Volume Fraction Of Metal Particles Research Articles

The effect of contact resistance on electrical conductivity in filled elastomer materials

This paper is focused on studying the charge transport between the particles in filled elastomer composites, and suggests a new modeling approach that would allow predicting the electrical conductivity of this material. Our approach is based on a combination of non-equilibrium Green's function (DFTB-NEGF) analysis for atomic-level electron quantum transport, and effective medium theory for calculating the said macroscopic transport properties of the material. The model can be used for predicting macroscopic material conductivity based on the information of material microstructure received by electron microscopy; explain changes of conductivity in deformed material and with temperature variation, and finally it can assist in finding the optimal material parameters such as particle shape, size distribution, and volume fraction to maximize the performance. The results of our modeling re-attest the known phenomenon that the electrical conductivity in percolated network is always dominated by direct particle-to-particle charge transport. We studied the electrical conductivity in a medium of high volume fraction of metallic particles dispersed in polymer matrix where thin polymer matrix layer covalently attached to the metallic particle contacts, and the thin polymer layer undergoes high local shear strain when hard particles slide along each other during deformation. These conditions allow the redistribution of electron density from metal to the polymer, and the conductance through normally insulating matrix can become comparable with the pinpoint conductance through the metal. These conditions can only occur in the place of direct particle contacts, therefore all criteria for percolated conductive network hold valid in this case. The integral conductance of thin “sandwiched” polymer layer strongly, but predictably depends on local contact geometry, mostly on particle surface curvature at place of contact. This allows predicting composite conductivity from the properties of each phase, loading, and particle shape and size distributions. Further, the conductance of polymer chain can significantly increase with the fluctuations of molecular shape caused by temperature and/or deformation. We infer that this effect is responsible for the major part of strain and temperature dependence of the conductivity that has been reported in the literature, although particle orientation and stacking at larger deformations may also contribute to the strain dependence.

Coherent perfect absorption in nonlocal particle composite medium

We explore the coherent perfect absorption of light in a nonlocal metal-dielectric composite film in which metallic nanoparticles (gold) are randomly embedded in the dielectric host medium (silica). The two coherent light beams illuminate the gold-silica composite slab respectively from the left and right sides at the same angle of incidence and the conditions required for coherent perfect absorption are investigated each as a function of different system parameters. Under different system parameters, we study the coherent perfect absorption of a nonlocal particle composite medium. A nonlocal effective medium theory is proposed to approximately describe the metal-dielectric composite film. The effective permittivity and effective permeability of the composite medium are approximated by using the effective medium theory under the model of coated sphere with core and shell. According to the effective dielectric parameters of the composite medium, we can obtain the transmission coefficient and reflection coefficient of the plane wave incident on the slab. By comparing and analyzing the coherent perfect absorptions of the composite medium under nonlocal and local conditions, we find that under the influence of nonlocal effect when the size of particle is very small, the frequency range of incident light that produces the coherent perfect absorption of the composite medium increases and the small size can also cause the coherent perfect absorption to occur in wider frequency range. Especially, we pay attention to the choosing of physical parameters in the design of coherent perfect absorption with macroscopic composite slab when we take the nonlocal effect (or spatial dispersion) into account. In the further calculation, the coherent perfect absorption of the composite medium can be realized by changing the system parameters such as the thickness of composite slab, the wavelength of incident light, the volume fraction of metal particles, etc. We also bring about the coherent perfect absorption at a small volume fraction which satisfies all the conditions. Finally, according to these results, we can realize the control of the coherent perfect absorption with nonlocal effect. Our study may be helpful in designing the optical nanoabsorbers.

Effective Microwave Dielectric Properties of Ensembles of Spherical Metal Particles

Knowledge of dielectric and magnetic properties is crucially important in the numerical modeling of high-temperature microwave processing of materials. To enhance the accuracy of modeling for metal powders and metal-containing composites, adequate description is required for the interaction of the electromagnetic field with the electrically conductive particles. A theoretical model for the calculation of effective complex dielectric permittivity of an ensemble of spherical metal particles surrounded by thin insulating layers is presented. The model is based on the effective medium approximation. It accounts for the nonuniform distribution of the electromagnetic field that exists inside individual particles when the electromagnetic wavelength or penetration depth is smaller than the particle size. The effective dielectric losses predicted by the model can be highly significant compared with the magnetic losses that arise due to the eddy currents induced in metal particles by microwaves. Reasonable agreement with the experiment has been demonstrated for the millimeter-wave absorption in metal–ceramic composites with significant volume fraction of metal particles. The model can be utilized for assessing the feasibility of microwave heating of powder metals and metal–ceramic composites.

