloidal chemistry method, which does not requires added surfactant, but rather treatment of the corresponding precursors in octadecene noncoordinative solvent. Sample quality was characterized by ED, TEM and X-ray diffraction. Based on a comparison with a dielectric continuum model, the observed features in the IR and Raman results are assigned to the surface optical (SO) modes of the corresponding nanoparticles (InP and GaP), and to SO/interface modes for InP/II-VI core-shell nanoparticles. For the latter systems, an evaluation of the ratio of the shell material thickness to the core radius is achieved. Reasonable agreement is obtained between the Raman and FIR results, as well as with the calculations. (Abstract shortened by UMI.)

Controlled Synthesis of Pd/Pt Core Shell Nanoparticles Using Area-selective Atomic Layer Deposition

PubMed Central

Cao, Kun; Zhu, Qianqian; Shan, Bin; Chen, Rong

2015-01-01

We report an atomic scale controllable synthesis of Pd/Pt core shell nanoparticles (NPs) via area-selective atomic layer deposition (ALD) on a modified surface. The method involves utilizing octadecyltrichlorosilane (ODTS) self-assembled monolayers (SAMs) to modify the surface. Take the usage of pinholes on SAMs as active sites for the initial core nucleation, and subsequent selective deposition of the second metal as the shell layer. Since new nucleation sites can be effectively blocked by surface ODTS SAMs in the second deposition stage, we demonstrate the successful growth of Pd/Pt and Pt/Pd NPs with uniform core shell structures and narrow size distribution. The size, shell thickness and composition of the NPs can be controlled precisely by varying the ALD cycles. Such core shell structures can be realized by using regular ALD recipes without special adjustment. This SAMs assisted area-selective ALD method of core shell structure fabrication greatly expands the applicability of ALD in fabricating novel structures and can be readily applied to the growth of NPs with other compositions. PMID:25683469

Predicted trends of core-shell preferences for 132 late transition-metal binary-alloy nanoparticles.

PubMed

Wang, Lin-Lin; Johnson, Duane D

2009-10-07

Transition-metal alloyed nanoparticles with core-shell features (shell enrichment by one of the metals) are becoming ubiquitous, from (electro-)catalysis to biomedical applications, due to their size control, performance, biocompatibility, and cost. We investigate 132 binary-alloyed nanoparticle systems (groups 8 to 11 in the Periodic Table) using density functional theory (DFT) and systematically explore their segregation energies to determine core-shell preferences. We find that core-shell preferences are generally described by two independent factors: (1) cohesive energy (related to vapor pressure) and (2) atomic size (quantified by the Wigner-Seitz radius), and the interplay between them. These independent factors are shown to provide general trends for the surface segregation preference for atoms in nanoparticles, as well as semi-infinite surfaces, and give a simple correlation (a "design map") for the alloying and catalytic behavior. Finally, we provide a universal description of core-shell preference via tight-binding theory (band-energy differences) that (i) quantitatively reproduces the DFT segregation energies and (ii) confirms the electronic origins and correlations for core-shell behavior.

Micro-Photoluminescence (micro-PL) Study of Core-Shell GaAs/GaAsSb Nanowires Grown by Self-Assisted Molecular Beam Epitaxy

DTIC Science & Technology

2015-06-18

public release; distribution is unlimited. Micro-Photoluminescence (micro-PL) Study of Core-Shell GaAs/GaAsSb Nanowires grown by Self-Assisted Molecular...U.S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 GaAsSb, Core Shell Nanowires , Micro Photoluminescence...University 1601 East Market Street Greensboro, NC 27411 -0001 ABSTRACT Micro-Photoluminescence (micro-PL) Study of Core-Shell GaAs/GaAsSb Nanowires grown by

Nonvolatile memory with Co-SiO2 core-shell nanocrystals as charge storage nodes in floating gate

NASA Astrophysics Data System (ADS)

Liu, Hai; Ferrer, Domingo A.; Ferdousi, Fahmida; Banerjee, Sanjay K.

2009-11-01

In this letter, we reported nanocrystal floating gate memory with Co-SiO2 core-shell nanocrystal charge storage nodes. By using a water-in-oil microemulsion scheme, Co-SiO2 core-shell nanocrystals were synthesized and closely packed to achieve high density matrix in the floating gate without aggregation. The insulator shell also can help to increase the thermal stability of the nanocrystal metal core during the fabrication process to improve memory performance.

Introduction of biotin or folic acid into polypyrrole magnetite core-shell nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nan, Alexandrina; Turcu, Rodica; Liebscher, Jürgen

2013-11-13

In order to contribute to the trend in contemporary research to develop magnetic core shell nanoparticles with better properties (reduced toxicity, high colloidal and chemical stability, wide scope of application) in straightforward and reproducible methods new core shell magnetic nanoparticles were developed based on polypyrrole shells functionalized with biotin and folic acid. Magnetite nanoparticles stabilized by sebacic acid were used as magnetic cores. The morphology of magnetite was determined by transmission electron microscopy TEM, while the chemical structure investigated by FT-IR.

Significant efficiency enhancement of hybrid solar cells using core-shell nanowire geometry for energy harvesting.

PubMed

Tsai, Shin-Hung; Chang, Hung-Chih; Wang, Hsin-Hua; Chen, Szu-Ying; Lin, Chin-An; Chen, Show-An; Chueh, Yu-Lun; He, Jr-Hau

2011-12-27

A novel strategy employing core-shell nanowire arrays (NWAs) consisting of Si/regioregular poly(3-hexylthiophene) (P3HT) was demonstrated to facilitate efficient light harvesting and exciton dissociation/charge collection for hybrid solar cells (HSCs). We experimentally demonstrate broadband and omnidirectional light-harvesting characteristics of core-shell NWA HSCs due to their subwavelength features, further supported by the simulation based on finite-difference time domain analysis. Meanwhile, core-shell geometry of NWA HSCs guarantees efficient charge separation since the thickness of the P3HT shells is comparable to the exciton diffusion length. Consequently, core-shell HSCs exhibit a 61% improvement of short-circuit current for a conversion efficiency (η) enhancement of 31.1% as compared to the P3HT-infiltrated Si NWA HSCs with layers forming a flat air/polymer cell interface. The improvement of crystal quality of P3HT shells due to the formation of ordering structure at Si interfaces after air mass 1.5 global (AM 1.5G) illumination was confirmed by transmission electron microscopy and Raman spectroscopy. The core-shell geometry with the interfacial improvement by AM 1.5G illumination promotes more efficient exciton dissociation and charge separation, leading to η improvement (∼140.6%) due to the considerable increase in V(oc) from 257 to 346 mV, J(sc) from 11.7 to 18.9 mA/cm(2), and FF from 32.2 to 35.2%, which is not observed in conventional P3HT-infiltrated Si NWA HSCs. The stability of the Si/P3HT core-shell NWA HSCs in air ambient was carefully examined. The core-shell geometry should be applicable to many other material systems of solar cells and thus holds high potential in third-generation solar cells.

Europa's differentiated internal structure: inferences from four Galileo encounters.

PubMed

Anderson, J D; Schubert, G; Jacobson, R A; Lau, E L; Moore, W B; Sjogren, W L

1998-09-25

Radio Doppler data from four encounters of the Galileo spacecraft with the jovian moon Europa have been used to refine models of Europa's interior. Europa is most likely differentiated into a metallic core surrounded by a rock mantle and a water ice-liquid outer shell, but the data cannot eliminate the possibility of a uniform mixture of dense silicate and metal beneath the water ice-liquid shell. The size of a metallic core is uncertain because of its unknown composition, but it could be as large as about 50 percent of Europa's radius. The thickness of Europa's outer shell of water ice-liquid must lie in the range of about 80 to 170 kilometers.

Evaluation of damage progression and mechanical behavior under compression of bone cements containing core-shell nanoparticles by using acoustic emission technique.

PubMed

Pacheco-Salazar, O F; Wakayama, Shuichi; Sakai, Takenobu; Cauich-Rodríguez, J V; Ríos-Soberanis, C R; Cervantes-Uc, J M

2015-06-01

In this work, the effect of the incorporation of core-shell particles on the fracture mechanisms of the acrylic bone cements by using acoustic emission (AE) technique during the quasi-static compression mechanical test was investigated. Core-shell particles were composed of a poly(butyl acrylate) (PBA) rubbery core and a methyl methacrylate/styrene copolymer (P(MMA-co-St)) outer glassy shell. Nanoparticles were prepared with different core-shell ratio (20/80, 30/70, 40/60 and 50/50) and were incorporated into the solid phase of bone cement at several percentages (5, 10 and 15 wt%). It was observed that the particles exhibited a spherical morphology averaging ca. 125 nm in diameter, and the dynamic mechanical analysis (DMA) thermograms revealed the desired structuring pattern of phases associated with core-shell structures. A fracture mechanism was proposed taking into account the detected AE signals and the scanning electron microscopy (SEM) micrographs. In this regard, core-shell nanoparticles can act as both additional nucleation sites for microcracks (and crazes) and to hinder the microcrack propagation acting as a barrier to its growth; this behavior was presented by all formulations. Cement samples containing 15 wt% of core-shell nanoparticles, either 40/60 or 50/50, were fractured at 40% deformation. This fact seems related to the coalescence of microcracks after they surround the agglomerates of core-shell nanoparticles to continue growing up. This work also demonstrated the potential of the AE technique to be used as an accurate and reliable detection tool for quasi-static compression test in acrylic bone cements. Copyright © 2015 Elsevier Ltd. All rights reserved.

Abnormal elastic modulus behavior in a crystalline-amorphous core-shell nanowire system.

PubMed

Lee, Jeong Hwan; Choi, Su Ji; Kwon, Ji Hwan; Van Lam, Do; Lee, Seung Mo; Kim, An Soon; Baik, Hion Suck; Ahn, Sang Jung; Hong, Seong Gu; Yun, Yong Ju; Kim, Young Heon

2018-06-13

We investigated the elastic modulus behavior of crystalline InAs/amorphous Al2O3 core-shell heterostructured nanowires with shell thicknesses varying between 10 and 90 nm by conducting in situ tensile tests inside a transmission electron microscope (TEM). Counterintuitively, the elastic modulus behaviors of InAs/Al2O3 core-shell nanowires differ greatly from those of bulk-scale composite materials, free from size effects. According to our results, the elastic modulus of InAs/Al2O3 core-shell nanowires increases, peaking at a shell thickness of 40 nm, and then decreases in the range of 50-90 nm. This abnormal behavior is attributed to the continuous decrease in the elastic modulus of the Al2O3 shell as the thickness increases, which is caused by changes in the atomic/electronic structure during the atomic layer deposition process and the relaxation of residual stress/strain in the shell transferred from the interfacial mismatch between the core and shell materials. A novel method for estimating the elastic modulus of the shell in a heterostructured core-shell system was suggested by considering these two effects, and the predictions from the suggested method coincided well with the experimental results. We also found that the former and latter effects account for 89% and 11% of the change in the elastic modulus of the shell. This study provides new insight by showing that the size dependency, which is caused by the inhomogeneity of the atomic/electronic structure and the residual stress/strain, must be considered to evaluate the mechanical properties of heterostructured nanowires.

Surface functionalization of magnetite nanoparticle: A new approach using condensation of alkoxysilanes

NASA Astrophysics Data System (ADS)

Rodriguez, A. F. R.; Costa, T. P.; Bini, R. A.; Faria, F. S. E. D. V.; Azevedo, R. B.; Jafelicci, M.; Coaquira, J. A. H.; Martínez, M. A. R.; Mantilla, J. C.; Marques, R. F. C.; Morais, P. C.

2017-09-01

In this study we report on successful production of two samples (BR15 and BR16) comprising magnetite (Fe3O4) nanoparticles ( 10 nm) surface-functionalized via hydrolysis and condensation of alkoxysilane agents, namely 3-aminopropyl-trimethoxisilane (APTS) and N-propyl-trimethoxisilane (NPTS). The as-produced samples were characterized using transmission electron microscopy (TEM), x-ray diffraction (XRD), magnetization measurements (5 K and 300 K hysteresis cycles and zero field-cooled/field-cooled measurements), and Mössbauer spectroscopy (77 and 297 K). The Mössbauer data supported the model picture of a core-shell magnetite-based system. This material system shows shell properties influenced by the surface-coating design, either APTS-coated (BR15) or APTS+NPTS-coated (sample BR16). Analyses of the Mössbauer spectra indicates that the APTS-coated sample presents Fe(III)-rich core and Fe(II)-rich shell with strong hyperfine field; whereas, the APTS+NPTS-coated sample leads to a mixture of two main nanostructures, one essentially surface-terminated with APTS whereas the other surface-terminated with NPTS, both presenting weak hyperfine fields compared with the single surface-coated sample. Magnetization measurements support the core-shell picture built from the analyses of the Mössbauer data. Our findings emphasize the capability of the Mössbauer spectroscopy in assessing subtle differences in surface-functionalized iron-based core-shell nanostructures.

Fabrication of Hierarchical Layer-by-Layer Assembled Diamond-based Core-Shell Nanocomposites as Highly Efficient Dye Absorbents for Wastewater Treatment

NASA Astrophysics Data System (ADS)

Zhao, Xinna; Ma, Kai; Jiao, Tifeng; Xing, Ruirui; Ma, Xilong; Hu, Jie; Huang, Hao; Zhang, Lexin; Yan, Xuehai

2017-03-01

The effective chemical modification and self-assembly of diamond-based hierarchical composite materials are of key importance for a broad range of diamond applications. Herein, we report the preparation of novel core-shell diamond-based nanocomposites for dye adsorption toward wastewater treatment through a layer-by-layer (LbL) assembled strategy. The synthesis of the reported composites began with the carboxyl functionalization of microdiamond by the chemical modification of diamond@graphene oxide composite through the oxidation of diamond@graphite. The carboxyl-terminated microdiamond was then alternatively immersed in the aqueous solution of amine-containing polyethylenimine and carboxyl-containing poly acrylic acid, which led to the formation of adsorption layer on diamond surface. Alternating (self-limiting) immersions in the solutions of the amine-containing and carboxyl-containing polymers were continued until the desired number of shell layers were formed around the microdiamond. The obtained core-shell nanocomposites were successfully synthesized and characterized by morphological and spectral techniques, demonstrating higher surface areas and mesoporous structures for good dye adsorption capacities than nonporous solid diamond particles. The LbL-assembled core-shell nanocomposites thus obtained demonstrated great adsorption capacity by using two model dyes as pollutants for wastewater treatment. Therefore, the present work on LbL-assembled diamond-based composites provides new alternatives for developing diamond hybrids as well as nanomaterials towards wastewater treatment applications.

Optimization and design of pigments for heat-insulating coatings

NASA Astrophysics Data System (ADS)

Wang, Guang-Hai; Zhang, Yue

2010-12-01

This paper reports that heat insulating property of infrared reflective coatings is obtained through the use of pigments which diffuse near-infrared thermal radiation. Suitable structure and size distribution of pigments would attain maximum diffuse infrared radiation and reduce the pigment volume concentration required. The optimum structure and size range of pigments for reflective infrared coatings are studied by using Kubelka—Munk theory, Mie model and independent scattering approximation. Taking titania particle as the pigment embedded in an inorganic coating, the computational results show that core-shell particles present excellent scattering ability, more so than solid and hollow spherical particles. The optimum radius range of core-shell particles is around 0.3 ~ 1.6 μm. Furthermore, the influence of shell thickness on optical parameters of the coating is also obvious and the optimal thickness of shell is 100-300 nm.

Core-Shell Structuring of Pure Metallic Aerogels towards Highly Efficient Platinum Utilization for the Oxygen Reduction Reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Bin; Hübner, René; Sasaki, Kotaro

The development of core–shell structures remains a fundamental challenge for pure metallic aerogels. Here we report the synthesis of Pd xAu-Pt core–shell aerogels composed of an ultrathin Pt shell and a composition-tunable Pd xAu alloy core. The universality of this strategy ensures the extension of core compositions to Pd transition-metal alloys. The core–shell aerogels exhibited largely improved Pt utilization efficiencies for the oxygen reduction reaction and their activities show a volcano-type relationship as a function of the lattice parameter of the core substrate. The maximum mass and specific activities are 5.25 A mg Pt -1 and 2.53 mA cm -2,more » which are 18.7 and 4.1 times higher than those of Pt/C, respectively, demonstrating the superiority of the core–shell metallic aerogels. The proposed core-based activity descriptor provides a new possible strategy for the design of future core–shell electrocatalysts.« less

Core-Shell Structuring of Pure Metallic Aerogels towards Highly Efficient Platinum Utilization for the Oxygen Reduction Reaction

DOE PAGES

Cai, Bin; Hübner, René; Sasaki, Kotaro; ...

2018-02-08

The development of core–shell structures remains a fundamental challenge for pure metallic aerogels. Here we report the synthesis of Pd xAu-Pt core–shell aerogels composed of an ultrathin Pt shell and a composition-tunable Pd xAu alloy core. The universality of this strategy ensures the extension of core compositions to Pd transition-metal alloys. The core–shell aerogels exhibited largely improved Pt utilization efficiencies for the oxygen reduction reaction and their activities show a volcano-type relationship as a function of the lattice parameter of the core substrate. The maximum mass and specific activities are 5.25 A mg Pt -1 and 2.53 mA cm -2,more » which are 18.7 and 4.1 times higher than those of Pt/C, respectively, demonstrating the superiority of the core–shell metallic aerogels. The proposed core-based activity descriptor provides a new possible strategy for the design of future core–shell electrocatalysts.« less

Nano-engineering of three-dimensional core/shell nanotube arrays for high performance supercapacitors

NASA Astrophysics Data System (ADS)

Grote, Fabian; Wen, Liaoyong; Lei, Yong

2014-06-01

Large-scale arrays of core/shell nanostructures are highly desirable to enhance the performance of supercapacitors. Here we demonstrate an innovative template-based fabrication technique with high structural controllability, which is capable of synthesizing well-ordered three-dimensional arrays of SnO2/MnO2 core/shell nanotubes for electrochemical energy storage in supercapacitor applications. The SnO2 core is fabricated by atomic layer deposition and provides a highly electrical conductive matrix. Subsequently a thin MnO2 shell is coated by electrochemical deposition onto the SnO2 core, which guarantees a short ion diffusion length within the shell. The core/shell structure shows an excellent electrochemical performance with a high specific capacitance of 910 F g-1 at 1 A g-1 and a good rate capability of remaining 217 F g-1 at 50 A g-1. These results shall pave the way to realize aqueous based asymmetric supercapacitors with high specific power and high specific energy.

Reconstruction of TiO2/MnO2-C nanotube/nanoflake core/shell arrays as high-performance supercapacitor electrodes

NASA Astrophysics Data System (ADS)

Xiong, Qinqin; Zheng, Cun; Chi, Hongzhong; Zhang, Jun; Ji, Zhenguo

2017-02-01

Construction of electrodes with fast reaction kinetics is of great importance for achieving advanced supercapacitors. Herein we report a facile combined synthetic strategy with atomic layer deposition (ALD) and electrodeposition to rationally fabricate nanotube/nanoflake core/shell arrays. ALD-TiO2 nanotubes are used as the skeleton core for assembly of electrodeposited MnO2-C nanoflake shells forming a core/shell structure. Highly porous architecture and good electrical conductivity are combined in this unique core/shell structure, resulting in fast ion/electron transfer. In tests of electrochemical performance, the TiO2/MnO2-C core/shell arrays are characterized as cathode for asymmetric supecapacitors and exhibit high specific capacitance (880 F g-1 at 2.5 A g-1), excellent rate properties (735 F g-1 at 30 A g-1) and good long-term cycling stability (94.3% capacitance retention after 20 000 cycles). The proposed electrode construction strategy is favorable for fabrication of other advanced supercapacitor electrodes.

Reconstruction of TiO2/MnO2-C nanotube/nanoflake core/shell arrays as high-performance supercapacitor electrodes.

PubMed

Xiong, Qinqin; Zheng, Cun; Chi, Hongzhong; Zhang, Jun; Ji, Zhenguo

2017-02-03

Construction of electrodes with fast reaction kinetics is of great importance for achieving advanced supercapacitors. Herein we report a facile combined synthetic strategy with atomic layer deposition (ALD) and electrodeposition to rationally fabricate nanotube/nanoflake core/shell arrays. ALD-TiO 2 nanotubes are used as the skeleton core for assembly of electrodeposited MnO 2 -C nanoflake shells forming a core/shell structure. Highly porous architecture and good electrical conductivity are combined in this unique core/shell structure, resulting in fast ion/electron transfer. In tests of electrochemical performance, the TiO 2 /MnO 2 -C core/shell arrays are characterized as cathode for asymmetric supecapacitors and exhibit high specific capacitance (880 F g -1 at 2.5 A g -1 ), excellent rate properties (735 F g -1 at 30 A g -1 ) and good long-term cycling stability (94.3% capacitance retention after 20 000 cycles). The proposed electrode construction strategy is favorable for fabrication of other advanced supercapacitor electrodes.

Structural and electronic properties of CdS/ZnS core/shell nanowires: A first-principles study

NASA Astrophysics Data System (ADS)

Kim, Hyo Seok; Kim, Yong-Hoon

2015-03-01

Carrying out density functional theory (DFT) calculation, we studied the relative effects of quantum confinement and strain on the electronic structures of II-IV semiconductor compounds with a large lattice-mismatch, CdS and ZnS, in the core/shell nanowire geometry. We considered different core radii and shell thickness of the CdS/ZnS core/shell nanowire, different surface facets, and various defects in the core/shell interface and surface regions. To properly describe the band level alignment at the core/shell boundary, we adopted the self-interaction correction (SIC)-DFT scheme. Implications of our findings in the context of device applications will be also discussed. This work was supported by the Basic Science Research Grant (No. 2012R1A1A2044793), Global Frontier Program (No. 2013-073298), and Nano-Material Technology Development Program (2012M3A7B4049888) of the National Research Foundation funded by the Ministry of Education, Science and Technology of Korea. Corresponding author

Evolution of silver/gold triangular nanoframes from prismatic silver/gold core/shell nanostructures and their SERS properties

NASA Astrophysics Data System (ADS)

Parthiban, P.; Sakar, M.; Balakumar, S.

2013-02-01

We report the evolution of Ag/Au triangular nanoframes from nano core/shell of Ag/Au and their surface enhanced Raman scattering (SERS) properties. The Ag/Au prismatic core/shell nanostructures were synthesized using chemical reduction method. It was observed that, on the addition of excess gold chloride (HAuCl4) solution, the morphology of nano core/shell was changed to alloy like triangular nanoframes. Accordingly, a shift was found towards higher wavelengths in the UV-Visible absorption peaks of Ag/Au nanoframes compare to Ag/Au nano core/shell. Consequently, the SERS effect of these Ag/Au anisotropic nanostructures were studied on methylene blue. The Ag/Au alloy like prismatic nanoframes showed improved SERS effect than that of prismatic core/shell nanostructures. The experimental findings were revealed that the improved SERS effect could be resulted from the enhanced surface plasmon resonance (SPR) due to the alloy like construction of Ag/Au system.

A solar-thermal energy harvesting scheme: enhanced heat capacity of molten HITEC salt mixed with Sn/SiO(x) core-shell nanoparticles.

PubMed

Lai, Chih-Chung; Chang, Wen-Chih; Hu, Wen-Liang; Wang, Zhiming M; Lu, Ming-Chang; Chueh, Yu-Lun

2014-05-07

We demonstrated enhanced solar-thermal storage by releasing the latent heat of Sn/SiO(x) core-shell nanoparticles (NPs) embedded in a eutectic salt. The microstructures and chemical compositions of Sn/SiO(x) core-shell NPs were characterized. In situ heating XRD provides dynamic crystalline information about the Sn/SiO(x) core-shell NPs during cyclic heating processes. The latent heat of ∼29 J g(-1) for Sn/SiO(x) core-shell NPs was measured, and 30% enhanced heat capacity was achieved from 1.57 to 2.03 J g(-1) K(-1) for the HITEC solar salt without and with, respectively, a mixture of 5% Sn/SiO(x) core-shell NPs. In addition, an endurance cycle test was performed to prove a stable operation in practical applications. The approach provides a method to enhance energy storage in solar-thermal power plants.

Fabrication of Fe3O4@CuO core-shell from MOF based materials and its antibacterial activity

NASA Astrophysics Data System (ADS)

Rajabi, S. K.; Sohrabnezhad, Sh.; Ghafourian, S.

2016-12-01

Magnetic Fe3O4@CuO nanocomposite with a core/shell structure was successfully synthesized via direct calcinations of magnetic Fe3O4@HKUST-1 in air atmosphere. The morphology, structure, magnetic and porous properties of the as-synthesized nano composites were characterized by using scanning electron microscope (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), and vibration sample magnetometer (VSM). The results showed that the nanocomposite material included a Fe3O4 core and a CuO shell. The Fe3O4@CuO core-shell can be separated easily from the medium by a small magnet. The antibacterial activity of Fe3O4-CuO core-shell was investigated against gram-positive and gram-negative bacteria. A new mechanism was proposed for inactivation of bacteria over the prepared sample. It was demonstrated that the core-shell exhibit recyclable antibacterial activity, acting as an ideal long-acting antibacterial agent.

Structural Basis for Near Unity Quantum Yield Core/Shell Nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

McBride, James; Treadway, Joe; Pennycook, Stephen J

2006-01-01

Aberration-corrected Z-contrast scanning transmission electron microscopy of core/shell nanocrystals shows clear correlations between structure and quantum efficiency. Uniform shell coverage is obtained only for a graded CdS/ZnS shell material and is found to be critical to achieving near 100% quantum yield. The sublattice sensitivity of the images confirms that preferential growth takes place on the anion-terminated surfaces. This explains the three-dimensional "nanobullet" shape observed in the case of core/shell nanorods.

Structures of p -shell double-Λ hypernuclei studied with microscopic cluster models

NASA Astrophysics Data System (ADS)

Kanada-En'yo, Yoshiko

2018-03-01

0 s -orbit Λ states in p -shell double-Λ hypernuclei (Z Λ Λ A ), Li Λ Λ 8 , Li Λ Λ 9 , Be Λ Λ 10 ,11 ,12 , B Λ Λ 12 ,13 , and C Λ Λ 14 are investigated. Microscopic cluster models are applied to core nuclear part and a potential model is adopted for Λ particles. The Λ -core potential is a folding potential obtained with effective G -matrix Λ -N interactions, which reasonably reproduce energy spectra of Z Λ A -1 . System dependence of the Λ -Λ binding energies is understood by the core polarization energy from nuclear size reduction. Reductions of nuclear sizes and E 2 transition strengths by Λ particles are also discussed.

Aerosol fabrication methods for monodisperse nanoparticles

DOEpatents

Jiang, Xingmao; Brinker, C Jeffrey

2014-10-21

Exemplary embodiments provide materials and methods for forming monodisperse particles. In one embodiment, the monodisperse particles can be formed by first spraying a nanoparticle-containing dispersion into aerosol droplets and then heating the aerosol droplets in the presence of a shell precursor to form core-shell particles. By removing either the shell layer or the nanoparticle core of the core-shell particles, monodisperse nanoparticles can be formed.

Efficient photocatalytic degradation of malachite green dye under visible irradiation by water soluble ZnS:Mn/ZnS core/shell nanoparticles

NASA Astrophysics Data System (ADS)

Khaparde, Rohini A.; Acharya, Smita A.

2018-05-01

ZnS:Mn/ ZnS core/shell nanoparticles was prepared by two step synthesis method. In first step, oleic acid - coated Mn doped ZnS core nanoparticles were prepared which were charged through ligand exchange. Shell of ZnS NPs was finally deposited upon the surface of charged Mn doped ZnS core. Scanning electron microscopy (SEM) image exhibit morphological confirmation of ZnS:Mn/ZnS core/shell. As Nano ZnS are the most suitable candidates for photocatalyst that extensively involved in degradation and complete mineralization of various toxic organic pollutants owing to its high efficiency, strong oxidizing power, non-toxicity, high photochemical and biological stability, corrosive resistance and low cost. Photodegradation of malachite green is systematically investigated by adding different molar proportional of ZnS:Mn/ZnS core/shell in the dye. The rate of de-coloration of dye is detected by UV-VIS absorption spectroscopy. Efficient detoriation in the colour of dye is attributed to the core /shell morphology of the particles.

ELECTRON-CAPTURE AND β-DECAY RATES FOR sd-SHELL NUCLEI IN STELLAR ENVIRONMENTS RELEVANT TO HIGH-DENSITY O–NE–MG CORES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, Toshio; Toki, Hiroshi; Nomoto, Ken’ichi, E-mail: suzuki@phys.chs.nihon-u.ac.jp

Electron-capture and β-decay rates for nuclear pairs in the sd-shell are evaluated at high densities and high temperatures relevant to the final evolution of electron-degenerate O–Ne–Mg cores of stars with initial masses of 8–10 M{sub ⊙}. Electron capture induces a rapid contraction of the electron-degenerate O–Ne–Mg core. The outcome of rapid contraction depends on the evolutionary changes in the central density and temperature, which are determined by the competing processes of contraction, cooling, and heating. The fate of the stars is determined by these competitions, whether they end up with electron-capture supernovae or Fe core-collapse supernovae. Since the competing processes aremore » induced by electron capture and β-decay, the accurate weak rates are crucially important. The rates are obtained for pairs with A = 20, 23, 24, 25, and 27 by shell-model calculations in the sd-shell with the USDB Hamiltonian. Effects of Coulomb corrections on the rates are evaluated. The rates for pairs with A = 23 and 25 are important for nuclear Urca processes that determine the cooling rate of the O–Ne–Mg core, while those for pairs with A = 20 and 24 are important for the core contraction and heat generation rates in the core. We provide these nuclear rates at stellar environments in tables with fine enough meshes at various densities and temperatures for studies of astrophysical processes sensitive to the rates. In particular, the accurate rate tables are crucially important for the final fates of not only O–Ne–Mg cores but also a wider range of stars, such as C–O cores of lower-mass stars.« less

Developing core-shell upconversion nanoparticles for optical encoding

NASA Astrophysics Data System (ADS)

Huang, Kai

Lanthanide-doped upconversion nanoparticles (UCNPs) are an emerging class of luminescent materials that emit UV or visible light under near infra-red (NIR) excitations, thereby possessing a large anti-Stokes shift property. Also considering their sharp emission bands, excellent photo- and chemical stability, and almost zero auto-fluorescence of their NIR excitation, UCNPs are advantageous for optical encoding. Fabricating core-shell structured UCNPs provides a promising strategy to tune and enhance their upconverting luminescence. However, the energy transfer between core and shell had been rarely studied. Moreover, this strategy had been limited by the difficulty of coating thick shells onto the large cores of UCNPs. To overcome these constraints, the overall aim of this project is to study the inter-layers energy transfer in core-shell UCNPs and to develop an approach for coating thicker shell onto the core UCNPs, in order to fabricate UCNPs with enhanced and tunable luminescence for optical encoding. The strategy for encapsulating UCNPs into hydrogel droplet to fabricate multi-color bead barcodes has also been developed. Firstly, to study the inter-layers energy transfer between the core and shell of coreshell UCNPs, the activator and sensitizer ions were separately doped in the core or shell by fabricating NaYF4:Er NaYF4:Yb and NaYF4:Yb NaYF4:Er UCNPs. This eliminated the intra-layer energy transfer, resulting in a luminescence that is solely based on the energy transfer between layers, which facilitated the study of inter-layers energy transfer. The results demonstrated that the NaYF4:Yb NaYF4:Er structure, with sensitizer ions doped in the core, was preferable because of the strong luminescence, through minimizing the cross relaxations between Er3+ and Yb3+ and the surface quenching. Based on these information, a strategy of enhancing and tuning upconversion luminescence of core-shell UCNPs by accumulating sensitizer in the core has been developed. Next, a strategy of coating a thick shell by lutetium doping has been developed. With a smaller ion radius compared to Y3+, when Lu3+ partially replace Y3+ in the NaYF4 UCNPs during nanoparticle synthesis, nucleation process is suppressed and the growth process is promoted, which are favorable for increasing the nanoparticle size and coating a thicker shell onto the core UCNPs. Through the rational doping of Lu3+, core UCNPs with bigger sizes and enhanced luminescence were produced. Using NaLuF4 as the shell material, shells with tremendous thickness were coated onto core UCNPs, with the shell/core ratio of up to 10:1. This led to the fabrication of multi-color UCNPs with well-designed core-shell structures with multiple layers and controllable thicknesses. Finally, a strategy of encapsulating these UCNPs to produce optically encoded micro-beads through high-throughput microfluidics has been developed. The hydrophobic UCNPs were first modified with Pluronic F127 to render them hydrophilic and uniformly distributed in the poly (ethylene glycol) diacrylate (PEGDA) hydrogel precursor. Droplets of the hydrogel precursor were formed in a microfluidic device and cross-linked into micro-beads under UV irradiation. Through encapsulation of multi-color UCNPs and by controlling their ratio, optically encoded multi-color micro-beads have been easily fabricated. These multi-color UCNPs and micro-bead barcodes have great potential for use in multiplexed bioimaging and detection.

Flexible 3D Fe@VO2 core-shell mesh: A highly efficient and easy-recycling catalyst for the removal of organic dyes.

PubMed

Li, Jing; Wang, Ruoqi; Su, Zhen; Zhang, Dandan; Li, Heping; Yan, Youwei

2018-10-01

Nowadays, it is extremely urgent to search for efficient and effective catalysts for water purification due to the severe worldwide water-contamination crises. Here, 3D Fe@VO 2 core-shell mesh, a highly efficient catalyst toward removal of organic dyes with excellent recycling ability in the dark is designed and developed for the first time. This novel core-shell structure is actually 304 stainless steel mesh coated by VO 2 , fabricated by an electrophoretic deposition method. In such a core-shell structure, Fe as the core allows much easier separation from the water, endowing the catalyst with a flexible property for easy recycling, while VO 2 as the shell is highly efficient in degradation of organic dyes with the addition of H 2 O 2 . More intriguingly, the 3D Fe@VO 2 core-shell mesh exhibits favorable performance across a wide pH range. The 3D Fe@VO 2 core-shell mesh can decompose organic dyes both in a light-free condition and under visible irradiation. The possible catalytic oxidation mechanism of Fe@VO 2 /H 2 O 2 system is also proposed in this work. Considering its facile fabrication, remarkable catalytic efficiency across a wide pH range, and easy recycling characteristic, the 3D Fe@VO 2 core-shell mesh is a newly developed high-performance catalyst for addressing the universal water crises. Copyright © 2018 Elsevier B.V. All rights reserved.

Centrifugal Deposited Au-Pd Core-Shell Nanoparticle Film for Room-Temperature Optical Detection of Hydrogen Gas.

PubMed

Song, Han; Luo, Zhijie; Liu, Mingyao; Zhang, Gang; Peng, Wang; Wang, Boyi; Zhu, Yong

2018-05-06

In the present work, centrifugal deposited Au-Pd core-shell nanoparticle (NP) film was proposed for the room-temperature optical detection of hydrogen gas. The size dimension of 44, 48, 54, and 62 nm Au-Pd core-shell nanocubes with 40 nm Au core were synthesized following a solution-based seed-mediated growth method. Compared to a pure Pd NP, this core-shell structure with an inert Au core could decrease the H diffusion length in the Pd shell. Through a modified centrifugal deposition process, continues film samples with different core-shell NPs were deposited on 10 mm diameter quartz substrates. Under various hydrogen concentration conditions, the optical response properties of these samples were characterized by an intensity-based optical fiber bundle sensor. Experimental results show that the continues film that was composed of 62 nm Au-Pd core-shell NPs has achieved a stable and repeatable reflectance response with low zero drift in the range of 4 to 0.1% hydrogen after a stress relaxation mechanism at first few loading/unloading cycles. Because of the short H diffusion length due to the thinner Pd shell, the film sample composed of 44 nm Au-Pd NPs has achieved a dramatically decreased response/recovery time to 4 s/30 s. The experiments present the promising prospect of this simple method to fabricate optical hydrogen sensors with controllable high sensitivity and response rate at low cost.

Theoretical studies of massive stars. II - Evolution of a 15 solar-mass star from carbon shell burning to iron core collapse

NASA Technical Reports Server (NTRS)

Sparks, W. M.; Endal, A. S.

