Multishell Structures Research Articles

Phonon Spectrum Engineering in Rolled-up Micro- and Nano-Architectures

We report on a possibility of efficient engineering of the acoustic phonon energy spectrum in multishell tubular structures produced by a novel high-tech method of self-organization of micro- and nano-architectures. The strain-driven roll-up procedure paved the way for novel classes of metamaterials such as single semiconductor radial micro- and nano-crystals and multi-layer spiral micro- and nano-superlattices. The acoustic phonon dispersion is determined by solving the equations of elastodynamics for InAs and GaAs material systems. It is shown that the number of shells is an important control parameter of the phonon dispersion together with the structure dimensions and acoustic impedance mismatch between the superlattice layers. The obtained results suggest that rolled up nano-architectures are promising for thermoelectric applications owing to a possibility of significant reduction of the thermal conductivity without degradation of the electronic transport.

Chemical Ordering and Surface Segregation in Cu–Pt Nanoalloys: The Synergetic Roles in the Formation of Multishell Structures

We performed Monte Carlo simulations coupled with MAEAM potentials to study the surface segregation and chemical ordering patterns in Cu–Pt nanoalloy particles for a broad range of sizes, shapes, composition, and temperature. It was found that both the Cu segregation on the surface and the chemical ordering in the core are the general rules and usually compete with each other. Surface segregation of Cu is enhanced with increasing particle size or surface openness or global Cu composition. Despite their different morphologies, most of the types of ordered phases in the core region are the same as bulk alloys. Due to the modification or suppression effects of surface segregation, the degrees of chemical ordering shift to the Pt-richer side and are more apparent in a large-sized particle. Particularly, at a narrow composition range, the multishell structures (onion-ring or multishell/maze-like core) form in (truncated) octahedrons, illustrating a subtle synergy between the segregated Cu {111} facets and the ...

Y₂O₃:Yb³⁺/Er³⁺ Hollow Spheres with Controlled Inner Structures and Enhanced Upconverted Photoluminescence.

Multishell Y2 O3 :Yb(3+) /Er(3+) hollow spheres with uniform morphologies and controllable inner structures are prepared successfully by using a glucose-template hydrothermal process followed by temperature-programmed calcination. Much enhanced upconverted photoluminescence of these Y2 O3 :Yb(3+) /Er(3+) are observed, which are due to the multiple reflections and the enhanced light-harvesting efficiency of the NIR light resulting from the special features of the multishell structures.

Versatile Ternary Manganese-Nickel-Cobalt Compounds in Multi-Shell Spherical Structures as Electrode Materials for High-Capacity Lithium-Ion Batteries

A full lithium-ion battery has been assembled based on nanoarchitectured ternary manganese-nickel-cobalt compounds, in which multi-shell spherical Mn0.54Ni0.13Co0.13(CO3)0.8 serves as anode and the subsequently lithiated Li-excess Li[Li0.2Mn0.54Ni0.13Co0.13]O2 with a yolk-shell structure acts as cathode. Multi-shell carbonate anode tested in a half cell with metallic lithium as the counter electrode reveals an unexpectedly high initial charge capacity of 1173.1 mAh/g at 25 mA/g. Accordingly, yolk-shell-structured Li-excess layered cathode material has been obtained through lithiation of carbonate compound, showing an initial discharge capacity of 250.7 mAh/g when cycled at 0.1 C (1C = 250 mA/g) in a half cell. Combination of nanostructured ternary transition metal carbonate anode and Li-excess layered cathode into a full lithium-ion battery results in a remarkable specific capacity above 250 mAh/g at 0.1 C in a voltage range of 0.1 - 4.0 V, which demonstrates as a very promising electrochemical device for future energy conversion and storage.

Interior Lamellar Assembly in Correlation to Top-Surface Banding in Crystallized Poly(ethylene adipate)

Novel approaches and schematic models have been used to provide insights in viewing lamellar assembly in ring-banded spherulites of a model polymer poly(ethylene adipate) (PEA) via correlations between the outer-surface and three-dimensional interior morphology. When crystallized at 28 °C, PEA in thick bulk forms exhibits a ring-banded top surface with bowl-like and dome-like height profile centering on its nucleus. The three-dimensional periodical assembly leads to not only the noticeable ring bands on exterior surfaces but also corrugated-board-like multishell structures in the interior of the spherulites. The corrugated-board structure has been found to be composed of plate-like lamellae, which first grow in a tangential direction and then turn to a radial direction; the radial plates taper to form thinner cilia-like lamellae due to the polymer chain concentration gradient periodically precipitated during the growth. Alternating sequences of plate-like lamellae in two perpendicular orientations (bending from tangential to radial) in PEA ring-banded spherulites during growth in a radial direction account for the spherulites confined in thin films to display two contrast circumferential rings with alternating interference colors. Scanning electron microscopy dissection graphs clearly revealed interior corrugated layer thickness in bulk forms, which matches well with the inter-ring spacing in thin films.