Induced polarization response of porous media with metallic particles — Part 2: Comparison with a broad database of experimental data

We have derived a set of new relationships describing polarization parameters in porous materials with disseminated particles made of a semiconductor, such as pyrite or magnetite. We have compared various predictions of this model to a broad set of experimental data. The chargeability was found to be controlled only by the volume fraction of metallic particles in agreement with the experimental data. The relaxation time, defined from the peak frequency of the phase, was observed to be proportional to the square of the size of the metallic particles and was independent of the salinity of the pore water solution. The relationship between the peak frequency and the grain size could be used to determine the diffusion coefficient of the [Formula: see text]- and [Formula: see text]-charge carriers in the semiconductor. This diffusion coefficient was consistent with the mobility of the charge carriers derived from theoretical considerations or electric-conductivity measurements. The resistivity of a mixture of a porous matrix characterized by a low-chargeability and dispersed semiconductors does not depend on the content of metallic grains, as long as the grains are below a percolation threshold (< 22 vol.%). Various experiments were performed using magnetite and pyrite at different grain sizes, weight fractions, and with/without porous materials (i.e., suspended in agar gel). These data were used to test some additional aspects of the model. We found excellent agreement between the model predictions and these experimental data.

Preparation and Microstructural Characterisation of Metal Injection Moulded Powder Metallurgical Components (MIM) in the Green and Sintered Conditions

Summary The aim of this work was to develop a reproducible method of preparation for green and brown bodies which, after injection moulding and sintering, would permit an entire MIM component to be microscopically examined for internal inhomogeneities such as porosity and segregation. The particular challenge was to prepare the fragile MIM microstructure prior to the sintering process free of artefacts. Three different methods of preparation (variations in the polishing substrates and suspensions used) were compared. To evaluate the quality of the resulting preparation, the microscopically determined volume fraction of metal particles was chosen. This was determined after set preparation times using quantitative microstructural analysis (QMA/QGA) and evaluated during the various stages and times of the preparation process. The feedstock composition which had a defined volume fraction of 68 % was used as the reference value. The preparation of the brown sintered body proved to be the most successful. The volume fraction determined microscopically measured 67 %. The duroplastic infiltration mounting resin penetrates into the open pore structure effectively stabilising and fixing the powder particles. In contrast the preparation of the green body proved to be much more difficult as the breaking out of the metal powder particles from the comparatively soft thermo-plastic binder was not able to be prevented completely. The volume fraction measured microscopically was 62 % which is about 6 % less than the actual value. The chemical removal of the binder from the surface of the green body significantly improved the overall result of the preparation as it was then possible to effectively fix the powder particles by subsequent infiltration with the duroplastic mounting resin, as in the case of the brown body. In addition to the qualitative appraisal of the microstructural specimens, quantitative microstructural analysis proved to be a valuable instrument for systematically and objectively evaluating the results of the preparation and for developing the preparation processes. Using the methods of preparation developed it is now possible to carry out qualitative examinations on almost artefact free microstructural specimens prior to the lengthy and costly thermal processing.

Surface plasmon characteristics of nanocrystalline gold/DLC composite films prepared by plasma CVD technique

Composite films containing gold nanoparticles embedded in diamond-like carbon (Au–DLC) matrix were deposited on glass and Si (1 0 0) substrates by using capacitatively coupled plasma (CCP) chemical vapour deposition technique (CVD). Particle size and metal volume fraction varied between 2.7–3.5 nm and 0.04–0.7, respectively with the amount of argon in the methane + argon gas mixture in the plasma. Bonding environment in these films were obtained from XPS, Raman and FTIR studies. Microstructural studies were carried out by SEM, XRD and TEM studies. Blue-shift of the surface plasmon resonance peak (located ∼540–561 nm) in the optical absorbance spectra of the films could be associated with the reduction of the particle size while red shift was associated with the increase in volume fraction of metal particles. The experimental results have been discussed in light of the core–shell model.