1980-01-01

The evolution of a Population I star of 15 solar masses is described from the carbon shell burning stage to the formation and collapse of an iron core. An unusual aspect of the evolution is that neon ignition occurs off-center and neon burning propagates inward by a series of shell flashes. The extent of the core burning is generally smaller than the Chandrasekhar mass, so that most of the nuclear energy generation occurs in shell sources. Because of degeneracy and the influence of rapid convective mixing, these shell sources are unstable and the core goes through large excursions in temperature and density. The small core also causes the shell sources to converge into a narrow mass region slightly above the Chandrasekhar mass. Thus, the final nucleosynthesis yields are generally small, with silicon being most strongly enhanced with respect to solar system abundances.

Petrology and geochemistry of the orbicular granitoid of Caldera, northern Chile. Models and hypotheses on the formation of radial orbicular textures

NASA Astrophysics Data System (ADS)

Díaz-Alvarado, Juan; Rodríguez, Natalia; Rodríguez, Carmen; Fernández, Carlos; Constanzo, Ítalo

2017-07-01

The orbicular granitoid of Caldera, located at the northern part of the Chilean Coastal Range, is a spectacular example of radial textures in orbicular structures. The orbicular body crops out as a 375 m2 tabular to lensoidal intrusive sheet emplaced in the Lower Jurassic Relincho pluton. The orbicular structures are 3-7 cm in diameter ellipsoids hosted in a porphyritic matrix. The orbicules are comprised by a Qtz-dioritic core (3-5 cm in diameter) composed by Pl + Hbl + Qtz + Bt ± Kfs with equiaxial textures and a gabbroic shell (2-3 cm in diameter) characterized by feathery and radiate textures with a plagioclase + hornblende paragenesis. The radial shell crystals are rooted and orthogonally disposed in the irregular contact with the core. The radial shell, called here inner shell, is in contact with the granodioritic equiaxial interorbicular matrix through a 2-3 mm wide poikilitic band around the orbicule (outer shell). The outer shell and the matrix surrounding the orbicules are characterized by the presence of large hornblende and biotite oikocrystals that include fine-grained rounded plagioclase and magnetite. The oikocrystals of both the outer shell and the matrix have a circumferential arrangement around the orbicule, i.e. orthogonal to the radial inner shell. The coarse-grained granodioritic interorbicular matrix present pegmatitic domains with large acicular hornblende and K-feldspar megacrysts. This work presents a review of the textural characteristics of the orbicules and a complete new mineral and whole-rock geochemical study of the different parts of the orbicular granitoid, together with thermobarometric and crystallographic data, and theoretical modeling of the crystallization and element partitioning processes. We propose a model for the formation of the orbicular radial textures consisting of several processes that are suggested to occur fast and consecutively: superheating, volatile exsolution, undercooling, geochemical fractionation and columnar and equiaxial crystallization. According to the obtained results, the formation of the orbicular granitoid of Caldera may have initiated 1) during the generation of a magmatic fracture in the crystallization front of the Relincho pluton, where the water released by the host crystal mush was dissolved in the new batch of dioritic magma. 2) The high influx of water-rich liquids induced superheating conditions in the newly intruding magma that became a depolymerized liquid, where the only solid particules were the small irregular fragments of the host mush dragged from the fracture walls. 3) Volatile exsolution promoted crystallization under undercooling conditions. 4) Undercooling and nucleation around the core (cold germs) involved the physical and geochemical fractionation between two sub-systems: a gabbroic sub-system that comprises the solid paragénesis with a residual water-rich liquid and a granodioritic sub-system. 5) The orbicules, including core and inner shell, behaved as viscous bodies (crystals + residual liquid) floating in the granodioritic magma. 6) Higher undercooling rates occurred at the starting stage, close to the liquidus, promoting columnar crystallization around the cores and formation of the shells. Conversely, in the granodioritic matrix sub-system, equiaxial crystallization was promoted by low relative crystallization rates. 7) The rest of the crystallization process evolved later in the outer shell and the matrix, as suggested by the poikilitic textures observed in both sides of the orbicule contact, and under conditions close to the solidus of both sub-systems (shell and matrix). The water-rich residual liquid expelled during the orbicular shell crystallization was mingled with the partially crystallized matrix magma, generating the pegmatitic domains with large Kfs megacrysts.

Magnetically tunable liquid dielectric with giant dielectric permittivity based on core-shell superparamagnetic iron oxide.

PubMed

Vinayasree, S; Nitha, T S; Tiwary, C S; Ajayan, P M; Joy, P A; Anantharaman, M R

2018-06-29

A liquid dielectric based on a core-shell architecture having a superparamagnetic iron oxide core and a shell of silicon dioxide was synthesized. The frequency dependence of dielectric properties was evaluated for different concentrations of iron oxide. The dependence of magnetic field on the dielectric properties was also studied. Aqueous ferrofluid exhibited a giant dielectric constant of 6.4 × 10 5 at 0.1 MHz at a concentration of 0.2 vol% and the loss tangent was 3. The large rise in dielectric constant at room temperature is modelled and explained using percolation theory and Maxwell-Wagner-Sillars type polarization. The ferrofluid is presumed to consist of nanocapacitor networks which are wired in series along the lateral direction and parallel along longitudinal direction. On the application of an external magnetic field, the chain formation and its alignment results in the variation of dielectric permittivity.

Core-in-shell sorbent for hot coal gas desulfurization

DOEpatents

Wheelock, Thomas D.; Akiti, Jr., Tetteh T.

2004-02-10

A core-in-shell sorbent is described herein. The core is reactive to the compounds of interest, and is preferably calcium-based, such as limestone for hot gas desulfurization. The shell is a porous protective layer, preferably inert, which allows the reactive core to remove the desired compounds while maintaining the desired physical characteristics to withstand the conditions of use.

Helium-Shell Nucleosynthesis and Extinct Radioactivities

NASA Technical Reports Server (NTRS)

Meyer, B. S.; The, L.-S.; Clayton, D. D.; ElEid, M. F.

2004-01-01

Although the exact site for the origin of the r-process isotopes remains mysterious, most thinking has centered on matter ejected from the cores of massive stars in core-collapse supernovae [13]. In the 1970's and 1980's, however, difficulties in understanding the yields from such models led workers to consider the possibility of r-process nucleosynthesis farther out in the exploding star, in particular, in the helium burning shell [4,5]. The essential idea was that shock passage through this shell would heat and compress this material to the point that the reactions 13C(alpha; n)16O and, especially, 22Ne(alpha; n)25Mg would generate enough neutrons to capture on preexisting seed nuclei and drive an "n process" [6], which could reproduce the r-process abundances. Subsequent work showed that the required 13C and 22Ne abundances were too large compared to the amounts available in realistic models [7] and recent thinking has returned to supernova core material or matter ejected from neutron star-neutron star collisions as the more likely r-process sites.

Experimental and theoretical charge density studies at subatomic resolution.

PubMed

Fischer, A; Tiana, D; Scherer, W; Batke, K; Eickerling, G; Svendsen, H; Bindzus, N; Iversen, B B

2011-11-17

Analysis of accurate experimental and theoretical structure factors of diamond and silicon reveals that the contraction of the core shell due to covalent bond formation causes significant perturbations of the total charge density that cannot be ignored in precise charge density studies. We outline that the nature and origin of core contraction/expansion and core polarization phenomena can be analyzed by experimental studies employing an extended Hansen-Coppens multipolar model. Omission or insufficient treatment of these subatomic charge density phenomena might yield erroneous thermal displacement parameters and high residual densities in multipolar refinements. Our detailed studies therefore suggest that the refinement of contraction/expansion and population parameters of all atomic shells is essential to the precise reconstruction of electron density distributions by a multipolar model. Furthermore, our results imply that also the polarization of the inner shells needs to be adopted, especially in cases where second row or even heavier elements are involved in covalent bonding. These theoretical studies are supported by direct multipolar refinements of X-ray powder diffraction data of diamond obtained from a third-generation synchrotron-radiation source (SPring-8, BL02B2).

Direct Observation of the Growth of Au-Pd Core-Shell Nanoparticles Using in situ Low-Dose Liquid Cell STEM imaging

DOE PAGES

Bhattarai, Nabraj; Prozorov, Tanya

2016-07-25

Bimetallic core-shell nanoparticles are widely used as catalysts in several industrial reactions, with core-shell structures permitting facile surface modification and allowing increased stability and durability, and cost-effectiveness of the catalysts. We report, for the first time, on observing the early stages of the formation of Au-Pd core-shell bimetallic nanoparticles via the seed-mediated growth in the presence of reducing agent, while employing the low-dose scanning transmission electron microscopy imaging with the fluid cell in situ. Use of the continuous flow in situ fluid cell platform allows for delivery of reagent solutions and generation of near-native reaction environment in the reaction chamber,more » and permits direct visualization of the early stages of formation of Au-Pd core-shell structures at low dose rate (0.1 e -/(Å 2s)) in the presence of ascorbic acid. No core-shell structures were detected in the absence of reducing agent at the electron dose of 32.6 e -/Å 2. While the core-shell structures formed in situ under the low-dose imaging closely resemble those obtained in solution synthesis, the reaction kinetics in the fluid cell is affected by the radiolysis of liquid reagents induced by electron beam, altering the rate-determining reaction steps. The enhanced reduction of Pd ions leads to initial rapid growth of the nascent Pd shell along the <111> direction at the Au interface, followed by a slower rearrangement of the outer Pd layer. The latter becomes the rate-determining step in the in situ reaction and appears to follow the oriented attachment-like movement to yield a remodeled, compact and stable Au-Pd core-shell nanostructure. Our findings highlight the differences between the two reaction pathways and aid in understanding the mechanism of formation of the core-shell nanostructure in situ.« less

Gold core@silver semishell Janus nanoparticles prepared by interfacial etching

NASA Astrophysics Data System (ADS)

Chen, Limei; Deming, Christopher P.; Peng, Yi; Hu, Peiguang; Stofan, Jake; Chen, Shaowei

2016-07-01

Gold core@silver semishell Janus nanoparticles were prepared by chemical etching of Au@Ag core-shell nanoparticles at the air/water interface. Au@Ag core-shell nanoparticles were synthesized by chemical deposition of a silver shell onto gold seed colloids followed by the self-assembly of 1-dodecanethiol onto the nanoparticle surface. The nanoparticles then formed a monolayer on the water surface of a Langmuir-Blodgett trough, and part of the silver shell was selectively etched away by the mixture of hydrogen peroxide and ammonia in the water subphase, where the etching was limited to the side of the nanoparticles that was in direct contact with water. The resulting Janus nanoparticles exhibited an asymmetrical distribution of silver on the surface of the gold cores, as manifested in transmission electron microscopy, UV-vis absorption, and X-ray photoelectron spectroscopy measurements. Interestingly, the Au@Ag semishell Janus nanoparticles exhibited enhanced electrocatalytic activity in oxygen reduction reactions, as compared to their Au@Ag and Ag@Au core-shell counterparts, likely due to a synergistic effect between the gold cores and silver semishells that optimized oxygen binding to the nanoparticle surface.Gold core@silver semishell Janus nanoparticles were prepared by chemical etching of Au@Ag core-shell nanoparticles at the air/water interface. Au@Ag core-shell nanoparticles were synthesized by chemical deposition of a silver shell onto gold seed colloids followed by the self-assembly of 1-dodecanethiol onto the nanoparticle surface. The nanoparticles then formed a monolayer on the water surface of a Langmuir-Blodgett trough, and part of the silver shell was selectively etched away by the mixture of hydrogen peroxide and ammonia in the water subphase, where the etching was limited to the side of the nanoparticles that was in direct contact with water. The resulting Janus nanoparticles exhibited an asymmetrical distribution of silver on the surface of the gold cores, as manifested in transmission electron microscopy, UV-vis absorption, and X-ray photoelectron spectroscopy measurements. Interestingly, the Au@Ag semishell Janus nanoparticles exhibited enhanced electrocatalytic activity in oxygen reduction reactions, as compared to their Au@Ag and Ag@Au core-shell counterparts, likely due to a synergistic effect between the gold cores and silver semishells that optimized oxygen binding to the nanoparticle surface. Electronic supplementary information (ESI) available: Additional TEM, UV-vis, XPS, and electrochemical data. See DOI: 10.1039/c6nr03368g

Broadband absorption and enhanced photothermal conversion property of octopod-like Ag@Ag2S core@shell structures with gradually varying shell thickness.

PubMed

Jiang, Qian; Zeng, Wenxia; Zhang, Canying; Meng, Zhaoguo; Wu, Jiawei; Zhu, Qunzhi; Wu, Daxiong; Zhu, Haitao

2017-12-19

Photothermal conversion materials have promising applications in many fields and therefore they have attracted tremendous attention. However, the multi-functionalization of a single nanostructure to meet the requirements of multiple photothermal applications is still a challenge. The difficulty is that most nanostructures have specific absoprtion band and are not flexible to different demands. In the current work, we reported the synthesis and multi-band photothermal conversion of Ag@Ag 2 S core@shell structures with gradually varying shell thickness. We synthesized the core@shell structures through the sulfidation of Ag nanocubes by taking the advantage of their spatially different reactivity. The resulting core@shell structures show an octopod-like mopgorlogy with a Ag 2 S bulge sitting at each corner of the Ag nanocubes. The thickness of the Ag 2 S shell gradually increases from the central surface towards the corners of the structure. The synthesized core@shell structures show a broad band absorption spectrum from 300 to 1100 nm. Enhanced photothermal conversion effect is observed under the illuminations of 635, 808, and 1064 nm lasers. The results indicate that the octopod-like Ag@Ag 2 S core@shell structures have characteristics of multi-band photothermal conversion. The current work might provide a guidance for the design and synthesis of multifunctional photothermal conversion materials.

Core-Shell Composite Fibers for High-Performance Flexible Supercapacitor Electrodes.

PubMed

Lu, Xiaoyan; Shen, Chen; Zhang, Zeyang; Barrios, Elizabeth; Zhai, Lei

2018-01-31

Core-shell nanofibers containing poly(acrylic acid) (PAA) and manganese oxide nanoparticles as the core and polypyrrole (PPy) as the shell were fabricated through electrospinning the solution of PAA and manganese ions (PAA/Mn 2+ ). The obtained nanofibers were stabilized by Fe 3+ through the interaction between Fe 3+ ions and carboxylate groups. Subsequent oxidation of Mn 2+ by KMnO 4 produced uniform manganese dioxide (MnO 2 ) nanoparticles in the fibers. A PPy shell was created on the fibers by immersing the fibers in a pyrrole solution where the Fe 3+ ions in the fiber polymerized the pyrrole on the fiber surfaces. In the MnO 2 @PAA/PPy core-shell composite fibers, MnO 2 nanoparticles function as high-capacity materials, while the PPy shell prevents the loss of MnO 2 during the charge/discharge process. Such a unique structure makes the composite fibers efficient electrode materials for supercapacitors. The gravimetric specific capacity of the MnO 2 @PAA/PPy core-shell composite fibers was 564 F/g based on cyclic voltammetry curves at 10 mV/s and 580 F/g based on galvanostatic charge/discharge studies at 5 A/g. The MnO 2 @PAA/PPy core-shell composite fibers also present stable cycling performance with 100% capacitance retention after 5000 cycles.

Synthesis and detection the oxidization of Co cores of Co@SiO2 core-shell nanoparticles by in situ XRD and EXAFS.

PubMed

Zhang, Kunhao; Zhao, Ziyan; Wu, Zhonghua; Zhou, Ying

2015-01-01

In this paper, the Co@SiO2 core-shell nanoparticles were prepared by the sol-gel method. The oxidization of Co core nanoparticles was studied by the synchrotron radiation-based techniques including in situ X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) up to 800°C in air and N2 protection conditions, respectively. It was found that the oxidization of Co cores is undergoing three steps regardless of being in air or in N2 protection condition. In the first step ranging from room temperature to 200°C, the Co cores were dominated by Co(0) state as well as small amount of Co(2+) ions. When temperature was above 300°C, the interface between Co cores and SiO2 shells was gradually oxidized into Co(2+), and the CoO layer was observed. As the temperature increasing to 800°C, the Co cores were oxidized to Co3O4 or Co3O4/CoO. Nevertheless, the oxidization kinetics of Co cores is different for the Co@SiO2 in air and N2 gas conditions. Generally, the O2 in the air could get through the SiO2 shells easily onto the Co core surface and induce the oxidization of the Co cores due to the mesoporous nature of the SiO2 shells. However, in N2 gas condition, the O atoms can only be from the SiO2 shells, so the diffusion effect of O atoms in the interface between Co core and SiO2 shell plays a key role.

Shape evolution of a core-shell spherical particle under hydrostatic pressure.

PubMed

Colin, Jérôme

2012-03-01

The morphological evolution by surface diffusion of a core-shell spherical particle has been investigated theoretically under hydrostatic pressure when the shear modulii of the core and shell are different. A linear stability analysis has demonstrated that depending on the pressure, shear modulii, and radii of both phases, the free surface of the composite particle may be unstable with respect to a shape perturbation. A stability diagram finally emphasizes that the roughness development is favored in the case of a hard shell with a soft core.

One-pot synthesis of biocompatible Te@phenol formaldehyde resin core-shell nanowires with uniform size and unique fluorescent properties by a synergized soft-hard template process.

PubMed

Qian, Haisheng; Zhu, Enbo; Zheng, Shunji; Li, Zhengquan; Hu, Yong; Guo, Changfa; Yang, Xingyun; Li, Liangchao; Tong, Guoxiu; Guo, Huichen

2010-12-10

One-pot hydrothermal process has been developed to synthesize uniform Te@phenol formaldehyde resin core-shell nanowires with unique fluorescent properties. A synergistic soft-hard template mechanism has been proposed to explain the formation of the core-shell nanowires. The Te@phenol formaldehyde resin core-shell nanowires display unique fluorescent properties, which give strong luminescent emission in the blue-violet and green regions with excitation wavelengths of 270 nm and 402 nm, respectively.

Self-assembly of core-shell structure PtO2@Pt nanodots and their formation evolution

NASA Astrophysics Data System (ADS)

Yang, Weijia; Liu, Junjie; Liu, Mingquan; Zhao, Zhicheng; Song, Yapeng; Tang, Xiufeng; Luo, Jianyi; Zeng, Qingguang; He, Xin

2018-05-01

Core-shell structure PtO2@Pt nanodots have been self-assembly by vacuum sputtering and high temperature annealing. First, Pt thin films with a small amount of PtO2 are grown on the sapphire substrates by vacuum sputtering. And then high temperature annealing on the thin films is carried out at 800 °C for 2 min to form Pt nanodots. During the cooling process, the atmosphere is deployed to supplant the nitrogen. Finally, even distributed core-shell structure PtO2@Pt nanodots with a diameter from 100 to 300 nm are achieved. Furthermore, the formation evolution of core-shell structure PtO2@Pt nanodots is also proposed. This work open up a new approach for fabricating core-shell structure nanodots.

Highly efficient near-infrared light-emitting diodes by using type-II CdTe/CdSe core/shell quantum dots as a phosphor

NASA Astrophysics Data System (ADS)

Shen, Huaibin; Zheng, Ying; Wang, Hongzhe; Xu, Weiwei; Qian, Lei; Yang, Yixing; Titov, Alexandre; Hyvonen, Jake; Li, Lin Song

2013-11-01

In this paper, we present an innovative method for the synthesis of CdTe/CdSe type-II core/shell structure quantum dots (QDs) using ‘greener’ chemicals. The PL of CdTe/CdSe type-II core/shell structure QDs ranges from 600 to 820 nm, and the as-synthesized core/shell structures show narrow size distributions and stable and high quantum yields (50-75%). Highly efficient near-infrared light-emitting diodes (LEDs) have been demonstrated by employing the CdTe/CdSe type-II core/shell QDs as emitters. The devices fabricated based on these type-II core/shell QDs show color-saturated near-infrared emission from the QD layers, a low turn-on voltage of 1.55 V, an external quantum efficiency (EQE) of 1.59%, and a current density and maximum radiant emittance of 2.1 × 103 mA cm-2 and 17.7 mW cm-2 at 8 V it is the first report to use type-II core/shell QDs as near-infrared emitters and these results may offer a practicable platform for the realization of near-infrared QD-based light-emitting diodes, night-vision-readable displays, and friend/foe identification system.

Core-shell designed scaffolds for drug delivery and tissue engineering.

PubMed

Perez, Roman A; Kim, Hae-Won

2015-07-01

Scaffolds that secure and deliver therapeutic ingredients like signaling molecules and stem cells hold great promise for drug delivery and tissue engineering. Employing a core-shell design for scaffolds provides a promising solution. Some unique methods, such as co-concentric nozzle extrusion, microfluidics generation, and chemical confinement reactions, have been successful in producing core-shelled nano/microfibers and nano/microspheres. Signaling molecules and drugs, spatially allocated to the core and/or shell part, can be delivered in a controllable and sequential manner for optimal therapeutic effects. Stem cells can be loaded within the core part on-demand, safely protected from the environments, which ultimately affords ex vivo culture and in vivo tissue engineering. The encapsulated cells experience three-dimensional tissue-mimic microenvironments in which therapeutic molecules are secreted to the surrounding tissues through the semi-permeable shell. Tuning the material properties of the core and shell, changing the geometrical parameters, and shaping them into proper forms significantly influence the release behaviors of biomolecules and the fate of the cells. This topical issue highlights the immense usefulness of core-shell designs for the therapeutic actions of scaffolds in the delivery of signaling molecules and stem cells for tissue regeneration and disease treatment. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Protein coated gold nanoparticles as template for the directed synthesis of highly fluorescent gold nanoclusters

NASA Astrophysics Data System (ADS)

Zhang, Lingyan; Han, Fei

2018-04-01

Bovine serum albumin (BSA) modified gold nanoparticles (AuNPs) was selected as template for the synthesis of AuNPs@gold nanoclusters (AuNCs) core/shell nanoparticles, in which BSA not only acted as dual functions agent for both anchoring and reducing Au3+ ions, but also was employed as a bridge between the AuNPs and AuNCs. Optical properties of AuNPs@AuNCs core/shell nanoparticles were studied using UV-visible and fluorescence spectroscopy. The prepared AuNPs@AuNCs core/shell nanoparticles exhibited sphere size uniformity with improved monodispersity, excellent fluorescence and fluorescent stability. Compared with AuNCs, AuNPs@AuNCs core/shell nanoparticles possessed large size and strong fluorescence intensity due to the effect of AuNPs as core. Moreover, the mechanism of the AuNPs induced fluorescence changes of the core/shell nanoparticles was first explored.

Highly flexible transparent self-healing composite based on electrospun core-shell nanofibers produced by coaxial electrospinning for anti-corrosion and electrical insulation

NASA Astrophysics Data System (ADS)

An, Seongpil; Liou, Minho; Song, Kyo Yong; Jo, Hong Seok; Lee, Min Wook; Al-Deyab, Salem S.; Yarin, Alexander L.; Yoon, Sam S.

2015-10-01

Coaxial electrospinning was used to fabricate two types of core-shell fibers: the first type with liquid resin monomer in the core and polyacrylonitrile in the shell, and the second type with liquid curing agent in the core and polyacrylonitrile in the shell. These two types of core-shell fibers were mutually entangled and embedded into two flexible transparent matrices thus forming transparent flexible self-healing composite materials. Such materials could be formed before only using emulsion electrospinning, rather than coaxial electrospinning. The self-healing properties of such materials are associated with release of healing agents (resin monomer and cure) from nanofiber cores in damaged locations with the subsequent polymerization reaction filing the micro-crack with polydimethylsiloxane. Transparency of these materials is measured and the anti-corrosive protection provided by them is demonstrated in electrochemical experiments.

Graphitic carbon nitride nanosheet@metal-organic framework core-shell nanoparticles for photo-chemo combination therapy

NASA Astrophysics Data System (ADS)

Chen, Rui; Zhang, Jinfeng; Wang, Yu; Chen, Xianfeng; Zapien, J. Antonio; Lee, Chun-Sing

2015-10-01

Recently, nanoscale metal-organic frameworks (NMOFs) have started to be developed as a promising platform for bioimaging and drug delivery. On the other hand, combination therapies using multiple approaches are demonstrated to achieve much enhanced efficacy. Herein, we report, for the first time, core-shell nanoparticles consisting of a photodynamic therapeutic (PDT) agent and a MOF shell while simultaneously carrying a chemotherapeutic drug for effective combination therapy. In this work, core-shell nanoparticles of zeolitic-imadazolate framework-8 (ZIF-8) as shell embedded with graphitic carbon nitride (g-C3N4) nanosheets as core are fabricated by growing ZIF-8 in the presence of g-C3N4 nanosheets. Doxorubicin hydrochloride (DOX) is then loaded into the ZIF-8 shell of the core-shell nanoparticles. The combination of the chemotherapeutic effects of DOX and the PDT effect of g-C3N4 nanosheets can lead to considerably enhanced efficacy. Furthermore, the red fluorescence of DOX and the blue fluorescence of g-C3N4 nanosheets provide the additional function of dual-color imaging for monitoring the drug release process.Recently, nanoscale metal-organic frameworks (NMOFs) have started to be developed as a promising platform for bioimaging and drug delivery. On the other hand, combination therapies using multiple approaches are demonstrated to achieve much enhanced efficacy. Herein, we report, for the first time, core-shell nanoparticles consisting of a photodynamic therapeutic (PDT) agent and a MOF shell while simultaneously carrying a chemotherapeutic drug for effective combination therapy. In this work, core-shell nanoparticles of zeolitic-imadazolate framework-8 (ZIF-8) as shell embedded with graphitic carbon nitride (g-C3N4) nanosheets as core are fabricated by growing ZIF-8 in the presence of g-C3N4 nanosheets. Doxorubicin hydrochloride (DOX) is then loaded into the ZIF-8 shell of the core-shell nanoparticles. The combination of the chemotherapeutic effects of DOX and the PDT effect of g-C3N4 nanosheets can lead to considerably enhanced efficacy. Furthermore, the red fluorescence of DOX and the blue fluorescence of g-C3N4 nanosheets provide the additional function of dual-color imaging for monitoring the drug release process. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04436g

Nanoscale zero-valent iron (nZVI): aspects of the core-shell structure and reactions with inorganic species in water.

PubMed

Yan, Weile; Herzing, Andrew A; Kiely, Christopher J; Zhang, Wei-Xian

2010-11-25

Aspects of the core-shell model of nanoscale zero-valent iron (nZVI) and their environmental implications were examined in this work. The structure and elemental distribution of nZVI were characterized by X-ray energy-dispersive spectroscopy (XEDS) with nanometer-scale spatial resolution in an aberration-corrected scanning transmission electron microscope (STEM). The analysis provides unequivocal evidence of a layered structure of nZVI consisting of a metallic iron core encapsulated by a thin amorphous oxide shell. Three aqueous environmental contaminants, namely Hg(II), Zn(II) and hydrogen sulfide, were studied to probe the reactive properties and the surface chemistry of nZVI. High-resolution X-ray photoelectron spectroscopy (HR-XPS) analysis of the reacted particles indicated that Hg(II) was sequestrated via chemical reduction to elemental mercury. On the other hand, Zn(II) removal was achieved via sorption to the iron oxide shell followed by zinc hydroxide precipitation. Hydrogen sulfide was immobilized on the nZVI surface as disulfide (S(2)(2-)) and monosulfide (S(2-)) species. Their relative abundance in the final products suggests that the retention of hydrogen sulfide occurs via reactions with the oxide shell to form iron sulfide (FeS) and subsequent conversion to iron disulfide (FeS(2)). The results presented herein highlight the multiple reactive pathways permissible with nZVI owing to its two functional constituents. The core-shell structure imparts nZVI with manifold functional properties previously unexamined and grants the material with potentially new applications. Copyright © 2010 Elsevier B.V. All rights reserved.

Tuning the synthesis of platinum-copper nanoparticles with a hollow core and porous shell for the selective hydrogenation of furfural to furfuryl alcohol

NASA Astrophysics Data System (ADS)

Huang, Shuangshuang; Yang, Nating; Wang, Shibin; Sun, Yuhan; Zhu, Yan

2016-07-01

Pt-Cu nanoparticles constructed with a hollow core and porous shell have been synthesized in which Pt-Cu cages with multiporous outermost shells are formed at the initial stage and then the Pt and Cu atoms in solution continuously fed these hollow-core of cages by passing through the porous tunnels of the outermost shells, finally leading to the formation of hollow structures with different sizes. Furthermore, these hollow-core Pt-Cu nanoparticles are more effective than the solid-core Pt-Cu nanoparticles for the catalytic hydrogenation of furfural toward furfuryl alcohol. The former can achieve almost 100% conversion of furfural with 100% selectivity toward the alcohol.Pt-Cu nanoparticles constructed with a hollow core and porous shell have been synthesized in which Pt-Cu cages with multiporous outermost shells are formed at the initial stage and then the Pt and Cu atoms in solution continuously fed these hollow-core of cages by passing through the porous tunnels of the outermost shells, finally leading to the formation of hollow structures with different sizes. Furthermore, these hollow-core Pt-Cu nanoparticles are more effective than the solid-core Pt-Cu nanoparticles for the catalytic hydrogenation of furfural toward furfuryl alcohol. The former can achieve almost 100% conversion of furfural with 100% selectivity toward the alcohol. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr03894h

Realistic Gamow shell model for resonance and continuum in atomic nuclei

NASA Astrophysics Data System (ADS)

Xu, F. R.; Sun, Z. H.; Wu, Q.; Hu, B. S.; Dai, S. J.

2018-02-01

The Gamow shell model can describe resonance and continuum for atomic nuclei. The model is established in the complex-moment (complex-k) plane of the Berggren coordinates in which bound, resonant and continuum states are treated on equal footing self-consistently. In the present work, the realistic nuclear force, CD Bonn, has been used. We have developed the full \\hat{Q}-box folded-diagram method to derive the realistic effective interaction in the model space which is nondegenerate and contains resonance and continuum channels. The CD-Bonn potential is renormalized using the V low-k method. With choosing 16O as the inert core, we have applied the Gamow shell model to oxygen isotopes.

Chemical and thermal stability of core-shelled magnetite nanoparticles and solid silica

NASA Astrophysics Data System (ADS)

Cendrowski, Krzysztof; Sikora, Pawel; Zielinska, Beata; Horszczaruk, Elzbieta; Mijowska, Ewa

2017-06-01

Pristine nanoparticles of magnetite were coated by solid silica shell forming core/shell structure. 20 nm thick silica coating significantly enhanced the chemical and thermal stability of the iron oxide. Chemical and thermal stability of this structure has been compared to the magnetite coated by mesoporous shell and pristine magnetite nanoparticles. It is assumed that six-membered silica rings in a solid silica shell limit the rate of oxygen diffusion during thermal treatment in air and prevent the access of HCl molecules to the core during chemical etching. Therefore, the core/shell structure with a solid shell requires a longer time to induce the oxidation of iron oxide to a higher oxidation state and, basically, even strong concentrated acid such as HCl is not able to dissolve it totally in one month. This leads to the desired performance of the material in potential applications such as catalysis and environmental protection.

Coulomb Excitation of Neutron-Rich Zn Isotopes: First Observation of the 21+ State in Zn80

NASA Astrophysics Data System (ADS)

van de Walle, J.; Aksouh, F.; Ames, F.; Behrens, T.; Bildstein, V.; Blazhev, A.; Cederkäll, J.; Clément, E.; Cocolios, T. E.; Davinson, T.; Delahaye, P.; Eberth, J.; Ekström, A.; Fedorov, D. V.; Fedosseev, V. N.; Fraile, L. M.; Franchoo, S.; Gernhauser, R.; Georgiev, G.; Habs, D.; Heyde, K.; Huber, G.; Huyse, M.; Ibrahim, F.; Ivanov, O.; Iwanicki, J.; Jolie, J.; Kester, O.; Köster, U.; Kröll, T.; Krücken, R.; Lauer, M.; Lisetskiy, A. F.; Lutter, R.; Marsh, B. A.; Mayet, P.; Niedermaier, O.; Nilsson, T.; Pantea, M.; Perru, O.; Raabe, R.; Reiter, P.; Sawicka, M.; Scheit, H.; Schrieder, G.; Schwalm, D.; Seliverstov, M. D.; Sieber, T.; Sletten, G.; Smirnova, N.; Stanoiu, M.; Stefanescu, I.; Thomas, J.-C.; Valiente-Dobón, J. J.; van Duppen, P.; Verney, D.; Voulot, D.; Warr, N.; Weisshaar, D.; Wenander, F.; Wolf, B. H.; Zielińska, M.

2007-10-01

Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 21+ state in Zn78 could be firmly established and for the first time the 2+→01+ transition in Zn80 was observed at 1492(1) keV. B(E2,21+→01+) values were extracted for Zn74,76,78,80 and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, Zn80 is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus Ni78.

Fabrication of Fe3O4@mSiO2 Core-Shell Composite Nanoparticles for Drug Delivery Applications

NASA Astrophysics Data System (ADS)

Uribe Madrid, Sergio I.; Pal, Umapada; Kang, Young Soo; Kim, Junghoon; Kwon, Hyungjin; Kim, Jungho

2015-05-01

We report the synthesis of Fe3O4@mSiO2 nanostructures of different meso-silica (mSiO2) shell thickness, their biocompatibility and behaviors for loading and release of a model drug ibuprofen. The composite nanostructures have superparamagnetic magnetite cores of 208 nm average size and meso-silica shells of 15 to 40 nm thickness. A modified Stöber method was used to grow the meso-silica shells over the hydrothermally grown monodispersed magnetite particles. The composite nanoparticles show very promising drug holding and releasing behaviors, which depend on the thickness of meso-silica shell. The biocompatibility of the meso-silica-coated and uncoated magnetite nanoparticles was tested through cytotoxicity assay on breast cancer (MCF-7), ovarian cancer (SKOV3), normal human lung fibroblasts MRC-5, and IMR-90 cells. The high drug holding capacity and reasonable biocompatibility of the nanostructures make them ideal agents for targeted drug delivery applications in human body.

Exploring the effect of band alignment and surface states on photoinduced electron transfer from CuInS2/CdS core/shell quantum dots to TiO2 electrodes.

PubMed

Sun, Mingye; Zhu, Dehua; Ji, Wenyu; Jing, Pengtao; Wang, Xiuying; Xiang, Weidong; Zhao, Jialong

2013-12-11

Photoinduced electron transfer (ET) processes from CuInS2/CdS core/shell quantum dots (QDs) with different core sizes and shell thicknesses to TiO2 electrodes were investigated by time-resolved photoluminescence (PL) spectroscopy. The ET rates and efficiencies from CuInS2/CdS QDs to TiO2 were superior to those of CuInS2/ZnS QDs. An enhanced ET efficiency was surprisingly observed for 2.0 nm CuInS2 core QDs after growth of the CdS shell. On the basis of the experimental and theoretical analysis, the improved performances of CuInS2/CdS QDs were attributed to the passivation of nonradiative traps by overcoating shell and enhanced delocalization of electron wave function from core to CdS shell due to lower conduction band offset. These results indicated that the electron distribution regulated by the band alignment between core and shell of QDs and the passivation of surface defect states could improve ET performance between donor and acceptor.

Advanced Structural and Inflatable Hybrid Spacecraft Module

NASA Technical Reports Server (NTRS)

Schneider, William C. (Inventor); delaFuente, Horacio M. (Inventor); Edeen, Gregg A. (Inventor); Kennedy, Kriss J. (Inventor); Lester, James D. (Inventor); Gupta, Shalini (Inventor); Hess, Linda F. (Inventor); Lin, Chin H. (Inventor); Malecki, Richard H. (Inventor); Raboin, Jasen L. (Inventor)

2001-01-01

An inflatable module comprising a structural core and an inflatable shell, wherein the inflatable shell is sealingly attached to the structural core. In its launch configuration, the wall thickness of the inflatable shell is collapsed by vacuum. Also in this configuration, the inflatable shell is collapsed and efficiently folded around the structural core. Upon deployment, the wall thickness of the inflatable shell is inflated; whereby the inflatable shell itself, is thereby inflated around the structural core, defining therein a large enclosed volume. A plurality of removable shelves are arranged interior to the structural core in the launch configuration. The structural core also includes at least one longeron that, in conjunction with the shelves, primarily constitute the rigid, strong, and lightweight load-bearing structure of the module during launch. The removable shelves are detachable from their arrangement in the launch configuration so that, when the module is in its deployed configuration and launch loads no longer exist, the shelves can be rearranged to provide a module interior arrangement suitable for human habitation and work. In the preferred embodiment, to provide efficiency in structural load paths and attachments, the shape of the inflatable shell is a cylinder with semi-toroidal ends.

