Au Volume Fraction Research Articles

Utility of realistic microscopy-based cell models in simulation studies of nanoparticle-enhanced photon radiotherapy

To enhance the effect of radiation on the tumor without increasing the dose to the patient, the combination of high-Z nanoparticles with radiotherapy has been proposed. In this work, we investigate the effects of the physical parameters of nanoparticles (NPs) on the Dose Enhancement Factor (DEF), and on the Sensitive Enhancement Ratio (SER) by applying a version of the Linear Quadratic Model. A method for constructing voxelized realistic cell geometries in Monte Carlo simulations from confocal microscopy images was developed and applied to Gliobastoma Multiforme cell lines (U87 and U373). The comparison of simulations with realistic geometry and spherical geometry shows that there is significant impact on the survival curves obtained for the same irradiation conditions. Using this model, the DEF and the SER are determined as a function of the concentration, size and distribution of gold nanoparticles within the cell. For small NPs, d AuNP = 10 nm, no clear trend in the DEF and SER was observed when the number of NPs within the cell increases. Experimentally, the variable number of NPs measured inside the U373 cells (ranging between 1.48 × 105 and 1.19 × 106) also did not influence much the observed cell survival upon irradiation of the cells with a Co-60 source. The same lack of trend is obtained when the Au content in the cell is kept constant, 0.897 mg/g, but the size of the NPs is changed. However, if the number of NPs is kept constant (7.91 × 105) and the size changes, there is a critical diameter above which the dose effect increases significantly. Using the realistic geometries, it was verified that the key parameter for the DEF and the SER enhancement is the volume fraction of Au in the cell, with NP size being a more important parameter than the number of NPs.

Electromagnetic Properties of Au/Fe53Ni47 Hybrid Granular Composite Materials

Complex permittivity and permeability spectra of Au/Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">53</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">47</sub> hybrid granular composite materials containing spherical Au and Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">53</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">47</sub> microparticles have been investigated from RF to microwave frequency range. In the 80 vol.% composite containing Au/Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">53</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">47</sub> hybrid particles, the metallic property was achieved at the critical volume fraction of Au, φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_Au</sub> = 0.04 by the electrical percolation of hybrid metallic particles; electrical conductivity at 1 kHz becomes more than 0.1 S/cm. A low-frequency plasmonic state with negative permittivity spectrum was observed above φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_Au</sub> . Meanwhile, the complex permeability of the hybrid composites showed a Lorentz-type frequency dispersion with the negative permeability spectrum caused by the magnetic resonance at several hybrid particle contents. Consequently, double negative permittivity and permeability spectra have been realized from about 100 MHz to several gigahertz.

Plasmonic and metallic optical properties of Au/SiO2 metal-insulator films

In this paper, the optical properties and the growth mechanism of Au/SiO2 metal-insulator films (MIFs) are investigated by combining ellipsometry and transmission electron microscopy. The ellipsometric measurements, analyzed by using effective medium theories, show that the growth mechanism involves a Volmer-Weber growth mode while the morphology and the optical properties of Au/SiO2 MIFs are directly related to the percolation of the Au nanostructures. Indeed, below the percolation threshold of Au, the MIFs consist of ellipsoidal Au inclusions embedded in a SiO2 matrix. These insulating films present anisotropic plasmonic properties, attributed to the asymmetric interactions between nanaoparticles (NPs), which can be modeled according to the interacted shape distributed nanoparticle effective medium theory. At the percolation threshold of Au, an insulator-to-metal transition is observed. The MIFs simultaneously exhibit plasmonic and metallic optical properties, which can be described by the Bruggeman theory. The density of free electrons increases and the MIFs become more and more conductive as the Au volume fraction increases. We also demonstrate that for a high Au volume fraction, Bruggeman and Maxwell Garnett theories converge toward the same results, suggesting that the film is composed of isolated SiO2 inclusion embedded in a gold matrix.

Influence of thermal annealing and radiation enhanced diffusion processes on surface plasmon resonance of gold implanted dielectric matrices

Gold nanoparticles (AuNPs) embedded in fused silica and sapphire dielectric matrices were synthesized by Au ion implantation. Systematic investigations were carried out to study the influence of implantation dose, post annealing temperature, swift heavy ion (SHI) irradiation and radiation enhanced diffusion (RED). Rutherford Backscattering Spectrometry (RBS) measurements were carried out to quantify concentration and depth profile of Au present in the host matrices. X-ray diffraction (XRD) was employed to characterize AuNPs formation. As-implanted and post-annealed films were irradiated using 100MeV Ag ions to investigate the effect of electronic energy deposition on size and shape of NPs, which is estimated indirectly by the peak shape analysis of surface plasmon resonance (SPR). The effect of volume fraction of Au and their redistribution is also reported. A strong absorption in near infra red region is also noticed and understood by the formation of percolated NPs in dielectric matrices. It is quite clear from these results that the effect of RED assisted Oswald ripening is much more pronounced than the conventional Oswald ripening for the growth of NPs in the case of silica host matrices. However for sapphire matrices, it seems that growth of NPs already completed during implantation and it may be attributed to the high diffusivity of Au in sapphire matrices during implantation process.