Synthesis and characterization of composite films of silver nanoparticles embedded in DLC matrix prepared by plasma CVD technique

Composite films containing silver nanoparticles embedded in diamond-like carbon (DLC) matrix were deposited on glass substrates by using capacitatively coupled plasma (CCP) chemical vapour deposition techninique (CVD). Particle size and metal volume fraction were tailored by varying the relative amount of methane of a gas mixture of methane + argon in the plasma. Optical constants of the films were evaluated. Bonding environment in these films were obtained from Raman and FTIR studies. Blue-shift of the surface plasmon resonance peak in the optical absorbance spectra of the films could be associated with the reduction of the particle size while red shift was associated with the increase in volume fraction of metal particles. The experimental results have been discussed in light of the existing Mie theory.

Characterization of nanocrystalline gold/DLC composite films synthesized by plasma CVD technique

Composite films containing gold nanoparticles embedded in diamond-like carbon (Au–DLC) matrix were deposited on glass and Si (1 0 0) substrates by using capacitatively coupled plasma (CCP) chemical vapour deposition technique (CVD). Particle size and metal volume fraction were tailored by varying the relative amount of argon in the methane + argon gas mixture in the plasma. Optical constants of the films were evaluated. Bonding environment in these films were obtained from Raman and Fourier transformed infrared spectra (FTIR) studies. Blue-shift of the surface plasmon resonance peak in the optical absorbance spectra of the films could be associated with the reduction of the particle size while red shift was observed with the increase in volume fraction of metal particles in the DLC films. Absorption spectra recorded in the reflection mode indicated dichromatism in these films.

Subwavelength imaging from a multilayered structure containing interleaved nonspherical metal-dielectric composites

A thin multilayered structure with interleaved nonspherical metal-dielectric composites slices and dielectric slices may be modeled as the metamaterial with anisotropic permittivity. The signs of diagonal elements of the permittivity tensor can be controlled by the particles' shape, the volume fraction of metal particles, and the incidental wavelengths. To one's interest, when the spheroidal nanoparticles are oblate in shape, the wavelength range in which components of the permittivity have different signs is widened, and the magnitude of optical absorption band becomes weak. Since both physical anisotropy and low absorption are helpful for improving the subwavelength image resolution, the multilayered structure containing metal-dielectric composite layer of nonspherical particles may be designed as a superlens device. In addition, the incident wavelength and the number of nanolayers are found to play crucial roles in enhancing the evanescent field performance too.

Effective dielectric response of nanostructured layers

AbstractThe Maxwell Garnett effective medium theory was originally developed for a very small volume fraction of metal particles in a transparent medium. In contrast to the bulk situation, it can be applied to high coverages for thin metal particulate films and predicts the plasmon resonance energy accurately in contrast to the Bruggeman effective medium theory. The comparison of the Maxwell Garnett approach to a more rigorous analysis of particulate films with the Thin Island Film theory shows that also the plasma energy of the plasmon resonance is very accurately obtained with the simple effective medium theory. Also a quite accurate splitting of the resonance energy through particle interaction is obtained. However, interband transitions and the optical coupling of the layer with the effective medium response to the substrate lead to substantial differences compared to the dipole approximation of the rigorous Thin Island Film theory. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Faraday magneto-optical rotation in compositionally graded films

We present a two-step homogenization method for studying the Faraday magneto-optical effect in graded metal-dielectric composite films of width W, in which the volume fraction of metal particles in a slice varies along the direction perpendicular to the film surface. First, we adopt the effective-medium theory to formulate the equivalent (local) dielectric permittivity tensor for a z slice. Second, the graded composite films are homogenized with an effective (overall) dielectric permittivity tensor including the diagonal and off-diagonal elements. Faraday rotation is studied as a function of the graded profile p(z) with the same total volume fraction. For a power-law form p(z)=a(z/W)m with different m, it is found that with increasing m, the magnitude of Faraday rotation becomes weak near the surface plasmon resonant band, accompanied with the redshift of the resonant center. Interestingly, it is possible to achieve strongly enhanced Faraday rotation in the high-frequency region, and to change the direction of rotation in the low-frequency one. Moreover, the magnitude can be further enhanced for needle-like particles. In the dilute limit, we show that Faraday rotation is indeed independent of m within Maxwell-Garnett theory.