Inflatable Vessel and Method

NASA Technical Reports Server (NTRS)

Raboin, Jasen L. (Inventor); Valle, Gerard D. (Inventor); Edeen, Gregg A. (Inventor); delaFuente, Horacio M. (Inventor); Schneider, William C. (Inventor); Spexarth, Gary R. (Inventor); Pandya, Shalini Gupta (Inventor); Johnson, Christopher J. (Inventor)

2003-01-01

An inflatable module comprising a structural core and an inflatable shell, wherein the inflatable shell is sealingly attached to the structural core. In its launch or pre-deployed configuration, the wall thickness of the inflatable shell is collapsed by vacuum. Also in this configuration, the inflatable shell is collapsed and efficiently folded around the structural core. Upon deployment, the wall thickness of the inflatable shell is inflated; whereby the inflatable shell itself, is thereby inflated around the structural core, defining therein a large enclosed volume. A plurality of removable shelves are arranged interior to the structural core in the launch configuration. The structural core also includes at least one longeron that, in conjunction with the shelves, primarily constitute the rigid, strong, and lightweight load-bearing structure of the module during launch. The removable shelves are detachable from their arrangement in the launch configuration so that, when the module is in its deployed configuration and launch loads no longer exist, the shelves can be rearranged to provide a module interior arrangement suitable for human habitation and work. In the preferred embodiment, to provide efficiency in structural load paths and attachments, the shape of the inflatable shell is a cylinder with semi-toroidal ends.

Controlled Formation of Radial Core-Shell Si/Metal Silicide Crystalline Heterostructures.

PubMed

Kosloff, Alon; Granot, Eran; Barkay, Zahava; Patolsky, Fernando

2018-01-10

The highly controlled formation of "radial" silicon/NiSi  core-shell nanowire heterostructures has been demonstrated for the first time. Here, we investigated the "radial" diffusion of nickel atoms into crystalline nanoscale silicon pillar 11 cores, followed by nickel silicide phase formation and the creation of a well-defined shell structure. The described approach is based on a two-step thermal process, which involves metal diffusion at low temperatures in the range of 200-400 °C, followed by a thermal curing step at a higher temperature of 400 °C. In-depth crystallographic analysis was performed by nanosectioning the resulting silicide-shelled silicon nanopillar heterostructures, giving us the ability to study in detail the newly formed silicide shells. Remarkably, it was observed that the resulting silicide shell thickness has a self-limiting behavior, and can be tightly controlled by the modulation of the initial diffusion-step temperature. In addition, electrical measurements of the core-shell structures revealed that the resulting shells can serve as an embedded conductive layer in future optoelectronic applications. This research provides a broad insight into the Ni silicide "radial" diffusion process at the nanoscale regime, and offers a simple approach to form thickness-controlled metal silicide shells in the range of 5-100 nm around semiconductor nanowire core structures, regardless the diameter of the nanowire cores. These high quality Si/NiSi core-shell nanowire structures will be applied in the near future as building blocks for the creation of utrathin highly conductive optically transparent top electrodes, over vertical nanopillars-based solar cell devices, which may subsequently lead to significant performance improvements of these devices in terms of charge collection and reduced recombination.

One-pot synthesis of iniferter-bound polystyrene core nanoparticles for the controlled grafting of multilayer shells

NASA Astrophysics Data System (ADS)

Marchyk, Nataliya; Maximilien, Jacqueline; Beyazit, Selim; Haupt, Karsten; Sum Bui, Bernadette Tse

2014-02-01

A novel approach using one-pot synthesis for the production of uniform, iniferter-bound polystyrene core nanoparticles of size 30-40 nm is described. Conventional oil-in-water emulsion polymerisation of styrene and divinylbenzene, combining a hybrid initiation system (thermal and UV), triggered sequentially, was employed to form the surface-bound thiocarbamate iniferters in situ. The iniferter cores were then used as seeds for re-initiating further polymerisation by UV irradiation to produce water-compatible core-shell nanoparticles. Grafting of various shell-types is demonstrated: linear polymers of poly(N-isopropylacrylamide) brushes, crosslinked polymers bearing different surface charges and molecularly imprinted polymers. The shell thickness was readily tuned by varying the monomers' concentration and polymerisation time. Our method is straightforward and in addition, gives access to the preparation of fluorescent seeds and the possibility of grafting nanosized multiple shells. The core-shell nanoparticles were fully characterised by dynamic light scattering, transmission electron microscopy, Fourier transform infrared spectroscopy and microelemental analysis.A novel approach using one-pot synthesis for the production of uniform, iniferter-bound polystyrene core nanoparticles of size 30-40 nm is described. Conventional oil-in-water emulsion polymerisation of styrene and divinylbenzene, combining a hybrid initiation system (thermal and UV), triggered sequentially, was employed to form the surface-bound thiocarbamate iniferters in situ. The iniferter cores were then used as seeds for re-initiating further polymerisation by UV irradiation to produce water-compatible core-shell nanoparticles. Grafting of various shell-types is demonstrated: linear polymers of poly(N-isopropylacrylamide) brushes, crosslinked polymers bearing different surface charges and molecularly imprinted polymers. The shell thickness was readily tuned by varying the monomers' concentration and polymerisation time. Our method is straightforward and in addition, gives access to the preparation of fluorescent seeds and the possibility of grafting nanosized multiple shells. The core-shell nanoparticles were fully characterised by dynamic light scattering, transmission electron microscopy, Fourier transform infrared spectroscopy and microelemental analysis. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr05295h

Atomistic tight-binding theory of excitonic splitting energies in CdX(X = Se, S and Te)/ZnS core/shell nanocrystals

NASA Astrophysics Data System (ADS)

Sukkabot, Worasak; Pinsook, Udomsilp

2017-01-01

Using the atomistic tight-binding theory (TB) and a configuration interaction description (CI), we numerically compute the excitonic splitting of CdX(X = Se, S and Te)/ZnS core/shell nanocrystals with the objective to explain how types of the core materials and growth shell thickness can provide the detailed manipulation of the dark-dark (DD), dark-bright (DB) and bright-bright (BB) excitonic splitting, beneficial for the active application of quantum information. To analyze the splitting of the excitonic states, the optical band gaps, ground-state wave function overlaps and atomistic electron-hole interactions tend to be numerically demonstrated. Based on the atomistic computations, the single-particle and excitonic gaps are mainly reduced with the increasing ZnS shell thickness owing to the quantum confinement. In the range of the higher to lower energies, the order of the single-particle gaps is CdSe/ZnS, CdS/ZnS and CdTe/ZnS core/shell nanocrystals, while one of the excitonic gaps is CdS/ZnS, CdSe/ZnS and CdTe/ZnS core/shell nanocrystals because of the atomistic electron-hole interaction. The strongest electron-hole interactions are mainly observed in CdSe/ZnS core/shell nanocrystals. In addition, the computational results underline that the energies of the dark-dark (DD), dark-bright (DB) and bright-bright (BB) excitonic splitting are generally reduced with the increasing ZnS growth shell thickness as described by the trend of the electron-hole exchange interaction. The high-to-low splitting of the excitonic states is demonstrated in CdSe/ZnS, CdTe/ZnS and CdS/ZnS core/shell nanocrystals because of the fashion in the electron-hole exchange interaction and overlaps of the electron-hole wave functions. As the resulting calculations, it is expected that CdS/ZnS core/shell nanocrystals are the best candidates to be the source of entangled photons. Finally, the comprehensive information on the excitonic splitting can enable the use of suitable core/shell nanocrystals for the entangled photons in the application of quantum information.

Electrosprayed nanoparticle delivery system for controlled release.

PubMed

Eltayeb, Megdi; Stride, Eleanor; Edirisinghe, Mohan; Harker, Anthony

2016-09-01

This study utilises an electrohydrodynamic technique to prepare core-shell lipid nanoparticles with a tunable size and high active ingredient loading capacity, encapsulation efficiency and controlled release. Using stearic acid and ethylvanillin as model shell and active ingredients respectively, we identify the processing conditions and ratios of lipid:ethylvanillin required to form nanoparticles. Nanoparticles with a mean size ranging from 60 to 70nm at the rate of 1.37×10(9) nanoparticles per minute were prepared with different lipid:ethylvanillin ratios. The polydispersity index was ≈21% and the encapsulation efficiency ≈70%. It was found that the rate of ethylvanillin release was a function of the nanoparticle size, and lipid:ethylvanillin ratio. The internal structure of the lipid nanoparticles was studied by transmission electron microscopy which confirmed that the ethylvanillin was encapsulated within a stearic acid shell. Fourier transform infrared spectroscopy analysis indicated that the ethylvanillin had not been affected. Extensive analysis of the release of ethylvanillin was performed using several existing models and a new diffusive release model incorporating a tanh function. The results were consistent with a core-shell structure. Copyright © 2016 Elsevier B.V. All rights reserved.

Enhanced Upconversion Luminescence in Yb3+/Tm3+-Codoped Fluoride Active Core/Active Shell/Inert Shell Nanoparticles through Directed Energy Migration.

PubMed

Qiu, Hailong; Yang, Chunhui; Shao, Wei; Damasco, Jossana; Wang, Xianliang; Ågren, Hans; Prasad, Paras N; Chen, Guanying

2014-01-03

The luminescence efficiency of lanthanide-doped upconversion nanoparticles is of particular importance for their embodiment in biophotonic and photonic applications. Here, we show that the upconversion luminescence of typically used NaYF₄:Yb 3+ 30%/Tm 3+ 0.5% nanoparticles can be enhanced by ~240 times through a hierarchical active core/active shell/inert shell (NaYF₄:Yb 3+ 30%/Tm 3+ 0.5%)/NaYbF₄/NaYF₄ design, which involves the use of directed energy migration in the second active shell layer. The resulting active core/active shell/inert shell nanoparticles are determined to be about 11 times brighter than that of well-investigated (NaYF₄:Yb 3+ 30%/Tm 3+ 0.5%)/NaYF₄ active core/inert shell nanoparticles when excited at ~980 nm. The strategy for enhanced upconversion in Yb 3+ /Tm 3+ -codoped NaYF₄ nanoparticles through directed energy migration might have implications for other types of lanthanide-doped upconversion nanoparticles.

The Spatial Distribution of Complex Organic Molecules in the L1544 Pre-stellar Core.

PubMed

Jiménez-Serra, Izaskun; Vasyunin, Anton I; Caselli, Paola; Marcelino, Nuria; Billot, Nicolas; Viti, Serena; Testi, Leonardo; Vastel, Charlotte; Lefloch, Bertrand; Bachiller, Rafael

2016-10-10

The detection of complex organic molecules (COMs) toward cold sources such as pre-stellar cores (with T<10 K), has challenged our understanding of the formation processes of COMs in the interstellar medium. Recent modelling on COM chemistry at low temperatures has provided new insight into these processes predicting that COM formation depends strongly on parameters such as visual extinction and the level of CO freeze out. We report deep observations of COMs toward two positions in the L1544 pre-stellar core: the dense, highly-extinguished continuum peak with A V ≥30 mag within the inner 2700 au; and a low-density shell with average A V ~7.5-8 mag located at 4000 au from the core's center and bright in CH 3 OH. Our observations show that CH 3 O, CH 3 OCH 3 and CH 3 CHO are more abundant (by factors ~2-10) toward the low-density shell than toward the continuum peak. Other COMs such as CH 3 OCHO, c-C 3 H 2 O, HCCCHO, CH 2 CHCN and HCCNC show slight enhancements (by factors ≤3) but the associated uncertainties are large. This suggests that COMs are actively formed and already present in the low-density shells of pre-stellar cores. The modelling of the chemistry of O-bearing COMs in L1544 indicates that these species are enhanced in this shell because i) CO starts freezing out onto dust grains driving an active surface chemistry; ii) the visual extinction is sufficiently high to prevent the UV photo-dissociation of COMs by the external interstellar radiation field; and iii) the density is still moderate to prevent severe depletion of COMs onto grains.

Optical studies of CdSe/HgSe and CdSe/Ag2Se core/shell nanoparticles embedded in gelatin

NASA Astrophysics Data System (ADS)

Azhniuk, Yu M.; Dzhagan, V. M.; Raevskaya, A. E.; Stroyuk, A. L.; Kuchmiy, S. Ya; Valakh, M. Ya; Zahn, D. R. T.

2008-11-01

CdSe/HgSe and CdSe/Ag2Se core-shell nanoparticles are obtained by colloidal synthesis from aqueous solutions in the presence of gelatin. Optical absorption, luminescence, and Raman spectra of the nanoparticles obtained are measured. The variation of the optical spectra of CdSe/HgSe and CdSe/Ag2Se core-shell nanoparticles with the shell thickness is discussed. Sharp non-monotonous variation of the photoluminescence spectra at low shell coverage is observed.

Nanowebs and nanocables of silicon carbide

NASA Astrophysics Data System (ADS)

Shim, Hyun Woo; Huang, Hanchen

2007-08-01

This paper presents two novel hierarchical structures of SiC-SiO2 core-shell nanowires: (a) nanocables in the form of multi-core and single shell and (b) nanowebs in the form of intersecting nanowires and nanocables, augmented by variable amounts of SiO2 membranes. The two structures are controllable through variations of substrate temperature and source chemistry. The hierarchical nanostructures, together with the controllability, may offer superb mechanical properties in composite applications. Finally, the authors propose a model of nanowebs and nanocables formation, as a result of nanowires intersection and alignment.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaur, Maninder; Dai, Qilin; Bowden, Mark E.

Chromium (Cr) forms a solid solution with iron (Fe) lattice when doped in core-shell iron -iron oxide nanocluster (NC) and shows a mixed phase of sigma (σ) FeCr and bcc Fe. The Cr dopant affects heavily the magnetization and magnetic reversal process, and causes the hysteresis loop to shrink near the zero field axis. Dramatic transformation happens from dipolar interaction (0 at. % Cr) to strong exchange interaction (8 at. % of Cr) is confirmed from the Henkel plot and delta M plot, and is explained by a water-melon model of core-shell NC system.

Dependence of weak interaction rates on the nuclear composition during stellar core collapse

NASA Astrophysics Data System (ADS)

Furusawa, Shun; Nagakura, Hiroki; Sumiyoshi, Kohsuke; Kato, Chinami; Yamada, Shoichi

2017-02-01

We investigate the influences of the nuclear composition on the weak interaction rates of heavy nuclei during the core collapse of massive stars. The nuclear abundances in nuclear statistical equilibrium (NSE) are calculated by some equation of state (EOS) models including in-medium effects on nuclear masses. We systematically examine the sensitivities of electron capture and neutrino-nucleus scattering on heavy nuclei to the nuclear shell effects and the single-nucleus approximation. We find that the washout of the shell effect at high temperatures brings significant change to weak rates by smoothing the nuclear abundance distribution: the electron capture rate decreases by ˜20 % in the early phase and increases by ˜40 % in the late phase at most, while the cross section for neutrino-nucleus scattering is reduced by ˜15 % . This is because the open-shell nuclei become abundant instead of those with closed neutron shells as the shell effects disappear. We also find that the single-nucleus description based on the average values leads to underestimations of weak rates. Electron captures and neutrino coherent scattering on heavy nuclei are reduced by ˜80 % in the early phase and by ˜5 % in the late phase, respectively. These results indicate that NSE like EOS accounting for shell washout is indispensable for the reliable estimation of weak interaction rates in simulations of core-collapse supernovae.

The effect of surface-bulk potential difference on the kinetics of intercalation in core-shell active cathode particles

NASA Astrophysics Data System (ADS)

Kazemiabnavi, Saeed; Malik, Rahul; Orvananos, Bernardo; Abdellahi, Aziz; Ceder, Gerbrand; Thornton, Katsuyo

2018-04-01

Surface modification of active cathode particles is commonly observed in battery research as either a surface phase evolving during the cycling process, or intentionally engineered to improve capacity retention, rate capability, and/or thermal stability of the cathode material. Here, a continuum-scale model is developed to simulate the galvanostatic charge/discharge of a cathode particle with core-shell heterostructure. The particle is assumed to be comprised of a core material encapsulated by a thin layer of a second phase that has a different open-circuit voltage. The effect of the potential difference between the surface and bulk phases (Ω) on the kinetics of lithium intercalation and the galvanostatic charge/discharge profiles is studied at different values of Ω, C-rates, and exchange current densities. The difference between the Li chemical potential in the surface and bulk phases of the cathode particle results in a concentration difference between these two phases. This leads to a charge/discharge asymmetry in the galvanostatic voltage profiles, causing a decrease in the accessible capacity of the particle. These effects are more significant at higher magnitudes of surface-bulk potential difference. The proposed model provides detailed insight into the kinetics and voltage behavior of the intercalation/de-intercalation processes in core-shell heterostructure cathode particles.

Full-Color Biomimetic Photonic Materials with Iridescent and Non-Iridescent Structural Colors

PubMed Central

Kawamura, Ayaka; Kohri, Michinari; Morimoto, Gen; Nannichi, Yuri; Taniguchi, Tatsuo; Kishikawa, Keiki

2016-01-01

The beautiful structural colors in bird feathers are some of the brightest colors in nature, and some of these colors are created by arrays of melanin granules that act as both structural colors and scattering absorbers. Inspired by the color of bird feathers, high-visibility structural colors have been created by altering four variables: size, blackness, refractive index, and arrangement of the nano-elements. To control these four variables, we developed a facile method for the preparation of biomimetic core-shell particles with melanin-like polydopamine (PDA) shell layers. The size of the core-shell particles was controlled by adjusting the core polystyrene (PSt) particles’ diameter and the PDA shell thicknesses. The blackness and refractive index of the colloidal particles could be adjusted by controlling the thickness of the PDA shell. The arrangement of the particles was controlled by adjusting the surface roughness of the core-shell particles. This method enabled the production of both iridescent and non-iridescent structural colors from only one component. This simple and novel process of using core-shell particles containing PDA shell layers can be used in basic research on structural colors in nature and their practical applications. PMID:27658446

Full-Color Biomimetic Photonic Materials with Iridescent and Non-Iridescent Structural Colors.

PubMed

Kawamura, Ayaka; Kohri, Michinari; Morimoto, Gen; Nannichi, Yuri; Taniguchi, Tatsuo; Kishikawa, Keiki

2016-09-23

The beautiful structural colors in bird feathers are some of the brightest colors in nature, and some of these colors are created by arrays of melanin granules that act as both structural colors and scattering absorbers. Inspired by the color of bird feathers, high-visibility structural colors have been created by altering four variables: size, blackness, refractive index, and arrangement of the nano-elements. To control these four variables, we developed a facile method for the preparation of biomimetic core-shell particles with melanin-like polydopamine (PDA) shell layers. The size of the core-shell particles was controlled by adjusting the core polystyrene (PSt) particles' diameter and the PDA shell thicknesses. The blackness and refractive index of the colloidal particles could be adjusted by controlling the thickness of the PDA shell. The arrangement of the particles was controlled by adjusting the surface roughness of the core-shell particles. This method enabled the production of both iridescent and non-iridescent structural colors from only one component. This simple and novel process of using core-shell particles containing PDA shell layers can be used in basic research on structural colors in nature and their practical applications.

Cadmium-free aqueous synthesis of ZnSe and ZnSe@ZnS core-shell quantum dots and their differential bioanalyte sensing potential

NASA Astrophysics Data System (ADS)

Mir, Irshad Ahmad; Rawat, Kamla; Bohidar, H. B.

2016-10-01

Herein we report a facile and cadmium-free approach to prepare water-soluble fluorescent ZnSe@ZnS core-shell quantum dots (QDs), using thioglycolic acid (TGA) ligand as a stabilizer and thiourea as a sulfur source. The optical properties and morphology of the obtained core-shell QDs were characterized by UV-vis and fluorescence spectroscopy, transmission electron microscopy (TEM), energy-dispersive x-ray analysis (EDX), x-ray diffraction (XRD), electrophoresis and dynamic light scattering (DLS) techniques. TEM analysis, and electrophoresis data showed that ZnSe core had an average size of 3.60 ± 0.12 nm and zeta potential of -38 mV; and for ZnSe@ZnS QDs, the mean size was 4.80 ± 0.20 nm and zeta potential was -45 mV. Compared to the core ZnSe QDs, the quantum yield of these core-shell structures was higher (13% versus 32%). These were interacted with five common bioanalytes such as, ascorbic acid, citric acid, oxalic acid, glucose and cholesterol which revealed fluorescence quenching due to concentration dependent binding of analytes to the core only, and core-shell QDs. The binding pattern followed the sequence: cholesterol < glucose < ascorbic acid < oxalic acid < citric acid for ZnSe, and cholesterol < glucose < oxalic acid < ascorbic acid < citric acid for core-shell QDs. Thus, enhanced binding was noticed for the analyte citric acid which may facilitate development of a fluorescence-based sensor based on the ZnSe core-only quantum dot platform. Further, the hydrophilic core-shell structure may find use in cell imaging applications.

Catalytic performance of M@Ni (M = Fe, Ru, Ir) core-shell nanoparticles towards ammonia decomposition for CO x -free hydrogen production

NASA Astrophysics Data System (ADS)

Chen, Xin; Zhou, Junwei; Chen, Shuangjing; Zhang, Hui

2018-06-01

To reduce the use of precious metals and maintain the catalytic activity for NH3 decomposition reaction, it is an effective way to construct bimetallic nanoparticles with special structures. In this paper, by using density functional theory methods, we investigated NH3 decomposition reaction on three types of core-shell nanoparticles M@Ni (M = Fe, Ru, Ir) with 13 core M atoms and 42 shell Ni atoms. The size of these three particles is about 1 nm. Benefit from alloying with Ru in this nanocluster, Ru@Ni core-shell nanoparticles exhibit catalytic activity comparable to that of single metal Ru, based on the analysis of the adsorption energy and potential energy diagram of NH3 decomposition, as well as N2 desorption processes. However, as for Fe@Ni and Ir@Ni core-shell nanoparticles, their catalytic activities are still unsatisfactory compared to the active metal Ru. In addition, in order to further explain the synergistic effect of bimetallic core-shell nanoparticles, the partial density of states were also calculated. The results show that d-band electrons provided by the core metal are the main factors affecting the entire catalytic process.

Direct Correlation of Excitonics with Efficiency in a Core-Shell Quantum Dot Solar Cell.

PubMed

Dana, Jayanta; Maiti, Sourav; Tripathi, Vaidehi S; Ghosh, Hirendra N

2018-02-16

Shell thickness dependent band-gap engineering of quasi type II core-shell material with higher carrier cooling time, lower interfacial defect states, and longer charge carrier recombination time can be a promising candidate for both photocatalysis and solar cell. In the present investigation, colloidal CdSe@CdS core-shells with different shell thickness (2, 4 and 6 monolayer CdS) were synthesized through hot injection method and have been characterized by high resolution transmission electron microscope (HRTEM) followed by steady state absorption and luminescence techniques. Ultrafast transient absorption (TA) studies suggest longer carrier cooling, lower interfacial surface states, and slower carrier recombination time in CdSe@CdS core-shell with increasing shell thickness. By TA spectroscopy, the role of CdS shell in power conversion efficiency (PCE) has been explained in detail. The measured PCE was found to initially increase and then decrease with increasing shell thickness. Shell thickness has been optimized to maximize the efficiency after correlating the shell controlled carrier cooling and recombination with PCE values and a maximum PCE of 3.88 % was obtained with 4 monolayers of CdS shell, which is found to be 57 % higher than compared to bare CdSe QDs. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hierarchically mesoporous CuO/carbon nanofiber coaxial shell-core nanowires for lithium ion batteries

PubMed Central

Park, Seok-Hwan; Lee, Wan-Jin

2015-01-01

Hierarchically mesoporous CuO/carbon nanofiber coaxial shell-core nanowires (CuO/CNF) as anodes for lithium ion batteries were prepared by coating the Cu2(NO3)(OH)3 on the surface of conductive and elastic CNF via electrophoretic deposition (EPD), followed by thermal treatment in air. The CuO shell stacked with nanoparticles grows radially toward the CNF core, which forms hierarchically mesoporous three-dimensional (3D) coaxial shell-core structure with abundant inner spaces in nanoparticle-stacked CuO shell. The CuO shells with abundant inner spaces on the surface of CNF and high conductivity of 1D CNF increase mainly electrochemical rate capability. The CNF core with elasticity plays an important role in strongly suppressing radial volume expansion by inelastic CuO shell by offering the buffering effect. The CuO/CNF nanowires deliver an initial capacity of 1150 mAh g−1 at 100 mA g−1 and maintain a high reversible capacity of 772 mAh g−1 without showing obvious decay after 50 cycles. PMID:25944615

Electrospinning of PLGA/gum tragacanth nanofibers containing tetracycline hydrochloride for periodontal regeneration.

PubMed

Ranjbar-Mohammadi, Marziyeh; Zamani, M; Prabhakaran, M P; Bahrami, S Hajir; Ramakrishna, S

2016-01-01

Controlled drug release is a process in which a predetermined amount of drug is released for longer period of time, ranging from days to months, in a controlled manner. In this study, novel drug delivery devices were fabricated via blend electrospinning and coaxial electrospinning using poly lactic glycolic acid (PLGA), gum tragacanth (GT) and tetracycline hydrochloride (TCH) as a hydrophilic model drug in different compositions and their performance as a drug carrier scaffold was evaluated. Scanning electron microscopy (SEM) results showed that fabricated PLGA, blend PLGA/GT and core shell PLGA/GT nanofibers had a smooth and bead-less morphology with the diameter ranging from 180 to 460 nm. Drug release studies showed that both the fraction of GT within blend nanofibers and the core-shell structure can effectively control TCH release rate from the nanofibrous membranes. By incorporation of TCH into core-shell nanofibers, drug release was sustained for 75 days with only 19% of burst release within the first 2h. The prolonged drug release, together with proven biocompatibility, antibacterial and mechanical properties of drug loaded core shell nanofibers make them a promising candidate to be used as drug delivery system for periodontal diseases. Copyright © 2015 Elsevier B.V. All rights reserved.

Facile preparation of magnetic metal organic frameworks core-shell nanoparticles for stimuli-responsive drug carrier

NASA Astrophysics Data System (ADS)

Li, Sheng; Bi, Ke; Xiao, Ling; Shi, Xiaowen

2017-12-01

Facile synthesis of core-shell magnetic MOFs for drug delivery is of significance due to the advantages of high drug load and easy separation. In this work, magnetic metal organic frameworks (MOFs, Fe3O4-NH2@MIL101-NH2) core-shell nanoparticles were synthesized rapidly in water phase by microwave irradiation using Fe3+ and 2-amino-1,4-benzenedicarboxylate (BDC-NH2) as metal ions and ligands respectively. The resulting magnetic MOFs exhibit large surface areas (96.04 m2 g-1), excellent magnetic response (20.47 emu g-1) and large mesopore volume (22.07 cm3 g-1) along with spherical morphologies with the diameters ranging from 140-330 nm. Using doxorubicin (DOX) as a model drug, the drug loading capacity of Fe3O4-NH2@MIL101-NH2 could reach 36.02%, substantially higher than pristine MIL101-NH2. Importantly, the release of DOX could be controlled by pH as well as the meso pore size of MOFs. The cytotoxicity assay showed that the magnetic MOFs have low cytotoxicity and good biocompatibility. The results suggest great potential of the magnetic MOFs core-shell nanoparticles fabricated in this study on controlled drug release of DOX.

Facile preparation of magnetic metal organic frameworks core-shell nanoparticles for stimuli-responsive drug carrier.

PubMed

Li, Sheng; Bi, Ke; Xiao, Ling; Shi, Xiaowen

2017-12-08

Facile synthesis of core-shell magnetic MOFs for drug delivery is of significance due to the advantages of high drug load and easy separation. In this work, magnetic metal organic frameworks (MOFs, Fe 3 O 4 -NH 2 @MIL101-NH 2 ) core-shell nanoparticles were synthesized rapidly in water phase by microwave irradiation using Fe 3+ and 2-amino-1,4-benzenedicarboxylate (BDC-NH 2 ) as metal ions and ligands respectively. The resulting magnetic MOFs exhibit large surface areas (96.04 m 2 g -1 ), excellent magnetic response (20.47 emu g -1 ) and large mesopore volume (22.07 cm 3 g -1 ) along with spherical morphologies with the diameters ranging from 140-330 nm. Using doxorubicin (DOX) as a model drug, the drug loading capacity of Fe 3 O 4 -NH 2 @MIL101-NH 2 could reach 36.02%, substantially higher than pristine MIL101-NH 2 . Importantly, the release of DOX could be controlled by pH as well as the meso pore size of MOFs. The cytotoxicity assay showed that the magnetic MOFs have low cytotoxicity and good biocompatibility. The results suggest great potential of the magnetic MOFs core-shell nanoparticles fabricated in this study on controlled drug release of DOX.

Mode-locked Er-doped fiber laser based on PbS/CdS core/shell quantum dots as saturable absorber.

PubMed

Ming, Na; Tao, Shina; Yang, Wenqing; Chen, Qingyun; Sun, Ruyi; Wang, Chang; Wang, Shuyun; Man, Baoyuan; Zhang, Huanian

2018-04-02

Previously, PbS/CdS core/shell quantum dots with excellent optical properties have been widely used as light-harvesting materials in solar cell and biomarkers in bio-medicine. However, the nonlinear absorption characteristics of PbS/CdS core/shell quantum dots have been rarely investigated. In this work, PbS/CdS core/shell quantum dots were successfully employed as nonlinear saturable absorber (SA) for demonstrating a mode-locked Er-doped fiber laser. Based on a film-type SA, which was prepared by incorporating the quantum dots with the polyvinyl alcohol (PVA), mode-locked Er-doped operation with a pulse width of 54 ps and a maximum average output power of 2.71 mW at the repetition rate of 3.302 MHz was obtained. Our long-time stable results indicate that the CdS shell can effectively protect the PbS core from the effect of photo-oxidation and PbS/CdS core/shell quantum dots were efficient SA candidates for demonstrating pulse fiber lasers due to its tunable absorption peak and excellent saturable absorption properties.

Radiative lifetimes of zincblende CdSe/CdS quantum dots

DOE PAGES

Gong, Ke; Martin, James E.; Shea-Rohwer, Lauren E.; ...

2015-01-02

Recent synthetic advances have made available very monodisperse zincblende CdSe/CdS quantum dots having near-unity photoluminescence quantum yields. Because of the absence of nonradiative decay pathways, accurate values of the radiative lifetimes can be obtained from time-resolved PL measurements. Radiative lifetimes can also be obtained from the Einstein relations, using the static absorption spectra and the relative thermal populations in the angular momentum sublevels. We found that one of the inputs into these calculations is the shell thickness, and it is useful to be able to determine shell thickness from spectroscopic measurements. We use an empirically corrected effective mass model tomore » produce a “map” of exciton wavelength as a function of core size and shell thickness. These calculations use an elastic continuum model and the known lattice and elastic constants to include the effect of lattice strain on the band gap energy. The map is in agreement with the known CdSe sizing curve and with the shell thicknesses of zincblende core/shell particles obtained from TEM images. Furthermore, if selenium–sulfur diffusion is included and lattice strain is omitted from the calculation then the resulting map is appropriate for wurtzite CdSe/CdS quantum dots synthesized at high temperatures, and this map is very similar to one previously reported (J. Am. Chem. Soc. 2009, 131, 14299). Radiative lifetimes determined from time-resolved measurements are compared to values obtained from the Einstein relations, and found to be in excellent agreement. For a specific core size (2.64 nm diameter, in the present case), radiative lifetimes are found to decrease with increasing shell thickness. Thus, this is similar to the size dependence of one-component CdSe quantum dots and in contrast to the size dependence in type-II quantum dots.« less

Fabrication of SiO2@ZrO2@Y2O3:Eu3+ core-multi-shell structured phosphor.

PubMed

Gao, Xuan; He, Diping; Jiao, Huan; Chen, Juan; Meng, Xin

2011-08-01

ZrO2 interface was designed to block the reaction between SiO2 and Y2O3 in SiO2@Y2O3:Eu coreshell structure phosphor. SiO2@ZrO2@Y2O3:Eu core-multi-shell phosphors were successfully synthesized by combing an LBL method with a Sol-gel process. Based on electron microscopy, X-ray diffraction, and spectroscopy experiments, compelling evidence for the formation of the Y2O3:Eu outer shell on ZrO2 were presented. The presence of ZrO2 layer on SiO2 core can block the reaction of SiO2 core and Y2O3 shell effectively. By this kind of structure, the reaction temperature of the SiO2 core and Y2O3 shell in the SiO2@Y2O3:Eu core-shell structure phosphor can be increased about 200-300 degrees C and the luminescent intensity of this structure phosphor can be improved obviously. Under the excitation of ultraviolet (254 nm), the Eu3+ ion mainly shows its characteristic red (611 nm, 5D0-7F2) emissions in the core-multi-shell particles from Y2O3:Eu3+ shells. The emission intensity of Eu3+ ions can be tuned by the annealing temperatures, the number of coating times, and the thickness of ZrO2 interface, respectively.

Multi-functional electrospun antibacterial core-shell nanofibrous membranes for prolonged prevention of post-surgical tendon adhesion and inflammation.

PubMed

Shalumon, K T; Sheu, Chialin; Chen, Chih-Hao; Chen, Shih-Heng; Jose, Gils; Kuo, Chang-Yi; Chen, Jyh-Ping

2018-05-01

The possibility of endowing an electrospun anti-adhesive barrier membrane with multi-functionality, such as lubrication, prevention of fibroblast attachment and anti-infection and anti-inflammation properties, is highly desirable for the management of post-surgical tendon adhesion. To this end, we fabricated core-shell nanofibrous membranes (CSNMs) with embedded silver nanoparticles (Ag NPs) in the poly(ethylene glycol) (PEG)/poly(caprolactone) (PCL) shell and hyaluronic acid (HA)/ibuprofen in the core. HA imparted a lubrication effect for smooth tendon gliding and reduced fibroblast attachment, while Ag NPs and ibuprofen functioned as anti-infection and anti-inflammation agents, respectively. CSNMs with a PEG/PCL/Ag shell (PPA) and HA core containing 0% (H/PPA), 10% (HI10/PPA), 30% (HI30/PPA) and 50% (HI50/PPA) ibuprofen were fabricated through co-axial electrospinning and assessed through microscopic, spectroscopic, thermal, mechanical and drug release analyses. Considering nutrient passage through the barrier, the microporous CSNMs exerted the same barrier effect but drastically increased the mass transfer coefficients of bovine serum albumin compared with the commercial anti-adhesive membrane SurgiWrap®. Cell attachment/focal adhesion formation of fibroblasts revealed effective reduction of initial cell attachment on the CSNM surface with minimum cytotoxicity (except HI50/PPA). The anti-bacterial effect against both Gram-negative and Gram-positive bacteria was verified to be due to the Ag NPs in the membranes. In vivo studies using H/PPA and HI30/PPA CSNMs and SurgiWrap® in a rabbit flexor tendon rupture model demonstrated the improved efficacy of HI30/PPA CSNMs in reducing inflammation and tendon adhesion formation based on gross observation, histological analysis and functional assays. We conclude that HI30/PPA CSNMs can act as a multifunctional barrier membrane to prevent peritendinous adhesion after tendon surgery. A multi-functional anti-adhesion barrier membrane that could reduce fibroblasts attachment and penetration while simultaneously prevent post-surgical infection and inflammation is urgently needed. To this end, we prepared electrospun core-shell hyaluronic acid + ibuprofen/polyethylene glycol + polycaprolactone + Ag nanoparticles nanofibrous membranes by co-axial electrospinning as an ideal anti-adhesive membrane. The core-shell structure could meet the need of a desirable anti-adhesion barrier through release of ibuprofen and Ag nanoparticles to reduce infection and inflammation while hyaluronic acid can reduce fibroblasts adhesion. The superior performance of this multi-functional core-shell nanofibrous membrane in preventing peritendinous adhesion and post-surgical inflammation was demonstrated in a rabbit flexor tendon rupture model. Copyright © 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Antiferromagnetic exchange coupling measurements on single Co clusters

NASA Astrophysics Data System (ADS)

Wernsdorfer, W.; Leroy, D.; Portemont, C.; Brenac, A.; Morel, R.; Notin, L.; Mailly, D.

2009-03-01

We report on single-cluster measurements of the angular dependence of the low-temperature ferromagnetic core magnetization switching field in exchange-coupled Co/CoO core-shell clusters (4 nm) using a micro-bridge DC superconducting quantum interference device (μ-SQUID). It is observed that the coupling with the antiferromagnetic shell induces modification in the switching field for clusters with intrinsic uniaxial anisotropy depending on the direction of the magnetic field applied during the cooling. Using a modified Stoner-Wohlfarth model, it is shown that the core interacts with two weakly coupled and asymmetrical antiferromagnetic sublattices. Ref.: C. Portemont, R. Morel, W. Wernsdorfer, D. Mailly, A. Brenac, and L. Notin, Phys. Rev. B 78, 144415 (2008)

Stability of core-shell nanowires in selected model solutions

NASA Astrophysics Data System (ADS)

Kalska-Szostko, B.; Wykowska, U.; Basa, A.; Zambrzycka, E.