Coating and enhanced photocurrent of vertically aligned zinc oxide nanowire arrays with metal sulfide materials.

Hybrid nanostructures combining zinc oxide (ZnO) and a metal sulfide (MS) semiconductor are highly important for energy-related applications. Controlled filling and coating of vertically aligned ZnO nanowire arrays with different MS materials was achieved via the thermal decomposition approach of single-source precursors in the gas phase by using a simple atmospheric-pressure chemical vapor deposition system. Using different precursors allowed us to synthesize multicomponent structures such as nanowires coated with alloy shell or multishell structures. Herein, we present the synthesis and structural characterization of the different structures, as well as an electrochemical characterization and a photovoltaic response of the ZnO-CdS system, in which the resulting photocurrent upon illumination indicates charge separation at the interface.

Versatile Ternary Manganese-Nickel-Cobalt Compounds in Multi-Shell Spherical Structures As Electrode Materials for High-Capacity Lithium Ion Batteries

Electrochemical performance of rechargeable lithium ion batteries significantly relies on electrochemical properties of both cathode and anode materials. Nanostructured electrode materials have been demonstrated to improve cycling stability and rate capability for lithium ion batteries. Here, ternary manganese-nickel-cobalt carbonate (Mn0.54Ni0.13Co0.13(CO3)0.8, marked as MNCCO3) was first synthesized by hydrothermal method, which shows multi-shell spherical structure from numerous agglomerated nanoparticles. MNCCO3 as anode material can deliver very high initial charge capacity of 997.8 mAh/g at a current density of 50 mA/g, and 821.2 mAh/g at 250 mA/g, respectively. Furthermore, the versatile ternary transition metal carbonate enables to produce two different derivates: manganese-nickel-cobalt oxide (0.54Mn3O4-0.13Co3O4-0.13NiO, marked as MNCO) in multi-shell caged structure after sintering and lithium-excess layered cathode material (Li[Li0.2Mn0.54Ni0.13Co0.13]O2, marked as LMNCO) in yolk-shell structure after lithiation. The yielding MNCO as anode material shows outstanding cycling stability, which can retain charge capacity of 270.6 mAh/g after 100 electrochemical cycles at 250 mA/g. Simultaneously, LMNCO as cathode material delivers high initial discharge capacities of 250.7, 173.0 and 80.9 mAh/g at 25, 250 and 1250 mA/g, and can retain 156.3 mAh/g at 250 mA/g after 100 cycles, with remarkable corresponding capacity retention of 90.3%. The potential full battery from multifunctional ternary manganese-nickel-cobalt compounds, in which MNCCO3 or MNCO as anode material and LMNCO as cathode material, can be fabricated for next generation high-capacity lithium ion batteries.

Key role of hydrates in determining ion rejection by polyamide membrane

Understanding the mechanism of ion rejection in the separation process remains a major hurdle in designing new membrane materials for seawater desalination. Here, we investigate the effects of water and aromatic polyamide (PA) membrane on the rejection of salt ions, such as Fe2+, Na+, and Cl−, by molecular dynamic simulations. Results demonstrate that water plays a key role in salt ion rejection because salt ions preferentially interact with water molecules to form hydrates with multishell structures, which aids the rejection of various salt ions. For FeCl2 aqueous solution, the innermost shell water molecules of a Fe2+ hydrate can hardly be replaced by other substances in their molecular dynamics simulations, so ions would be highly rejected if the effective diameter of a water channel (EDC) in the membrane is smaller than that of the innermost shell of a hydrate. However, the water molecules in the second water shell can be replaced by the atoms of the membrane when the EDC is smaller than the size of the second shell (about 9 Å). Besides, although the sizes of these ions approximate to those of water molecules, the rejection level of PA membrane to salt ions is higher than that to water, which is accounted for by the formation of hydrate. POLYM. ENG. SCI., 55:466–473, 2015. © 2014 Society of Plastics Engineers