On the Mechanical and Physical Properties of Recycled Polymer Matrix Composites Reinforced with Cooper Powder

The influence of cooper powder as reinforcing phase on the main mechanical and physical properties of recycled polyethylene matrix composites has been investigated. The obtained elastic modulus increases up to the upper adopted reinforcing level (∼10 [vol. %]), while elongation and fracture energy decrease. The UTS values remain quite constant within the reinforcing content interval. Electrical resistivity proved to depend, to a great extent, on the reinforcing particle distribution inside the polymer matrix. It has a sudden drop when a continuous electrical conductive path is formed at a critical volume fraction of metal particles. At a lower content, instead, it slowly decreases as reinforcing powder content increases. Both the mechanical properties and values for electrical resistivity are similar to those published for polymers obtained directly from monomers.

Surface plasmon effect in nanocrystalline copper/DLC composite films by electrodeposition technique

Composite films of nanocrystalline copper embedded in DLC matrix prepared by electrodeposition technique were studied for their optical properties. Particle size and metal volume fractions were tailored by varying the amount of copper containing salt in the electrolyte. Blue-shift of the surface plasmon resonance peak in the absorbance spectra of the films was observed with the reduction in size and volume fraction of metal particles. Mie theory was found to describe the experimental spectra quite well.

Optical nonlinearity enhancement of compositionally graded films

We present a theoretical description for the effective linear and nonlinear optical properties of compositionally graded films consisting of nonlinear metal particles and linear dielectric particles. The volume fraction of metal particles varies along the direction perpendicular to the film. To account for the composition gradient, we resort to effective medium approximation to investigate the equivalent (local) dielectric constant and third-order nonlinear susceptibility. As a result, the effective second-rank dielectric constant tensor and fourth-rank nonlinear optical susceptibility tensor are directly determined by regarding the graded film as a multilayer one. We predict that for a power-law composition gradient p(z)=zm, the increase of m leads to large enhancement of the optical nonlinearity and hence the figure of merit in the high-frequency region. On the other hand, for a given total volume fraction, we find that the optical nonlinearity enhancement for the composition gradient case is larger than the one in non-graded case. Moreover, we can choose different graded profile to realize the appreciable optical nonlinearity enhancement. Therefore, the compositionally graded film can be served as a suitable candidate material for obtaining the large optical nonlinearity and optimal figure of merit.

Surface plasmon effect in nanocrystalline copper/DLC composite films by an electrodeposition technique

Composite films of nanocrystalline copper embedded in diamond-like carbon (DLC) matrix were deposited on SnO2-coated glass substrates by using an electrochemical technique. Particle size and metal volume fraction were tailored by varying the amount of copper containing salt (copper acetate) in the electrolyte. Red-shift of the surface plasmon resonance peak in the optical absorbance spectra of the films was observed with the reduction in size and increase in volume fraction of metal particles. Surface plasmon peak was not observed in the absorption spectra below a critical particle size and metal concentration of the nanoncomposite films. Mie scattering theory was found to describe the experimental spectra better than the Maxwell–Garnett (M–G) effective medium theory.

Surface plasmon resonance in nanocrystalline silver in a ZnO matrix

Silver nanoparticles embedded in ZnO matrix were deposited onto fused silica substrates using high pressure (~40 Pa) d.c. sputtering techniques. The particle size in the films was tailored by varying the system pressure and substrate temperature, while the metal volume fraction was controlled by adjusting the relative time of sputtering of the targets. Blue-shift of the surface plasmon resonance peak was observed with the reduction in size and volume fraction of metal particles. A surface plasmon peak in the absorption spectra was found to be absent in the films with particle size and metal concentration below a critical value. A sharp absorption edge in the absorbance spectra within the UV-VIS range indicated semiconducting behavior of the ultrafine silver particles. Films deposited at lower substrate temperature showed a narrow distribution of nanoparticles, nearly spherical in shape. Increase in substrate temperature resulted in a non-uniform size and shape in the films due to the agglomeration of the nanoparticles. These size and shape distributions have a profound effect on the optical absorbance spectra and result in a broad and asymmetric surface plasmon band. A shape distribution introduced in the Maxwell-Garnett or Bruggeman effective medium theory was found to give a reasonable description of the experimentally observed optical absorption spectra.