2015-03-01

This paper presents the studies of stability of magnetic core-shell nanowires prepared by electrochemical deposition from an acidic solution containing iron in the core and modified surface layer. The obtained nanowires were tested according to their durability in distilled water, 0.01 M citric acid, 0.9% NaCl, and commercial white wine (12% alcohol). The proposed solutions were chosen in such a way as to mimic food related environment due to a possible application of nanowires as additives to, for example, packages. After 1, 2 and 3 weeks wetting in the solutions, nanoparticles were tested by Infrared Spectroscopy, Atomic Absorption Spectroscopy, Transmission Electron Microscopy and X-ray diffraction methods.

Electronic, Optical, and Thermal Properties of Reduced-Dimensional Semiconductors

NASA Astrophysics Data System (ADS)

Huang, Shouting

Reduced-dimensional materials have attracted tremendous attention because of their new physics and exotic properties, which are of great interests for fundamental science. More importantly, the manipulation and engineering of matter on an atomic scale yield promising applications for many fields including nanoelectronics, nanobiotechnology, environments, and renewable energy. Because of the unusual quantum confinement and enhanced surface effect of reduced-dimensional materials, traditional empirical models suffer from necessary but unreliable parameters extracted from previously-studied bulk materials. In this sense, quantitative, parameter-free approaches are highly useful for understanding properties of reduced-dimensional materials and, furthermore, predicting their novel applications. The first-principles density functional theory (DFT) is proven to be a reliable and convenient tool. In particular, recent progress in many-body perturbation theory (MBPT) makes it possible to calculate excited-state properties, e.g., quasiparticle (QP) band gap and optical excitations, by the first-principles approach based on DFT. Therefore, during my PhD study, I employed first-principles calculations based on DFT and MBPT to systematically study fundamental properties of typical reduced-dimensional semiconductors, i.e., the electronic structure, phonons, and optical excitations of core-shell nanowires (NWs) and graphene-like two-dimensional (2D) structures of current interests. First, I present first-principles studies on how to engineer band alignments of nano-sized radial heterojunctions, Si/Ge core-shell NWs. Our calculation reveals that band offsets in these one-dimensional (1D) nanostructures can be tailored by applying axial strain or varying core-shell sizes. In particular, the valence band offset can be efficiently tuned across a wide range and even be diminished via applied strain. Two mechanisms contribute to this tuning of band offsets. Furthermore, varying the size of Si/Ge core-shell NWs and corresponding quantum confinement is shown to be efficient for modifying both valence and conduction band offsets simultaneously. Our proposed approaches to control band offsets in nano-sized heterojunctions may be of practical interest for nanoelectronic and photovoltaic applications. Additionally, I also studied the lattice vibrational modes of Si/Ge core-shell N-Ws. Our calculations show that the internal strain induced by the lattice mismatch between core and shell plays an important role in significantly shifting the frequency of characteristic optical modes of core-shell NWs. In particular, our simulation demonstrates that these frequency shifts can be detected by Raman-scattering experiments, giving rise to a convenient and nondestructive way to obtain structural information of core-shell materials. Meanwhile, another type of collective modes, the radial breathing modes (RBM), is identified in Si-core/Ge-shell NWs and their frequency dependence is explained by an elastic media model. Our studied vibrational modes and their frequency evolution are useful for thermoelectric applications based on core-shell nanostructures. Then I studied optical properties and exciton spectra of 2D semiconducting carbon structures. The energy spectra and wavefunctions of excitons in the 2D graphene derivatives, i.e., graphyne and graphane, are found to be strongly modified by quantum confinement, making them qualitatively different from the usual Rydberg series. However, their parity and optical selection rules are preserved. Thus a one-parameter hydrogenic model is applied to quantitatively explain the ab initio exciton spectra, and allows one to extrapolate the electron-hole binding energy from optical spectroscopies of 2D semiconductors without costly simulations. Meanwhile, our calculated optical absorption spectrum and enhanced spin singlet-triplet splitting project graphyne, an allotrope of graphene, as a good candidate for intriguing energy and biomedical applications. Lastly, we report first-principles results on electronic structures of 2D graphene-like system, i.e., silicene. For planar and simply buckled silicene structures, we confirm their zero-gap nature and show a significant renormalization of their Fermi velocity by including many-electron effects. However, the other two recently proposed silicene structures exhibit a finite band gap, indicating that they are gapped semiconductors instead of expected Dirac-fermion semimetals. This finite band gap of the latter two structures is preserved even with the Ag substrate included. The gap opening is explained by the symmetry breaking of the buckled structures. Moreover, our GW calculation reveals enhanced many-electron effects in these 2D structures. Finally the band gap of the latter two structures can be tuned in a wide range by applying strain.

Thermoresponsive electrospun fibers for water harvesting applications

NASA Astrophysics Data System (ADS)

Thakur, Neha; Baji, Avinash; Ranganath, Anupama Sargur

2018-03-01

Temperature triggered switchable cellulose acetate-poly(N-isopropylacrylamide) (CA-PNIPAM) core-shell and blend nanofibers are fabricated for controlled moisture harvesting applications. Core-shell fibers are fabricated using a co-axial electrospinning setup whereas the conventional electrospinning setup is employed for fabricating the blend fibers. Investigation of their wettability behaviour demonstrated that the blend fibers are superhydrophilic whereas the core-shell fibers are hydrophilic at ambient temperature. Furthermore, both the samples have an ability to switch between the two states viz. hydrophilic to hydrophobic state based on thermal stimulus. The core-shell fibers are shown to have higher moisture sorption ability compared to the blend fibers. This study investigates the mechanism behind the switchable wettability behaviour of the core-shell fibers and demonstrates the crucial role played by the functional groups present on the surface layer of fibers in governing their moisture collection efficiency.

Highly Stretchable and Transparent Supercapacitor by Ag-Au Core-Shell Nanowire Network with High Electrochemical Stability.

PubMed

Lee, Habeom; Hong, Sukjoon; Lee, Jinhwan; Suh, Young Duk; Kwon, Jinhyeong; Moon, Hyunjin; Kim, Hyeonseok; Yeo, Junyeob; Ko, Seung Hwan

2016-06-22

Stretchable and transparent electronics have steadily attracted huge attention in wearable devices. Although Ag nanowire is the one of the most promising candidates for transparent and stretchable electronics, its electrochemical instability has forbidden its application to the development of electrochemical energy devices such as supercapacitors. Here, we introduce a highly stretchable and transparent supercapacitor based on electrochemically stable Ag-Au core-shell nanowire percolation network electrode. We developed a simple solution process to synthesize the Ag-Au core-shell nanowire with excellent electrical conductivity as well as greatly enhanced chemical and electrochemical stabilities compared to pristine Ag nanowire. The proposed core-shell nanowire-based supercapacitor still possesses fine optical transmittance and outstanding mechanical stability up to 60% strain. The Ag-Au core-shell nanowire can be a strong candidate for future wearable electrochemical energy devices.

Design of Aerosol Coating Reactors: Precursor Injection

PubMed Central

Buesser, Beat; Pratsinis, Sotiris E.

2013-01-01

Particles are coated with thin shells to facilitate their processing and incorporation into liquid or solid matrixes without altering core particle properties (coloristic, magnetic, etc.). Here, computational fluid and particle dynamics are combined to investigate the geometry of an aerosol reactor for continuous coating of freshly-made titanium dioxide core nanoparticles with nanothin silica shells by injection of hexamethyldisiloxane (HMDSO) vapor downstream of TiO2 particle formation. The focus is on the influence of HMDSO vapor jet number and direction in terms of azimuth and inclination jet angles on process temperature and coated particle characteristics (shell thickness and fraction of uncoated particles). Rapid and homogeneous mixing of core particle aerosol and coating precursor vapor facilitates synthesis of core-shell nanoparticles with uniform shell thickness and high coating efficiency (minimal uncoated core and free coating particles). PMID:23658471

Subwavelength core/shell cylindrical nanostructures for novel plasmonic and metamaterial devices

NASA Astrophysics Data System (ADS)

Kim, Kyoung-Ho; No, You-Shin

2017-12-01

In this review, we introduce novel plasmonic and metamaterial devices based on one-dimensional subwavelength nanostructures with cylindrical symmetry. Individual single devices with semiconductor/metal core/shell or dielectric/metal core/multi-shell structures experience strong light-matter interaction and yield unique optical properties with a variety of functions, e.g., invisibility cloaking, super-scattering/super-absorption, enhanced luminescence and nonlinear optical activities, and deep subwavelength-scale optical waveguiding. We describe the rational design of core/shell cylindrical nanostructures and the proper choice of appropriate constituent materials, which allow the efficient manipulation of electromagnetic waves and help to overcome the limitations of conventional homogeneous nanostructures. The recent developments of bottom-up synthesis combined with the top-down fabrication technologies for the practical applications and the experimental realizations of 1D subwavelength core/shell nanostructure devices are briefly discussed.

Sample-morphology effects on x-ray photoelectron peak intensities. III. Simulated spectra of model core–shell nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Powell, Cedric J., E-mail: cedric.powell@nist.gov; Chudzicki, Maksymilian; Werner, Wolfgang S. M.

2015-09-15

The National Institute of Standards and Technology database for the simulation of electron spectra for surface analysis has been used to simulate Cu 2p photoelectron spectra for four types of spherical copper–gold nanoparticles (NPs). These simulations were made to extend the work of Tougaard [J. Vac. Sci. Technol. A 14, 1415 (1996)] and of Powell et al. [J. Vac. Sci. Technol. A 31, 021402 (2013)] who performed similar simulations for four types of planar copper–gold films. The Cu 2p spectra for the NPs were compared and contrasted with analogous results for the planar films and the effects of elastic scatteringmore » were investigated. The new simulations were made for a monolayer of three types of Cu/Au core–shell NPs on a Si substrate: (1) an Au shell of variable thickness on a Cu core with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm; (2) a Cu shell of variable thickness on an Au core with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm; and (3) an Au shell of variable thickness on a 1 nm Cu shell on an Au core with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm. For these three morphologies, the outer-shell thickness was varied until the Cu 2p{sub 3/2} peak intensity was the same (within 2%) as that found in our previous work with planar Cu/Au morphologies. The authors also performed similar simulations for a monolayer of spherical NPs consisting of a CuAu{sub x} alloy (also on a Si substrate) with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm. In the latter simulations, the relative Au concentration (x) was varied to give the same Cu 2p{sub 3/2} peak intensity (within 2%) as that found previously. For each morphology, the authors performed simulations with elastic scattering switched on and off. The authors found that elastic-scattering effects were generally strong for the Cu-core/Au-shell and weak for the Au-core/Cu-shell NPs; intermediate elastic-scattering effects were found for the Au-core/Cu-shell/Au-shell NPs. The shell thicknesses required to give the selected Cu 2p{sub 3/2} peak intensity for the three types of core–shell NPs were less than the corresponding film thicknesses of planar samples since Cu 2p photoelectrons can be detected from the sides and, for the smaller NPs, bottoms of the NPs. Elastic-scattering effects were also observed on the Au atomic fractions found for the CuAu{sub x} NP alloys with different diameters.« less

Coupling Resonances of Surface Plasmon in Gold Nanorod/Copper Chalcogenide Core-Shell Nanostructures and Their Enhanced Photothermal Effect.

PubMed

Li, Yingying; Pan, Guiming; Liu, Qiyu; Ma, Liang; Xie, Ying; Zhou, Li; Hao, Zhonghua; Wang, Ququan

2018-06-04

Dual plasmonic Au@Cu 2-x S core-shell nanorods (NRs) have been fabricated by using a hydrothermal method and plasmon-coupled effect between the Au core and Cu 2-x S shell in the near-infrared (NIR) region. The extinction spectrum of Au@Cu 2-x S NRs is dominated by the surface plasmon resonance (SPR) of the Cu 2-x S shell, the transverse surface plasmon resonance (TSPR), and the longitudinal surface plasmon resonance (LSPR) of the Au NRs. With the Cu 2-x S shell increasing (fixed Au NRs), the TSPR peak slightly redshifts and the LSPR and SPR peaks blueshift, owing to competition between the redshift of the refractive index effect and blueshift from the plasmon coupled effect. Although, for Au@Cu 2 S NRs, only TSPR and LSPR peaks can be seen and a redshift arises with the increasing Cu 2 S shell thickness, implying that no plasmonic coupling between Au NRs and Cu 2 S shell occurred. The extinction spectrum of the Au@Cu 2-x S NRs with three coupled resonance peaks is simulated by using the FDTD method, taking into account the electron-transfer effect. The dispersion properties of the coupling of Au@Cu 2-x S NRs with the LSPR of the initial Au core are studied experimentally by changing the length of the Au NRs, which are explained theoretically by the coupled harmonic oscillator model. The calculated coupled coefficients between SPR of the Cu 2-x S shell and LSPR of the Au NRs is 180 meV, which is much stronger than that of TSPR of Au NRs of 55 meV. Finally, the enhanced photothermal effect of Au@Cu 2-x S NRs has been demonstrated. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Copper nanowire-graphene core-shell nanostructure for highly stable transparent conducting electrodes.

PubMed

Ahn, Yumi; Jeong, Youngjun; Lee, Donghwa; Lee, Youngu

2015-03-24

A copper nanowire-graphene (CuNW-G) core-shell nanostructure was successfully synthesized using a low-temperature plasma-enhanced chemical vapor deposition process at temperatures as low as 400 °C for the first time. The CuNW-G core-shell nanostructure was systematically characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman, and X-ray photoelectron spectroscopy measurements. A transparent conducting electrode (TCE) based on the CuNW-G core-shell nanostructure exhibited excellent optical and electrical properties compared to a conventional indium tin oxide TCE. Moreover, it showed remarkable thermal oxidation and chemical stability because of the tight encapsulation of the CuNW with gas-impermeable graphene shells. The potential suitability of CuNW-G TCE was demonstrated by fabricating bulk heterojunction polymer solar cells. We anticipate that the CuNW-G core-shell nanostructure can be used as an alternative to conventional TCE materials for emerging optoelectronic devices such as flexible solar cells, displays, and touch panels.

Rapid Synthesis and Formation Mechanism of Core-Shell-Structured La-Doped SrTiO3 with a Nb-Doped Shell

PubMed Central

Park, Nam-Hee; Akamatsu, Takafumi; Itoh, Toshio; Izu, Noriya; Shin, Woosuck

2015-01-01

To provide a convenient and practical synthesis process for metal ion doping on the surface of nanoparticles in an assembled nanostructure, core-shell-structured La-doped SrTiO3 nanocubes with a Nb-doped surface layer were synthesized via a rapid synthesis combining a rapid sol-precipitation and hydrothermal process. The La-doped SrTiO3 nanocubes were formed at room temperature by a rapid dissolution of NaOH pellets during the rapid sol-precipitation process, and the Nb-doped surface (shell) along with Nb-rich edges formed on the core nanocubes via the hydrothermal process. The formation mechanism of the core-shell-structured nanocubes and their shape evolution as a function of the Nb doping level were investigated. The synthesized core-shell-structured nanocubes could be arranged face-to-face on a SiO2/Si substrate by a slow evaporation process, and this nanostructured 10 μm thick thin film showed a smooth surface. PMID:28793420

Estimating changes in mean body temperature for humans during exercise using core and skin temperatures is inaccurate even with a correction factor.

PubMed

Jay, Ollie; Reardon, Francis D; Webb, Paul; Ducharme, Michel B; Ramsay, Tim; Nettlefold, Lindsay; Kenny, Glen P

2007-08-01

Changes in mean body temperature (DeltaT(b)) estimated by the traditional two-compartment model of "core" and "shell" temperatures and an adjusted two-compartment model incorporating a correction factor were compared with values derived by whole body calorimetry. Sixty participants (31 men, 29 women) cycled at 40% of peak O(2) consumption for 60 or 90 min in the Snellen calorimeter at 24 or 30 degrees C. The core compartment was represented by esophageal, rectal (T(re)), and aural canal temperature, and the shell compartment was represented by a 12-point mean skin temperature (T(sk)). Using T(re) and conventional core-to-shell weightings (X) of 0.66, 0.79, and 0.90, mean DeltaT(b) estimation error (with 95% confidence interval limits in parentheses) for the traditional model was -95.2% (-83.0, -107.3) to -76.6% (-72.8, -80.5) after 10 min and -47.2% (-40.9, -53.5) to -22.6% (-14.5, -30.7) after 90 min. Using T(re), X = 0.80, and a correction factor (X(0)) of 0.40, mean DeltaT(b) estimation error for the adjusted model was +9.5% (+16.9, +2.1) to -0.3% (+11.9, -12.5) after 10 min and +15.0% (+27.2, +2.8) to -13.7% (-4.2, -23.3) after 90 min. Quadratic analyses of calorimetry DeltaT(b) data was subsequently used to derive best-fitting values of X for both models and X(0) for the adjusted model for each measure of core temperature. The most accurate model at any time point or condition only accounted for 20% of the variation observed in DeltaT(b) for the traditional model and 56% for the adjusted model. In conclusion, throughout exercise the estimation of DeltaT(b) using any measure of core temperature together with mean skin temperature irrespective of weighting is inaccurate even with a correction factor customized for the specific conditions.

The Betelgeuse Project II: Asteroseismology

NASA Astrophysics Data System (ADS)

Nance, S.; Sullivan, J. M.; Diaz, M.; Wheeler, J. Craig

2018-06-01

We explore the question of whether the interior state of massive red supergiant supernova progenitors can be effectively probed with asteroseismology. We have computed a suite of ten models with ZAMS masses from 15 to 25 M⊙ in intervals of 1 M⊙ including the effects of rotation, with the stellar evolutionary code MESA. We estimate characteristic frequencies and convective luminosities of convective zones at two illustrative stages, core helium burning and off-center convective carbon burning. We also estimate the power that might be delivered to the surface to modulate the luminous output considering various efficiencies and dissipation mechanisms. The inner convective regions should generate waves with characteristic periods of ˜ 20 days in core helium burning, ˜10 days in helium shell burning, and 0.1 to 1 day in shell carbon burning. Acoustic waves may avoid both shock and diffusive dissipation relatively early in core helium burning throughout most of the structure. In shell carbon burning, years before explosion, the signal generated in the helium shell might in some circumstances be weak enough to avoid shock dissipation, but is subject to strong thermal dissipation in the hydrogen envelope. Signals from a convective carbon-burning shell are very likely to be even more severely damped by within the envelope. In the most optimistic case, early in core helium burning, waves arriving close to the surface could represent luminosity fluctuations of a few millimagnitudes, but the conditions in the very outer reaches of the envelope suggest severe thermal damping there.

Development of SiO2@TiO2 core-shell nanospheres for catalytic applications

NASA Astrophysics Data System (ADS)

Kitsou, I.; Panagopoulos, P.; Maggos, Th.; Arkas, M.; Tsetsekou, A.

2018-05-01

Silica-titania core-shell nanospheres, CSNp, were prepared via a simple and environmentally friendly two step route. First, silica cores were prepared through the hydrolysis-condensation reaction of silicic acid in the presence of hyperbranched poly(ethylene)imine (HBPEI) followed by repeating washing, centrifugation and, finally, calcination steps. To create the core-shell structure, various amounts of titanium isopropoxide were added to the cores and after that a HBPEI-water solution was added to hydrolyze the titanium precursor. Washing with ethanol and heat treatment followed. The optimization of processing parameters led to well-developed core-shell structures bearing a homogeneous nanocrystalline anatase coating over each silica core. The photocatalytic activity for NO was examined in a continuous flux photocatalytic reactor under real environmental conditions. The results revealed a very potent photocatalyst as the degradation percentage reached 84.27% for the core-shell material compared to the 82% of pure titania with the photodecomposition rates measured at 0.62 and 0.55 μg·m-2·s-1, respectively. In addition, catalytic activities of the CSNp and pure titania were investigated by monitoring the reduction of 4-nitrophenol to 4-aminophenol by an excess of NaBH4. Both materials exhibited excellent catalytic activity (100%), making the core-shell material a promising alternative catalyst to pure titania for various applications.

Silica-modified luminescent LaPO4 :Eu@LaPO4 @SiO2 core/shell nanorods: Synthesis, structural and luminescent properties.

PubMed

Ansari, Anees A

2018-02-01

Monoclinic-type tetragonal LaPO 4 :Eu (core) and LaPO 4 :Eu@LaPO 4 (core/shell) nanorods (NRs) were successfully prepared using a urea-based co-precipitation process under ambient conditions. An amorphous silica layer was coated around the luminescent core/shell NRs via the sol-gel process to improve their solubility and colloidal stability in aqueous and non-aqueous media. The prepared nano-products were systematically characterized by X-ray diffraction pattern, transmission electron microscopy, energy dispersive X-ray analysis, and FTIR, UV/Vis, and photoluminescence spectroscopy to examine their phase purity, crystal phase, surface chemistry, solubility and luminescence characteristics. The length and diameter of the nano-products were in the range 80-120 nm and 10-15 nm, respectively. High solubility of the silica-modified core/shell/Si NRs was found for the aqueous medium. The luminescent core NRs exhibited characteristic excitation and emission transitions in the visible region that were greatly affected by surface growth of insulating LaPO 4 and silica layers due to the multiphonon relaxation rate. Our luminescence spectral results clearly show a distinct difference in intensities for core, core/shell, and core/shell/Si NRs. Highly luminescent NRs with good solubility could be useful candidates for a variety of photonic-based biomedical applications. Copyright © 2017 John Wiley & Sons, Ltd.

Robust and Stable Cu Nanowire@Graphene Core-Shell Aerogels for Ultraeffective Electromagnetic Interference Shielding.

PubMed

Wu, Shiting; Zou, Mingchu; Li, Zhencheng; Chen, Daqin; Zhang, Hui; Yuan, Yongjun; Pei, Yongmao; Cao, Anyuan

2018-06-01

Cu nanowires (CuNWs) are considered as a promising candidate to develop high performance metal aerogels, yet the construction of robust and stable 3D porous structures remains challenging which severely limits their practical applications. Here, graphene-hybridized CuNW (CuNW@G) core-shell aerogels are fabricated by introducing a conformal polymeric coating and in situ transforming it into multilayered graphene seamlessly wrapped around individual CuNWs through a mild thermal annealing process. The existence of the outer graphene shell reinforces the 3D bulk structure and significantly slows down the oxidation process of CuNWs, resulting in improved mechanical property and highly stable electrical conductivity. When applied in electromagnetic interference shielding, the CuNW@G core-shell aerogels exhibit an average effectiveness of ≈52.5 dB over a wide range (from 8.2 to 18 GHz) with negligible degradation under ambient conditions for 40 d. Mechanism analysis reveals that the graphene shell with functional groups enables dual reflections on the core-shell and a multiple dielectric relaxation process, leading to enhanced dielectric loss and energy dissipation within the core-shell aerogels. The flexible core-shell-structured CuNW@G aerogels, with superior mechanical robustness and electrical stability, have potential applications in many areas such as advanced energy devices and functional composites. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direct Fabrication of Monodisperse Silica Nanorings from Hollow Spheres - A Template for Core-Shell Nanorings.

PubMed

Zhong, Kuo; Li, Jiaqi; Liu, Liwang; Brullot, Ward; Bloemen, Maarten; Volodin, Alexander; Song, Kai; Van Dorpe, Pol; Verellen, Niels; Clays, Koen

2016-04-27

We report a new type of nanosphere colloidal lithography to directly fabricate monodisperse silica (SiO2) nanorings by means of reactive ion etching of hollow SiO2 spheres. Detailed TEM, SEM, and AFM structural analysis is complemented by a model describing the geometrical transition from hollow sphere to ring during the etching process. The resulting silica nanorings can be readily redispersed in solution and subsequently serve as universal templates for the synthesis of ring-shaped core-shell nanostructures. As an example we used silica nanorings (with diameter of ∼200 nm) to create a novel plasmonic nanoparticle topology, a silica-Au core-shell nanoring, by self-assembly of Au nanoparticles (<20 nm) on the ring's surface. Spectroscopic measurements and finite difference time domain simulations reveal high quality factor multipolar and antibonding surface plasmon resonances in the near-infrared. By loading different types of nanoparticles on the silica core, hybrid and multifunctional composite nanoring structures could be realized for applications such as MRI contrast enhancement, catalysis, drug delivery, plasmonic and magnetic hyperthermia, photoacoustic imaging, and biochemical sensing.

Methanol oxidation reaction on core-shell structured Ruthenium-Palladium nanoparticles: Relationship between structure and electrochemical behavior

NASA Astrophysics Data System (ADS)

Kübler, Markus; Jurzinsky, Tilman; Ziegenbalg, Dirk; Cremers, Carsten

2018-01-01

In this work the relationship between structural composition and electrochemical characteristics of Palladium(Pd)-Ruthenium(Ru) nanoparticles during alkaline methanol oxidation reaction is investigated. The comparative study of a standard alloyed and a precisely Ru-core-Pd-shell structured catalyst allows for a distinct investigation of the electronic effect and the bifunctional mechanism. Core-shell catalysts benefit from a strong electronic effect and an efficient Pd utilization. It is found that core-shell nanoparticles are highly active towards methanol oxidation reaction for potentials ≥0.6 V, whereas alloyed catalysts show higher current outputs in the lower potential range. However, differential electrochemical mass spectrometry (DEMS) experiments reveal that the methanol oxidation reaction on core-shell structured catalysts proceeds via the incomplete oxidation pathway yielding formaldehyde, formic acid or methyl formate. Contrary, the alloyed catalyst benefits from the Ru atoms at its surface. Those are found to be responsible for high methanol oxidation activity at lower potentials as well as for complete oxidation of CH3OH to CO2 via the bifunctional mechanism. Based on these findings a new Ru-core-Pd-shell-Ru-terrace catalyst was synthesized, which combines the advantages of the core-shell structure and the alloy. This novel catalyst shows high methanol electrooxidation activity as well as excellent selectivity for the complete oxidation pathway.

Engineering of high performance supercapacitor electrode based on Fe-Ni/Fe{sub 2}O{sub 3}-NiO core/shell hybrid nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Ashutosh K., E-mail: ashuvishen@gmail.com, E-mail: aksingh@bose.res.in; Mandal, Kalyan

The present work reports on fabrication and supercapacitor applications of a core/shell Fe-Ni/Fe{sub 2}O{sub 3}-NiO hybrid nanostructures (HNs) electrode. The core/shell Fe-Ni/Fe{sub 2}O{sub 3}-NiO hybrid nanostructures have been fabricated through a two step method (nanowire fabrication and their controlled oxidation). The 1D hybrid nanostructure consists of highly porous shell layer (redox active materials NiO and Fe{sub 2}O{sub 3}) and the conductive core (FeNi nanowire). Thus, the highly porous shell layer allows facile electrolyte diffusion as well as faster redox reaction kinetics; whereas the conductive FeNi nanowire core provides the proficient express way for electrons to travel to the current collector,more » which helps in the superior electrochemical performance. The core/shell Fe-Ni/Fe{sub 2}O{sub 3}-NiO hybrid nanostructures electrode based supercapacitor shows very good electrochemical performances in terms of high specific capacitance nearly 1415 F g{sup −1} at a current density of 2.5 A g{sup −1}, excellent cycling stability and rate capability. The high quality electrochemical performance of core/shell hybrid nanostructures electrode shows its potential as an alternative electrode for forthcoming supercapacitor devices.« less

Anoxic and oxic removal of humic acids with Fe@Fe2O3 core-shell nanowires: a comparative study.

PubMed

Wu, Hao; Ai, Zhihui; Zhang, Lizhi

2014-04-01

In this study we comparatively investigate the removal of humic acids with Fe@Fe2O3 core-shell nanowires under anoxic and oxic conditions. The products of humic acids after reacting with Fe@Fe2O3 core-shell nanowires under anoxic and oxic conditions were carefully examined with three-dimensional excitation emission matrix fluorescence spectroscopy and gas chromatography mass spectrometry. It was found that humic acids were removed by Fe@Fe2O3 core-shell nanowires via adsorption under anoxic condition. Langmuir adsorption isotherm was applicable to describe the adsorption processes. Kinetics of humic acids adsorption onto Fe@Fe2O3 core-shell nanowires was found to follow pseudo-second-order rate equation. By contrast, the oxic removal of humic acids with Fe@Fe2O3 core-shell nanowires involved adsorption and subsequent oxidation of humic acids because Fe@Fe2O3 core-shell nanowires could activate molecular oxygen to produce reactive oxygen species to oxidize humic acids. This subsequent oxidation of humic acids could improve the oxic removal rate to 2.5 times that of anoxic removal, accompanying with about 8.4% of mineralization. This study provides a new method for humic acids removal and also sheds light on the effects of humic acids on the pollutant removal by nano zero-valent iron. Copyright © 2014 Elsevier Ltd. All rights reserved.

Core-shell structure of Miglyol/poly(D,L-lactide)/Poloxamer nanocapsules studied by small-angle neutron scattering.

PubMed

Rübe, Andrea; Hause, Gerd; Mäder, Karsten; Kohlbrecher, Joachim

2005-10-03

The contrast variation technique in small angle neutron scattering (SANS) was used to investigate the inner structure of nanocapsules on the example of poly(D,L-lactide) (PLA) nanocapsules. The determination of the PLA and Poloxamer shell thickness was the focus of this study. Highest sensitivity on the inner structure of the nanocapsules was obtained when the scattering length density of the solvent was varied between the one of the Miglyol core and the PLA shell. According to the fit data the PLA shell thickness was 9.8 nm. The z-averaged radius determined by SANS experiments correlated well with dynamic light scattering (DLS) results, although DLS values were systematically slightly higher than the ones measured by SANS. This could be explained by taking into account the influence of Poloxamer attached to the nanocapsules surface. For a refined fit model with a second shell consisting of Poloxamer, SANS values and DLS values fitted well with each other. The characterization method presented here is significant because detailed insights into the nanocapsule and the Poloxamer shell were gained for the first time. This method could be used to develop strategies for the optimization of the shell properties concerning controlled release and to study changes in the shell structure during degradation processes.

Theoretical studies of massive stars. I - Evolution of a 15-solar-mass star from the zero-age main sequence to neon ignition

NASA Technical Reports Server (NTRS)

Endal, A. S.

1975-01-01

The evolution of a star with mass 15 times that of the sun from the zero-age main sequence to neon ignition has been computed by the Henyey method. The hydrogen-rich envelope and all shell sources were explicitly included in the models. An algorithm has been developed for approximating the results of carbon burning, including the branching ratio for the C-12 + C-12 reaction and taking some secondary reactions into account. Penetration of the convective envelope into the core is found to be unimportant during the stages covered by the models. Energy transfer from the carbon-burning shell to the core by degenerate electron conduction becomes important after the core carbon-burning stage. Neon ignition will occur in a semidegenerate core and will lead to a mild 'flash.' Detailed numerical results are given in an appendix. Continuation of the calculations into later stages and variations with the total mass of the star will be discussed in later papers.

Electrostatically assisted fabrication of silver-dielectric core/shell nanoparticles thin film capacitor with uniform metal nanoparticle distribution and controlled spacing.

PubMed

Li, Xue; Niitsoo, Olivia; Couzis, Alexander

2016-03-01

An electrostatically-assisted strategy for fabrication of thin film composite capacitors with controllable dielectric constant (k) has been developed. The capacitor is composed of metal-dielectric core/shell nanoparticle (silver/silica, Ag@SiO2) multilayer films, and a backfilling polymer. Compared with the simple metal particle-polymer mixtures where the metal nanoparticles (NP) are randomly dispersed in the polymer matrix, the metal volume fraction in our capacitor was significantly increased, owing to the densely packed NP multilayers formed by the electrostatically assisted assembly process. Moreover, the insulating layer of silica shell provides a potential barrier that reduces the tunneling current between neighboring Ag cores, endowing the core/shell nanocomposites with a stable and relatively high dielectric constant (k) and low dielectric loss (D). Our work also shows that the thickness of the SiO2 shell plays a dominant role in controlling the dielectric properties of the nanocomposites. Control over metal NP separation distance was realized not only by variation the shell thickness of the core/shell NPs but also by introducing a high k nanoparticle, barium strontium titanate (BST) of relatively smaller size (∼8nm) compared to 80-160nm of the core/shell Ag@SiO2 NPs. The BST assemble between the Ag@SiO2 and fill the void space between the closely packed core/shell NPs leading to significant enhancement of the dielectric constant. This electrostatically assisted assembly method is promising for generating multilayer films of a large variety of NPs over large areas at low cost. Copyright © 2015 Elsevier Inc. All rights reserved.

Metal-Organic Frameworks Derived Porous Core/Shell Structured ZnO/ZnCo2O4/C Hybrids as Anodes for High-Performance Lithium-Ion Battery.

PubMed

Ge, Xiaoli; Li, Zhaoqiang; Wang, Chengxiang; Yin, Longwei

2015-12-09

Metal-organic frameworks (MOFs) derived porous core/shell ZnO/ZnCo2O4/C hybrids with ZnO as a core and ZnCo2O4 as a shell are for the first time fabricated by using core/shell ZnCo-MOF precursors as reactant templates. The unique MOFs-derived core/shell structured ZnO/ZnCo2O4/C hybrids are assembled from nanoparticles of ZnO and ZnCo2O4, with homogeneous carbon layers coated on the surface of the ZnCo2O4 shell. When acting as anode materials for lithium-ion batteries (LIBs), the MOFs-derived porous ZnO/ZnCo2O4/C anodes exhibit outstanding cycling stability, high Coulombic efficiency, and remarkable rate capability. The excellent electrochemical performance of the ZnO/ZnCo2O4/C LIB anodes can be attributed to the synergistic effect of the porous structure of the MOFs-derived core/shell ZnO/ZnCo2O4/C and homogeneous carbon layer coating on the surface of the ZnCo2O4 shells. The hierarchically porous core/shell structure offers abundant active sites, enhances the electrode/electrolyte contact area, provides abundant channels for electrolyte penetration, and also alleviates the structure decomposition induced by Li(+) insertion/extraction. The carbon layers effectively improve the conductivity of the hybrids and thus enhance the electron transfer rate, efficiently prevent ZnCo2O4 from aggregation and disintegration, and partially buffer the stress induced by the volume change during cycles. This strategy may shed light on designing new MOF-based hybrid electrodes for energy storage and conversion devices.

Self-Assembled Core-Shell CdTe/Poly(3-hexylthiophene) Nanoensembles as Novel Donor-Acceptor Light-Harvesting Systems.

PubMed

Istif, Emin; Kagkoura, Antonia; Hernandez-Ferrer, Javier; Stergiou, Anastasios; Skaltsas, Theodosis; Arenal, Raul; Benito, Ana M; Maser, Wolfgang K; Tagmatarchis, Nikos

2017-12-27

The self-assembly of novel core-shell nanoensembles consisting of regioregular poly(3-hexylthiophene) nanoparticles (P3HT NPs ) of 100 nm as core and semiconducting CdTe quantum dots (CdTe QDs ) as shell with a thickness of a few tens of nanometers was accomplished by employing a reprecipitation approach. The structure, morphology, and composition of CdTe QDs /P3HT NPs nanoensembles were confirmed by high-resolution scanning transmission microscopy and dynamic light-scattering studies. Intimate interface contact between the CdTe QDs shell and the P3HT NPs core leads to the stabilization of the CdTe QDs /P3HT NPs nanoensemble as probed by the steady-state absorption spectroscopy. Effective quenching of the characteristic photoluminescence of CdTe QDs at 555 nm, accompanied by simultaneous increase in emission of P3HT NPs at 660 and 720 nm, reveals photoinduced charge-transfer processes. Probing the redox properties of films of CdTe QDs /P3HT NPs further proves the formation of a stabilized core-shell system in the solid state. Photoelectrochemical assays on CdTe QDs /P3HT NPs films show a reversible on-off photoresponse at a bias voltage of +0.8 V with a 3 times increased photocurrent compared to CdTe QDs . The improved charge separation is directly related to the unique core-shell configuration, in which the outer CdTe QDs shell forces the P3HT NPs core to effectively act as electron acceptor. The creation of novel donor-acceptor core-shell hybrid materials via self-assembly is transferable to other types of conjugated polymers and semiconducting nanoparticles. This work, therefore, opens new pathways for the design of improved optoelectronic devices.

