Nanoparticle Chains Research Articles

Spin dynamics investigations of multifunctional ambient scalable Fe3O4 surface decorated ZnO magnetic nanocomposite using FMR

Microwave spin resonance behavior of the Fe3O4 surface decorated ZnO nanocomposites (FZNC) has been investigated by ferromagnetic resonance (FMR). Modified hydrothermal method has been adopted to fabricate FZNC samples with Fe3O4 nanoparticles chains were used as seeds in the uniform magnetic field to decorate them on the surface of the ZnO nanoparticles in a unique configuration. Spin dynamics investigation confirms the transition of ZnO from diamagnetic to ferromagnetic as the sharp FMR spectra converts to the broad spectra with Fe3O4 nanoparticles incorporation. A single broad FMR spectra confirms that no isolated Fe3+ or Zn2+ ions exist which is also in agreement with XRD confirming suitable composite formation. Further, the increase in Fe3O4 concentration leads to decrease in g-value which is resulting from the internal field enhancement due to magnetic ordering. Also, various spin resonance parameters were calculated for the FZNC which provides a detail information about the magnetic ordering, exchange coupling and anisotropy. Elemental analysis confirms the presence of Fe and Zn simultaneously and transmission electron microscopy (TEM) image show the presence of Fe3O4 on the grain boundaries of ZnO which has been confirmed by taking high-resolution TEM and electron diffraction patterns on both sides of the interface. These unique structural configuration of the FZNC has tremendous potential in various magneto-optoelectronic, spintronics and electro-chemical applications.

Self-assembly of superstructures at all scales

Summary Controllable assembly of molecular and nanoscale building blocks into uniform superstructures up to bulk dimensions remains a key challenge in the next phase of nanotechnology development. Here, we report the self-assembly of superstructures at all scales by taking advantage of the partial miscibility of water and 1-butanol to generate transient aqueous emulsion droplets that can encapsulate the target materials and introduce them into template holes. Further diffusion of water into 1-butanol depletes the emulsion droplets, assembling the building blocks into one well-defined superstructure in each hole. Superstructuring of various types and shapes of nanoparticles, biomolecules, and inorganic compounds could be achieved without the need for surfactants and chemical modifications. The versatility, scalability, low-cost, and accurate positioning are crucial advantages for the future development of advanced precision manufacturing.

Influence of a Magnetic Field on the Growth and Magnetic Properties of Zn0.15Fe2.85O4 Nanoparticle Chains

With the assistance of a magnetic field, Hsyn, a series of Zn0.15Fe2.85O4 (ZFO) nanoparticle chains (NCs) with a mean particle diameter of around ∼140 nm and different chain lengths are synthesized...

Electrocatalytic performance of Au@Cu Nanoparticle Chains as Sensor for Determination of Piroxicam

Electrocatalytic performance of Au@Cu Nanoparticle Chains as Sensor for Determination of Piroxicam

Linear chains of Ag nanoparticles embedded in dielectric films for SERS applications in analytical chemistry.

In line with the approach known as shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), in which Raman signal amplification of analytes is provided by metallic nanoparticles with an ultrathin silica or alumina shell, we report here on a Surface-Enhanced Raman Spectroscopy (SERS) substrate consisting of periodic lines of Ag nanoparticles embedded in dielectric surfaces for enhancing Raman signals. This paper demonstrates the possibility to use these so-called ‘PLANEDSERS’ substrates as washable and reusable chemical sensors with a good level of repeatability. Large-area Ag nanoparticle arrays are produced by glancing-angle ion-beam sputtering deposition on nanorippled patterns and are protected from the chemical environment (atmospheric or liquid solutions) by a robust and functionalizable thin dielectric layer of alumina or silicon nitride. Our results show that linear assemblies of ellipsoidal nanoparticles (size ∼15 nm) separated by interparticle gaps of approximately 5 nm generate enough near-field intensity enhancement to give rise to significant SERS signals of non-Raman-resonant bipyridine molecules without chemical contact between molecules and Ag nanoparticles. Moreover, the optical dichroic response of these plasmonic assemblies allows for the possibility of tuning the excitation wavelength of the Raman spectra over a wide spectral range. This study is a first step towards designing a substrate-platform without chemical specificity to enhance in equal manner all the weak Raman signals of usual organic molecules and to avoid loss of balance in favour of only one species as usual in SERS experiments. The quantitative detection ranges for bipyridine used as a probe test molecule are around between 10−3 to 10−6 M.

Теплопроводность наножидкостей: влияние формы частиц

The paper proposes a modified Maxwell formula applied to the calculation of the thermal conductivity of nanofluids. It is shown that the use of elongated particles or chains of nanoparticles leads to a significant increase in thermal conductivity. Theoretical estimates based on the proposed model are in good agreement with experimental data.