Calculation of adsorption-induced differential external reflectance infrared spectra of particulate metals deposited on a substrate

The existence of inverted IR bands in both external and internal reflectance infrared (IR) spectra of CO chemisorbed on particulate metals deposited on a moderately IR-reflecting substrate is well documented. This apparently striking phenomenon, in which the intensity of the reflected IR beam is higher in the presence of CO than in its absence, is in fact a simple consequence of Fresnel’s reflectance laws, as already shown in a former work [J. Electroanal. Chem. 529 (2002) 145] in which the effect of the CO adsorbate was assumed to be a small, arbitrarily fixed change of the complex refractive index of a thin layer of metal particles embedded in a dielectric matrix, this thin layer being modelled in the framework of Bruggeman’s effective medium theory. In the present work, using a simple yet realistic model for the adsorption of CO on a metal particle, and an advanced effective medium model [Phys. Rev. B 49 (1994) 7137] for the thin layer of metal particles, we have been able to calculate quantitatively the small changes of the refractive index of the thin layer due to the adsorption of CO, and therefore to calculate, also quantitatively, the shape and intensity of the bands that should be observed. Again, inverted bands are predicted to appear under certain circumstances, which shows that no new phenomenon need be invoked for explaining the appearance of these inverted bands, but only the well-known Fresnel’s reflectance laws. Obviously, since the intensity of the bands is quantitatively calculated, the magnitude of the enhancement (when present) of the intensity of the adsorbate bands, i.e., the magnitude of the surface enhancement of infrared absorption (SEIRA) effect, is obtained. Importantly, both band inversion and SEIRA are found to depend on the fill factor (volume fraction of metal particles in the thin layer), and not on the size of the metal particles.

Surface plasmon resonance in nanocrystalline silver particles embedded in SiO2 matrix

Nanocomposite films containing silver particles embedded in SiO2 matrix wereprepared by high pressure (~40 Pa) d.c. sputtering technique in an argon plasma on fusedsilica substrate. Particle size and metal volume fraction were tailored by varying thesubstrate temperature (Ts~233-300 K) and deposition time (15-240 s). Reduction in size and volume fraction of metal particles culminated in blue-shift of thesurface plasmon resonance peak in the optical absorbance spectra of the films. Absenceof surface plasmon peak in the absorption spectra below a critical particle size and metalconcentration of the nanocomposite films and appearance of sharp absorption edge inthe absorbance spectra within the UV-VIS range indicated the semiconducting behaviourof the ultrafine silver particles. Experimental absorbance spectra were theoreticallysimulated by Mie scattering theory and Maxwell-Garnett effective medium theory.

Temperature effect on nonlinear optical response of metal–dielectric composite with interfacial layers

The dependence of nonlinear optical response on temperature is investigated theoretically for a metal–dielectric composite with interfacial layers in a dilute limit. We show that the effect of interfacial layers on the nonlinear optical response of such composites is more prominent at low temperatures than at high temperatures, that the interfacial factor depends on the volume fraction of metallic particles and the frequency of the incident wave, and that an optimal interfacial layer is found for which the nonlinear optical response is able to be enhanced to a maximal. It is shown that weak nonlinearity can be greatly enhanced if the interfacial factor, frequency and volume fraction are chosen appropriately.

Optical Bistability of Metallic Particle Composites

The intrinsic optical bistability of nonlinear composites, in which linear small metallic spherical particles are embedded in a weakly nonlinear dielectric host is investigated by using the self-consistent mean-field approximation and spectral representation. It is found that the threshold intensity strongly depends on the metallic volume fraction and component properties, and there exists a critical volume fraction of metallic particles; beyond the critical fraction, bistability cannot be observed.