Room temperature exchange bias in multiferroic BiFeO3 nano- and microcrystals with antiferromagnetic core and two-dimensional diluted antiferromagnetic shell

NASA Astrophysics Data System (ADS)

Zhang, Chuang; Wang, Shou Yu; Liu, Wei Fang; Xu, Xun Ling; Li, Xiu; Zhang, Hong; Gao, Ju; Li, De Jun

2017-05-01

Exchange bias (EB) of multiferroics presents many potential opportunities for magnetic devices. However, instead of using low-temperature field cooling in the hysteresis loop measurement, which usually shows an effective approach to obtain obvious EB phenomenon, there are few room temperature EB. In this article, extensive studies on room temperature EB without field cooling were observed in BiFeO3 nano- and microcrystals. Moreover, with increasing size the hysteresis loops shift from horizontal negative exchange bias (NEB) to positive exchange bias (PEB). In order to explain the tunable EB behaviors with size dependence, a phenomenological qualitative model based on the framework of antiferromagnetic (AFM) core-two-dimensional diluted antiferromagnet in a field (2D-DAFF) shell structure was proposed. The training effect (TE) ascertained the validity of model and the presence of unstable magnetic structure using Binek's model. Experimental results show that the tunable EB effect can be explained by the competition of ferromagnetic (FM) exchange coupling and AFM exchange coupling interaction between AFM core and 2D-DAFF shell. Additionally, the local distortion of lattice fringes was observed in hexagonal-shaped BiFeO3 nanocrystals with well-dispersed behavior. The electrical conduction properties agreed well with the space charge-limited conduction mechanism.

Phosphine-free synthesis and characterization of type-II ZnSe/CdS core-shell quantum dots

NASA Astrophysics Data System (ADS)

Ghasemzadeh, Roghayyeh; Armanmehr, Mohammad Hasan; Abedi, Mohammad; Fateh, Davood Sadeghi; Bahreini, Zaker

2018-01-01

A phosphine-free route for synthesis of type-II ZnSe/CdS core-shell quantum dots, using green, low cost and environmentally friendly reagents and phosphine-free solvents such as 1-octadecene (ODE) and liquid paraffin has been reported. Hot-injection technique has been used for the synthesis of ZnSe core quantum dots. The CdS shell quantum dots prepared by reaction of CdO precursor and S powder in 1-octadecene (ODE). The ZnSe/CdS core-shell quantum dots were synthesized via successive ion layer adsorption and reaction (SILAR) technique. The characterization of produced quantum dots were performed by absorption and fluorescence spectroscopy, X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The results showed the formation of type-II ZnSe/CdS core-shell quantum dots with FWHM 32 nm and uniform size distribution.

Titanium dioxide@polypyrrole core-shell nanowires for all solid-state flexible supercapacitors

NASA Astrophysics Data System (ADS)

Yu, Minghao; Zeng, Yinxiang; Zhang, Chong; Lu, Xihong; Zeng, Chenghui; Yao, Chenzhong; Yang, Yangyi; Tong, Yexiang

2013-10-01

Herein, we developed a facile two-step process to synthesize TiO2@PPy core-shell nanowires (NWs) on carbon cloth and reported their improved electrochemical performance for flexible supercapacitors (SCs). The fabricated solid-state SC device based on TiO2@PPy core-shell NWs not only has excellent flexibility, but also exhibits remarkable electrochemical performance.Herein, we developed a facile two-step process to synthesize TiO2@PPy core-shell nanowires (NWs) on carbon cloth and reported their improved electrochemical performance for flexible supercapacitors (SCs). The fabricated solid-state SC device based on TiO2@PPy core-shell NWs not only has excellent flexibility, but also exhibits remarkable electrochemical performance. Electronic supplementary information (ESI) available: Experimental details, XRD pattern, FT-IR absorption spectrum and CV curves of TiO2@PPy NWs, and SEM images of the PPy. See DOI: 10.1039/c3nr03578f

Water-soluble core/shell nanoparticles for proton therapy through particle-induced radiation

NASA Astrophysics Data System (ADS)

Park, Jeong Chan; Jung, Myung-Hwan; Kim, Maeng Jun; Kim, Kye-Ryung

2015-02-01

Metallic nanoparticles have been used in biomedical applications such as magnetic resonance imaging (MRI), therapy, and drug delivery systems. Metallic nanoparticles as therapeutic tools have been demonstrated using radio-frequency magnetic fields or near-infrared light. Recently, therapeutic applications of metallic nanomaterials combined with proton beams have been reported. Particle-induced radiation from metallic nanoparticles, which can enhance the therapeutic effects of proton therapy, was released when the nanoparticles were bombarded by a high-energy proton beam. Core/shell nanoparticles, especially Au-coated magnetic nanoparticles, have drawn attention in biological applications due to their attractive characteristics. However, studies on the phase transfer of organic-ligand-based core/shell nanoparticles into water are limited. Herein, we demonstrated that hydrophobic core/shell structured nanomaterials could be successfully dispersed in water through chloroform/surfactant mixtures. The effects of the core/shell nanomaterials and the proton irradiation on Escherichia coli (E. coli) were also explored.

Enhanced exchange bias and improved ferromagnetic properties in Permalloy-BiFe0.95Co0.05O3 core-shell nanostructures.

PubMed

Javed, K; Li, W J; Ali, S S; Shi, D W; Khan, U; Riaz, S; Han, X F

2015-12-14

Hybrid core-shell nanostructures consisting of permalloy (Ni80Fe20) and multiferroic(BiFeO3, BFO/BiFe0.95Co0.05O3, BFC) materials were synthesized by a two-step method, based on wet chemical impregnation and subsequent electrodeposition within porous alumina membranes. Structural and magnetic characterizations have been done to investigate doping effect on magnetic properties and exchange bias. The magnetometry analysis revealed significant enhancements of the exchange bias and coercivity in NiFe-BFC core-shell nanostructures as compared with NiFe-BFO core-shell nanostructures. The enhancements can be attributed to the effective reduction of ferromagnet domain sizes between adjacent layers of core-shell structure. It indicates that it is possible to improve properties of multiferroic composites by site-engineering method. Our approach opens a pathway to obtain optimized nanostructured multiferroic composites exhibiting tunable magnetic properties.

Size-exclusion chromatography using core-shell particles.

PubMed

Pirok, Bob W J; Breuer, Pascal; Hoppe, Serafine J M; Chitty, Mike; Welch, Emmet; Farkas, Tivadar; van der Wal, Sjoerd; Peters, Ron; Schoenmakers, Peter J

2017-02-24

Size-exclusion chromatography (SEC) is an indispensable technique for the separation of high-molecular-weight analytes and for determining molar-mass distributions. The potential application of SEC as second-dimension separation in comprehensive two-dimensional liquid chromatography demands very short analysis times. Liquid chromatography benefits from the advent of highly efficient core-shell packing materials, but because of the reduced total pore volume these materials have so far not been explored in SEC. The feasibility of using core-shell particles in SEC has been investigated and contemporary core-shell materials were compared with conventional packing materials for SEC. Columns packed with very small core-shell particles showed excellent resolution in specific molar-mass ranges, depending on the pore size. The analysis times were about an order of magnitude shorter than what could be achieved using conventional SEC columns. Copyright © 2016 Elsevier B.V. All rights reserved.

Electrosprayed core-shell polymer-lipid nanoparticles for active component delivery

NASA Astrophysics Data System (ADS)

Eltayeb, Megdi; Stride, Eleanor; Edirisinghe, Mohan

2013-11-01

A key challenge in the production of multicomponent nanoparticles for healthcare applications is obtaining reproducible monodisperse nanoparticles with the minimum number of preparation steps. This paper focus on the use of electrohydrodynamic (EHD) techniques to produce core-shell polymer-lipid structures with a narrow size distribution in a single step process. These nanoparticles are composed of a hydrophilic core for active component encapsulation and a lipid shell. It was found that core-shell nanoparticles with a tunable size range between 30 and 90 nm and a narrow size distribution could be reproducibly manufactured. The results indicate that the lipid component (stearic acid) stabilizes the nanoparticles against collapse and aggregation and improves entrapment of active components, in this case vanillin, ethylmaltol and maltol. The overall structure of the nanoparticles produced was examined by multiple methods, including transmission electron microscopy and differential scanning calorimetry, to confirm that they were of core-shell form.

A pathway for the growth of core-shell Pt-Pd nanoparticles

DOE PAGES

Narula, Chaitanya Kumar; Yang, Xiaofan; Li, Chen; ...

2015-10-12

In this study, the aging of both Pt-Pd nanoparticles and core-shell Pt-Pd nanoparticles has been reported to result in alloying of Pt with Pd. In comparison to monometallic Pt catalysts, the growth of Pd-Pt bimetallics is slower; however, the mechanism of growth of particles and the mechanism by which Pd improves the hydrothermal durability of bimetallic Pd-Pt particles remains uncertain. In our work on hydrothermal aging of core-shell Pt-Pd nanoparticles, synthesized by solution methods, with varying Pd:Pt ratio of 1:4, 1:1, and 4:1, we compare the growth of core-shell Pt-Pd nanoparticles and find that particles grow by migrating and joiningmore » together. The unique feature of the observed growth is that Pd shells from both particles open up and join, allowing the cores to merge. At high temperatures, alloying occurs in good agreement with reports by other workers.« less

Polyethylenimine-immobilized core-shell nanoparticles: synthesis, characterization, and biocompatibility test.

PubMed

Ratanajanchai, Montri; Soodvilai, Sunhapas; Pimpha, Nuttaporn; Sunintaboon, Panya

2014-01-01

Herein, we prepared PEI-immobilized core-shell particles possessing various types of polymer cores via a visible light-induced surfactant-free emulsion polymerization (SFEP) of three vinyl monomers: styrene (St), methyl methacrylate (MMA), and 2-hydroxyethyl methacrylate (HEMA). An effect of monomers on the polymerization and characteristics of resulting products was investigated. Monomers with high polarity can provide high monomer conversion, high percentage of grafted PEI, stable particles with uniform size distribution but less amino groups per particles. All prepared nanoparticles exhibited a core-shell nanostructure, containing PEI on the shell with hydrodynamic size around 140-230nm. For in-vitro study in Caco-2 cells, we found that the incorporation of PEI into these core-shell nanoparticles can significantly reduce its cytotoxic effect and also be able to internalized within the cells. Accordingly, these biocompatible particles would be useful for various biomedical applications, including gene transfection and intracellular drug delivery. © 2013.

Nitride stabilized core/shell nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuttiyiel, Kurian Abraham; Sasaki, Kotaro; Adzic, Radoslav R.

Nitride stabilized metal nanoparticles and methods for their manufacture are disclosed. In one embodiment the metal nanoparticles have a continuous and nonporous noble metal shell with a nitride-stabilized non-noble metal core. The nitride-stabilized core provides a stabilizing effect under high oxidizing conditions suppressing the noble metal dissolution during potential cycling. The nitride stabilized nanoparticles may be fabricated by a process in which a core is coated with a shell layer that encapsulates the entire core. Introduction of nitrogen into the core by annealing produces metal nitride(s) that are less susceptible to dissolution during potential cycling under high oxidizing conditions.

Gold core@silver semishell Janus nanoparticles prepared by interfacial etching.

PubMed

Chen, Limei; Deming, Christopher P; Peng, Yi; Hu, Peiguang; Stofan, Jake; Chen, Shaowei

2016-08-14

Gold core@silver semishell Janus nanoparticles were prepared by chemical etching of Au@Ag core-shell nanoparticles at the air/water interface. Au@Ag core-shell nanoparticles were synthesized by chemical deposition of a silver shell onto gold seed colloids followed by the self-assembly of 1-dodecanethiol onto the nanoparticle surface. The nanoparticles then formed a monolayer on the water surface of a Langmuir-Blodgett trough, and part of the silver shell was selectively etched away by the mixture of hydrogen peroxide and ammonia in the water subphase, where the etching was limited to the side of the nanoparticles that was in direct contact with water. The resulting Janus nanoparticles exhibited an asymmetrical distribution of silver on the surface of the gold cores, as manifested in transmission electron microscopy, UV-vis absorption, and X-ray photoelectron spectroscopy measurements. Interestingly, the Au@Ag semishell Janus nanoparticles exhibited enhanced electrocatalytic activity in oxygen reduction reactions, as compared to their Au@Ag and Ag@Au core-shell counterparts, likely due to a synergistic effect between the gold cores and silver semishells that optimized oxygen binding to the nanoparticle surface.

Magnetically separable {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-Ce-doped TiO{sub 2} core-shell nanocomposites: Fabrication and visible-light-driven photocatalytic activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Minqiang, E-mail: jbmwgkc@126.com; Li, Di; Jiang, Deli

2012-08-15

Novel visible-light-induced {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-Ce-doped-TiO{sub 2} core-shell nanocomposite photocatalysts capable of magnetic separation have been synthesized by a facile sol-gel and after-annealing process. The as-obtained core-shell nanocomposite is composed of a central {gamma}-Fe{sub 2}O{sub 3} core with a strong response to external fields, an interlayer of SiO{sub 2}, and an outer layer of Ce-doped TiO{sub 2} nanocrystals. UV-vis spectra analysis indicates that Ce doping in the compound results in a red-shift of the absorption edge, thus offering increased visible light absorption. We show that such a {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-Ce-doped-TiO{sub 2} core-shell nanocomposite with appreciated Ce doping amount exhibitsmore » much higher visible-light photocatalytic activity than bare TiO{sub 2} and undoped {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-TiO{sub 2} core-shell nanocomposite toward the degradation of rhodamine B (RhB). Moreover, the {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-Ce-doped-TiO{sub 2} core-shell nanocomposite photocatalysts could be easily separated and reused from the treated water under application of an external magnetic field. - Graphical abstract: Novel {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-Ce-doped-TiO{sub 2} core/shell nanocomposite photocatalysts with enhanced photocatalytic activity and fast magnetic separability were prepared. Highlights: Black-Right-Pointing-Pointer Novel {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-Ce-doped TiO{sub 2} core/shell composite photocatalysts were prepared. Black-Right-Pointing-Pointer The resulting core/shell composite show high visible light photocatalytic activity. Black-Right-Pointing-Pointer The nanocomposite photocatalysts can be easily recycled with excellent durability.« less

Enhanced Upconversion Luminescence in Yb3+/Tm3+-Codoped Fluoride Active Core/Active Shell/Inert Shell Nanoparticles through Directed Energy Migration

PubMed Central

Qiu, Hailong; Yang, Chunhui; Shao, Wei; Damasco, Jossana; Wang, Xianliang; Ågren, Hans; Prasad, Paras N.; Chen, Guanying

2014-01-01

The luminescence efficiency of lanthanide-doped upconversion nanoparticles is of particular importance for their embodiment in biophotonic and photonic applications. Here, we show that the upconversion luminescence of typically used NaYF4:Yb3+30%/Tm3+0.5% nanoparticles can be enhanced by ~240 times through a hierarchical active core/active shell/inert shell (NaYF4:Yb3+30%/Tm3+0.5%)/NaYbF4/NaYF4 design, which involves the use of directed energy migration in the second active shell layer. The resulting active core/active shell/inert shell nanoparticles are determined to be about 11 times brighter than that of well-investigated (NaYF4:Yb3+30%/Tm3+0.5%)/NaYF4 active core/inert shell nanoparticles when excited at ~980 nm. The strategy for enhanced upconversion in Yb3+/Tm3+-codoped NaYF4 nanoparticles through directed energy migration might have implications for other types of lanthanide-doped upconversion nanoparticles. PMID:28348285

Fabrication of polyacrylate core-shell nanoparticles via spray drying method

NASA Astrophysics Data System (ADS)

Chen, Pengpeng; Cheng, Zenghui; Chu, Fuxiang; Xu, Yuzhi; Wang, Chunpeng

2016-05-01

Fine polyacrylate particles are thought to be environmental plastisols for car industry. However, these particles are mainly dried through demulsification of the latexes, which is not reproducible and hard to be scaled up. In this work, a spray drying method had been applied to the plastisols-used acrylate latex. By adjusting the core/shell ratio, spray drying process of the latex was fully studied. Scanning electronic microscopy observation of the nanoparticles before and after spray drying indicated that the core-shell structures could be well preserved and particles were well separated by spray drying if the shell was thick enough. Otherwise, the particles fused into each other and core-shell structures were destroyed. Polyacrylate plastisols were developed using diisononylphthalate as a plasticizer, and plastigels were obtained after heat treatment of the sols. Results showed that the shell thickness also had a great influence on the storage stability of the plastisols and mechanical properties of the plastigels.

Synthesis and properties MFe2O4 (M = Fe, Co) nanoparticles and core-shell structures

NASA Astrophysics Data System (ADS)

Yelenich, O. V.; Solopan, S. O.; Greneche, J. M.; Belous, A. G.

2015-08-01

Individual Fe3-xO4 and CoFe2O4 nanoparticles, as well as Fe3-xO4/CoFe2O4 core/shell structures were synthesized by the method of co-precipitation from diethylene glycol solutions. Core/shell structure were synthesized with CoFe2O4-shell thickness of 1.0, 2.5 and 3.5 nm. X-ray diffraction patterns of individual nanoparticles and core/shell are similar and indicate that all synthesized samples have a cubic spinel structure. Compares Mössbauer studies of CoFe2O4, Fe3-xO4 nanoparticles indicate superparamagnetic properties at 300 K. It was shown that individual magnetite nanoparticles are transformed into maghemite through oxidation during the synthesis procedure, wherein the smallest nanoparticles are completely oxidized while a magnetite core does occur in the case of the largest nanoparticles. The Mössbauer spectra of core/shell nanoparticles with increasing CoFe2O4-shell thickness show a gradual decrease in the relative intensity of the quadrupole doublet and significant decrease of the mean isomer shift value at both RT and 77 K indicating a decrease of the superparamagnetic relaxation phenomena. Specific loss power for the prepared ferrofluids was experimentally calculated and it was determined that under influence of ac-magnetic field magnetic fluid based on individual CoFe2O4 and Fe3-xO4 particles are characterized by very low heating temperature, when magnetic fluids based on core/shell nanoparticles demonstrate higher heating effect.

Biocompatible magnetic core-shell nanocomposites for engineered magnetic tissues

NASA Astrophysics Data System (ADS)

Rodriguez-Arco, Laura; Rodriguez, Ismael A.; Carriel, Victor; Bonhome-Espinosa, Ana B.; Campos, Fernando; Kuzhir, Pavel; Duran, Juan D. G.; Lopez-Lopez, Modesto T.

2016-04-01

The inclusion of magnetic nanoparticles into biopolymer matrixes enables the preparation of magnetic field-responsive engineered tissues. Here we describe a synthetic route to prepare biocompatible core-shell nanostructures consisting of a polymeric core and a magnetic shell, which are used for this purpose. We show that using a core-shell architecture is doubly advantageous. First, gravitational settling for core-shell nanocomposites is slower because of the reduction of the composite average density connected to the light polymer core. Second, the magnetic response of core-shell nanocomposites can be tuned by changing the thickness of the magnetic layer. The incorporation of the composites into biopolymer hydrogels containing cells results in magnetic field-responsive engineered tissues whose mechanical properties can be controlled by external magnetic forces. Indeed, we obtain a significant increase of the viscoelastic moduli of the engineered tissues when exposed to an external magnetic field. Because the composites are functionalized with polyethylene glycol, the prepared bio-artificial tissue-like constructs also display excellent ex vivo cell viability and proliferation. When implanted in vivo, the engineered tissues show good biocompatibility and outstanding interaction with the host tissue. Actually, they only cause a localized transitory inflammatory reaction at the implantation site, without any effect on other organs. Altogether, our results suggest that the inclusion of magnetic core-shell nanocomposites into biomaterials would enable tissue engineering of artificial substitutes whose mechanical properties could be tuned to match those of the potential target tissue. In a wider perspective, the good biocompatibility and magnetic behavior of the composites could be beneficial for many other applications.The inclusion of magnetic nanoparticles into biopolymer matrixes enables the preparation of magnetic field-responsive engineered tissues. Here we describe a synthetic route to prepare biocompatible core-shell nanostructures consisting of a polymeric core and a magnetic shell, which are used for this purpose. We show that using a core-shell architecture is doubly advantageous. First, gravitational settling for core-shell nanocomposites is slower because of the reduction of the composite average density connected to the light polymer core. Second, the magnetic response of core-shell nanocomposites can be tuned by changing the thickness of the magnetic layer. The incorporation of the composites into biopolymer hydrogels containing cells results in magnetic field-responsive engineered tissues whose mechanical properties can be controlled by external magnetic forces. Indeed, we obtain a significant increase of the viscoelastic moduli of the engineered tissues when exposed to an external magnetic field. Because the composites are functionalized with polyethylene glycol, the prepared bio-artificial tissue-like constructs also display excellent ex vivo cell viability and proliferation. When implanted in vivo, the engineered tissues show good biocompatibility and outstanding interaction with the host tissue. Actually, they only cause a localized transitory inflammatory reaction at the implantation site, without any effect on other organs. Altogether, our results suggest that the inclusion of magnetic core-shell nanocomposites into biomaterials would enable tissue engineering of artificial substitutes whose mechanical properties could be tuned to match those of the potential target tissue. In a wider perspective, the good biocompatibility and magnetic behavior of the composites could be beneficial for many other applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00224b

Reciprocal responsiveness of nucleus accumbens shell and core dopamine to food- and drug-conditioned stimuli.

PubMed

Bassareo, Valentina; Musio, Paolo; Di Chiara, Gaetano

2011-04-01

Drugs of abuse and palatable food share the ability to stimulate dopamine (DA) transmission in the nucleus accumbens shell. However, while the stimulation of shell DA by food undergoes habituation, that by drugs of abuse does not. This study aims to directly compare the changes of extracellular DA, by microdialysis, in shell and core and prefrontal cortex (PFCX) in response to food- and drug-conditioned stimuli (CSs). Rats were trace-conditioned by Fonzies box (FB) or vanilla box (VB; CS), followed by food: Fonzies, intraoral chocolate solution (food-unconditioned stimulus (US)) and morphine (1.0 mg/Kg sc; drug US). Control (unconditioned) rats received standard food instead of Fonzies, tap water instead of chocolate, saline instead of morphine. Food-CSs increased core but not shell DA, while drug-CSs did the opposite. Food and drug-CSs both increased PFCX DA. Exposure to food-CSs potentiated core and PFCX DA response to food while shell responsiveness was dependent upon the relative CS and US nature. If the CS was intrinsic to the food US (CS = FB/US = Fonzies) the response of shell DA to the US was abolished. If the CS was extrinsic to the food US (CS = FB/US = chocolate; CS = VB/US = Fonzies), shell DA increased in response to the US. Exposure to the drug-CS potentiated the DA response to the drug-US in the shell and in the PFCX, but not in the core. Drug-CSs differentially activate DA as compared to food-CSs in shell and core and differentially affect DA response to the US in these areas. These differences might be relevant for the role of DA in the mechanism of drug addiction.

AFM Investigation of Liquid-Filled Polymer Microcapsules Elasticity.

PubMed

Sarrazin, Baptiste; Tsapis, Nicolas; Mousnier, Ludivine; Taulier, Nicolas; Urbach, Wladimir; Guenoun, Patrick

2016-05-10

Elasticity of polymer microcapsules (MCs) filled with a liquid fluorinated core is studied by atomic force microscopy (AFM). Accurately characterized spherical tips are employed to obtain the Young's moduli of MCs having four different shell thicknesses. We show that those moduli are effective ones because the samples are composites. The strong decrease of the effective MC elasticity (from 3.0 to 0.1 GPa) as the shell thickness decreases (from 200 to 10 nm) is analyzed using a novel numerical approach. This model describes the evolution of the elasticity of a coated half-space according to the contact radius, the thickness of the film, and the elastic moduli of bulk materials. This numerical model is consistent with the experimental data and allows simulating the elastic behavior of MCs at high frequencies (5 MHz). While the quasi-static elasticity of the MCs is found to be very dependent on the shell thickness, the high frequency (5 MHz) elastic behavior of the core leads to a stable behavior of the MCs (from 2.5 to 3 GPa according to the shell thickness). Finally, the effect of thermal annealing on the MCs elasticity is investigated. The Young's modulus is found to decrease because of the reduction of the shell thickness due to the loss of the polymer.

Research advances in polymer emulsion based on "core-shell" structure particle design.

PubMed

Ma, Jian-zhong; Liu, Yi-hong; Bao, Yan; Liu, Jun-li; Zhang, Jing

2013-09-01

In recent years, quite many studies on polymer emulsions with unique core-shell structure have emerged at the frontier between material chemistry and many other fields because of their singular morphology, properties and wide range of potential applications. Organic substance as a coating material onto either inorganic or organic internal core materials promises an unparalleled opportunity for enhancement of final functions through rational designs. This contribution provides a brief overview of recent progress in the synthesis, characterization, and applications of both inorganic-organic and organic-organic polymer emulsions with core-shell structure. In addition, future research trends in polymer composites with core-shell structure are also discussed in this review. Copyright © 2013 Elsevier B.V. All rights reserved.

Tuning the synthesis of platinum-copper nanoparticles with a hollow core and porous shell for the selective hydrogenation of furfural to furfuryl alcohol.

PubMed

Huang, Shuangshuang; Yang, Nating; Wang, Shibin; Sun, Yuhan; Zhu, Yan

2016-08-07

Pt-Cu nanoparticles constructed with a hollow core and porous shell have been synthesized in which Pt-Cu cages with multiporous outermost shells are formed at the initial stage and then the Pt and Cu atoms in solution continuously fed these hollow-core of cages by passing through the porous tunnels of the outermost shells, finally leading to the formation of hollow structures with different sizes. Furthermore, these hollow-core Pt-Cu nanoparticles are more effective than the solid-core Pt-Cu nanoparticles for the catalytic hydrogenation of furfural toward furfuryl alcohol. The former can achieve almost 100% conversion of furfural with 100% selectivity toward the alcohol.

The influence of shell thickness of Au@TiO2 core-shell nanoparticles on the plasmonic enhancement effect in dye-sensitized solar cells.

PubMed

Liu, Wei-Liang; Lin, Fan-Cheng; Yang, Yu-Chen; Huang, Chen-Hsien; Gwo, Shangjr; Huang, Michael H; Huang, Jer-Shing

2013-09-07

Plasmonic core-shell nanoparticles (PCSNPs) can function as nanoantennas and improve the efficiency of dye-sensitized solar cells (DSSCs). To achieve maximum enhancement, the morphology of PCSNPs needs to be optimized. Here we precisely control the morphology of Au@TiO2 PCSNPs and systematically study its influence on the plasmonic enhancement effect. The enhancement mechanism was found to vary with the thickness of the TiO2 shell. PCSNPs with a thinner shell mainly enhance the current, whereas particles with a thicker shell improve the voltage. While pronounced plasmonic enhancement was found in the near infrared regime, wavelength-independent enhancement in the visible range was observed and attributed to the plasmonic heating effect. Emission lifetime measurement confirms that N719 molecules neighboring nanoparticles with TiO2 shells exhibit a longer lifetime than those in contact with metal cores. Overall, PCSNPs with a 5 nm shell give the highest efficiency enhancement of 23%. Our work provides a new synthesis route for well-controlled Au@TiO2 core-shell nanoparticles and gains insight into the plasmonic enhancement in DSSCs.

Low temperature grown ZnO@TiO{sub 2} core shell nanorod arrays for dye sensitized solar cell application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goh, Gregory Kia Liang; Le, Hong Quang, E-mail: lehq@imre.a-star.edu.sg; Huang, Tang Jiao

High aspect ratio ZnO nanorod arrays were synthesized on fluorine-doped tin oxide glasses via a low temperature solution method. By adjusting the growth condition and adding polyethylenimine, ZnO nanorod arrays with tunable length were successfully achieved. The ZnO@TiO{sub 2} core shells structures were realized by a fast growth method of immersion into a (NH{sub 4}){sub 2}·TiF{sub 6} solution. Transmission electron microscopy, X-ray Diffraction and energy dispersive X-ray measurements all confirmed the existence of a titania shell uniformly covering the ZnO nanorod's surface. Results of solar cell testing showed that addition of a TiO{sub 2} shell to the ZnO nanorod significantlymore » increased short circuit current (from 4.2 to 5.2 mA/cm{sup 2}), open circuit voltage (from 0.6 V to 0.8 V) and fill factor (from 42.8% to 73.02%). The overall cell efficiency jumped from 1.1% for bare ZnO nanorod to 3.03% for a ZnO@TiO{sub 2} core shell structured solar cell with a 18–22 nm shell thickness, a nearly threefold increase. - Graphical abstract: The synthesis process of coating TiO{sub 2} shell onto ZnO nanorod core is shown schematically. A thin, uniform, and conformal shell had been grown on the surface of the ZnO core after immersing in the (NH{sub 4}){sub 2}·TiF{sub 6} solution for 5–15 min. - Highlights: • ZnO@TiO{sub 2} core shell nanorod has been grown on FTO substrate using low temperature solution method. • TEM, XRD, EDX results confirmed the existing of titana shell, uniformly covered rod's surface. • TiO{sub 2} shell suppressed recombination, demonstrated significant enhancement in cell's efficiency. • Core shell DSSC's efficiency achieved as high as 3.03%, 3 times higher than that of ZnO nanorods.« less

Zirconium(IV) oxide: New coating material for nanoresonators for shell-isolated nanoparticle-enhanced Raman spectroscopy

NASA Astrophysics Data System (ADS)

Krajczewski, Jan; Abdulrahman, Heman Burhanalden; Kołątaj, Karol; Kudelski, Andrzej

2018-03-01

One tool that can be used for determining the structure and composition of surfaces of various materials (even in in situ conditions) is shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). In SHINERS measurements, the surface under investigation is covered with a layer of surface-protected plasmonic nanoparticles, and then the Raman spectrum of the surface analysed is recorded. The plasmonic cores of the used core-shell structures act as electromagnetic nanoresonators, significantly locally enhancing the intensity of the electric field of the incident radiation, leading to a large increase in the efficiency of the generation of the Raman signal from molecules in the close proximity to the deposited SHINERS nanoresonators. A protective layer (from transparent dielectrics such as SiO2, Al2O3 or TiO2) prevents direct interaction between the plasmonic metal and the analysed surface (such interactions may lead to changes in the structure of the surface) and, in the case of plasmonic cores other than gold cores, the dielectric layer increases the chemical stability of the metal core. In this contribution, we show for the first time that core-shell nanoparticles having a silver core (both a solid and hollow one) and a shell of zirconium(IV) oxide are very efficient SHINERS nanoresonators that are significantly more stable in acidic and alkaline media than the silver-silica core-shell structures typically used for SHINERS experiments.

Semipermeable Elastic Microcapsules for Gas Capture and Sensing.

PubMed

Nabavi, Seyed Ali; Vladisavljević, Goran T; Gu, Sai; Manović, Vasilije

2016-09-27

Monodispersed microcapsules for gas capture and sensing were developed consisting of elastic semipermeable polymer shells of tunable size and thickness and pH-sensitive, gas selective liquid cores. The microcapsules were produced using glass capillary microfluidics and continuous on-the-fly photopolymerization. The inner fluid was 5-30 wt % K2CO3 solution with m-cresol purple, the middle fluid was a UV-curable liquid silicon rubber containing 0-2 wt % Dow Corning 749 fluid, and the outer fluid was aqueous solution containing 60-70 wt % glycerol and 0.5-2 wt % stabilizer (poly(vinyl alcohol), Tween 20, or Pluronic F-127). An analytical model was developed and validated for prediction of the morphology of the capsules under osmotic stress based on the shell properties and the osmolarity of the storage and core solutions. The minimum energy density and UV light irradiance needed to achieve complete shell polymerization were 2 J·cm(-2) and 13.8 mW·cm(-2), respectively. After UV exposure, the curing time for capsules containing 0.5 wt % Dow Corning 749 fluid in the middle phase was 30-40 min. The CO2 capture capacity of 30 wt % K2CO3 capsules was 1.6-2 mmol/g depending on the capsule size and shell thickness. A cavitation bubble was observed in the core when the internal water was abruptly removed by capillary suction, whereas a gradual evaporation of internal water led to buckling of the shell. The shell was characterized using TGA, DSC, and FTIR. The shell degradation temperature was 450-460 °C.

Titanium dioxide@polypyrrole core-shell nanowires for all solid-state flexible supercapacitors.

PubMed

Yu, Minghao; Zeng, Yinxiang; Zhang, Chong; Lu, Xihong; Zeng, Chenghui; Yao, Chenzhong; Yang, Yangyi; Tong, Yexiang

2013-11-21

Herein, we developed a facile two-step process to synthesize TiO2@PPy core-shell nanowires (NWs) on carbon cloth and reported their improved electrochemical performance for flexible supercapacitors (SCs). The fabricated solid-state SC device based on TiO2@PPy core-shell NWs not only has excellent flexibility, but also exhibits remarkable electrochemical performance.

Lithography-Free Fabrication of Core-Shell GaAs Nanowire Tunnel Diodes.

PubMed

Darbandi, A; Kavanagh, K L; Watkins, S P

2015-08-12

GaAs core-shell p-n junction tunnel diodes were demonstrated by combining vapor-liquid-solid growth with gallium oxide deposition by atomic layer deposition for electrical isolation. The characterization of an ensemble of core-shell structures was enabled by the use of a tungsten probe in a scanning electron microscope without the need for lithographic processing. Radial tunneling transport was observed, exhibiting negative differential resistance behavior with peak-to-valley current ratios of up to 3.1. Peak current densities of up to 2.1 kA/cm(2) point the way to applications in core-shell photovoltaics and tunnel field effect transistors.

Highly selective and sensitive methanol gas sensor based on molecular imprinted silver-doped LaFeO3 core-shell and cage structures

NASA Astrophysics Data System (ADS)

Rong, Qian; Zhang, Yumin; Lv, Tianping; Shen, Kaiyuan; Zi, Baoye; Zhu, Zhongqi; Zhang, Jin; Liu, Qingju

2018-04-01

Silver-doped LaFeO3 molecularly imprinted polymers (SLMIPs) were synthesized by a sol-gel method combined with molecularly imprinted technology as precursors. The precursors were then used to prepare SLMIPs cage (SLM-cage) and SLMIPs core-shell (SLM-core-shell) structures by using a carbon sphere as the template and hydrothermal synthesis, respectively. The structures, morphologies, and surface areas of these materials were determined, as well as their gas-sensing properties and related mechanisms. The SLM-cage and SLM-core-shell samples exhibited good responses to methanol gas, with excellent selectivity. The response and optimum working temperature were 16.98 °C and 215 °C, 33.7 °C and 195 °C, respectively, with corresponding response and recovery times of 45 and 50 s (SLM-cage) and 42 and 57 s (SLM-core-shell) for 5 ppm methanol gas. Notably, the SLM-cage and SLM-core-shell samples exhibited lower responses (≤5 and ≤7, respectively) to other gases, including ethanol, ammonia, benzene, acetone, and toluene. Thus, these materials show potential as practical methanol detectors.

Super-tough, ultra-stretchable and strongly compressive hydrogels with core-shell latex particles inducing efficient aggregation of hydrophobic chains.

PubMed

Ren, Xiuyan; Huang, Chang; Duan, Lijie; Liu, Baijun; Bu, Lvjun; Guan, Shuang; Hou, Jiliang; Zhang, Huixuan; Gao, Guanghui

2017-05-14

Toughness, strechability and compressibility for hydrogels were ordinarily balanced for their use as mechanically responsive materials. For example, macromolecular microsphere composite hydrogels with chemical crosslinking exhibited excellent compression strength and strechability, but poor tensile stress. Here, a novel strategy for the preparation of a super-tough, ultra-stretchable and strongly compressive hydrogel was proposed by introducing core-shell latex particles (LPs) as crosslinking centers for inducing efficient aggregation of hydrophobic chains. The core-shell LPs always maintained a spherical shape due to the presence of a hard core even by an external force and the soft shell could interact with hydrophobic chains due to hydrophobic interactions. As a result, the hydrogels reinforced by core-shell LPs exhibited not only a high tensile strength of 1.8 MPa and dramatic elongation of over 20 times, but also an excellent compressive performance of 13.5 MPa at a strain of 90%. The Mullins effect was verified for the validity of core-shell LP-reinforced hydrogels by inducing aggregation of hydrophobic chains. The novel strategy strives to provide a better avenue for designing and developing a new generation of hydrophobic association tough hydrogels with excellent mechanical properties.

Nonpolar InGaN/GaN Core-Shell Single Nanowire Lasers.