Dual mechanism of photoresponse in composite Si–Au nanolayers on crystalline silicon

Silicon‐based structures comprised of crystalline silicon substrates and active layers of mixed silicon and gold nanoparticles were fabricated and characterized. Several layer compositions were studied. The investigated structures demonstrate very large spectral sensitivity (more than 10 A W−1) in the wide spectral range (400–1000 nm). Such large sensitivity implies presence of photocurrent amplification. A model which involves dual mechanism of the photoresponse was proposed in order to explain the appearance of the photocurrent amplification in the investigated structures.Spectral sensitivity of the structure with composite layer of Si and Au nanoparticles on Si substrate (Au volume fraction is ∼50%) at reverse bias voltage of −0.4 V.

Conduction and convection heat transfer characteristics of water-based au nanofluids in a square cavity with differentially heated side walls subjected to constant temperatures

The present work deals with the natural convection in a square cavity filled with the water-based Au nanofluid. The cavity is heated on the vertical and cooled from the adjacent wall, while the other two horizontal walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles? volume fraction on the heat transfer characteristics of Au nanofluids at the given base fluid?s (i.e. water) Rayleigh number. Accurate results are presented over a wide range of the base fluid Rayleigh number and the volume fraction of Au nanoparticles. It is shown that adding nanoparticles in a base fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the use of nanofluids can reduce the heat transfer rate instead of increasing it.

In situ growth of gold colloids within alginate films

Gold–alginate bionanocomposite films were prepared by impregnation of alginate films withHAuCl4 followed by reduction with glucose. The mannuronate over guluronate ratio (M/G) of the polymer as well as the initial polymer concentration wereshown to influence the film thickness, the amount of trappedAu3 + ions, and the volume fraction of Au(0) nanoparticles but not the size of these colloids(about 4 nm). The homogeneity of the gold colloid dispersion within the alginate gels wasstudied by transmission electron microscopy (TEM) and confirmed by simulation of thesurface plasmon resonance (SPR) spectra using the Maxwell–Garnett model. Thecalculated spectra also provided fruitful information about the gold colloid/alginateinterface. Overall, the whole process is controlled by the balance between theM/G ratio, defining the polymer affinity for Au(III) species, and the solution viscosity,controlling the diffusion phenomena.

Optical and electrical properties of Au nanoparticles in two-dimensional networks: an effective cluster model

We report a study of the optical and electric properties of Au nanoparticle networks grown on the porous alumina membrane by dry atom sputtering deposition approach. An effective cluster model was developed to evaluate the dielectric function and the electrical conductivities of the nanoparticle networks by taking into account the effects of the Au particle size, the Au volume fraction, and the particle-particle interaction. The calculated transmission spectra from the model were in good agreement with the experimental data. The percolation threshold of the as-fabricated structure was predicted to occur at Au volume fraction of 0.18, consistent with the dc electric resistance measurement.

Dependence of fiber texture on composition in metal-insulator Au–SiO2 composite thin films

The authors show that the evolution of metal fiber texture in phase segregated metal-insulator composite thin films depends strongly on the composition. Using x-ray diffraction pole figures, they measured the strength of the Au (111) fiber texture as a function of composition in the phase segregated Au–SiO2 system, codeposited by magnetron sputtering at room temperature. They find that for very low SiO2 volume fractions, less than 5%, Au has low resistivity and a strong (111) fiber texture similar to that of pure Au. For higher SiO2 volume fractions, up to 30%, the strength of the Au fiber texture decreases more rapidly with increasing SiO2 volume fraction than can be attributed to the decreasing Au volume fraction. They propose that the rapid decrease in Au (111) fiber texture strength is consistent with Zener pinning of Au grains by second-phase SiO2 particles. For SiO2 volume fractions greater than 30%, the Au fiber texture is lost as the Au phase becomes disrupted, the films become insulating, and the microstructure changes to randomly oriented Au islands within an insulating matrix of SiO2.

Microstructure and electrical conductivity of Au–MgF2 nanoparticle cermet films

Abstract Au–MgF 2 nanoparticle cermet films with Au volume fraction of 6–50% were prepared by radio-frequency magnetron co-sputtering and analyzed by X-ray diffraction, X-ray photoelectron spectroscopy and temperature-varying four-wire technique. Microstructure analysis shows that the films are composed of mainly amorphous MgF 2 matrix with embedded fcc Au nanoparticles with a mean size of 9.8–21.4 nm. The electrical properties of the films from 54 to 300 K were measured. The results show that the electrical percolation threshold occurs between Au 40 vol.% and 50%, and around the percolation threshold the electrical conductivity of the films changes by four orders.