Directed assembly of barium titanate nanopeapods via solvothermal processing with a mixed surfactant system

Barium titanate (BaTiO3) peapod nanocomposites were prepared by the controlled capture of nanoparticles (NPs) in scrolling hexaniobate (HNB) nanosheets. BaTiO3 NPs and proton-exchanged potassium hexaniobate were treated solvothermally at 220 °C for 6 h in toluene to produce linear NP chains confined within multiwalled HNB nanoscrolls. This method consistently produced nanopeapods with average filling fractions greater than 70%. The controlled introduction of nanocomponents along with a combination of oleylamine and oleic acid surfactants was critical to the success of these reactions. The ability to form BaTiO3@HNB significantly expands the number of important peapod composites accessible by the controlled NP capture.

In situ self-assembled N-rich carbon on pristine graphene as a highly effective support and cocatalyst of short Pt nanoparticle chains for superior electrocatalytic activity toward methanol oxidation.

Highly conductive cocatalysts with great promotion effects are critical for the development of pristine graphene supported Pt-based catalysts for the methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). However, identification of these cocatalysts and controlled fabrication of Pt/cocatalyst/graphene hybrids with superior catalytic performance present great challenges. For the first time, pristine graphene supported N-rich carbon (NC) has been controllably fabricated via ionic-liquid-based in situ self-assembly for in situ growth of small and uniformly dispersed Pt NP chains to improve the MOR catalytic activity. It is discovered that the NC serves simultaneously as a linker to facilitate in situ nucleation of Pt, a stabilizer to restrict its growth and aggregation, and a structure-directing agent to induce the formation of Pt NP chains. The obtained nanohybrid shows a much higher forward peak current density than commercial Pt/C and most reported noncovalently functionalized carbon (NFC) supported Pt catalysts, a lower onset potential than almost all commercial Pt/C and NFC supported Pt, and greatly enhanced durability compared to graphene supported Pt NPs and commercial Pt/C. The superior catalytic performance is ascribed to the uniformly dispersed, small-diameter, and short Pt NP chains supported on highly conductive G@NC providing high ECSA and improved CO tolerance and the NC with high content of graphitic N greatly enhancing the intrinsic activity and CO tolerance of Pt and offering numerous binding sites for robustly attaching Pt. This work not only identifies and controllably fabricates a novel cocatalyst to significantly promote the catalytic activity of pristine graphene supported Pt but provides a facile and economical strategy for the controlled synthesis of high-performance integrated catalysts for the MOR in DMFCs.

Many-body effective thermal conductivity in phase-change nanoparticle chains due to near-field radiative heat transfer

In dense systems composed of numerous nanoparticles, direct simulations of near-field radiative heat transfer (NFRHT) require considerable computational resources. NFRHT for the simple one-dimensional nanoparticle chains embedded in a non-absorbing host medium is investigated from the point of view of the continuum by means of an approach combining the many-body radiative heat transfer theory and the Fourier law. Effects of the phase change of the insulator-metal transition material (VO2), the complex many-body interaction (MBI) and the host medium relative permittivity on the characteristic effective thermal conductivity (ETC) are analyzed. The ETC for VO2 nanoparticle chains below the transition temperature can be as high as 50 times of that above the transition temperature due to the phase change effect. The strong coupling in the insulator-phase VO2 nanoparticle chain accounts for its high ETC as compared to the low ETC for the chain at the metallic phase, where there is a mismatch between the characteristic thermal frequency and resonance frequency. The strong MBI is in favor of the ETC. For SiC nanoparticle chains, the MBI even can double the ETC as compared to those without considering the MBI effect. For the dense chains, a strong MBI enhances the ETC due to the strong inter-particles couplings. When the chains go more and more dilute, the MBI can be neglected safely due to negligible couplings. The host medium relative permittivity significantly affects the inter-particles couplings, which accounts for the permittivity-dependent ETC for the VO2 nanoparticle chains.

Thermal and dipolar interaction effect on the relaxation in a linear chain of magnetic nanoparticles

We perform computer simulations to study the relaxation in a one-dimensional chain of dipolar interacting magnetic nanoparticles (MNPs). Using the two-level approximation of the energy barrier, we perform kinetic Monte Carlo simulations to probe the relaxation mechanism as a function of dipolar interaction strength and temperature. The anisotropy axes of the MNPs are assumed to have random orientations. At high temperatures, the magnetization decay curve is exponential for weak dipolar interactions. It is found that dipolar interactions slow down the magnetic relaxation and increase the effective Néel relaxation time τN, which is affected by thermal fluctuations. In the weak dipolar limit, there is a perfect agreement between simulated and analytically evaluated values of τN for a wide range of temperatures. Microscopic analyses such as magnetic moments correlations and dynamic domain formation also suggest an increase in ferromagnetic coupling with an increase in dipolar interaction strength or decrease in thermal fluctuations. We believe that the concepts presented in this work are relevant in the context of applications such as data storage, digital data processing, and magnetic hyperthermia, in which the linear chain of MNPs are pervasive.