PubMed

Li, Changyi; Wright, Jeremy B; Liu, Sheng; Lu, Ping; Figiel, Jeffrey J; Leung, Benjamin; Chow, Weng W; Brener, Igal; Koleske, Daniel D; Luk, Ting-Shan; Feezell, Daniel F; Brueck, S R J; Wang, George T

2017-02-08

We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core-shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core-shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core-shell nanowires, despite significantly shorter cavity lengths and reduced active region volume. Mode simulations show that due to the core-shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. The results show the viability of this p-i-n nonpolar core-shell nanowire architecture, previously investigated for next-generation light-emitting diodes, as low-threshold, coherent UV-visible nanoscale light emitters, and open a route toward monolithic, integrable, electrically injected single-nanowire lasers operating at room temperature.

Fuel cell performance of palladium-platinum core-shell electrocatalysts synthesized in gram-scale batches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khateeb, Siddique; Su, Dong; Guerreo, Sandra

This article presents the performance of palladium-platinum core-shell catalysts (Pt/Pd/C) for oxygen reduction synthesized in gram-scale batches in both liquid cells and polymer-electrolyte membrane fuel cells. Core-shell catalyst synthesis and characterization, ink fabrication, and cell assembly details are discussed. The Pt mass activity of the Pt/Pd core-shell catalyst was 0.95 A mg –1 at 0.9 V measured in liquid cells (0.1 M HClO4), which was 4.8 times higher than a commercial Pt/C catalyst. The performances of Pt/Pd/C and Pt/C in large single cells (315 cm 2) were assessed under various operating conditions. The core-shell catalyst showed consistently higher performance thanmore » commercial Pt/C in fuel cell testing. A 20–60 mV improvement across the whole current density range was observed on air. Sensitivities to temperature, humidity, and gas composition were also investigated and the core-shell catalyst showed a consistent benefit over Pt under all conditions. However, the 4.8 times activity enhancement predicated by liquid cell measurements was not fully realized in fuel cells.« less

Electrospun core-shell fibers for robust silicon nanoparticle-based lithium ion battery anodes.

PubMed

Hwang, Tae Hoon; Lee, Yong Min; Kong, Byung-Seon; Seo, Jin-Seok; Choi, Jang Wook

2012-02-08

Because of its unprecedented theoretical capacity near 4000 mAh/g, which is approximately 10-fold larger compared to those of the current commercial graphite anodes, silicon has been the most promising anode for lithium ion batteries, particularly targeting large-scale energy storage applications including electrical vehicles and utility grids. Nevertheless, Si suffers from its short cycle life as well as the limitation for scalable electrode fabrication. Herein, we develop an electrospinning process to produce core-shell fiber electrodes using a dual nozzle in a scalable manner. In the core-shell fibers, commercially available nanoparticles in the core are wrapped by the carbon shell. The unique core-shell structure resolves various issues of Si anode operations, such as pulverization, vulnerable contacts between Si and carbon conductors, and an unstable sold-electrolyte interphase, thereby exhibiting outstanding cell performance: a gravimetric capacity as high as 1384 mAh/g, a 5 min discharging rate capability while retaining 721 mAh/g, and cycle life of 300 cycles with almost no capacity loss. The electrospun core-shell one-dimensional fibers suggest a new design principle for robust and scalable lithium battery electrodes suffering from volume expansion. © 2011 American Chemical Society

Template-Free Hydrothermal Synthesis, Mechanism, and Photocatalytic Properties of Core-Shell CeO2 Nanospheres

NASA Astrophysics Data System (ADS)

Li, Huijie; Meng, Fanming; Gong, Jinfeng; Fan, Zhenghua; Qin, Rui

2018-03-01

CeO2 nanospheres with the core-shell nanostructure have been successfully synthesized by a template-free hydrothermal method. The structures, morphologies and optical properties of core-shell CeO2 nanospheres were analyzed by X-ray diffraction (XRD), TG, Fourier transform infrared spectroscopy, XRD, EDS, SAED, scanning electron microscopy and transmission electron microscopy, UV-Vis diffuse reflectance spectra, Raman analyses. The degradation efficiencies of core-shell CeO2 nanospheres for methyl orange were as high as 93.49, 95.67 and 98.28% within 160 min, and the rates of photo degradation of methyl orange by core-shell CeO2 nanospheres under UV-light were 0.01693, 0.01782 and 0.02375 min-1. Methyl orange was degraded in photocatalytic oxidation processes, which mainly gave the credit to a large number of reactive species including h+, surface superoxide species ·O2 -, and ·OH radicals. The core-shell structure, small crystallite size and the conversion between Ce3+ and Ce4+ of CeO2 nanospheres were of importance for its catalytic activity. These results demonstrated the possibility of improving the efficient catalysts of the earth abundant CeO2 catalysts.

The multifunctional wound dressing with core-shell structured fibers prepared by coaxial electrospinning

NASA Astrophysics Data System (ADS)

Wei, Qilin; Xu, Feiyang; Xu, Xingjian; Geng, Xue; Ye, Lin; Zhang, Aiying; Feng, Zengguo

2016-06-01

The non-woven wound dressing with core-shell structured fibers was prepared by coaxial electrospinning. The polycaprolactone (PCL) was electrospun as the fiber's core to provide mechanical strength whereas collagen was fabricated into the shell in order to utilize its good biocompatibility. Simultaneously, the silver nanoparticles (Ag-NPs) as anti-bacterial agent were loaded in the shell whereas the vitamin A palmitate (VA) as healing-promoting drug was encapsulated in the core. Resulting from the fiber's core-shell structure, the VA released from the core and Ag-NPs present in the shell can endow the dressing both heal-promoting and anti-bacteria ability simultaneously, which can greatly enhance the dressing's clinical therapeutic effect. The dressing can maintain high swelling ratio of 190% for 3 d indicating its potential application as wet dressing. Furthermore, the dressing's anti-bacteria ability against Staphylococcus aureus was proved by in vitro anti-bacteria test. The in vitro drug release test showed the sustainable release of VA within 72 h, while the cell attachment showed L929 cells can well attach on the dressing indicating its good biocompatibility. In conclusion, the fabricated nanofibrous dressing possesses multiple functions to benefit wound healing and shows promising potential for clinical application.

Highly selective and sensitive methanol gas sensor based on molecular imprinted silver-doped LaFeO3 core-shell and cage structures.

PubMed

Rong, Qian; Zhang, Yumin; Lv, Tianping; Shen, Kaiyuan; Zi, Baoye; Zhu, Zhongqi; Zhang, Jin; Liu, Qingju

2018-04-06

Silver-doped LaFeO 3 molecularly imprinted polymers (SLMIPs) were synthesized by a sol-gel method combined with molecularly imprinted technology as precursors. The precursors were then used to prepare SLMIPs cage (SLM-cage) and SLMIPs core-shell (SLM-core-shell) structures by using a carbon sphere as the template and hydrothermal synthesis, respectively. The structures, morphologies, and surface areas of these materials were determined, as well as their gas-sensing properties and related mechanisms. The SLM-cage and SLM-core-shell samples exhibited good responses to methanol gas, with excellent selectivity. The response and optimum working temperature were 16.98 °C and 215 °C, 33.7 °C and 195 °C, respectively, with corresponding response and recovery times of 45 and 50 s (SLM-cage) and 42 and 57 s (SLM-core-shell) for 5 ppm methanol gas. Notably, the SLM-cage and SLM-core-shell samples exhibited lower responses (≤5 and ≤7, respectively) to other gases, including ethanol, ammonia, benzene, acetone, and toluene. Thus, these materials show potential as practical methanol detectors.

Fuel cell performance of palladium-platinum core-shell electrocatalysts synthesized in gram-scale batches

DOE PAGES

Khateeb, Siddique; Su, Dong; Guerreo, Sandra; ...

2016-05-03

This article presents the performance of palladium-platinum core-shell catalysts (Pt/Pd/C) for oxygen reduction synthesized in gram-scale batches in both liquid cells and polymer-electrolyte membrane fuel cells. Core-shell catalyst synthesis and characterization, ink fabrication, and cell assembly details are discussed. The Pt mass activity of the Pt/Pd core-shell catalyst was 0.95 A mg –1 at 0.9 V measured in liquid cells (0.1 M HClO4), which was 4.8 times higher than a commercial Pt/C catalyst. The performances of Pt/Pd/C and Pt/C in large single cells (315 cm 2) were assessed under various operating conditions. The core-shell catalyst showed consistently higher performance thanmore » commercial Pt/C in fuel cell testing. A 20–60 mV improvement across the whole current density range was observed on air. Sensitivities to temperature, humidity, and gas composition were also investigated and the core-shell catalyst showed a consistent benefit over Pt under all conditions. However, the 4.8 times activity enhancement predicated by liquid cell measurements was not fully realized in fuel cells.« less

Principles and Methods for the Rational Design of Core-Shell Nanoparticle Catalysts with Ultralow Noble Metal Loadings.

PubMed

Hunt, Sean T; Román-Leshkov, Yuriy

2018-05-15

Conspecuts Commercial and emerging renewable energy technologies are underpinned by precious metal catalysts, which enable the transformation of reactants into useful products. However, the noble metals (NMs) comprise the least abundant elements in the lithosphere, making them prohibitively scarce and expensive for future global-scale technologies. As such, intense research efforts have been devoted to eliminating or substantially reducing the loadings of NMs in various catalytic applications. These efforts have resulted in a plethora of heterogeneous NM catalyst morphologies beyond the traditional supported spherical nanoparticle. In many of these new architectures, such as shaped, high index, and bimetallic particles, less than 20% of the loaded NMs are available to perform catalytic turnovers. The majority of NM atoms are subsurface, providing only a secondary catalytic role through geometric and ligand effects with the active surface NM atoms. A handful of architectures can approach 100% NM utilization, but severe drawbacks limit general applicability. For example, in addition to problems with stability and leaching, single atom and ultrasmall cluster catalysts have extreme metal-support interactions, discretized d-bands, and a lack of adjacent NM surface sites. While monolayer thin films do not possess these features, they exhibit such low surface areas that they are not commercially relevant, serving predominantly as model catalysts. This Account champions core-shell nanoparticles (CS NPs) as a vehicle to design highly active, stable, and low-cost materials with high NM utilization for both thermo- and electrocatalysis. The unique benefits of the many emerging NM architectures could be preserved while their fundamental limitations could be overcome through reformulation via a core-shell morphology. However, the commercial realization of CS NPs remains challenging, requiring concerted advances in theory and manufacturing. We begin by formulating seven constraints governing proper core material design, which naturally point to early transition metal ceramics as suitable core candidates. Two constraints prove extremely challenging. The first relates to the core modifying the shell work function and d-band. To properly investigate materials that could satisfy this constraint, we discuss our development of a new heat, quench, and exfoliation (HQE) density functional theory (DFT) technique to model heterometallic interfaces. This technique is used to predict how transition metal carbides can favorably tune the catalytic properties of various NM monolayer shell configurations. The second challenging constraint relates to the scalable manufacturing of CS NP architectures with independent synthetic control of the thickness and composition of the shell and the size and composition of the core. We discuss our development of a synthetic method that enables high temperature self-assembly of tunable CS NP configurations. Finally, we discuss how these principles and methods were used to design catalysts for a variety of applications. These include the design of a thermally stable sub-monolayer CS catalyst, a highly active methanol electrooxidation catalyst, CO-tolerant Pt catalysts, and a hydrogen evolution catalyst that is less expensive than state-of-the-art NM-free catalysts. Such core-shell architectures offer the promise of ultralow precious metal loadings while ceramic cores hold the promise of thermodynamic stability and access to unique catalytic activity/tunability.

Synthesis, characterization and evaluation of uniformly sized core-shell imprinted microspheres for the separation trans-resveratrol from giant knotweed

NASA Astrophysics Data System (ADS)

Zhang, Zhaohui; Liu, Li; Li, Hui; Yao, Shouzhuo

2009-09-01

A novel core-shell molecularly imprinting microspheres (MIMs) with trans-resveratrol as the template molecule; acrylamide (AA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as cross-linker, was prepared based on SiO 2 microspheres with surface imprinting technique. These core-shell trans-resveratrol imprinted microspheres were characterized by infrared spectra (IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and high performance liquid chromatography (HPLC). The results showed that these core-shell imprinted microspheres, which take on perfect spherical shape with average shell thickness of 150 nm, exhibit especially selective recognition for trans-resveratrol. These imprinted microspheres were applied as solid-phase extraction materials for selective extraction of trans-resveratrol from giant knotweed extracting solution successfully.

Quantum Monte Carlo simulation of the ferroelectric or ferrielectric nanowire with core shell morphology

NASA Astrophysics Data System (ADS)

Feraoun, A.; Zaim, A.; Kerouad, M.

2016-09-01

By using the Quantum Monte Carlo simulation; the electric properties of a nanowire, consisting of a ferroelectric core of spin-1/2 surrounded by a ferroelectric shell of spin-1/2 with ferro- or anti-ferroelectric interfacial coupling have been studied within the framework of the Transverse Ising Model (TIM). We have examined the effects of the shell coupling Js, the interfacial coupling JInt, the transverse field Ω, and the temperature T on the hysteresis behavior and on the electric properties of the system. The remanent polarization and the coercive field as a function of the transverse field and the temperature are examined. A number of characteristic behavior have been found such as the appearance of triple hysteresis loops for appropriate values of the system parameters.

Morphology and electronic structure of the oxide shell on the surface of iron nanoparticles.

PubMed

Wang, Chongmin; Baer, Donald R; Amonette, James E; Engelhard, Mark H; Antony, Jiji; Qiang, You

2009-07-01

An iron (Fe) nanoparticle exposed to air at room temperature will be instantly covered by an oxide shell that is typically approximately 3 nm thick. The nature of this native oxide shell, in combination with the underlying Fe(0) core, determines the physical and chemical behavior of the core-shell nanoparticle. One of the challenges of characterizing core-shell nanoparticles is determining the structure of the oxide shell, that is, whether it is FeO, Fe(3)O(4), gamma-Fe(2)O(3), alpha-Fe(2)O(3), or something else. The results of prior characterization efforts, which have mostly used X-ray diffraction and spectroscopy, electron diffraction, and transmission electron microscopic imaging, have been framed in terms of one of the known Fe-oxide structures, although it is not necessarily true that the thin layer of Fe oxide is a known Fe oxide. In this Article, we probe the structure of the oxide shell on Fe nanoparticles using electron energy loss spectroscopy (EELS) at the oxygen (O) K-edge with a spatial resolution of several nanometers (i.e., less than that of an individual particle). We studied two types of representative particles: small particles that are fully oxidized (no Fe(0) core) and larger core-shell particles that possess an Fe core. We found that O K-edge spectra collected for the oxide shell in nanoparticles show distinct differences from those of known Fe oxides. Typically, the prepeak of the spectra collected on both the core-shell and the fully oxidized particles is weaker than that collected on standard Fe(3)O(4). Given the fact that the origin of this prepeak corresponds to the transition of the O 1s electron to the unoccupied state of O 2p hybridized with Fe 3d, a weak pre-edge peak indicates a combination of the following four factors: a higher degree of occupancy of the Fe 3d orbital; a longer Fe-O bond length; a decreased covalency of the Fe-O bond; and a measure of cation vacancies. These results suggest that the coordination configuration in the oxide shell on Fe nanoparticles is defective as compared to that of their bulk counterparts. Implications of these defective structural characteristics on the properties of core-shell structured iron nanoparticles are discussed.

Electrical breakdown and nanogap formation of indium oxide core/shell heterostructure nanowires.

PubMed

Jung, Minkyung; Song, Woon; Sung Lee, Joon; Kim, Nam; Kim, Jinhee; Park, Jeunghee; Lee, Hyoyoung; Hirakawa, Kazuhiko

2008-12-10

We report the electrical breakdown behavior and subsequent nanogap formation of In(2)O(3)/InO(x) core/shell heterostructure nanowires with substrate-supported and suspended structures. The radial heterostructure nanowires, composed of crystalline In(2)O(3) cores and amorphous In-rich shells, are grown by chemical vapor deposition. As the nanowires broke down, they exhibited two distinct current drops in the current-voltage characteristics. The tips of the broken nanowires were found to have a cone or a volcano shape depending on the width of the nanowire. The shape, the size, and the position of the nanogap depend strongly on the device structure and the nanowire dimensions. The substrate-supported and the suspended devices exhibit distinct breakdown behavior which can be explained by the diffusive thermal transport model. The breakdown temperature of the nanowire is estimated to be about 450 K, close to the melting temperature of indium. We demonstrated the usefulness of this technique by successful fabrication of working pentacene field-effect transistors.

Self-assembled core-shell nanoparticles for combined chemotherapy and photodynamic therapy of resistant head and neck cancers.

PubMed

He, Chunbai; Liu, Demin; Lin, Wenbin

2015-01-27

Combination therapy enhances anticancer efficacy of both drugs via synergistic effects. We report here nanoscale coordination polymer (NCP)-based core-shell nanoparticles carrying high payloads of cisplatin and the photosensitizer pyrolipid, NCP@pyrolipid, for combined chemotherapy and photodynamic therapy (PDT). NCP@pyrolipid releases cisplatin and pyrolipid in a triggered manner to synergistically induce cancer cell apoptosis and necrosis. In vivo pharmacokinetic and biodistribution studies in mice show prolonged blood circulation times, low uptake in normal organs, and high tumor accumulation of cisplatin and pyrolipid. Compared to monotherapy, NCP@pyrolipid shows superior potency and efficacy in tumor regression (83% reduction in tumor volume) at low drug doses in the cisplatin-resistant human head and neck cancer SQ20B xenograft murine model. We elucidated the in vitro/vivo fate of the lipid layer and its implications on the mechanisms of actions. This study suggests multifunctional NCP core-shell nanoparticles as a versatile and effective drug delivery system for potential translation to the clinic.

Tailored Core Shell Cathode Powders for Solid Oxide Fuel Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swartz, Scott

2015-03-23

In this Phase I SBIR project, a “core-shell” composite cathode approach was evaluated for improving SOFC performance and reducing degradation of lanthanum strontium cobalt ferrite (LSCF) cathode materials, following previous successful demonstrations of infiltration approaches for achieving the same goals. The intent was to establish core-shell cathode powders that enabled high performance to be obtained with “drop-in” process capability for SOFC manufacturing (i.e., rather than adding an infiltration step to the SOFC manufacturing process). Milling, precipitation and hetero-coagulation methods were evaluated for making core-shell composite cathode powders comprised of coarse LSCF “core” particles and nanoscale “shell” particles of lanthanum strontiummore » manganite (LSM) or praseodymium strontium manganite (PSM). Precipitation and hetero-coagulation methods were successful for obtaining the targeted core-shell morphology, although perfect coverage of the LSCF core particles by the LSM and PSM particles was not obtained. Electrochemical characterization of core-shell cathode powders and conventional (baseline) cathode powders was performed via electrochemical impedance spectroscopy (EIS) half-cell measurements and single-cell SOFC testing. Reliable EIS testing methods were established, which enabled comparative area-specific resistance measurements to be obtained. A single-cell SOFC testing approach also was established that enabled cathode resistance to be separated from overall cell resistance, and for cathode degradation to be separated from overall cell degradation. The results of these EIS and SOFC tests conclusively determined that the core-shell cathode powders resulted in significant lowering of performance, compared to the baseline cathodes. Based on the results of this project, it was concluded that the core-shell cathode approach did not warrant further investigation.« less

Tunable luminescent emission characterization of type-I and type-II systems in CdS-ZnSe core-shell nanoparticles: Raman and photoluminescence study.

PubMed

Ca, Nguyen Xuan; Lien, V T K; Nghia, N X; Chi, T T K; Phan, The-Long

2015-11-06

We used wet chemical methods to synthesize core-shell nanocrystalline samples CdS(d)/ZnSe N , where d = 3-6 nm and N = 1-5 are the size of CdS cores and the number of monolayers grown on the cores, respectively. By annealing typical CdS(d)/ZnSe N samples (with d = 3 and 6 nm and N = 2) at 300 °C for various times t an = 10-600 min, we created an intermediate layer composed of Zn1-x Cd x Se and Cd1-x Zn x S alloys with various thicknesses. The formation of core-shell structures and intermediate layers was monitored by Raman scattering and UV-vis absorption spectrometers. Careful photoluminescence studies revealed that the as-prepared CdS(d)/ZnSe N samples with d = 5 nm and N = 2-4, and the annealed samples CdS(3 nm)/ZnSe2 with t an ≤ 60 min and CdS(6 nm)/ZnSe2 with t an ≤ 180 min, show the emission characteristics of type-II systems. Meanwhile, the other samples show the emission characteristics of type-I systems. These results prove that the partial separation of photoexcited carriers between the core and shell is dependent strongly on the engineered core-shell nanostructures, meaning the sizes of the core, shell, and intermediate layers. With the tunable luminescence properties, CdS-ZnSe-based core-shell materials are considered as promising candidates for multiple-exciton generation and single-photon sources.

Core-shell hydrogel beads with extracellular matrix for tumor spheroid formation.

PubMed

Yu, L; Grist, S M; Nasseri, S S; Cheng, E; Hwang, Y-C E; Ni, C; Cheung, K C

2015-03-01

Creating multicellular tumor spheroids is critical for characterizing anticancer treatments since they may provide a better model of the tumor than conventional monolayer culture. Moreover, tumor cell interaction with the extracellular matrix can determine cell organization and behavior. In this work, a microfluidic system was used to form cell-laden core-shell beads which incorporate elements of the extracellular matrix and support the formation of multicellular spheroids. The bead core (comprising a mixture of alginate, collagen, and reconstituted basement membrane, with gelation by temperature control) and shell (comprising alginate hydrogel, with gelation by ionic crosslinking) were simultaneously formed through flow focusing using a cooled flow path into the microfluidic chip. During droplet gelation, the alginate acts as a fast-gelling shell which aids in preventing droplet coalescence and in maintaining spherical droplet geometry during the slower gelation of the collagen and reconstituted basement membrane components as the beads warm up. After droplet gelation, the encapsulated MCF-7 cells proliferated to form uniform spheroids when the beads contained all three components: alginate, collagen, and reconstituted basement membrane. The dose-dependent response of the MCF-7 cell tumor spheroids to two anticancer drugs, docetaxel and tamoxifen, was compared to conventional monolayer culture.

All-oxide Raman-active traps for light and matter: probing redox homeostasis model reactions in aqueous environment.

PubMed

Alessandri, Ivano; Depero, L E

2014-04-09

Core-shell colloidal crystals can act as very efficient traps for light and analytes. Here it is shown that Raman-active probes can be achieved using SiO2-TiO2 core-shell beads. These systems are successfully tested in monitoring of glutathione redox cycle at physiological concentration in aqueous environment, without need of any interfering enhancers. These materials represent a promising alternative to conventional, metal-based SERS probes for investigating chemical and biochemical reactions under real working conditions. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Plateau-Rayleigh Crystal Growth of Nanowire Heterostructures: Strain-Modified Surface Chemistry and Morphological Control in One, Two, and Three Dimensions.

PubMed

Day, Robert W; Mankin, Max N; Lieber, Charles M

2016-04-13

One-dimensional (1D) structures offer unique opportunities for materials synthesis since crystal phases and morphologies that are difficult or impossible to achieve in macroscopic crystals can be synthesized as 1D nanowires (NWs). Recently, we demonstrated one such phenomenon unique to growth on a 1D substrate, termed Plateau-Rayleigh (P-R) crystal growth, where periodic shells develop along a NW core to form diameter-modulated NW homostructures with tunable morphologies. Here we report a novel extension of the P-R crystal growth concept with the synthesis of heterostructures in which Ge (Si) is deposited on Si (Ge) 1D cores to generate complex NW morphologies in 1, 2, or 3D. Depositing Ge on 50 nm Si cores with a constant GeH4 pressure yields a single set of periodic shells, while sequential variation of GeH4 pressure can yield multimodulated 1D NWs with two distinct sets of shell periodicities. P-R crystal growth on 30 nm cores also produces 2D loop structures, where Ge (Si) shells lie primarily on the outside (inside) of a highly curved Si (Ge) core. Systematic investigation of shell morphology as a function of growth time indicates that Ge shells grow in length along positive curvature Si cores faster than along straight Si cores by an order of magnitude. Short Ge deposition times reveal that shells develop on opposite sides of 50 and 100 nm Si cores to form straight 1D morphologies but that shells develop on the same side of 20 nm cores to produce 2D loop and 3D spring structures. These results suggest that strain mediates the formation of 2 and 3D morphologies by altering the NW's surface chemistry and that surface diffusion of heteroatoms on flexible freestanding 1D substrates can facilitate this strain-mediated mechanism.

Structural transformation and photoluminescence modification of AgInS2 nanoparticles induced by ZnS shell formation

NASA Astrophysics Data System (ADS)

Hamanaka, Yasushi; Yukitoki, Daichi; Kuzuya, Toshihiro

2015-09-01

AgInS2 nanoparticles were capped by ZnS via a widely used procedure to fabricate core/shell nanoparticles with highly efficient luminescence. The nanoparticle structures were investigated by ultrahigh-resolution analytical electron microscopy. We found that Zn-Ag-In-S nanoparticles were created by ZnS capping at ˜480 K, which suggests that the luminescence enhancement reported for such core/shell nanoparticles is not caused by the passivation of surface defects by ZnS shells but by Zn doping. Quasi-core/shell nanoparticles could be obtained by ZnS capping without heating. However, their luminescence efficiency remained unchanged, indicating that surface passivation was ineffective when ZnS shells were formed at room temperature.

Monte Carlo simulation of dynamic phase transitions and frequency dispersions of hysteresis curves in core/shell ferrimagnetic cubic nanoparticle

NASA Astrophysics Data System (ADS)

Vatansever, Erol

2017-05-01

By means of Monte Carlo simulation method with Metropolis algorithm, we elucidate the thermal and magnetic phase transition behaviors of a ferrimagnetic core/shell nanocubic system driven by a time dependent magnetic field. The particle core is composed of ferromagnetic spins, and it is surrounded by an antiferromagnetic shell. At the interface of the core/shell particle, we use antiferromagnetic spin-spin coupling. We simulate the nanoparticle using classical Heisenberg spins. After a detailed analysis, our Monte Carlo simulation results suggest that present system exhibits unusual and interesting magnetic behaviors. For example, at the relatively lower temperature regions, an increment in the amplitude of the external field destroys the antiferromagnetism in the shell part of the nanoparticle, leading to a ground state with ferromagnetic character. Moreover, particular attention has been dedicated to the hysteresis behaviors of the system. For the first time, we show that frequency dispersions can be categorized into three groups for a fixed temperature for finite core/shell systems, as in the case of the conventional bulk systems under the influence of an oscillating magnetic field.

Chalcone dendrimer stabilized core-shell nanoparticles—a comparative study on Co@TiO2, Ag@TiO2 and Co@AgCl nanoparticles for antibacterial and antifungal activity

NASA Astrophysics Data System (ADS)

Vanathi Vijayalakshmi, R.; Praveen Kumar, P.; Selvarani, S.; Rajakumar, P.; Ravichandran, K.

2017-10-01

A series of core@shell nanoparticles (Co@TiO2, Ag@TiO2 and Co@AgCl) stabilized with zeroth generation triazolylchalcone dendrimer was synthesized using reduction transmetalation method. The coordination of chalcone dendrimer with silver ions was confirmed by UV-vis spectroscopy. The NMR spectrum ensures the number of protons and carbon signals in the chalcone dendrimer. The prepared samples were structurally characterized by XRD, FESEM and HRTEM analysis. The SAED and XRD analyses exhibited the cubic structure with d hkl   =  2.2 Å, 1.9 Å and 1.38 Å. The antibacterial and antifungal activities of the dendrimer stabilized core@shell nanoparticles (DSCSNPs) were tested against the pathogens Bacillus subtilis, Proteus mirabilis, Candida albicans and Aspergillus nigir from which it is identified that the dendrimer stabilized core shell nanoparticles with silver ions at the shell (Co@AgCl) shows effectively high activity against the tested pathogen following the other core@shell nanoparticles viz Ag@TiO2 and Co@TiO2.

Dye-sensitized solar cells employing a SnO2-TiO2 core-shell structure made by atomic layer deposition.

PubMed

Karlsson, Martin; Jõgi, Indrek; Eriksson, Susanna K; Rensmo, Håkan; Boman, Mats; Boschloo, Gerrit; Hagfeldt, Anders

2013-01-01

This paper describes the synthesis and characterization of core-shell structures, based on SnO2 and TiO2, for use in dye-sensitized solar cells (DSC). Atomic layer deposition is employed to control and vary the thickness of the TiO2 shell. Increasing the TiO2 shell thickness to 2 nm improved the device performance of liquid electrolyte-based DSC from 0.7% to 3.5%. The increase in efficiency originates from a higher open-circuit potential and a higher short-circuit current, as well as from an improvement in the electron lifetime. SnO2-TiO2 core-shell DSC devices retain their photovoltage in darkness for longer than 500 seconds, demonstrating that the electrons are contained in the core material. Finally core-shell structures were used for solid-state DSC applications using the hole transporting material 2,2',7,7',-tetrakis(N, N-di-p-methoxyphenyl-amine)-9,9',-spirofluorene. Similar improvements in device performance were obtained for solid-state DSC devices.

Thermoresponsive Cellulose Acetate-Poly(N-isopropylacrylamide) Core-Shell Fibers for Controlled Capture and Release of Moisture.

PubMed

Thakur, Neha; Sargur Ranganath, Anupama; Sopiha, Kostiantyn; Baji, Avinash

2017-08-30

In this study, we used core-shell electrospinning to fabricate cellulose acetate-poly(N-isopropylacrylamide) (CA-PNIPAM) fibrous membranes and demonstrated the ability of these fibers to capture water from a high humid atmosphere and release it when thermally stimulated. The wettability of the fibers was controlled by using thermoresponsive PNIPAM as the shell layer. Scanning electron and fluorescence microscopes are used to investigate the microstructure of the fibers and confirm the presence of the core and shell phases within the fibers. The moisture capturing and releasing ability of these core-shell CA-PNIPAM fibers was compared with those of the neat CA and neat PNIPAM fibers at room temperature as well as at an elevated temperature. At room temperature, the CA-PNIPAM core-shell fibers are shown to have the maximum moisture uptake capacity among the three samples. The external temperature variations which trigger the moisture response behavior of these CA-PNIPAM fibers fall within the range of typical day and night cycles of deserts, demonstrating the potential use of these fibers for water harvesting applications.

Theoretical Studies of Nanocluster Formation

DTIC Science & Technology

2016-05-26

background, technical approach 2. Core-shell nanoclusters (Mg/Cu, Si/Al, etc.) - energetic additives for propellants , explosives - gas generators...shell nanocluster synthesis Core-shell nanoclusters such as SiAln, NinAlm, Aln(CuO)m, etc. may be useful ingredients in propellants and explosives

Multifunctional Au-Fe3O4@MOF core-shell nanocomposite catalysts with controllable reactivity and magnetic recyclability

NASA Astrophysics Data System (ADS)

Ke, Fei; Wang, Luhuan; Zhu, Junfa

2014-12-01

The recovery and reuse of expensive catalysts are important in both heterogeneous and homogeneous catalysis due to economic and environmental reasons. This work reports a novel multifunctional magnetic core-shell gold catalyst which can be easily prepared and shows remarkable catalytic properties in the reduction of 4-nitrophenol. The novel Au-Fe3O4@metal-organic framework (MOF) catalyst consists of a superparamagnetic Au-Fe3O4 core and a porous MOF shell with controllable thickness. Small Au nanoparticles (NPs) of 3-5 nm are mainly sandwiched between the Fe3O4 core and the porous MOF shell. Catalytic studies show that the core-shell structured Au-Fe3O4@MOF catalyst has a much higher catalytic activity than other reported Au-based catalysts toward the reduction of 4-nitrophenol. Moreover, this catalyst can be easily recycled due to the presence of the superparamagnetic core. Therefore, compared to conventional catalysts used in the reduction of 4-nitrophenol, this porous MOF-based magnetic catalyst is green, cheap and promising for industrial applications.The recovery and reuse of expensive catalysts are important in both heterogeneous and homogeneous catalysis due to economic and environmental reasons. This work reports a novel multifunctional magnetic core-shell gold catalyst which can be easily prepared and shows remarkable catalytic properties in the reduction of 4-nitrophenol. The novel Au-Fe3O4@metal-organic framework (MOF) catalyst consists of a superparamagnetic Au-Fe3O4 core and a porous MOF shell with controllable thickness. Small Au nanoparticles (NPs) of 3-5 nm are mainly sandwiched between the Fe3O4 core and the porous MOF shell. Catalytic studies show that the core-shell structured Au-Fe3O4@MOF catalyst has a much higher catalytic activity than other reported Au-based catalysts toward the reduction of 4-nitrophenol. Moreover, this catalyst can be easily recycled due to the presence of the superparamagnetic core. Therefore, compared to conventional catalysts used in the reduction of 4-nitrophenol, this porous MOF-based magnetic catalyst is green, cheap and promising for industrial applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05421k

Ab initio results for intermediate-mass, open-shell nuclei

NASA Astrophysics Data System (ADS)

Baker, Robert B.; Dytrych, Tomas; Launey, Kristina D.; Draayer, Jerry P.

2017-01-01

A theoretical understanding of nuclei in the intermediate-mass region is vital to astrophysical models, especially for nucleosynthesis. Here, we employ the ab initio symmetry-adapted no-core shell model (SA-NCSM) in an effort to push first-principle calculations across the sd-shell region. The ab initio SA-NCSM's advantages come from its ability to control the growth of model spaces by including only physically relevant subspaces, which allows us to explore ultra-large model spaces beyond the reach of other methods. We report on calculations for 19Ne and 20Ne up through 13 harmonic oscillator shells using realistic interactions and discuss the underlying structure as well as implications for various astrophysical reactions. This work was supported by the U.S. NSF (OCI-0904874 and ACI -1516338) and the U.S. DOE (DE-SC0005248), and also benefitted from the Blue Waters sustained-petascale computing project and high performance computing resources provided by LSU.

Optical absorption of carbon-gold core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Wang, Zhaolong; Quan, Xiaojun; Zhang, Zhuomin; Cheng, Ping

2018-01-01

In order to enhance the solar thermal energy conversion efficiency, we propose to use carbon-gold core-shell nanoparticles dispersed in liquid water. This work demonstrates theoretically that an absorbing carbon (C) core enclosed in a plasmonic gold (Au) nanoshell can enhance the absorption peak while broadening the absorption band; giving rise to a much higher solar absorption than most previously studied core-shell combinations. The exact Mie solution is used to evaluate the absorption efficiency factor of spherical nanoparticles in the wavelength region from 300 nm to 1100 nm as well as the electric field and power dissipation profiles inside the nanoparticles at specified wavelengths (mostly at the localized surface plasmon resonance wavelength). The field enhancement by the localized plasmons at the gold surfaces boosts the absorption of the carbon particle, resulting in a redshift of the absorption peak with increased peak height and bandwidth. In addition to spherical nanoparticles, we use the finite-difference time-domain method to calculate the absorption of cubic core-shell nanoparticles. Even stronger enhancement can be achieved with cubic C-Au core-shell structures due to the localized plasmonic resonances at the sharp edges of the Au shell. The solar absorption efficiency factor can exceed 1.5 in the spherical case and reach 2.3 in the cubic case with a shell thickness of 10 nm. Such broadband absorption enhancement is in great demand for solar thermal applications including steam generation.

Synthesis and controllable oxidation of monodisperse cobalt-doped wüstite nanoparticles and their core-shell stability and exchange-bias stabilization.

PubMed

Chen, Chih-Jung; Chiang, Ray-Kuang; Kamali, Saeed; Wang, Sue-Lein

2015-09-14

Cobalt-doped wüstite (CWT), Co0.33Fe0.67O, nanoparticles were prepared via the thermal decomposition of CoFe2-oleate complexes in organic solvents. A controllable oxidation process was then performed to obtain Co0.33Fe0.67O/CoFe2O4 core-shell structures with different core-to-shell volume ratios and exchange bias properties. The oxidized core-shell samples with a ∼4 nm CoFe2O4 shell showed good resistance to oxygen transmission. Thus, it is inferred that the cobalt ferrite shell provides a better oxidation barrier performance than magnetite in the un-doped case. The hysteresis loops of the oxidized 19 nm samples exhibited a high exchange bias field (H(E)), an enhanced coercivity field (H(C)), and a pronounced vertical shift, thus indicating the presence of a strong exchange bias coupling effect. More importantly, the onset temperature of H(E) was found to be higher than 200 K, which suggests that cobalt doping increases the Néel temperature (T(N)) of the CWT core. In general, the results show that the homogeneous dispersion of Co in iron precursors improves the stability of the final CWT nanoparticles. Moreover, the CoFe2O4 shells formed following oxidation increase the oxidation resistance of the CWT cores and enhance their anisotropy energy.

