Chains Of Nanospheres Research Articles

Thermal stability of electrodeposited platinum nanowires and morphological transformations at elevated temperatures

Pt nanowires were prepared by template electrodeposition using ion track etched polymer membranes and analysed with respect to their thermal stability. Driven by Rayleigh instability, the polycrystalline Pt nanostructures experienced structural transformations and finally fragmented into linear chains of nanospheres at temperatures much below the melting point of bulk Pt. Morphological changes were systematically studied by electron microscopy and compared with previously reported results on other metal nanowires and theoretical predictions. In addition, nanowires could readily be interconnected to two-dimensional assemblies by taking advantage of the rapid diffusion processes. This study will help to predict the durability of integrated nanowires and contributes to the understanding of thermal-induced transformations for polycrystalline nanowires.

Second-harmonic generation in integrated nanosphere chains

The second-harmonic generation in a three-dimensional subwavelength photonic circuit consisting of spherical semiconductors with large second-order nonlinear susceptibility has been investigated by using a multiple-scattering method. The second-harmonic fields along a single chain, around a corner, and split at forked structures have been demonstrated using the three-dimensional confinement effects of subwavelength light. Our results show that the second-harmonic generations can be realized in the three-dimensional subwavelength photonic circuit and provide an alternative route for the design of integrated three-dimensional nonlinear devices.

Coherent magnetic plasmon modes in a contacting gold nano-sphere chain on a gold Slab

A coupled magnetic resonator waveguide, composed of a contacting gold nanosphere chain on a gold slab, is proposed and investigated. A broadband coherent magnetic plasmon mode can be excited in this one dimensional nanostructure. By employing the Lagrangian formalism and the Fourier transform method, the dispersion properties of the wave vector and group velocity of the magnetic plasmon mode are investigated. Small group velocity can be obtained from this system which can be applied as subwavelength slow wave waveguides.

Raman Spectroscopy and Field Emission Scanning Electron Microscopic Studies on Carbon Nanomaterials

Raman analysis is one of the main methods use to investigate type of graphitized carbon nanomaterials. It provides information on the vibration of crystal lattice, electron structure and regularity of crystal structure of the graphitized carbon materials. In this work the single step chemical vapour deposition (CVD) method was introduced for the direct growth of all as-synthesized carbon nanomaterials; carbon nanotubes (CNTs), carbon nanofiber (CNF), carbon nanosphere chain (CNSC) and CNT heterojunctions (HJCNTs). Series of metal catalysts were formulated from Ni, Fe, Cr and Cu, and were used in the synthesis of the respected carbon nanomaterials (CNMs). By introducing the right combination of the reaction conditions consisting of the formulated catalyst, reaction temperature and flow rate as well as type of carbon source resulted in the formation of different types of carbon nanomaterials. Raman spectra analysis revealed that the used of acetylene and ethanol as the carbon precursors are proficient to produce different form of carbon nanomaterials as depicted by the evolution of the G-band and D-band intensities. The FESEM micrographs obtained confirmed the morphology and types of the respected carbon nanomaterials synthesized in this study.

Surface plasmon-polariton propagation in piecewise linear chains of composite nanospheres: The role of optical gain and chain layout

The energy transport properties of plasmonic waveguides can be analyzed by solving the dispersion relation for surface plasmon-polaritons (SPPs). We use this approach to derive an approximate analytical expression for SPP propagation length when the waveguide is composed of linearly arranged metallic nanoparticles, while assuming that metal losses are small or partially compensated by gain. Applied to metal-dielectric (composite) nanospheres, the obtained expression allows us to optimize the performance of the waveguide and arrive at a number of practical design rules. Specifically, we show that SPP attenuation can be minimized at a certain interparticle distance for transverse modes, but gradually grows for both longitudinal and transverse modes with the increase of particle separation. We also show that the two basic methods of supplying gain to the system, i.e., embedding the particles into a gain medium or having a metal-gain composition for the particles, do not perform equally well and the former method is more efficient, but the way the two methods affect depends on the polarization of SPPs. To investigate the role of the nanoparticles' arrangement in determining SPP characteristics, we follow a purely numerical approach and consider a two-segment bent waveguide as an example. Analyzing the waveguide's transmission shows that it behaves in an oscillatory manner with respect to the angle between the two segments and is therefore higher for certain angles than for the others. This suggests that, in the design of waveguides with bends, careful attention needs to be paid in order to avoid bend angles that yield low transmission and to choose angles that give maximum transmission.