Drilling couples and refined constitutive equations in the resultant geometrically non-linear theory of elastic shells

It is well known that distribution of displacements through the shell thickness is non-linear, in general. We introduce a modified polar decomposition of shell deformation gradient and a vector of deviation from the linear displacement distribution. When strains are assumed to be small, this allows one to propose an explicit definition of the drilling couples which is proportional to tangential components of the deviation vector. The consistent second approximation to the complementary energy density of the geometrically non-linear theory of isotropic elastic shells is constructed. From differentiation of the density we obtain the consistently refined constitutive equations for 2D surface stretch and bending measures. These equations are then inverted for 2D stress resultants and stress couples. The second-order terms in these constitutive equations take consistent account of influence of undeformed midsurface curvatures. The drilling couples are explicitly expressed by the stress couples, undeformed midsurface curvatures, and amplitudes of quadratic part of displacement distribution through the thickness. The drilling couples are shown to be much smaller than the stress couples, and their influence on the stress and strain state of the shell is negligible. However, such very small drilling couples have to be admitted in non-linear analyses of irregular multi-shell structures, e.g. shells with branches, intersections, or technological junctions. In such shell problems six 2D couple resultants are required to preserve the structure of the resultant shell theory at the junctions during entire deformation process.

Electrophoretic Mobilities of a Viral Capsid, Its Capsid Protein, and Their Relation to Viral Assembly

The self-assembly of many viral capsids is dominated by protein-protein electrostatic interactions. To have a better understanding of this process, it is important to know how the protein and the capsid surface charges vary as a function of the pH and ionic strength. In this work, using phase analysis light scattering, we measured the electrophoretic mobility (EM) of the cowpea chlorotic mottle virus (CCMV), its capsid protein (CP), and a cleaved CP that lacks its basic terminus, as a function of pH and ionic strength. The EM measurements of the CP are difficult to carry out due to its tendency to self-assemble into capsids; we show how to circumvent this problem by appropriately changing the CP concentration. We found that the isoelectric points (pIs) of the virion and of the CP are insensitive to ionic strength. The onset of multishell structures in the phase diagram of the CCMV CP as a function of ionic strength and pH (and its absence in the brome mosaic virus (BMV) CP phase diagram) can be related to the pI of the capsid. We propose that the transition from multiwall shells to nanotube structures is due to a change in the spontaneous curvature of the CP at its pI. A nonzero limit of the EM at high ionic strength is characteristic of a soft colloid, but a near identity of the EMs of empty capsids and those containing RNA indicates that the EM reflects only the charge distribution in the CP. The Henry equation has been used to provide approximate values of the capsid surface charge as a function of pH and I.

The synthesis of a core–shell hybrid composite micro-sphere with controllable homogenous or heterogeneous multi-shell structure by multiple-growth via a combination method

The preparation of controllable multi-shell nano and micro particles has great significance not only for their potential applications but also for fabricating novel composite functional advanced materials. In this paper, MSiO2, MTiO2 and SSiO2 with good monodispersity and no agglomeration among spheres have been synthesized successfully based on Stöber's method. MSiO2 were characterized as the silica with a worm-like mesopore structure and with uniform pore sizes of about 2.0nm, and about 700m2/g of specific surface area. A core–shell hybrid composite micron-sized spherical particle with multi-shell structures by using the synthesized MSiO2, MTiO2 and SSiO2 with a combination method has been designed and fabricated. The multiple-layers of these spherical particles can be controllably prepared via multiple deposits in an alcohol solution system, and the standard deviations of particle size of each sample are less than 3%. The temperature and the seeds mass effect on the morphologies of MSiO2/SSiO2 and MSiO2/SSiO2/SSiO2 via multiple-growth by coating solid silica layers have been investigated. In order to illustrate the sphere with multi-shell structure may have multi-functionalized, the MSiO2 sphere embedded methylene blue in the pores and coated with solid silica shell was fabricated.

Quasi-effective medium theory for multi-layered magneto-dielectric structures

We present a quasi-effective medium theory that determines the optical properties of multi-layered composites beyond the quasi-static limit. The proposed theory exactly reproduces the far field scattering/extinction cross sections through an iterative process in which mode-dependent quasi-effective impedances of the composite system are introduced. In the large wavelength limit our theory is consistent with the Maxwell–Garnett formalism. Possible applications in determining the hybridization particle resonances of multi-shell structures and electromagnetic cloaking are identified.