Modelling the optical properties of aerosols in a chemical transport model

NASA Astrophysics Data System (ADS)

Andersson, E.; Kahnert, M.

2015-12-01

According to the IPCC fifth assessment report (2013), clouds and aerosols still contribute to the largest uncertainty when estimating and interpreting changes to the Earth's energy budget. Therefore, understanding the interaction between radiation and aerosols is both crucial for remote sensing observations and modelling the climate forcing arising from aerosols. Carbon particles are the largest contributor to the aerosol absorption of solar radiation, thereby enhancing the warming of the planet. Modelling the radiative properties of carbon particles is a hard task and involves many uncertainties arising from the difficulties of accounting for the morphologies and heterogeneous chemical composition of the particles. This study aims to compare two ways of modelling the optical properties of aerosols simulated by a chemical transport model. The first method models particle optical properties as homogeneous spheres and are externally mixed. This is a simple model that is particularly easy to use in data assimilation methods, since the optics model is linear. The second method involves a core-shell internal mixture of soot, where sulphate, nitrate, ammonia, organic carbon, sea salt, and water are contained in the shell. However, by contrast to previously used core-shell models, only part of the carbon is concentrated in the core, while the remaining part is homogeneously mixed with the shell. The chemical transport model (CTM) simulations are done regionally over Europe with the Multiple-scale Atmospheric Transport and CHemistry (MATCH) model, developed by the Swedish Meteorological and Hydrological Institute (SMHI). The MATCH model was run with both an aerosol dynamics module, called SALSA, and with a regular "bulk" approach, i.e., a mass transport model without aerosol dynamics. Two events from 2007 are used in the analysis, one with high (22/12-2007) and one with low (22/6-2007) levels of elemental carbon (EC) over Europe. The results of the study help to assess the significance of aerosol morphology for modelling radiative forcing and aerosol optical properties relevant to interpreting remote sensing observations. The uncertainties introduced by the optics model are gauged by comparing them to model uncertainties related to the inclusion or omission of aerosol dynamic processes.

Irradiation effect of low-energy ion on polyurethane nanocoating containing metal oxide nanoparticles

NASA Astrophysics Data System (ADS)

Verma, Jaya; Nigam, Subhasha; Sinha, Surbhi; Sikarwar, B. S.; Bhattacharya, Arpita

2017-12-01

Irradiation effect of low-energy ion beam has been investigated on nanocoating developed with silica, titania and silica-titania core-shell nanoparticles embedded in an organic binder for nanopaint application. In this work, we have taken polyurethane as a model organic binder. Silica nanoparticles have been prepared through sol-gel synthesis with a particle size of 85 nm. Titania and core-shell nanoparticles have been prepared through both sol-gel and peptization process. Particle sizes obtained were 107 nm for titania and 240 nm for core-shell nanoparticles prepared through sol-gel process and 75 nm for TiO2 and 144 nm for core-shell nanoparticles prepared through peptization process. The coating formulations were developed with the above nanoparticles individually and nanoparticle concentration was varied from 1 to 6 wt% and the best performance in terms of hydrophobicity was obtained with 4 wt % of the nanoparticles in polyurethane coating formulation. All the coating formulations prepared were applied on a glass substrate and dried at 100°C. The dry film thickness obtained was around 100 µm in each case. These films dried on glass substrate were irradiated by nitrogen and argon ion beam with energy of 26 keV at fluences of 1014 to 1016 ions/cm2. The anti-algal property of the irradiated samples was improved and hydrophobicity was reduced.

On the time-variable nature of Titan's obliquity

NASA Astrophysics Data System (ADS)

Noyelles, Benoit; Nimmo, Francis

2014-05-01

Titan presents an unexpectedly high obliquity (Stiles et al. 2008, Meriggiola & Iess 2012) while its topography and gravity suggest a non-hydrostatic ice shell (Hemingway et al. 2013). We here present a 6-dof model of the rotation of Titan simultaneously simulating the full orientation of the shell and the inner core, and considering a global subsurface ocean with a partially-compensated shell of spatially-variable thickness. Between 10 and 13% of our realistic interior models induce a resonance with the annual forcing, that dramatically raises the obliquity. The relevant model Titans are composed of a 130-140 km thick shell floating on a ~250 km thick ocean. The observed obliquity should not be considered as a mean one but as an instantaneous one, that should vary by ~7 arcmin over the duration of the Cassini mission.

CdSe/AsS core-shell quantum dots: preparation and two-photon fluorescence.

PubMed

Wang, Junzhong; Lin, Ming; Yan, Yongli; Wang, Zhe; Ho, Paul C; Loh, Kian Ping

2009-08-19

Arsenic(II) sulfide (AsS)-coated CdSe core-shell nanocrystals can be prepared by a cluster-complex deposition approach under mild conditions. At 60 degrees C, growth of an AsS shell onto a CdSe nanocrystal can be realized through the crystallization of a cluster complex of AsS/butylamine in a mixed solvent of isopropanol/chloroform. The new, type I core-shell nanocrystal exhibits markedly enhanced one-photon fluorescence as well two-photon upconversion fluorescence. The nanocrystals can be used for infrared-excited upconversion cellular labeling.

Production of silver-silica core-shell nanocomposites using ultra-short pulsed laser ablation in nanoporous aqueous silica colloidal solutions

NASA Astrophysics Data System (ADS)

Santagata, A.; Guarnaccio, A.; Pietrangeli, D.; Szegedi, Á.; Valyon, J.; De Stefanis, A.; De Bonis, A.; Teghil, R.; Sansone, M.; Mollica, D.; Parisi, G. P.

2015-05-01

Ultra-short pulsed laser ablation of materials in liquid has been demonstrated to be a versatile technique for nanoparticles production. In a previous paper, it has been described, for the first time, how by laser ablation in a liquid system, silver nanoparticles can be loaded onto SBA-15 and MCM-41 supports which show promising catalytic properties for the oxidation of Volatile Organic Compounds (VOCs). The aim of the present research is to demonstrate the formation of stable silver-silica core-shell nanoparticles by direct laser ablation (Ti:Sa; 800 nm pulse duration: 120 fs repetition rate: 1 kHz, pulse energy: 3.6 mJ, fluence: 9 J cm  -  2) of a Ag target submerged in a static colloidal solution of MCM-41 or SBA-15 silica nanoporous materials. In previous studies, it was discovered that a side and negligible product of the laser ablation process of silver performed in water-silica systems, could be related to the formation of silver-silica core-shell nanoparticles. In order to emphasize this side process some modifications to the laser ablation experimental set-up were performed. Among these, the most important one, in order to favor the production of the core-shell systems, was to keep the liquid silica suspension firm. The laser generated nanomaterials were then analyzed using TEM morphologic characterization. By UV-vis absorption spectra the observed features have been related to components of the colloidal solution as well as to the number of the incident laser pulses. In this manner characterizations on both the process and the resulting suspension have been performed. Significant amount of small sized silver-silica core-shell nanoparticles have been detected in the studied systems. The size distribution, polydispersivity, UV-vis plasmonic bands and stability of the produced silver-silica core-shell nanocomposites have been related to the extent of damage induced in the nanoporous silica structure during the ablation procedure adopted here. In presence of SBA-15 the silver-silica core-shell nanoparticles observed by TEM are smaller and more homogeneously dispersed if compared with the core-shell system obtained when the MCM-41 mesoporous silica was used. The outcomes show that the choice of the mesoporous silica material can affect the silica shell thickness in addition to the Ag NPs size distribution. With this regard, TEM images evidence that in MCM-41 the silver-silica core-shell nanostructures display a silica layer thickness between 1-10 nm conversely, for SBA-15, the silver-silica core-shell nanoparticles are finely dispersed and the silica shell shows, when present, an average thickness of about 5 nm.

Continuum and three-nucleon force effects on Be 9 energy levels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Langhammer, Joachim; Navrátil, Petr; Quaglioni, Sofia

2015-02-05

In this paper, we extend the recently proposed ab initio no-core shell model with continuum to include three-nucleon (3N) interactions beyond the few-body domain. The extended approach allows for the assessment of effects of continuum degrees of freedom as well as of the 3N force in ab initio calculations of structure and reaction observables of p- and lower-sd-shell nuclei. As a first application we concentrate on energy levels of the 9Be system for which all excited states lie above the n- 8Be threshold. For all energy levels, the inclusion of the continuum significantly improves the agreement with experiment, which wasmore » an issue in standard no-core shell model calculations. Furthermore, we find the proper treatment of the continuum indispensable for reliable statements about the quality of the adopted 3N interaction from chiral effective field theory. Finally, in particular, we find the 1/2 + resonance energy, which is of astrophysical interest, in good agreement with experiment.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang Shumin; Tian Hongwei; Pei Yanhui

A novel hedgehog-like core/shell structure, consisting of a high density of vertically aligned graphene sheets and a thin graphene shell/a copper core (VGs-GS/CC), has been synthesized via a simple one-step synthesis route using radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD). Scanning and transmission electron microscopy investigations show that the morphology of this core/shell material could be controlled by deposition time. For a short deposition time, only multilayer graphene shell tightly surrounds the copper particle, while as the deposition time is relative long, graphene sheets extend from the surface of GS/CC. The GS can protect CC particles from oxidation. The growth mechanismmore » for the obtained GS/CC and VGs-GS/CC has been revealed. Compared to VGs, VGs-GS/CC material exhibits a better electron field emission property. This investigation opens a possibility for designing a core/shell structure of different carbon-metal hybrid materials for a wide variety of practical applications. - Graphical abstract: With increasing deposition time, graphene sheets extend from the surface of GS/CC, causing the multilayer graphene encapsulated copper to be converted into vertically aligned graphene sheets-graphene shell/copper core structure. Highlights: Black-Right-Pointing-Pointer A novel hedgehog-like core/shell structure has been synthesized. Black-Right-Pointing-Pointer The structure consists of vertical graphene sheets-graphene shell and copper core. Black-Right-Pointing-Pointer The morphology of VGs-GS/CC can be controlled by choosing a proper deposition time. Black-Right-Pointing-Pointer With increasing deposition time, graphene sheets extend from the surface of GS/CC. Black-Right-Pointing-Pointer VGs-GS/CC exhibits a better electron field emission property as compared with VGs.« less

Polystyrene Core-Silica Shell Particles with Defined Nanoarchitectures as a Versatile Platform for Suspension Array Technology.

PubMed

Sarma, Dominik; Gawlitza, Kornelia; Rurack, Knut

2016-04-19

The need for rapid and high-throughput screening in analytical laboratories has led to significant growth in interest in suspension array technologies (SATs), especially with regard to cytometric assays targeting a low to medium number of analytes. Such SAT or bead-based assays rely on spherical objects that constitute the analytical platform. Usually, functionalized polymer or silica (SiO2) microbeads are used which each have distinct advantages and drawbacks. In this paper, we present a straightforward synthetic route to highly monodisperse SiO2-coated polystyrene core-shell (CS) beads for SAT with controllable architectures from smooth to raspberry- and multilayer-like shells by varying the molecular weight of poly(vinylpyrrolidone) (PVP), which was used as the stabilizer of the cores. The combination of both organic polymer core and a structurally controlled inorganic SiO2 shell in one hybrid particle holds great promises for flexible next-generation design of the spherical platform. The particles were characterized by electron microscopy (SEM, T-SEM, and TEM), thermogravimetry, flow cytometry, and nitrogen adsorption/desorption, offering comprehensive information on the composition, size, structure, and surface area. All particles show ideal cytometric detection patterns and facile handling due to the hybrid structure. The beads are endowed with straightforward modification possibilities through the defined SiO2 shells. We successfully implemented the particles in fluorometric SAT model assays, illustrating the benefits of tailored surface area which is readily available for small-molecule anchoring. Very promising assay performance was shown for DNA hybridization assays with quantification limits down to 8 fmol.

Synthesis and functionalization of NaGdF4:Yb,Er@NaGdF4 core-shell nanoparticles for possible application as multimodal contrast agents.

PubMed

Baziulyte-Paulaviciene, Dovile; Karabanovas, Vitalijus; Stasys, Marius; Jarockyte, Greta; Poderys, Vilius; Sakirzanovas, Simas; Rotomskis, Ricardas

2017-01-01

Upconverting nanoparticles (UCNPs) are promising, new imaging probes capable of serving as multimodal contrast agents. In this study, monodisperse and ultrasmall core and core-shell UCNPs were synthesized via a thermal decomposition method. Furthermore, it was shown that the epitaxial growth of a NaGdF 4 optical inert layer covering the NaGdF 4 :Yb,Er core effectively minimizes surface quenching due to the spatial isolation of the core from the surroundings. The mean diameter of the synthesized core and core-shell nanoparticles was ≈8 and ≈16 nm, respectively. Hydrophobic UCNPs were converted into hydrophilic ones using a nonionic surfactant Tween 80. The successful coating of the UCNPs by Tween 80 has been confirmed by Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM), powder X-ray diffraction (XRD), photoluminescence (PL) spectra and magnetic resonance (MR) T1 relaxation measurements were used to characterize the size, crystal structure, optical and magnetic properties of the core and core-shell nanoparticles. Moreover, Tween 80-coated core-shell nanoparticles presented enhanced optical and MR signal intensity, good colloidal stability, low cytotoxicity and nonspecific internalization into two different breast cancer cell lines, which indicates that these nanoparticles could be applied as an efficient, dual-modal contrast probe for in vivo bioimaging.

Armored spring-core superconducting cable and method of construction

DOEpatents

McIntyre, Peter M.; Soika, Rainer H.

2002-01-01

An armored spring-core superconducting cable (12) is provided. The armored spring-core superconducting cable (12) may include a spring-core (20), at least one superconducting strand (24) wound onto the spring-core (20), and an armored shell (22) that encases the superconducting strands (24). The spring-core (20) is generally a perforated tube that allows purge gases and cryogenic liquids to be circulated through the armored superconducting cable (12), as well as managing the internal stresses within the armored spring-core superconducting cable (12). The armored shell (22) manages the external stresses of the armored spring-core superconducting cable (12) to protect the fragile superconducting strands (24). The armored spring-core superconducting cable (12) may also include a conductive jacket (34) formed outwardly of the armored shell (22).

A novel "modularized" optical sensor for pH monitoring in biological matrixes.

PubMed

Liu, Xun; Zhang, Shang-Qing; Wei, Xing; Yang, Ting; Chen, Ming-Li; Wang, Jian-Hua

2018-06-30

A novel core-shell structure optical pH sensor is developed with upconversion nanoparticles (UCNPs) serving as the core and silica as the shell, followed by grafting bovineserumalbumin (BSA) as another shell via glutaraldehyde cross-linking. The obtained core-shell-shell structure is shortly termed as UCNPs@SiO 2 @BSA, and its surface provides a platform for loading various pH sensitive dyes, which are alike "modules" to make it feasible for measuring pHs within different pH ranges by simply regulating the type of dyes. Generally, a single pH sensitive dye is adopted to respond within a certain pH range. This study employs bromothymol blue (BTB) and rhodamine B (RhB) to facilitate their responses to pH variations within two ranges, i.e., pH 5.99-8.09 and pH 4.98-6.40, respectively, with detection by ratio-fluorescence protocol. The core-shell-shell structure offers superior sensitivity, which is tens of times more sensitive than those achieved by ratio-fluorescence approaches based on various nanostructures, and favorable stability is achieved in high ionic strength medium. In addition, this sensor exhibits superior photostability under continuous excitation at 980 nm. Thanks to the near infrared excitation in the core-shell-shell structure, it effectively avoids the self-fluorescence from biological samples and thus facilitates accurate sensing of pH in various biological sample matrixes. Copyright © 2018 Elsevier B.V. All rights reserved.

Facile synthesis of Ag@ZIF-8 core-shell heterostructure nanowires for improved antibacterial activities

NASA Astrophysics Data System (ADS)

Guo, Yu-Feng; Fang, Wei-Jun; Fu, Jie-Ru; Wu, Yun; Zheng, Jun; Gao, Gui-Qi; Chen, Cheng; Yan, Rui-Wen; Huang, Shou-Guo; Wang, Chun-Chang

2018-03-01

Compared with pure MOFs, core-shell heterostructures of noble-metal@MOFs have attracted tremendous interest due to their unique structure and extensive applications. In the present study, we have successfully synthesized well-defined core-shell Ag@ZIF-8 nanowires. The products growth process has been investigated by examining the products obtained at different intervals and the thickness of ZIF-8 shell ranging from 30 to 100 nm can be technically obtained by tuning the quantity of Ag nanowires. Ag@ZIF-8 has been proven to possess large specific surfaces and high thermal stability. Additionally, the antibacterial activity of Ag@ZIF-8 is further tested against Bacillus subtilis and Escherichia coli BL21. The results reveal that Ag@ZIF-8 core-shell heterostructure nanowires have effective activities against the two types of bacterial strains.

Remote p-type Doping in GaSb/InAs Core-shell Nanowires

PubMed Central

Ning, Feng; Tang, Li-Ming; Zhang, Yong; Chen, Ke-Qiu

2015-01-01

By performing first-principles calculation, we investigated the electronic properties of remotely p-type doping GaSb nanowire by a Zn-doped InAs shell. The results show that for bare zinc-blende (ZB) [111] GaSb/InAs core-shell nanowire the Zn p-type doped InAs shell donates free holes to the non-doped GaSb core nanowire without activation energy, significantly increasing the hole density and mobility of nanowire. For Zn doping in bare ZB [110] GaSb/InAs core-shell nanowire the hole states are compensated by surface states. We also studied the behaviors of remote p-type doing in two-dimensional (2D) GaSb/InAs heterogeneous slabs, and confirmed that the orientation of nanowire side facet is a key factor for achieving high efficient remote p-type doping. PMID:26028535

Synthesis and characterization of magnetic and non-magnetic core-shell polyepoxide micrometer-sized particles of narrow size distribution.

PubMed

Omer-Mizrahi, Melany; Margel, Shlomo

2009-01-15

Core polystyrene microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. Uniform polyglycidyl methacrylate/polystyrene core-shell micrometer-sized particles were prepared by emulsion polymerization at 73 degrees C of glycidyl methacrylate in the presence of the core polystyrene microspheres. Core-shell particles with different properties (size, surface morphology and composition) have been prepared by changing various parameters belonging to the above seeded emulsion polymerization process, e.g., volumes of the monomer glycidyl methacrylate and the crosslinker monomer ethylene glycol dimethacrylate. Magnetic Fe(3)O(4)/polyglycidyl methacrylate/polystyrene micrometer-sized particles were prepared by coating the former core-shell particles with magnetite nanoparticles via a nucleation and growth mechanism. Characterization of the various particles has been accomplished by routine methods such as light microscopy, SEM, FTIR, BET and magnetic measurements.

Magnetism and Mössbauer study of formation of multi-core γ -Fe2O3 nanoparticles

NASA Astrophysics Data System (ADS)

Kamali, Saeed; Bringas, Eugenio; Hah, Hien-Yoong; Bates, Brian; Johnson, Jacqueline A.; Johnson, Charles E.; Stroeve, Pieter

2018-04-01

A systematic investigation of magnetic nanoparticles and the formation of a core-shell structure, consisting of multiple maghemite (γ -Fe2O3) nanoparticles as the core and silica as the shell, has been performed using various techniques. High-resolution transmission electron microscopy clearly shows isolated maghemite nanoparticles with an average diameter of 13 nm and the formation of a core-shell structure. Low temperature Mössbauer spectroscopy reveals the presence of pure maghemite nanoparticles with all vacancies at the B-sites. Isothermal magnetization and zero-field-cooled and field-cooled measurements are used for investigating the magnetic properties of the nanoparticles. The magnetization results are in good accordance with the contents of the magnetic core and the non-magnetic shell. The multiple-core γ -Fe2O3 nanoparticles show similar behavior to isolated particles of the same size.

Morphology-Controlled Synthesis of Au/Cu₂FeSnS₄ Core-Shell Nanostructures for Plasmon-Enhanced Photocatalytic Hydrogen Generation.

PubMed

Ha, Enna; Lee, Lawrence Yoon Suk; Man, Ho-Wing; Tsang, Shik Chi Edman; Wong, Kwok-Yin

2015-05-06

Copper-based chalcogenides of earth-abundant elements have recently arisen as an alternate material for solar energy conversion. Cu2FeSnS4 (CITS), a quaternary chalcogenide that has received relatively little attention, has the potential to be developed into a low-cost and environmentlly friendly material for photovoltaics and photocatalysis. Herein, we report, for the first time, the synthesis, characterization, and growth mechanism of novel Au/CITS core-shell nanostructures with controllable morphology. Precise manipulations in the core-shell dimensions are demonstrated to yield two distinct heterostructures with spherical and multipod gold nanoparticle (NP) cores (Au(sp)/CITS and Au(mp)/CITS). In photocatalytic hydrogen generation with as-synthesized Au/CITS NPs, the presence of Au cores inside the CITS shell resulted in higher hydrogen generation rates, which can be attributed to the surface plasmon resonance (SPR) effect. The Au(sp)/CITS and Au(mp)/CITS core-shell NPs enhanced the photocatalytic hydrogen generation by about 125% and 240%, respectively, compared to bare CITS NPs.

Bioprinting Using Mechanically Robust Core-Shell Cell-Laden Hydrogel Strands.

PubMed

Mistry, Pritesh; Aied, Ahmed; Alexander, Morgan; Shakesheff, Kevin; Bennett, Andrew; Yang, Jing

2017-06-01

The strand material in extrusion-based bioprinting determines the microenvironments of the embedded cells and the initial mechanical properties of the constructs. One unmet challenge is the combination of optimal biological and mechanical properties in bioprinted constructs. Here, a novel bioprinting method that utilizes core-shell cell-laden strands with a mechanically robust shell and an extracellular matrix-like core has been developed. Cells encapsulated in the strands demonstrate high cell viability and tissue-like functions during cultivation. This process of bioprinting using core-shell strands with optimal biochemical and biomechanical properties represents a new strategy for fabricating functional human tissues and organs. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Water-soluble pH-responsive dendritic core-shell nanocarriers for polar dyes based on poly(ethylene imine).

PubMed

Xu, Shangjie; Luo, Ying; Haag, Rainer

2007-08-07

A simple general synthetic concept to build dendritic core-shell architectures with pH-labile linkers based on hyperbranched PEI cores and biocompatible PEG shells is presented. Using these dendritic core-shell architectures as nanocarriers, the encapsulation and transport of polar dyes of different sizes is studied. The results show that the acid-labile nanocarriers exhibit much higher transport capacities for dyes than unfunctionalized hyperbranched PEI. The cleavage of imine bonds and controlled release of the polar dyes revealed that weak acidic condition (pH approximately 5.0) could cleave the imine bonds linker and release the dyes up to five times faster than neutral conditions (pH = 7.4).

Band bending at the heterointerface of GaAs/InAs core/shell nanowires monitored by synchrotron X-ray photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Khanbabaee, B.; Bussone, G.; Knutsson, J. V.; Geijselaers, I.; Pryor, C. E.; Rieger, T.; Demarina, N.; Grützmacher, D.; Lepsa, M. I.; Timm, R.; Pietsch, U.

2016-10-01

Unique electronic properties of semiconductor heterostructured nanowires make them useful for future nano-electronic devices. Here, we present a study of the band bending effect at the heterointerface of GaAs/InAs core/shell nanowires by means of synchrotron based X-ray photoelectron spectroscopy. Different Ga, In, and As core-levels of the nanowire constituents have been monitored prior to and after cleaning from native oxides. The cleaning process mainly affected the As-oxides and was accompanied by an energy shift of the core-level spectra towards lower binding energy, suggesting that the As-oxides turn the nanowire surfaces to n-type. After cleaning, both As and Ga core-levels revealed an energy shift of about -0.3 eV for core/shell compared to core reference nanowires. With respect to depth dependence and in agreement with calculated strain distribution and electron quantum confinement, the observed energy shift is interpreted by band bending of core-levels at the heterointerface between the GaAs nanowire core and the InAs shell.

Electrosprayed core-shell solid dispersions of acyclovir fabricated using an epoxy-coated concentric spray head.

PubMed

Liu, Zhe-Peng; Cui, Lei; Yu, Deng-Guang; Zhao, Zhuan-Xia; Chen, Lan

2014-01-01

A novel structural solid dispersion (SD) taking the form of core-shell microparticles for poorly water-soluble drugs is reported for the first time. Using polyvinylpyrrolidone (PVP) as a hydrophilic polymer matrix, the SDs were fabricated using coaxial electrospraying (characterized by an epoxy-coated concentric spray head), although the core fluids were unprocessable using one-fluid electrospraying. Through manipulating the flow rates of the core drug-loaded solutions, two types of core-shell microparticles with tunable drug contents were prepared. They had average diameters of 1.36±0.67 and 1.74±0.58 μm, and were essentially a combination of nanocomposites with the active ingredient acyclovir (ACY) distributed in the inner core, and the sweeter sucralose and transmembrane enhancer sodium dodecyl sulfate localized in the outer shell. Differential scanning calorimetry and X-ray diffraction results demonstrated that ACY, sodium dodecyl sulfate, and sucralose were well distributed in the PVP matrix in an amorphous state because of favorable second-order interactions. In vitro dissolution and permeation studies showed that the core-shell microparticle SDs rapidly freed ACY within 1 minute and promoted nearly eightfold increases in permeation rate across the sublingual mucosa compared with raw ACY powders.

Influence of heat treatment on hole transfer dynamics in core-shell quantum dot/organic hole conductor hybrid films

NASA Astrophysics Data System (ADS)

Sun, Mingye; Zheng, Youjin; Zhang, Lei; Zhao, Liping; Zhang, Bing

2017-08-01

The influence of heat treatment on hole transfer (HT) processes from the CdSe/ZnS and CdSe/CdS/ZnS quantum dots (QDs) to 4,4‧,4″-Tris(carbazol-9-yl)-triphenylamine (TCTA) in QD/TCTA hybrid films has been researched with time-resolved photoluminescence (PL) spectroscopy. The PL dynamic results demonstrated a heat-treatment-temperature-dependent HT process from the core-shell CdSe QDs to TCTA. The HT rates and efficiencies can be effectively increased due to reduced distance between core-shell CdSe QDs and TCTA after heat treatment. The CdS shell exhibited a more obvious effect on HT from the core-shell CdSe QDs to TCTA than on electron transfer to TiO2, due to higher barrier for holes to tunnel through CdS shell and larger effective mass of holes in CdS than electrons. These results indicate that heat treatment would be an effective means to further optimize solid-state QD sensitized solar cells and rational design of CdS shell is significant.

Core-shell-shell heterostructures of α-NaLuF4:Yb/Er@NaLuF4:Yb@MF2 (M = Ca, Sr, Ba) with remarkably enhanced upconversion luminescence.

PubMed

Su, Yue; Liu, Xiuling; Lei, Pengpeng; Xu, Xia; Dong, Lile; Guo, Xianmin; Yan, Xingxu; Wang, Peng; Song, Shuyan; Feng, Jing; Zhang, Hongjie

2016-07-05

Core-shell-shell heterostructures of α-NaLuF4:Yb/Er@NaLuF4:Yb@MF2 (M = Ca, Sr, Ba) have been successfully fabricated via the thermal decomposition method. Upconversion nanoparticles (UCNPs) were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), upconversion luminescence (UCL) spectroscopy, etc. Under 980 nm excitation, the emission intensities of the UCNPs are remarkably enhanced after coating the MF2 (M = Ca, Sr, and Ba) shell. Among these samples, CaF2 coated UCNPs show the strongest overall emission, while BaF2 coated UCNPs exhibit the longest lifetime. These results demonstrate that alkaline earth metal fluorides are ideal materials to improve the UCL properties. Meanwhile, although the lattice mismatch between the ternary NaREF4 core and the binary MF2 (M = Sr and Ba) shell is relatively large, the successfully synthesized NaLuF4:Yb/Er@NaLuF4:Yb@MF2 indicates a new outlook on the fabrication of heterostructural core-shell UCNPs.

Facile consecutive solvothermal growth of highly fluorescent InP/ZnS core/shell quantum dots using a safer phosphorus source.

PubMed

Byun, Ho-June; Song, Woo-Seuk; Yang, Heesun

2011-06-10

The work presents a facile, stepwise synthetic approach for the production of highly fluorescent InP/ZnS core/shell quantum dots (QDs) by using a safer phosphorus (P) precursor. First, InP quantum dots (QDs) were solvothermally prepared at 180 °C for 24 h by using a P source of P(N(CH(3))(2))(3). The as-grown InP QDs were consecutively placed in another solvothermal condition for ZnS shell overcoating. In contrast to the almost non-fluorescent InP QDs, due to their highly defective surface states, the ZnS-coated InP QDs were highly fluorescent as a result of effective surface passivation. After the shell growth, the resulting InP/ZnS core/shell QDs were subjected to a size-sorting processing, by which red- to green-emitting QDs with quantum yields (QYs) of 24-60% were produced. Solvothermal shell growth parameters such as the reaction time and Zn/In solution concentration ratio were varied and optimized toward the highest QYs of core/shell QDs.

Facile consecutive solvothermal growth of highly fluorescent InP/ZnS core/shell quantum dots using a safer phosphorus source

NASA Astrophysics Data System (ADS)

Byun, Ho-June; Song, Woo-Seuk; Yang, Heesun

2011-06-01

The work presents a facile, stepwise synthetic approach for the production of highly fluorescent InP/ZnS core/shell quantum dots (QDs) by using a safer phosphorus (P) precursor. First, InP quantum dots (QDs) were solvothermally prepared at 180 °C for 24 h by using a P source of P(N(CH3)2)3. The as-grown InP QDs were consecutively placed in another solvothermal condition for ZnS shell overcoating. In contrast to the almost non-fluorescent InP QDs, due to their highly defective surface states, the ZnS-coated InP QDs were highly fluorescent as a result of effective surface passivation. After the shell growth, the resulting InP/ZnS core/shell QDs were subjected to a size-sorting processing, by which red- to green-emitting QDs with quantum yields (QYs) of 24-60% were produced. Solvothermal shell growth parameters such as the reaction time and Zn/In solution concentration ratio were varied and optimized toward the highest QYs of core/shell QDs.

Construction of CdS@UIO-66-NH2 core-shell nanorods for enhanced photocatalytic activity with excellent photostability.

PubMed

Liang, Qian; Cui, Sainan; Liu, Changhai; Xu, Song; Yao, Chao; Li, Zhongyu

2018-08-15

A novel class of CdS@UIO-66-NH 2 core shell heterojunction was fabricated by the facile in-situ solvothermal method. Characterizations show that porous UIO-66-NH 2 shell not only allows the visible light to be absorbed on CdS nanorod core, but also provides abundant catalytic active sites as well as an intimate heterojunction interface between UIO-66-NH 2 shell and CdS nanorod core. By taking advantage of this property, the core-shell composite presents highly solar-driven photocatalytic performance compared with pristine UIO-66-NH 2 and CdS nanorod for the degradation of organic dyes including malachite green (MG) and methyl orange (MO), and displays superior photostability after four recycles. Furthermore, the photoelectrochemical performance of CdS@UIO-66-NH 2 can be measured by the UV-vis spectra, Mott-Schottky plots and photocurrent. The remarkably enhanced photocatalytic activity of CdS@UIO-66-NH 2 can be ascribed to high surface areas, intimate interaction on molecular scale and the formation of one-dimensional heterojunction with n-n type. What's more, the core-shell heterostructural CdS@UIO-66-NH 2 can facilitate the effective separation and transfer of the photoinduced interfacial electron-hole pairs and protect CdS nanorod core from photocorrosion. Copyright © 2018 Elsevier Inc. All rights reserved.

The functional divide for primary reinforcement of D-amphetamine lies between the medial and lateral ventral striatum: is the division of the accumbens core, shell, and olfactory tubercle valid?

PubMed

Ikemoto, Satoshi; Qin, Mei; Liu, Zhong-Hua

2005-05-18

When projection analyses placed the nucleus accumbens and olfactory tubercle in the striatal system, functional links between these sites began to emerge. The accumbens has been implicated in the rewarding effects of psychomotor stimulants, whereas recent work suggests that the medial accumbens shell and medial olfactory tubercle mediate the rewarding effects of cocaine. Interestingly, anatomical evidence suggests that medial portions of the shell and tubercle receive afferents from common zones in a number of regions. Here, we report results suggesting that the current division of the ventral striatum into the accumbens core and shell and the olfactory tubercle does not reflect the functional organization for amphetamine reward. Rats quickly learned to self-administer D-amphetamine into the medial shell or medial tubercle, whereas they failed to learn to do so into the accumbens core, ventral shell, or lateral tubercle. Our results suggest that primary reinforcement of amphetamine is mediated via the medial portion of the ventral striatum. Thus, the medial shell and medial tubercle are more functionally related than the medial and ventral shell or the medial and lateral tubercle. The current core-shell-tubercle scheme should be reconsidered in light of recent anatomical data and these functional findings.

Modified ferrite core-shell nanoparticles magneto-structural characterization

NASA Astrophysics Data System (ADS)

Klekotka, Urszula; Piotrowska, Beata; Satuła, Dariusz; Kalska-Szostko, Beata

2018-06-01

In this study, ferrite nanoparticles with core-shell structures and different chemical compositions of both the core and shell were prepared with success. Proposed nanoparticles have in the first and second series magnetite core, and the shell is composed of a mixture of ferrites with Fe3+, Fe2+ and M ions (where M = Co2+, Mn2+ or Ni2+) with a general composition of M0.5Fe2.5O4. In the third series, the composition is inverted, the core is composed of a mixture of ferrites and as a shell magnetite is placed. Morphology and structural characterization of nanoparticles were done using Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), and Infrared spectroscopy (IR). While room temperature magnetic properties were measured using Mössbauer spectroscopy (MS). It is seen from Mössbauer measurements that Co always increases hyperfine magnetic field on Fe atoms at RT, while Ni and Mn have opposite influences in comparison to pure Fe ferrite, regardless of the nanoparticles structure.

The synthesis of four-layer gold-silver-polymer-silver core-shell nanomushroom with inbuilt Raman molecule for surface-enhanced Raman scattering

NASA Astrophysics Data System (ADS)

Jiang, Tao; Wang, Xiaolong; Zhou, Jun

2017-12-01

A facial two-step reduction method was proposed to synthesize four-layer gold-silver-polymer-silver (Au@Ag@PSPAA@Ag) core-shell nanomushrooms (NMs) with inbuilt Raman molecule. The surface-enhanced Raman scattering (SERS) intensity of 4MBA adhered on the surface of Au core gradually increased with the modification of middle Ag shell and then Ag mushroom cap due to the formation of two kinds of ultra-small interior nanogap. Compared with the initial Au nanoparticles, the SERS enhancement ratio of the Au@Ag@PSPAA@Ag NMs approached to nearly 40. The novel core-shell NMs also exhibited homogeneous SERS signals for only one sample and reproducible signals for 10 different samples, certified by the low relative standard deviation values of less than 10% and 15% for the character peaks of 4-mercaptobenzoic acid, respectively. Such a novel four-layer core-shell nanostructure with reliable SERS performance has great potential application in quantitative SERS-based immunoassay.

Core-shell biopolymer nanoparticle delivery systems: synthesis and characterization of curcumin fortified zein-pectin nanoparticles.

PubMed

Hu, Kun; Huang, Xiaoxia; Gao, Yongqing; Huang, Xulin; Xiao, Hang; McClements, David Julian

2015-09-01

Biopolymer core-shell nanoparticles were fabricated using a hydrophobic protein (zein) as the core and a hydrophilic polysaccharide (pectin) as the shell. Particles were prepared by coating cationic zein nanoparticles with anionic pectin molecules using electrostatic deposition (pH 4). The core-shell nanoparticles were fortified with curcumin (a hydrophobic bioactive molecule) at a high loading efficiency (>86%). The resulting nanoparticles were spherical, relatively small (diameter ≈ 250 nm), and had a narrow size distribution (polydispersity index ≈ 0.24). The encapsulated curcumin was in an amorphous (rather than crystalline form) as detected by differential scanning calorimetry (DSC). Fourier transform infrared (FTIR) and Raman spectra indicated that the encapsulated curcumin interacted with zein mainly through hydrophobic interactions. The nanoparticles were converted into a powdered form that had good water-dispersibility. These core-shell biopolymer nanoparticles could be useful for incorporating curcumin into functional foods and beverages, as well as dietary supplements and pharmaceutical products. Copyright © 2015 Elsevier Ltd. All rights reserved.