Baleen-Mimicking Virtual Filters for Rapid Detection of Pathogenic Bacteria in Water Using Magnetic Nanoparticle Chains and a Halbach Ring.

We have developed a virtual filter that quickly and efficiently captures and detects pathogenic bacteria in large amounts of water. The virtual filter comprised magnetic nanoparticle chains (MNCs) obtained by cross-linking alginate-coated magnetic nanoparticles (MNPs). When the MNC solution in a disposable plastic tube was exposed to an external magnetic field, the MNCs were aligned along the magnetic field lines, forming a filter similar to a whale's baleen filtering system. A Halbach ring that increased the magnetic field inside the ring was used as the source of an external magnetic field. The Halbach ring produced a more uniform and denser alignment of MNCs than any other ring array. To demonstrate the performance of the virtual filter comprising MNCs, Escherichia coli (E. coli) O157-spiked water was injected into the virtual filter comprising polyethyleneimine-coated MNCs, and the concentration of E. coli O157 captured by electrostatic interaction was determined using qPCR analysis. The bacterial capture efficiency using MNCs was 90% at a flow rate of 5 mL/min, and the detection limit after 10 min of preconcentration of bacteria was 10 cfu/mL, which is 100 times lower than that obtained using qPCR alone.

Steady-state temperature distribution under near-field radiative heat transfer inside a linear chain of polaritonic nanoparticles

Thermal transport mediated by near-field interactions is superdiffusive in an ordered network of nanoparticles, such as linear chains. Based on such nanostructures, here we study a classical thermal-nonequilibrium problem, that is, the steady-state temperature distribution inside the chain of equally spaced polaritonic nanoparticles. The existence of the linear temperature profile and anomalous temperature variations in the inner region and near the boundary of a dense chain embedded in vacuum, respectively, is demonstrated by analyzing the effective radiative thermal conductivity within the system. Such temperature distributions are closely relevant to the strength of propagating surface modes sensitive to the chain density and dielectric material. We also demonstrate that, the presence of a homogeneous nonabsorbing background medium renders the steady-state temperature profile of the dense chain nonlinear, as well as enhancing drastically the long-distance heat exchange by two orders of magnitude relative to the vacuum case. This enhancement is a result of the high density of propagating waves in the medium, and is further confirmed by analyzing the energy density distribution over the chain. Furthermore, in a complex system consisting of many parallel chains, we show that, in steady state, temperatures of the thermal drive chain are allowed to tailor by its neighboring chains due to many-body interactions. This work opens ways to qualitatively assess and manipulate the stationary temperature field in advanced nanostructures, such as topological plasmonic chains and nanoparticle arrays.

Radiative heat flux through a topological Su-Schrieffer-Heeger chain of plasmonic nanoparticles

We investigate the radiative heat transport along a Su-Schrieffer-Heeger chain of InSb nanoparticles. We show that in the topological non-trivial phase, the edge modes dominate the radiative heat transport despite their strong localization at the edges of the finite chain due to a long-range coupling of the first and last particle. We further discuss the scaling laws of the heat transfer with respect to the chain length for the longitudinal and transversal band- and edge modes and conclude that both type of modes obey the same scaling law.

Computational predictions of enhanced magnetic particle imaging performance by magnetic nanoparticle chains

The magnetic particle imaging (MPI) performance of collections of chains of magnetic nanoparticles with Néel and Brownian relaxation mechanisms was studied by carrying out simulations based on the Landau–Lifshitz–Gilbert equation and rotational Brownian dynamics, respectively. The effect of magnetic dipole–dipole interactions within chains on the time-domain average magnetic dipole moment and corresponding dynamic hysteresis loops, harmonic spectra, and point spread functions (PSFs) of the particle chains was evaluated. The results show that interactions within chains lead to ‘square-like’ dynamic hysteresis loops and enhanced MPI performance, compared to chains of non-interacting nanoparticles. For nanoparticles with the Brownian relaxation mechanism, subjected to a superimposed alternating and ramping magnetic field mimicking the magnetic field in MPI applications, we studied the dependence of x-space MPI performance of particle chains on parameters such as the amplitude of the alternating magnetic field, surface-to-surface separation between nanoparticles, solvent viscosity, and the number of nanoparticles in a chain. The results illustrate that magnetic dipole-dipole interactions within a chain contribute to enhanced MPI performance, and also suggest that there exist optimal values of the above parameters that lead to the best x-space MPI performance, i.e. maximum peak signal intensity and smallest full-width-at-half-maximum in PSFs.

Directing the Diffusion of a Nonmagnetic Nanosized Active Particle with External Magnetic Fields.