Geometric isotope effects on small chloride ion water clusters with path integral molecular dynamics simulations

The geometric isotope effects on the structures of hydrated chloride ionic hydrogen bonded clusters are explored by carrying out path integral molecular dynamics simulations. First, an outer shell coordinate is selected to display the rearrangement of single and multi hydration shell cluster structures. Next, to show the competition of intramolecular and intermolecular nuclear quantum effects, the intramolecular OH∗ stretching and intermolecular ion–water wagging motions are studied for single and multi shell structures, respectively. The results indicate that the intermolecular nuclear quantum effects stabilize the ionic hydrogen bonds in single shell structures, while they are destabilized through the competition with intramolecular nuclear quantum effects in multi shell structures. In addition, the correlations between ion–water stretching motion and other cluster vibrational coordinates are discussed. The results indicate that the intermolecular nuclear quantum effects on the cluster structures are strongly related to the cooperation of the water–water hydrogen bond interactions.

SiO2–Ag–SiO2–TiO2 multi-shell structures: plasmon enhanced photocatalysts with wide-spectral-response

Tailorable synthesis of plasmon enhanced catalysts with high solar-light harvesting and energy-conversion efficiency has attracted wide interest due to its scientific and technological importance. In this paper, novel SiO2–Ag–SiO2–TiO2 multi-shell photocatalysts with wide-spectral-response were systematically designed and controllably synthesized, where the SiO2 spheres were used as the cores, and the SiO2 interlayers coated on the Ag nanoparticle (NP) shells were used to separate the Ag from the TiO2 shell. The structures of the SiO2–Ag–SiO2–TiO2 multi-shell photocatalysts can be tailored by changing the thickness of SiO2 interlayers from 1 to 2, 5, 8, 12, and 20 nm, while the anatase N-doped TiO2 shells with visible light response are maintained at a thickness of 20 nm. The photocatalytic activity tests show that the enhanced photocatalytic efficiency under both ultraviolet (UV) and visible light irradiation is related to the existence of Ag NP shells and the thickness of SiO2 interlayers. The complicated coupling mechanisms between TiO2 and a plasmon are systematically discussed, and a clear physical picture for the complicated coupling processes is presented. The main reasons for the enhancement of the photocatalytic activity of the SiO2–Ag–SiO2–TiO2 multi-shell structures are the localized surface plasmon resonance (LSPR) effect and scattering effect induced by Ag NPs.

Diffusion of the vacancy defect leading to the formation of multi-shell structures in the nanowire and nanobridge

Accelerated molecular dynamics has been employed to study the phase transformation of the Au nanobridge and freestanding nanowire from a face center cubic structure with 15 atoms in the cross section to a helical multi-shell structure at room temperature. The translation of vacancy defect displays an important role to cause the transformation of the nanowire and nanobridge. Due to the difference in boundary conditions, the different defect dynamics are observed for nanobridge and nanowire. The fact leads the formation of 11-4 and 12-4 structures in the nanobridge and nanowire, respectively. The 11-4 nanowire has been verified to be a metastable structure, which prefers becoming a 12-4 structure if the defect exists. In addition, the atomic arrangements of 11-4 and 12-4 structures were analyzed by the angular correlation function, and were found to possess a specific coordinated relationship between their inner and outer shells.

Helical multi-shell structures in gold nanobridge and suspending nanowire

Phase transformations of ultra-thin (<2 nm) 〈 110 〉 gold nanobridges and nanowires of 11-4, 12-5, 13-6, 14-7-1, and 15-8-1 helical multi-shell (HMS) structures were investigated by accelerated molecular dynamics at room temperature. The ultra-thin nanowires with face-centered-cubic (FCC) structure can easily transform into the HMS structure by shear-like transformation and dissociation of the inner and outer shells of the nanowire. The latter leads to twist deformation and the formation of the helical structure. It is noted that the shear-like transformation leads to the formation of quasi-hexagonal atomic packing on the surface. Owing to the constrained atoms at both ends of the nanobridge, collective rearrangements of atoms at the nanobridge/bulk crystal junction were observed in the formation of HMS nanobridges. Except for the 15-8-1 structure, configurations of the HMS structures in nanobridges and nanowires are similar. The helical angles of different types of HMS nanowires are measured: 11-4, 13-6, and 15-8-1 nanowire are 4, 2.5, and 2°, respectively, whereas the 12-5 and 14-7-1 nanobridges with even number of outer shell atoms have zero helical angle. The characteristic angles between atoms in HMS gold structures have an extra 75, 105, 135, 150, and 165° when compared with bulk FCC crystal. The result of the pristine stress distribution shows that the tensile stresses extend over the interior of the nanowires that consist of only two atomic shells.