Inhibitive effect of Pt on Pd-hydride formation of Pd@Pt core-shell electrocatalysts: An in situ EXAFS and XRD study

DOE PAGES

Wise, Anna M.; Richardson, Peter W.; Price, Stephen W. T.; ...

2017-12-27

In situ EXAFS and XRD have been used to study the electrochemical formation of hydride phases, H abs, in 0.5 M H 2SO 4 for a Pd/C catalyst and a series of Pd@Pt core-shell catalysts with varying Pt shell thickness, from 0.5 to 4 monolayers. Based on the XRD data a 3% lattice expansion is observed for the Pd/C core catalyst upon hydride formation at 0.0 V. In contrast, the expansion was ≤0.6% for all of the core-shell catalysts. The limited extent of the lattice expansion observed suggests that hydride formation, which may occur during periodic active surface area measurementsmore » conducting during accelerated aging tests or driven by H 2 crossover in PEM fuel cells, is unlikely to contribute significantly to the degradation of Pd@Pt core-shell electrocatalysts in contrast to the effects of oxide formation.« less

Inhibitive effect of Pt on Pd-hydride formation of Pd@Pt core-shell electrocatalysts: An in situ EXAFS and XRD study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wise, Anna M.; Richardson, Peter W.; Price, Stephen W. T.

In situ EXAFS and XRD have been used to study the electrochemical formation of hydride phases, H abs, in 0.5 M H 2SO 4 for a Pd/C catalyst and a series of Pd@Pt core-shell catalysts with varying Pt shell thickness, from 0.5 to 4 monolayers. Based on the XRD data a 3% lattice expansion is observed for the Pd/C core catalyst upon hydride formation at 0.0 V. In contrast, the expansion was ≤0.6% for all of the core-shell catalysts. The limited extent of the lattice expansion observed suggests that hydride formation, which may occur during periodic active surface area measurementsmore » conducting during accelerated aging tests or driven by H 2 crossover in PEM fuel cells, is unlikely to contribute significantly to the degradation of Pd@Pt core-shell electrocatalysts in contrast to the effects of oxide formation.« less

Synthesis of bimetallic Pt-Pd core-shell nanocrystals and their high electrocatalytic activity modulated by Pd shell thickness

NASA Astrophysics Data System (ADS)

Li, Yujing; Wang, Zhi Wei; Chiu, Chin-Yi; Ruan, Lingyan; Yang, Wenbing; Yang, Yang; Palmer, Richard E.; Huang, Yu

2012-01-01

Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications.Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications. Electronic supplementary information (ESI) available: Supplementary TEM, EELS, EDS, Electro-chemical measurement data can be found. See DOI: 10.1039/c1nr11374g

Core-shell titanium dioxide-titanium nitride nanotube arrays with near-infrared plasmon resonances

NASA Astrophysics Data System (ADS)

Farsinezhad, Samira; Shanavas, Thariq; Mahdi, Najia; Askar, Abdelrahman M.; Kar, Piyush; Sharma, Himani; Shankar, Karthik

2018-04-01

Titanium nitride (TiN) is a ceramic with high electrical conductivity which in nanoparticle form, exhibits localized surface plasmon resonances (LSPRs) in the visible region of the solar spectrum. The ceramic nature of TiN coupled with its dielectric loss factor being comparable to that of gold, render it attractive for CMOS polarizers, refractory plasmonics, surface-enhanced Raman scattering and a whole host of sensing applications. We report core-shell TiO2-TiN nanotube arrays exhibiting LSPR peaks in the range 775-830 nm achieved by a simple, solution-based, low cost, large area-compatible fabrication route that does not involve laser-writing or lithography. Self-organized, highly ordered TiO2 nanotube arrays were grown by electrochemical anodization of Ti thin films on fluorine-doped tin oxide-coated glass substrates and then conformally coated with a thin layer of TiN using atomic layer deposition. The effects of varying the TiN layer thickness and thermal annealing on the LSPR profiles were also investigated. Modeling the TiO2-TiN core-shell nanotube structure using two different approaches, one employing effective medium approximations coupled with Fresnel coefficients, resulted in calculated optical spectra that closely matched the experimentally measured spectra. Modeling provided the insight that the observed near-infrared resonance was not collective in nature, and was mainly attributable to the longitudinal resonance of annular nanotube-like TiN particles redshifted due to the presence of the higher permittivity TiO2 matrix. The resulting TiO2-TiN core-shell nanotube structures also function as visible light responsive photocatalysts, as evidenced by their photoelectrochemical water-splitting performance under light emitting diode illumination using 400, 430 and 500 nm photons.

The Spatial Distribution of Complex Organic Molecules in the L1544 Pre-stellar Core

PubMed Central

Jiménez-Serra, Izaskun; Vasyunin, Anton I.; Caselli, Paola; Marcelino, Nuria; Billot, Nicolas; Viti, Serena; Testi, Leonardo; Vastel, Charlotte; Lefloch, Bertrand; Bachiller, Rafael

2016-01-01

The detection of complex organic molecules (COMs) toward cold sources such as pre-stellar cores (with T<10 K), has challenged our understanding of the formation processes of COMs in the interstellar medium. Recent modelling on COM chemistry at low temperatures has provided new insight into these processes predicting that COM formation depends strongly on parameters such as visual extinction and the level of CO freeze out. We report deep observations of COMs toward two positions in the L1544 pre-stellar core: the dense, highly-extinguished continuum peak with AV ≥30 mag within the inner 2700 au; and a low-density shell with average AV ~7.5-8 mag located at 4000 au from the core’s center and bright in CH3OH. Our observations show that CH3O, CH3OCH3 and CH3CHO are more abundant (by factors ~2-10) toward the low-density shell than toward the continuum peak. Other COMs such as CH3OCHO, c-C3H2O, HCCCHO, CH2CHCN and HCCNC show slight enhancements (by factors ≤3) but the associated uncertainties are large. This suggests that COMs are actively formed and already present in the low-density shells of pre-stellar cores. The modelling of the chemistry of O-bearing COMs in L1544 indicates that these species are enhanced in this shell because i) CO starts freezing out onto dust grains driving an active surface chemistry; ii) the visual extinction is sufficiently high to prevent the UV photo-dissociation of COMs by the external interstellar radiation field; and iii) the density is still moderate to prevent severe depletion of COMs onto grains. PMID:27733899

Study of CT Scan Flooding System at High Temperature and Pressure

NASA Astrophysics Data System (ADS)

Chen, X. Y.

2017-12-01

CT scan flooding experiment can scan micro-pore in different flooding stages by the use of CT scan technology, without changing the external morphology and internal structure of the core, and observe the distribution characterization in pore medium of different flooding fluid under different pressure.thus,it can rebuilt the distribution images of oil-water distribution in different flooding stages. However,under extreme high pressure and temperature conditions,the CT scan system can not meet the requirements. Container of low density materials or thin shell can not resist high pressure,while high density materials or thick shell will cause attenuation and scattering of X-ray. The experiment uses a simple Ct scanning systems.X ray from a point light source passing trough a micro beryllium shell on High pressure stainless steal container,continuously irradiates the core holder that can continuously 360° rotate along the core axis. A rare earth intensifying screen behind the core holder emitting light when irradiated with X ray can show the core X ray section image. An optical camera record the core X ray images through a transparency high pressure glazing that placed on the High pressure stainless steal container.Thus,multiple core X ray section images can reconstruct the 3D core reconstruction after a series of data processing.The experiment shows that both the micro beryllium shell and rare earth intensifying screen can work in high temperature and high pressure environment in the stainless steal container. This way that X-ray passes through a thin layer of micro beryllium shell , not high pressure stainless steal shell,avoid the attenuation and scattering of X-ray from the container shell,while improving the high-pressure experiment requirements.

Characterization of Fe3O4/SiO2/Gd2O(CO3)2 core/shell/shell nanoparticles as T1 and T2 dual mode MRI contrast agent.

PubMed

Yang, Meicheng; Gao, Lipeng; Liu, Kai; Luo, Chunhua; Wang, Yiting; Yu, Lei; Peng, Hui; Zhang, Wen

2015-01-01

Core/shell/shell structured Fe3O4/SiO2/Gd2O(CO3)2 nanoparticles were successfully synthesized. Their properties as a new type of T1-T2 dual model contrast agent for magnetic resonance imaging were investigated. Due to the introduce of a separating SiO2 layer, the magnetic coupling between Gd2O(CO3)2 and Fe3O4 could be modulated by the thickness of SiO2 layer and produce appropriate T1 and T2 signal. Additionally, the existence of Gd(3+) enhances the transverse relaxivity of Fe3O4 possibly because of the magnetic coupling between Gd(3+) and Fe3O4. The Fe3O4/SiO2/Gd2O(CO3)2 nanoparticles exhibit good biocompatibility, showing great potential for biomedical applications. Copyright © 2014 Elsevier B.V. All rights reserved.

Microcapsules with a pH responsive polymer: influence of the encapsulated oil on the capsule morphology.

PubMed

Wagdare, Nagesh A; Marcelis, Antonius T M; Boom, Remko M; van Rijn, Cees J M

2011-11-01

Microcapsules were prepared by microsieve membrane cross flow emulsification of Eudragit FS 30D/dichloromethane/edible oil mixtures in water, and subsequent phase separation induced by extraction of the dichloromethane through an aqueous phase. For long-chain triglycerides and jojoba oil, core-shell particles were obtained with the oil as core, surrounded by a shell of Eudragit. Medium chain triglyceride (MCT oil) was encapsulated as relatively small droplets in the Eudragit matrix. The morphology of the formed capsules was investigated with optical and SEM microscopy. Extraction of the oil from the core-shell capsules with hexane resulted in hollow Eudragit capsules with porous shells. It was shown that the differences are related to the compatibility of the oils with the shell-forming Eudragit. An oil with poor compatibility yields microcapsules with a dense Eudragit shell on a single oil droplet as the core; oils having better compatibility yield porous Eudragit spheres with several oil droplets trapped inside. Copyright © 2011 Elsevier B.V. All rights reserved.

Threefold rotational symmetry in hexagonally shaped core-shell (In,Ga)As/GaAs nanowires revealed by coherent X-ray diffraction imaging.

PubMed

Davtyan, Arman; Krause, Thilo; Kriegner, Dominik; Al-Hassan, Ali; Bahrami, Danial; Mostafavi Kashani, Seyed Mohammad; Lewis, Ryan B; Küpers, Hanno; Tahraoui, Abbes; Geelhaar, Lutz; Hanke, Michael; Leake, Steven John; Loffeld, Otmar; Pietsch, Ullrich

2017-06-01

Coherent X-ray diffraction imaging at symmetric hhh Bragg reflections was used to resolve the structure of GaAs/In 0.15 Ga 0.85 As/GaAs core-shell-shell nanowires grown on a silicon (111) substrate. Diffraction amplitudes in the vicinity of GaAs 111 and GaAs 333 reflections were used to reconstruct the lost phase information. It is demonstrated that the structure of the core-shell-shell nanowire can be identified by means of phase contrast. Interestingly, it is found that both scattered intensity in the (111) plane and the reconstructed scattering phase show an additional threefold symmetry superimposed with the shape function of the investigated hexagonal nanowires. In order to find the origin of this threefold symmetry, elasticity calculations were performed using the finite element method and subsequent kinematic diffraction simulations. These suggest that a non-hexagonal (In,Ga)As shell covering the hexagonal GaAs core might be responsible for the observation.

Study of Charge Transport in Vertically Aligned Nitride Nanowire Based Core Shell P-I-N Junctions

DTIC Science & Technology

2016-07-01

Vertically- Aligned Nitride Nanowire Based Core Shell P-I-N Junctions Distribution Statement A. Approved for public release; distribution is...Study of Charge Transport in Vertically- Aligned Nitride Nanowire Based Core Shell P-I-N Junctions Grant Number: HDTRA1-14-1-0003 Principal...Investigator: Abhishek Motayed University of Maryland DISTRIBUTION A: Public Release Study of Charge Transport in Vertically-Aligned Nitride Nanowire

Superstructures of self assembled multiferroic core shell nanoparticles and studies on magneto electric interactions

DTIC Science & Technology

2014-08-19

Box 12211 Research Triangle Park, NC 27709-2211 Core-shell nanoparticles, frrite, ferroelectric , magnetoelectric REPORT DOCUMENTATION PAGE 11...of ferrite- ferroelectric core-shell nanofibers and studies on magneto- electric interactions Appl. Phys. Lett. 104, 052910 (2014); 10.1063/1.4864113...1.4893699] A ferromagnetic- ferroelectric composite is a multiferroic in which the magneto-electric (ME) interaction is facilitated by mechanical forces.1–6

Optimization and photomodification of extremely broadband optical response of plasmonic core-shell obscurants.

PubMed

de Silva, Vashista C; Nyga, Piotr; Drachev, Vladimir P

2016-12-15

Plasmonic resonances of the metallic shells depend on their nanostructure and geometry of the core, which can be optimized for the broadband extinction normalized by mass. The fractal nanostructures can provide a broadband extinction. It allows as well for a laser photoburning of holes in the extinction spectra and consequently windows of transparency in a controlled manner. The studied core-shell microparticles synthesized using colloidal chemistry consist of gold fractal nanostructures grown on precipitated calcium carbonate (PCC) microparticles or silica (SiO 2 ) microspheres. The optimization includes different core sizes and shapes, and shell nanostructures. It shows that the rich surface of the PCC flakes is the best core for the fractal shells providing the highest mass normalized extinction over the extremely broad spectral range. The mass normalized extinction cross section up to 3m 2 /g has been demonstrated in the broad spectral range from the visible to mid-infrared. Essentially, the broadband response is a characteristic feature of each core-shell microparticle in contrast to a combination of several structures resonant at different wavelengths, for example nanorods with different aspect ratios. The photomodification at an IR wavelength makes the window of transparency at the longer wavelength side. Copyright © 2016 Elsevier Inc. All rights reserved.

Irreversible phase transitions due to laser-based T-jump heating of precursor Eu:ZrO{sub 2}/Tb:Y{sub 2}O{sub 3} core/shell nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gunawidjaja, Ray; Diez-y-Riega, Helena; Eilers, Hergen, E-mail: eilers@wsu.edu

2015-09-15

Amorphous precursors of Eu-doped-ZrO{sub 2}/Tb-doped-Y{sub 2}O{sub 3} (p-Eu:ZrO{sub 2}/p-Tb:Y{sub 2}O{sub 3}) core/shell nanoparticles are rapidly heated to temperatures between 200 °C and 950 °C for periods between 2 s and 60 s using a CO{sub 2} laser. During this heating process the nanoparticles undergo irreversible phase changes. The fluorescence spectra due to Eu{sup 3+} dopants in the core and Tb{sup 3+} dopants in the shell are used to identify distinct phases within the material and to generate time/temperature phase diagrams. Such phase diagrams can potentially help to determine unknown time/temperature histories in thermosensor applications. - Graphical abstract: A CO{sub 2}more » laser is used for rapid heating of p-Eu:ZrO{sub 2}/p-Tb:Y{sub 2}O{sub 3} core/shell nanoparticles. Optical spectra are used to identify distinct phases and to determine its thermal history. - Highlights: • Synthesized oxide precursors of lanthanide doped core/shell nanoparticles. • Heated core/shell nanoparticles via laser-based T-jump technique. • Observed time- and temperature-dependent irreversible phase transition.« less

B80 and B101-103 clusters: Remarkable stability of the core-shell structures established by validated density functionalsa)

NASA Astrophysics Data System (ADS)

Li, Fengyu; Jin, Peng; Jiang, De-en; Wang, Lu; Zhang, Shengbai B.; Zhao, Jijun; Chen, Zhongfang

2012-02-01

Prompted by the very recent claim that the volleyball-shaped B80 fullerene [X. Wang, Phys. Rev. B 82, 153409 (2010), 10.1103/PhysRevB.82.153409] is lower in energy than the B80 buckyball [N. G. Szwacki, A. Sadrzadeh, and B. I. Yakobson, Phys. Rev. Lett. 98, 166804 (2007), 10.1103/PhysRevLett.98.166804] and core-shell structure [J. Zhao, L. Wang, F. Li, and Z. Chen, J. Phys. Chem. A 114, 9969 (2010), 10.1021/jp1018873], and inspired by the most recent finding of another core-shell isomer as the lowest energy B80 isomer [S. De, A. Willand, M. Amsler, P. Pochet, L. Genovese, and S. Goedecher, Phys. Rev. Lett. 106, 225502 (2011), 10.1103/PhysRevLett.106.225502], we carefully evaluated the performance of the density functional methods in the energetics of boron clusters and confirmed that the core-shell construction (stuffed fullerene) is thermodynamically the most favorable structural pattern for B80. Our global minimum search showed that both B101 and B103 also prefer a core-shell structure and that B103 can reach the complete core-shell configuration. We called for great attention to the theoretical community when using density functionals to investigate boron-related nanomaterials.

Core-shell rhodium sulfide catalyst for hydrogen evolution reaction / hydrogen oxidation reaction in hydrogen-bromine reversible fuel cell

NASA Astrophysics Data System (ADS)

Li, Yuanchao; Nguyen, Trung Van

2018-04-01

Synthesis and characterization of high electrochemical active surface area (ECSA) core-shell RhxSy catalysts for hydrogen evolution oxidation (HER)/hydrogen oxidation reaction (HOR) in H2-Br2 fuel cell are discussed. Catalysts with RhxSy as shell and different percentages (5%, 10%, and 20%) of platinum on carbon as core materials are synthesized. Cyclic voltammetry is used to evaluate the Pt-equivalent mass specific ECSA and durability of these catalysts. Transmission electron microscopy (TEM), X-ray Photoelectron spectroscopy (XPS) and Energy-dispersive X-ray spectroscopy (EDX) techniques are utilized to characterize the bulk and surface compositions and to confirm the core-shell structure of the catalysts, respectively. Cycling test and polarization curve measurements in the H2-Br2 fuel cell are used to assess the catalyst stability and performance in a fuel cell. The results show that the catalysts with core-shell structure have higher mass specific ECSA (50 m2 gm-Rh-1) compared to a commercial catalyst (RhxSy/C catalyst from BASF, 6.9 m2 gm-Rh-1). It also shows better HOR/HER performance in the fuel cell. Compared to the platinum catalyst, the core-shell catalysts show more stable performance in the fuel cell cycling test.

High ink absorption performance of inkjet printing based on SiO2@Al13 core-shell composites

NASA Astrophysics Data System (ADS)

Chen, YiFan; Jiang, Bo; Liu, Li; Du, Yunzhe; Zhang, Tong; Zhao, LiWei; Huang, YuDong

2018-04-01

The increasing growth of the inkjet market makes the inkjet printing more necessary. A composite material based on core-shell structure has been developed and applied to prepare inkjet printing layer. In this contribution, the ink printing record layers based on SiO2@Al13 core-shell composite was elaborated. The prepared core-shell composite materials were characterized by X-ray photoelectron spectroscopy (XPS), zeta potential, X-ray diffraction (XRD), scanning electron microscopy (SEM). The results proved the presence of electrostatic adsorption between SiO2 molecules and Al13 molecules with the formation of the well-dispersed system. In addition, based on the adsorption and the liquid permeability analysis, SiO2@Al13 ink printing record layer achieved a relatively high ink uptake (2.5 gmm-1) and permeability (87%), respectively. The smoothness and glossiness of SiO2@Al13 record layers were higher than SiO2 record layers. The core-shell structure facilitated the dispersion of the silica, thereby improved its ink absorption performance and made the clear printed image. Thus, the proposed procedure based on SiO2@Al13 core-shell structure of dye particles could be applied as a promising strategy for inkjet printing.

Gram-level synthesis of core-shell structured catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells

NASA Astrophysics Data System (ADS)

Luo, Mingchuan; Wei, Lingli; Wang, Fanghui; Han, Kefei; Zhu, Hong

2014-12-01

Over the past decade, Pt based core-shell structured alloys have been studied extensively as oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cells (PEMFCs) because of their distinctive electrochemical performance and low Pt loading. In this paper, a facile route based on microwave-assisted polyol method and chemical dealloying process is proposed to synthesize carbon supported core-shell structured nanoparticles (NPs) in gram-level for ORR electrocatalysis in PEMFCs. The obtained samples are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). These physical characterization indicate that the final synthesized NPs are highly dispersed on the carbon support, and in a core-shell structure with CuPt alloy as the core and Pt as the shell. Electrochemical measurements, conducted by cyclic voltammetry (CV) and rotating disk electrode (RDE) tests, show the core-shell structured catalyst exhibit a 3× increase in mass activity and a 2× increase in specific activity over the commercial Pt/C catalyst, respectively. These results demonstrate that this route can be a reliable way to synthesize low-Pt catalyst in large-scale for PEMFCs.

Monodisperse core/shell Ni/FePt nanoparticles and their con-version to Ni/Pt to catalyze oxygen reduction

DOE PAGES

Zhang, Sen; Hao, Yizhou; Su, Dong; ...

2014-10-28

We report a size-controllable synthesis of monodisperse core/shell Ni/FePt nanoparticles (NPs) via a seed-mediated growth and their subsequent conversion to Ni/Pt NPs. Preventing surface oxidation of the Ni seeds is essential for the growth of uniform FePt shells. These Ni/FePt NPs have a thin (≈ 1 nm) FePt shell, and can be converted to Ni/Pt by acetic acid wash to yield active catalysts for oxygen reduction reaction (ORR). Tuning the core size allow for optimization of their electrocatalytic activity. The specific activity and mass activity of 4.2 nm/0.8 nm core/shell Ni/FePt reach 1.95 mA/cm² and 490 mA/mg Pt at 0.9more » V ( vs. reversible hydrogen electrode, RHE), which are much higher than those of benchmark commercial Pt catalyst (0.34 mA/cm² and 92 mA/mg Pt at 0.9 V). Our studies provide a robust approach to monodisperse core/shell NPs with non-precious metal core, making it possible to develop advanced NP catalysts with ultralow Pt content for ORR and many other heterogeneous reactions.« less

Magnetic response of hybrid ferromagnetic and antiferromagnetic core-shell nanostructures

NASA Astrophysics Data System (ADS)

Khan, U.; Li, W. J.; Adeela, N.; Irfan, M.; Javed, K.; Wan, C. H.; Riaz, S.; Han, X. F.

2016-03-01

The synthesis of FeTiO3-Ni(Ni80Fe20) core-shell nanostructures by a two-step method (sol-gel and DC electrodeposition) has been demonstrated. XRD analysis confirms the rhombohedral crystal structure of FeTiO3(FTO) with space group R3&cmb.macr;. Transmission electron microscopy clearly depicts better morphology of nanostructures with shell thicknesses of ~25 nm. Room temperature magnetic measurements showed significant enhancement of magnetic anisotropy for the permalloy (Ni80Fe20)-FTO over Ni-FTO core-shell nanostructures. Low temperature magnetic measurements of permalloy-FeTiO3 core-shell structure indicated a strong exchange bias mechanism with magnetic coercivity below the antiferromagnetic Neel temperature (TN = 59 K). The exchange bias is attributed to the alignment of magnetic moments in the antiferromagnetic material at low temperature. Our scheme opens a path towards optimum automotive systems and wireless communications wherein broader bandwidths and smaller sizes are required.The synthesis of FeTiO3-Ni(Ni80Fe20) core-shell nanostructures by a two-step method (sol-gel and DC electrodeposition) has been demonstrated. XRD analysis confirms the rhombohedral crystal structure of FeTiO3(FTO) with space group R3&cmb.macr;. Transmission electron microscopy clearly depicts better morphology of nanostructures with shell thicknesses of ~25 nm. Room temperature magnetic measurements showed significant enhancement of magnetic anisotropy for the permalloy (Ni80Fe20)-FTO over Ni-FTO core-shell nanostructures. Low temperature magnetic measurements of permalloy-FeTiO3 core-shell structure indicated a strong exchange bias mechanism with magnetic coercivity below the antiferromagnetic Neel temperature (TN = 59 K). The exchange bias is attributed to the alignment of magnetic moments in the antiferromagnetic material at low temperature. Our scheme opens a path towards optimum automotive systems and wireless communications wherein broader bandwidths and smaller sizes are required. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07946b

Understanding the Thermal Stability of Palladium-Platinum Core-Shell Nanocrystals by In Situ Transmission Electron Microscopy and Density Functional Theory.

PubMed

Vara, Madeline; Roling, Luke T; Wang, Xue; Elnabawy, Ahmed O; Hood, Zachary D; Chi, Miaofang; Mavrikakis, Manos; Xia, Younan

2017-05-23

Core-shell nanocrystals offer many advantages for heterogeneous catalysis, including precise control over both the surface structure and composition, as well as reduction in loading for rare and costly metals. Although many catalytic processes are operated at elevated temperatures, the adverse impacts of heating on the shape and structure of core-shell nanocrystals are yet to be understood. In this work, we used ex situ heating experiments to demonstrate that Pd@Pt 4L core-shell nanoscale cubes and octahedra are promising for catalytic applications at temperatures up to 400 °C. We also used in situ transmission electron microscopy to monitor the thermal stability of the core-shell nanocrystals in real time. Our results demonstrate a facet dependence for the thermal stability in terms of shape and composition. Specifically, the cubes enclosed by {100} facets readily deform shape at a temperature 300 °C lower than that of the octahedral counterparts enclosed by {111} facets. A reversed trend is observed for composition, as alloying between the Pd core and the Pt shell of an octahedron occurs at a temperature 200 °C lower than that for the cubic counterpart. Density functional theory calculations provide atomic-level explanations for the experimentally observed behaviors, demonstrating that the barriers for edge reconstruction determine the relative ease of shape deformation for cubes compared to octahedra. The opposite trend for alloying of the core-shell structure can be attributed to a higher propensity for subsurface Pt vacancy formation in octahedra than in cubes.

Tuning the field distribution and fabrication of an Al@ZnO core-shell nanostructure for a SPR-based fiber optic phenyl hydrazine sensor.

PubMed

Tabassum, Rana; Kaur, Parvinder; Gupta, Banshi D

2016-05-27

We report the fabrication and characterization of a surface plasmon resonance (SPR)-based fiber optic sensor that uses coatings of silver and aluminum (Al)-zinc oxide (ZnO) core-shell nanostructure (Al@ZnO) for the detection of phenyl hydrazine (Ph-Hyd). To optimize the volume fraction (f) of Al in ZnO and the thickness of the core-shell nanostructure layer (d), the electric field intensity along the normal to the multilayer system is simulated using the two-dimensional multilayer matrix method. The Al@ZnO core-shell nanostructure is prepared using the laser ablation technique. Various probes are fabricated with different values of f and an optimized thickness of core-shell nanostructure for the characterization of the Ph-Hyd sensor. The performance of the Ph-Hyd sensor is evaluated in terms of sensitivity. It is found that the Ag/Al@ZnO nanostructure core-shell-coated SPR probe with f = 0.25 and d = 0.040 μm possesses the maximum sensitivity towards Ph-Hyd. These results are in agreement with the simulated ones obtained using electric field intensity. In addition, the performance of the proposed probe is compared with that of probes coated with (i) Al@ZnO nanocomposite, (ii) Al nanoparticles and (iii) ZnO nanoparticles. It is found that the probe coated with an Al@ZnO core-shell nanostructure shows the largest resonance wavelength shift. The detailed mechanism of the sensing (involving chemical reactions) is presented. The sensor also manifests optimum performance at pH 7.

Application of Powder Diffraction Methods to the Analysis of Short- and Long-Range Atomic Order in Nanocrystalline Diamond and SiC: The Concept of the Apparent Lattice Parameter (alp)

NASA Technical Reports Server (NTRS)

Palosz, B.; Grzanka, E.; Gierlotka, S.; Stelmakh, S.; Pielaszek, R.; Bismayer, U.; Weber, H.-P.; Palosz, W.

2003-01-01

Two methods of the analysis of powder diffraction patterns of diamond and SiC nanocrystals are presented: (a) examination of changes of the lattice parameters with diffraction vector Q ('apparent lattice parameter', alp) which refers to Bragg scattering, and (b), examination of changes of inter-atomic distances based on the analysis of the atomic Pair Distribution Function, PDF. Application of these methods was studied based on the theoretical diffraction patterns computed for models of nanocrystals having (i) a perfect crystal lattice, and (ii), a core-shell structure, i.e. constituting a two-phase system. The models are defined by the lattice parameter of the grain core, thickness of the surface shell, and the magnitude and distribution of the strain field in the shell. X-ray and neutron experimental diffraction data of nanocrystalline SiC and diamond powders of the grain diameter from 4 nm up to micrometers were used. The effects of the internal pressure and strain at the grain surface on the structure are discussed based on the experimentally determined dependence of the alp values on the Q-vector, and changes of the interatomic distances with the grain size determined experimentally by the atomic Pair Distribution Function (PDF) analysis. The experimental results lend a strong support to the concept of a two-phase, core and the surface shell structure of nanocrystalline diamond and SiC.

Effects of density stratification on the frequencies of the inertial-gravity modes of the Earth's fluid core

NASA Astrophysics Data System (ADS)

Seyed-Mahmoud, B.; Moradi, A.; Kamruzzaman, M.; Naseri, H.

2015-08-01

The Earth's outer core is a rotating ellipsoidal shell of compressible, stratified and self-gravitating fluid. As such, in the treatment of geophysical problems a realistic model of this body needs to be considered. In this work, we consider compressible and stratified fluid core models with different stratification parameters, related to the local Brunt-Väisälä frequency, in order to study the effects of the core's density stratification on the frequencies of some of the inertial-gravity modes of this body. The inertial-gravity modes of the core are free oscillations with periods longer than 12 hr. Historically, an incompressible and homogeneous fluid is considered to study these modes and analytical solutions are known for the frequencies and the displacement eigenfunctions of a spherical model. We show that for a compressible and stratified spherical core model the effects of non-neutral density stratification may be significant, and the frequencies of these modes may change from model to model. For example, for a spherical core model the frequency of the spin-over mode, the (2, 1, 1) mode, is unaffected while that of the (4, 1, 1) mode is changed from -0.410 for the Poincaré core model to -0.434, -0.447 and -0.483 for core models with the stability parameter β = -0.001, -0.002 and -0.005, respectively, a maximum change of about 18 per cent when β = -0.005. Our results also show that for small stratification parameter, |β| ≤ 0.005, the frequency of an inertial-gravity mode is a nearly linear function of β but the slope of the line is different for different modes, and that the effects of density stratification on the frequency of a mode is likely related to its spatial structure, which remains the same in different Earth models. We also compute the frequencies of some of the modes of the `PREM' (spherical shell) core model and show that the frequencies of these modes may also be significantly affected by non-zero β.

Self-assembly of star micelle into vesicle in solvents of variable quality: the star micelle retains its core-shell nanostructure in the vesicle.

PubMed

Liu, Nijuan; He, Qun; Bu, Weifeng

2015-03-03

Intra- and intermolecular interactions of star polymers in dilute solutions are of fundamental importance for both theoretical interest and hierarchical self-assembly into functional nanostructures. Here, star micelles with a polystyrene corona and a small ionic core bearing platinum(II) complexes have been regarded as a model of star polymers to mimic their intra- and interstar interactions and self-assembled behaviors in solvents of weakening quality. In the chloroform/methanol mixture solvents, the star micelles can self-assemble to form vesicles, in which the star micelles shrink significantly and are homogeneously distributed on the vesicle surface. Unlike the morphological evolution of conventional amphiphiles from micellar to vesicular, during which the amphiphilic molecules are commonly reorganized, the star micelles still retain their core-shell nanostructures in the vesicles and the coronal chains of the star micelle between the ionic cores are fully interpenetrated.

The Design of 3D-Printed Lattice-Reinforced Thickness-Varying Shell Molds for Castings.

PubMed

Shangguan, Haolong; Kang, Jinwu; Yi, Jihao; Zhang, Xiaochuan; Wang, Xiang; Wang, Haibin; Huang, Tao

2018-03-30

3D printing technologies have been used gradually for the fabrication of sand molds and cores for castings, even though these molds and cores are dense structures. In this paper, a generation method for lattice-reinforced thickness-varying shell molds is proposed and presented. The first step is the discretization of the STL (Stereo Lithography) model of a casting into finite difference meshes. After this, a shell is formed by surrounding the casting with varying thickness, which is roughly proportional to the surface temperature distribution of the casting that is acquired by virtually cooling it in the environment. A regular lattice is subsequently constructed to support the shell. The outside surface of the shell and lattice in the cubic mesh format is then converted to STL format to serve as the external surface of the new shell mold. The internal surface of the new mold is the casting's surface with the normals of all of the triangles in STL format reversed. Experimental verification was performed on an Al alloy wheel hub casting. Its lattice-reinforced thickness-varying shell mold was generated by the proposed method and fabricated by the binder jetting 3D printing. The poured wheel hub casting was sound and of good surface smoothness. The cooling rate of the wheel hub casting was greatly increased due to the shell mold structure. This lattice-reinforced thickness-varying shell mold generation method is of great significance for mold design for castings to achieve cooling control.

The Design of 3D-Printed Lattice-Reinforced Thickness-Varying Shell Molds for Castings

PubMed Central

Shangguan, Haolong; Kang, Jinwu; Yi, Jihao; Zhang, Xiaochuan; Wang, Xiang; Wang, Haibin; Huang, Tao

2018-01-01

3D printing technologies have been used gradually for the fabrication of sand molds and cores for castings, even though these molds and cores are dense structures. In this paper, a generation method for lattice-reinforced thickness-varying shell molds is proposed and presented. The first step is the discretization of the STL (Stereo Lithography) model of a casting into finite difference meshes. After this, a shell is formed by surrounding the casting with varying thickness, which is roughly proportional to the surface temperature distribution of the casting that is acquired by virtually cooling it in the environment. A regular lattice is subsequently constructed to support the shell. The outside surface of the shell and lattice in the cubic mesh format is then converted to STL format to serve as the external surface of the new shell mold. The internal surface of the new mold is the casting’s surface with the normals of all of the triangles in STL format reversed. Experimental verification was performed on an Al alloy wheel hub casting. Its lattice-reinforced thickness-varying shell mold was generated by the proposed method and fabricated by the binder jetting 3D printing. The poured wheel hub casting was sound and of good surface smoothness. The cooling rate of the wheel hub casting was greatly increased due to the shell mold structure. This lattice-reinforced thickness-varying shell mold generation method is of great significance for mold design for castings to achieve cooling control. PMID:29601543

Ab initio description of p-shell hypernuclei.

PubMed

Wirth, Roland; Gazda, Daniel; Navrátil, Petr; Calci, Angelo; Langhammer, Joachim; Roth, Robert

2014-11-07

We present the first ab initio calculations for p-shell single-Λ hypernuclei. For the solution of the many-baryon problem, we develop two variants of the no-core shell model with explicit Λ and Σ(+),Σ(0),Σ(-) hyperons including Λ-Σ conversion, optionally supplemented by a similarity renormalization group transformation to accelerate model-space convergence. In addition to state-of-the-art chiral two- and three-nucleon interactions, we use leading-order chiral hyperon-nucleon interactions and a recent meson-exchange hyperon-nucleon interaction. We validate the approach for s-shell hypernuclei and apply it to p-shell hypernuclei, in particular to (Λ)(7)Li, (Λ)(9)Be, and (Λ)(13)C. We show that the chiral hyperon-nucleon interactions provide ground-state and excitation energies that generally agree with experiment within the cutoff dependence. At the same time we demonstrate that hypernuclear spectroscopy provides tight constraints on the hyperon-nucleon interactions.

Physical property control in core/shell inorganic nanostructures for fluorescence and magnetic targeting applications

NASA Astrophysics Data System (ADS)

Roberts, Stephen K.

Nanomaterials show immense promise for the future in numerous areas of application. Properties that are unique from the bulk material and are tunable allow for innovation in material design. This thesis will focus on controlling the physical properties of core/shell nanostructures to enhance the utility of the materials. The first focus is on the impact of different solvent mixtures during the shell growth phase of SILAR based core/shell quantum dot synthesis is studied. Gaining insight into the mechanism for SILAR growth of core/shell nanoparticles allows improved synthetic yields and precursor binding, providing enhanced control to synthesis of core/shell nanoparticles. The second focus of this thesis is exploring the use of magnetic nanoparticles for magnetic drug targeting for cardiovascular conditions. Magnetic targeting for drug delivery enables increased local drug concentration, while minimizing non-specific interactions. In order to be effective for magnetic targeting, it must be shown that low magnetic strength is sufficient to capture flowing nanoparticles. By demonstrating the binding of a therapeutic agent to the surface at medicinal levels, the viability for use as a nanoparticle drug delivery system is improved.