Surface Plasmon Resonances in Strongly Coupled Gold Nanosphere Chains from Monomer to Hexamer

We present experimental data on the light scattering properties of linear chains of gold nanoparticles with up to six nanoparticles and an interparticle spacing of 1 nm. A red shift of the surface plasmon resonance with increasing chain length is observed. An exponential model applied to the experimental data allows determination of an asymptotic maximum resonance at a chain length of 10-12 particles. The optical data are compared with analytical and numerical calculation methods (EEM and BEM).

Complex bound and leaky modes in chains of plasmonic nanospheres

Bound and leaky modes with complex wavenumber in chains (linear arrays) of plasmonic nanospheres are characterized for both longitudinal and transverse polarization states (with respect to the array axis). The proposed method allows for the description of each mode evolution when varying frequency. As a consequence, full characterization of the guided modes with complex wavenumber is provided in terms of propagation direction, guidance or radiance, proper or improper, and physical or nonphysical conditions. Each nanosphere is modeled according to the single dipole approximation, and the metal permittivity is described by the Drude model. Modal wavenumbers are obtained by computing the complex zeroes of the homogeneous equation characterizing the field in the one dimensional periodic array. The required periodic Green's function is analytically continued into the complex wavenumber space by using the Ewald method. Furthermore, a parametric analysis of the mode wavenumbers is performed with respect to the geometrical parameters of the array.

Cryogenic Transmission Electron Microscopy Study of Amelogenin Self-Assembly at Different pH

Cryogenic transmission electron microscopy (cryo-EM) was used to explore the self-assembly of recombinant murine amelogenin (rM179) in vitro.Our cryo-EM data showed that amelogenin self-assembly is a strongly pH-dependent process. At pH 4.4 the main fraction of the protein exists in a monomeric form, although some peculiar structures consisting of chains of monomers were also observed. At pH 5.8 large nanospheres comprising ring-like structures ∼50 nm in diameter were the most abundant particle class. Similarly, at pH 8.0 amelogenins self-assembled into ring-like oligomers of different sizes, which subsequently assembled into nanospheres 15–20 nm in diameter. Furthermore, at pH 7.2, which is close to a physiological pH, branched chains of nanospheres were observed. Our results show that amelogenin assembly is a multistep hierarchical process and provides new insight into the control of enamel mineralization.

Complex-ωapproach versus complex-kapproach in description of gain-assisted surface plasmon-polariton propagation along linear chains of metallic nanospheres

Propagation characteristics of surface plasmon-polaritons (SPPs) in linear chains of metallic nanospheres (LCMNs) can be found from a dispersion equation, by assuming that either frequency or wave number of a SPP is real. In this paper, we present a comparative study of SPP modes corresponding to the two types of complex solutions for an infinitely long LCMN embedded in a gain medium. We show that even though gain predominantly affects the SPP dispersion obtained with real frequency, both solutions result in the same dispersion and attenuation of SPP modes, when Ohmic losses are almost compensated by gain. In this regime, an analytic expression for the propagation length of SPPs exists, and the SPPs' dispersion is determined by a real equation. We also demonstrate that for a given amount of gain $($below the amplification limit of $~$$1000$ cm${}^{\ensuremath{-}1})$, transversely polarized SPPs attenuate slower than longitudinally polarized SPPs and are, therefore, preferable for the purpose of energy transfer in gain-supplied LCMNs. The transmission windows for SPP modes of different polarizations do not overlap each other, which facilitates realization of LCMN-based plasmonic filters. Our results may prove useful in design optimization of all-optical chips for power-efficient optical supercomputers.

Theoretical and Experimental Studies of the Optical Properties of Conjoined Gold−Palladium Nanospheres

We identify and report on UV−vis spectral features of AucorePdshell nanoparticles. Chains of conjoined nanospheres are formed with clear core/shell segregation and identified via experimental spectral red shifts of λmax and scanning transmission electron microscopy (STEM) imaging. Theoretical calculations performed using the discrete dipole approximation (DDA) validate our findings. The DDA simulation method is then used to delve further into possible spectroscopic implications of geometric and environmental changes. Structural configurations including extended chains of nanospheres, differing levels of nanosphere conjoinment, and increased Pd shell thickness are investigated, as well as variations of the surrounding dielectric medium.

Low-loss plasmonic waveguide based on gain-assisted periodic metal nanosphere chains

We propose a low-loss nanoscale waveguide based on gain-assisted plasmonic resonance metallic nanosphere chain. We demonstrate that by employing a gain material or even an appropriate dielectric for the host environment, waveguide loss can be reduced dramatically. A highly efficient pseudo-orthonormal basis expansion method for obtaining the complex dielectric spectra of the low-loss transmission has been developed. Eigenmode analysis revealed the physical origin of those low-loss waveguiding modes, which opens the possibility to achieve waveguiding other than using conventional dipolar resonances of individual particles. A scheme based on electron beam lithography and chemically synthesized nanoparticles has been proposed to fabricate the device.