With the help of molecular dynamics simulations we show that an arbitrary nonmagnetic active particle with a size below one micrometer, being immersed in a suspension of magnetic nanoparticles, can diffuse faster along the direction of an applied field than perpendicular to the latter. This effect is demonstrated in monodisperse and polydisperse systems of magnetic nanoparticles for magnetic fields of moderate strength. The ability to direct a nonmagnetic active particle along the magnetic field stems from the formation of chains of magnetic nanoparticles aligned with the field direction. Such chains form effective channels through which the active particle can diffuse. We combine the investigations of the diffusion and transport efficiency of the active particle parallel and perpendicular to the field with the structural analysis of the magnetic nanoparticle system and find that the ability to direct an active particle of a given size can be maximized by changing magnetic particle concentration. The optimal transport efficiency is achieved at a concentration of magnetic material that provides a mean width of the effective tunnels that matches the effective size of the active particle.

Solvo-Driven Dimeric Nanoplasmon Coupling Under DNA Direction

Strong coupling is a prerequisite for nanoassemblies to deliver functions and applications unrealizable by noninteracting building units. DNA-Directed metamaterials, albeit highly programmable, oft...

Modified Mean-Field Theory of One-Dimensional Spin Models with Anisotropy and Long-Range Dipolar Interactions

The effects of interactions and anisotropy on the magnetic properties of linear chains of superparamagnetic nanoparticles are studied theoretically by mapping the problem onto spin models. With zero anisotropy, the magnetic dipole moments are free to rotate, and the system resembles a classical ferromagnetic Heisenberg model with long-range dipolar interactions. With strong anisotropy, they are constrained to align with the chain, and the system resembles the classical ferromagnetic Ising model with long-range interactions. Using a modified mean-field theory, expressions for the magnetization curve and initial magnetic susceptibility are derived from the response of a single particle subject to an effective field arising from the applied field and the interactions with the other particles. Various approximations for the effective field are tested against results from Monte Carlo simulations. It is shown that, for physically relevant interaction strengths, reliable theoretical predictions for both the zero-anisotropy and strong-anisotropy cases can be derived in a simple closed form.

Hysteresis in a linear chain of magnetic nanoparticles

We perform kinetic Monte Carlo simulation to study the magnetic hysteresis in a one-dimensional chain of magnetic nanoparticles (MNPs). The hysteresis behavior is systematically analyzed as a function of several key parameters: anisotropy axis orientation, dipolar interaction strength λ, frequency ν of the applied magnetic field, and temperature T. The anisotropy axes of all the MNPs are assumed to make an angle α with the chain axis. In the absence of dipolar interaction and thermal fluctuations, the hysteresis follows the Stoner–Wohlfarth model as expected. Extremely weak hysteresis is observed with small values of dipolar interaction strength for ν=105Hz and T=300K. On the other hand, there is a significant hysteresis even for weakly interacting MNPs with ν=109Hz. The hysteresis properties are strongly dependent on these parameters. Due to an increase in the ferromagnetic coupling, the hysteresis loop area increases with λ. The coercive field Hc and the amount of heat dissipated EH due to hysteresis decrease rapidly with α and T for small values of λ and ν=105Hz, while for large λ, they fall very slowly. When ν is very large (=109Hz), EH and Hc are found to have negligible dependence on T irrespective of λ. The results with a small value of frequency should be taken into account in the interpretation of the experiments and efficient usage of magnetic hyperthermia.

Modeling the Magnetic-Hyperthermia Response of Linear Chains of Nanoparticles with Low Anisotropy: A Key to Improving Specific Power Absorption

Fil: Valdes, Daniela Paola. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche.; Argentina

Comparative Study of Light Guiding by Freestanding Linear Chains of Spherical Au and Si Nanoparticles

Electromagnetic energy guiding by free‐standing straight finite chains of Au and Si spherical nanoparticles is comparatively studied on the basis of a system of integral equations for self‐consistent currents excited inside particles. Self‐consistent currents are given in terms of an electric field T‐scattering tensor (dyadic) operator of a single particle of any shape. Simplifying the T‐scattering operator, the equations system is resolved analytically in the nearest‐neighbor coupling approximation. Interactions beyond the nearest neighbors are accounted for by the perturbative theory. It is shown that electromagnetic excitation propagates along a chain of coupled particles without radiation losses in the form of a dark mode. The resonant conditions for the coupling parameter yield the frequency of the dark mode and the corresponding radius of the particles. As a result, unlike Au chains, no long‐range electromagnetic energy transfer was revealed along the Si chains. Physically, in both cases of Au and Si spheres, the resonant frequencies fall within the bands of the corresponding electric dipole Mie resonances. However, the positive value of the real part of the Si refraction index at the resonant frequency causes exponential excitation currents decreasing with the particle number.