Monte Carlo simulations of the structure of Pt-based bimetallic nanoparticles

Pt-based bimetallic nanoparticles have attracted significant attention as a promising replacement for expensive Pt nanoparticles. In the systematic design of bimetallic nanoparticles, it is important to understand their preferred atomic structures. However, compared with unary systems, alloy nanoparticles present greater structural complexity with various compositional configurations, such as mixed-alloy, core–shell, and multishell structures. In this paper, we developed a unified empirical potential model for various Pt-based binary alloys, such as Pd–Pt, Cu–Pt, Au–Pt and Ag–Pt. Within this framework, we performed a series of Monte Carlo (MC) simulations that quantify the energetically favorable atomic arrangements of Pt-based alloy nanoparticles: an intermetallic compound structure for the Pd–Pt alloy, an onion-like multishell structure for the Cu–Pt alloy, and core–shell structures (Au@Pt and Ag@Pt) for the Au–Pt and Ag–Pt alloys. The equilibrium nanoparticle structures for the four alloy types were compared with each other, and the structural features can be interpreted in terms of the interplay of their material properties, such as the surface energy and heat of formation.

Energy landscapes of ion clusters in isotropic quadrupolar and octupolar traps

The energy landscapes of ion clouds confined in isotropic quadrupolar and octupolar traps are characterized for several representative cluster sizes. All clusters exhibit stable multishell structures that belong to separate funnels. Quadrupolar confinement leads to more homogeneous clusters and denser distributions of isomers than octupolar confinement. Statistical analysis of the transition states indicates that the barriers associated with intrashell motion are lower but more asymmetric and more cooperative compared to intershell motion. The relaxation between low-energy funnels with different arrangements of shells mostly exhibits Arrhenius kinetics, with a weak variation of the activation energy at higher temperatures.

Nb2O5 nanowire photoanode sensitized by a composition-tuned CdSxSe1−x shell

Nb2O5 nanowires (NWs) were grown by the thermal oxidation of Nb foils. The thermal chemical vapor transport of CdS/CdSe powders produces Nb2O5–CdSxSe1−x core–shell NWs with complete composition tuning. In the alloy composition, CdSe-like and CdS-like phases exist in the outer and inner regions of the shell, respectively, forming unique multi-shell structures. As x increases, the thickness of the CdSe-like outer shell decreases, while that of the CdS-like inner shell increases. We fabricated photoelectrochemical (PEC) cells using the as-grown Nb2O5–CdSxSe1−x NWs and measured their photocurrents and hydrogen generation rates under AM 1.5G irradiation. The PEC cells showed excellent photoconversion efficiency, which is comparable to that of TiO2–CdSxSe1−x NWs. It indicates that the present Nb2O5 NW promises an excellent photoanode of solar cell devices. The multi-shell structures increase the PEC performance by producing novel band alignment for efficient electron–hole separation following enhanced visible-range photon absorption.

On the Melting and Freezing of Au−Pt Nanoparticles Confined in Single-Walled Carbon Nanotubes

A MD simulation method is used to simulate the melting and freezing of Au−Pt nanoparticles confined in armchair single-walled carbon tubes ((n,n)-SWNTs), applying the second-moment approximation of the tight-binding potentials for metal−metal interactions and Lennard-Jones potential for the metal−carbon interactions. The carbon atoms on the SWNTs are taken to be fixed. The structures, total energies, Lindemman indices, and radial and axial density distributions are used to examine the behaviors of melting and freezing for Au−Pt nanoparticles confined in (n,n)-SWNTs. The nucleation analysis is carried out in terms of classical nucleation theory. The simulation results demonstrate that the solid Au−Pt clusters confined within (n,n)-SWNTs have multishell structures, even in a melted cluster. In addition, for the confined Au−Pt nanoparticles, Pt atoms tend to stay at the position close to the SWNT wall, which is different from free Au−Pt nanoparticles. Simulation results reveal that SWNTs and compositions of nanoparticles have significant effects on the structures and physical properties of the confined Au−Pt nanoparticles. On the other hand, some important thermodynamic and dynamic parameters are estimated based on MD simulations and compared with available theoretical and experimental results.