Undamped collective surface plasmon oscillations along metallic nanosphere chains

The random-phase-approximation semiclassical scheme for describing plasmon excitations in large metallic nanospheres (with radius ∼10–60 nm) is developed for the case when a dynamical electric field is present. The spectrum of plasmons in metallic nanospheres is determined including both surface and volume-type excitations and their mutual connections. It is demonstrated that only dipole-type surface plasmons can be excited by a homogeneous dynamical electric field. The Lorentz friction due to irradiation of electromagnetic energy by plasmon oscillations is analyzed with respect to sphere dimension. The resulting shift in resonance frequency due to plasmon damping is compared with experimental data for various sphere radii. Wave-type collective oscillations of surface plasmons in long chains of metallic nanospheres are described. The undamped region for collective plasmon propagation along the metallic chain is found in agreement with previous numerical simulations.

Controllable and Large-Scale Synthesis of Carbon Nanofibers, Bamboo-Like Nanotubes, and Chains of Nanospheres over Fe/SnO2 and Their Microwave-Absorption Properties

Carbon nanofibers (CNFs), bamboo-like carbon nanotubes (CNTs), and chains of carbon nanospheres (CNSs) were produced selectively in large quantities in the pyrolysis of acetylene at 500, 600, and 700 °C, respectively, over Fe/SnO2 nanoparticles generated by means of a combined sol−gel and hydrogen-reduction method. One advantage of this approach is that there is no need of using a dilute gas such as argon or nitrogen. It is found that the pyrolysis temperature has considerable effect on the yield, morphology, and microwave-absorption properties of the obtained materials. The corresponding yields of CNFs, bamboo-like CNTs, and chains of CNSs are high, up to 25595, 36791, and 37039%, respectively. Thus, a simple and environment-friendly approach has been proposed for mass production of CNFs, bamboo-like CNTs, and chain of CNSs in a controllable manner. In addition, the as-prepared carbon materials are demonstrated to show good microwave-absorption properties. On the basis of the results, we propose a possib...

Plasmonic Resonances of Closely Coupled Gold Nanosphere Chains

The optical properties of an ordered array of gold nanospheres have been calculated using the T-matrix method in the regime where the near-fields of the particles are strongly coupled. The array consists of a one-dimensional chain of spheres of 15 nm diameter where the number of spheres in the chain and interparticle spacing is varied. Calculations have been performed with chains up to 150 particles in length and with an interparticle spacing between 0.5 and 30 nm. Incident light polarized along the axis of the chain (longitudinal) and perpendicular (transverse) to it are considered, and in the latter case for wavevectors along and perpendicular to the chain axis. For fixed chain length the longitudinal plasmon resonance red shifts, relative to the resonance of an isolated sphere, as the interparticle spacing is reduced. The shift in the plasmon resonance does not appear to follow an exponential dependence upon gap size for these extended arrays of particles. The peak shift is inversely proportional to th...

Optical response of linear chains of metal nanospheres and nanospheroids

A semi-analytical method for computing the electric field surrounding a finite linear chain of metal nanospheres and nanospheroids is described. In treating chains or clusters of spheres, a common approach is to use the spherical-harmonic addition theorem to relate the multipole expansion coefficients between different spheres. A method is described here that avoids the use of spherical-harmonic addition theorems, which are not applicable to spheroidal chains. Simulations are given that illustrate the large field enhancements that can occur in the gaps between silver nanoparticles arising from plasmon resonances.

Responsive nanomaterials for engineering asset evaluation and condition monitoring

Responsive nanomaterials are being developed through interdisciplinary research to improve and evaluate the performance of engineering assets. An overview of the work is given here. Nanomaterials are defined as bulk materials that have nanoparticle components. Responsive materials are defined as having an intrinsic ability to sense their condition and potentially respond when performance of the material is being affected or degraded. Responsive nanomaterials are a new class of material being developed by integrating nanoscale particles into host materials to provide the properties that we want. Nanomaterials can have unique combinations of properties such as a high surface area to volume ratio of the nanophase components, improved stiffness and strength, supercapacitance, electrical conductivity, magnetic properties, lightweight, photonic, and other properties. The focus of this paper is on development of responsive materials based on commercially available nanoscale materials that can be put into applications now. The nanoscale materials considered are carbon nanofibres, carbon nanosphere chains, long carbon nanotubes, and the intermediate products of these materials. Nanoengineering of multifunctional responsive materials is predicted to open up many new opportunities in the field of condition monitoring and asset evaluation, not just for structures, but also for humans, electronics, and the environment. New classes of responsive nanomaterials such as piezoresponsive, magnetoresponsive, photoresponsive, thermoresponsive and others may eventually enable the design of engineering assets that are self-monitoring and partially self-repairable, thus making high technology machines, vehicles, and structures safer for society and safeguarded against misuse.

Powering up nanoparticles: versatile carbon materials for engineering and medicine

Given carbon’s unique properties and versatility,1–4 carbon nanomaterials are being used in an increasing number of engineering and medical applications. For example, when carbon nanoparticles are dispersed in matrix materials like epoxy, polyurethane, rubber, cement, or ice, they confer unique electrical and magnetic properties, unlocking a number of new and exciting applications. When such materials are placed under strain, changes in electrical resistance (piezoresistive) and magnetic properties (piezomagnetic) emerge. In an electrolyte, the materials can expand due to an applied voltage.3 An interdisciplinary research team5 is developing carbon materials for commercialization in products such as spray-on continuous sensors for structural health monitoring (SHM), smart nanocomposites that are self-sensing, nanoreinforced laminated composites (NRLCs) that are tough in shear, and carbon nanotube (CNT) electrical fibers. This article provides a summary of how these composites are being developed at our facility to form different prototypes for diverse applications. Carbon nanofibers (CNFs) are multiwall, highly graphitic, low-cost fibers6 with diameters ranging from 70 to 200 nm and lengths up to a few hundred microns: see Figure 1(a). The fiber walls sit at an angle of about 20 degrees to the fiber axis and terminate along the surface of the fiber in a zigzag form. Remarkably, a relatively small loading of CNFs in a polymer matrix material can improve its mechanical properties and affect its electrical conductivity, piezoresistive, electromagnetic shielding, and heat dissipation characteristics. As such, promising CNF Figure 1. Nanomaterials for engineering and medical applications: (a) carbon nanofibers (CNFs) produced by Applied Sciences Inc., (b) carbon nanosphere chains (CNSCs) produced by Clean Technologies Inc., and (c) an 11mm-long carbon nanotube (CNT) array produced by the University of Cincinnati.

A computational study of the optical response of strongly coupled metal nanoparticle chains

We study the optical response of strongly coupled metal nanoparticle chains using rigorous multiple scattering calculations. The collective resonant frequency of silver nanosphere chains and the coupling between chains are considered. The coupling between silver nanoparticle chains are understood by the transmission and reflection calculations of 2D periodic arrays of nanospheres. The results are in agreement with recent experiments. The splitting of plasmon resonance modes for different polarizations of the incident light are explored. Our results show that the transverse mode resonant wavelength is very sensitive to the inter-chain distance. Results on the effect of disorder are also presented.

Propagation of surface plasmons in ordered and disordered chains of metal nanospheres

We report a numerical investigation of surface plasmon (SP) propagation in ordered and disordered linear chains of metal nanospheres. In our simulations, SPs are excited at one end of a chain by a near-field tip. We then find numerically the SP amplitude as a function of propagation distance. Two types of SPs are discovered. The first SP, which we call the ordinary or quasistatic, is mediated by short-range, near-field electromagnetic interaction in the chain. This excitation is strongly affected by Ohmic losses in the metal and by disorder in the chain. These two effects result in spatial decay of the quasistatic SP by means of absorptive and radiative losses, respectively. The second SP is mediated by longer range, far-field interaction of nanospheres. We refer to this SP as the extraordinary or nonquasistatic. The nonquasistatic SP cannot be effectively excited by a near-field probe due to the small integral weight of the associated spectral line. Because of that, at small propagation distances, this SP is dominated by the quasistatic SP. However, the nonquasistatic SP is affected by Ohmic and radiative losses to a much smaller extent than the quasistatic one. Because of that, the nonquasistatic SP becomes dominant sufficiently far from the exciting tip and can propagate with little further losses of energy to remarkable distances. The unique physical properties of the nonquasistatic SP can be utilized in all-optical integrated photonic systems.

Morphological evolution of Au nanowires controlled by Rayleigh instability

A sound knowledge and understanding of the thermal stability of nanowires is aprerequisite for the reliable implementation of nanowire-based devices. We investigate themorphology of Au nanowires annealed isothermally at different temperatures. Duringthe processes, triggered by heating, the wires undergo various configurationalchanges to finally break up into chains of nanospheres at much lower than bulkmelting temperatures due to capillary or so-called Rayleigh instability. The role ofthree parameters, namely, wire diameter, temperature, and annealing time, onthe final morphology is investigated. Both the average sphere diameter and themean spacing between adjacent spheres are larger than the values predicted formaterials with isotropic surface energy. Possible reasons are discussed in the paper.