Role of ceramic matrix and Au fraction on the morphology and optical properties of cosputtered Au-ceramic thin films

Surface sensitive x-ray scattering studies were carried out to understand the morphology of cermet thin films prepared by cosputtering metallic gold and ceramic materials on float glass substrates. It has been observed that the morphology of Au clusters in cermet thin films depends strongly on the matrix during growth, even if, all other conditions are kept identical. In particular, nearly isotropic growth of Au clusters, to form nanoparticles, is found in silica and alumina matrices, while anisotropic columnar-like growth of Au clusters, to form a nanorod-like shape, is found in a titanium oxide matrix. Thickness of the films was also found very different, which is likely to be related to the different sputtering yields of the ceramic materials. The volume fraction of Au estimated from the electron density profile shows that the total volume or the amount of Au is different in films of different ceramic matrices. This suggests that even the sputtering yield of Au is very different in the presence of different ceramic atmosphere, which is likely to be responsible for having a different morphology of Au clusters in different matrices. Optical absorption spectra of the films, on the other hand, show linear dependence of the absorption peak position with the volume fraction of Au and independent of both the ceramic matrix and morphology of Au clusters.

Preparation and characterization of Au/SiO2 multilayer composite films with nonspherical Au particles

Au/SiO2 multilayer composite films containing nonspherical Au particles were prepared by a magnetron sputtering method. Uniform size and shape distributions of Au particles were obtained in these films. Au particles embedded in these films can be shaped into spheres or ellipsoids by controlling the thickness of the Au layer, and the thermal annealing temperature and time duration. Their linear optical properties were characterized in the wavelength range between 300–1000 nm. Their effective nonlinear optical susceptibility, χ(3), was found to be much larger than that prepared by the cosputtering method at low Au volume fraction. We attributed the enhancement of the value of χ(3) to the more uniform size and shape distribution, as well as the higher two-dimensional metal particle density in the multilayer films.

Spectro-ellipsometric studies of Au/SiO2 nanocomposite films

Au/SiO2 nanocomposite films in which Au nanoparticles were embedded in SiO2 matrix were fabricated via alternating sputtering of SiO2 and Au layers. In particular, we kept the nominal thickness of the Au layers below the threshold for the continuous layer formation whereas that of SiO2 layers was sufficient to form continuous layers. Transmission electron microscopy (TEM) images revealed that the Au nanoparticles were spherical in shape and that their average size was linearly proportional to the nominal thickness of Au layers. To account for the absorption variation of the composite films, including the absorption peak around 530 nm due to the surface plasmon resonance (SPR), we used Maxwell–Garnett effective medium theory (EMT) together with the modified Drude model. As it turned out, the combination of the modified Maxwell–Garnett effective medium theory and the aforementioned modification of the Drude model, which took the size of Au nanoparticles into consideration, were sufficient to model the variable–angle spectroscopic ellipsometry spectra. The values of the fitting parameters, such as film thickness, volume fraction of Au, and the diameter of Au nanoparticles, extracted from the modeling procedure were in good agreement with the results of TEM and spectrophotometer measurements.

Surface plasmon resonance of electrochemically deposited Au-black

Au-black, a kind of gold nanostructure, was electrochemically deposited on a Au-vapor-deposited glass plate, and its optical properties were evaluated with a surface plasmon resonance (SPR) measurement system. The Au-black was found to exhibit an extraordinary high resonance angle (minimum reflectance angle) compared to that of the Au-vapor-deposited glass plate. We proposed a five-layer model, which consists of glass, Cr, Au, Au-black, and solution layers, to explain the high resonance angle of the Au-black plate. The calculation was based on the Fresnel formulas extended for multilayers. When the Bruggeman formula was used to obtain a refractive index of the Au-black layer, the numerical simulation could qualitatively explain the experimental observations. The curve fitting method by the five-layer model enabled us to simultaneously estimate the thickness of the Au-black layer and the volume fraction of Au in Au-black.

Temperature dependence of the resistivity in Au-YBa2Cu3Ox sintered composites

Abstract We combine experimental and numerical techniques to investigate the temperature dependence of the resistivity ρ in metal–superconductor (M─S) Au─YBa2Cu3Ox (Au─YBCO) sintered composites. The experimental data for ρ are studied as a function of the Au volume fraction φ. Below the superconductor critical temperature T < 92 K, a systematic shift of the M─S transition threshold φS is observed as T varies. Up to T = 200 K, the resistivity curves present a maximum. Both the amplitude of the maximum and the corresponding composition vary with T. Our experimental results are well described by a random conductor network model which incorporates porosity and interface resistances. The interface resistance computed from the model is consistent with a simple picture of local modifications of the oxygen concentration at the YBCO─YBCO and Au─YBCO contacts.

Temperature dependence of the resistivity in Au─YBa2Cu3Oxsintered composites

Abstract We combine experimental and numerical techniques to investigate the temperature dependence of the resistivity ρ in metal–superconductor (M─S) Au─YBa2Cu3Ox (Au─YBCO) sintered composites. The experimental data for ρ are studied as a function of the Au volume fraction φ. Below the superconductor critical temperature T < 92 K, a systematic shift of the M─S transition threshold φS is observed as T varies. Up to T = 200 K, the resistivity curves present a maximum. Both the amplitude of the maximum and the corresponding composition vary with T. Our experimental results are well described by a random conductor network model which incorporates porosity and interface resistances. The interface resistance computed from the model is consistent with a simple picture of local modifications of the oxygen concentration at the YBCO─YBCO and Au─YBCO contacts.

Preparation and optical properties of gold-dispersed (Pb, La)TiO 3 thin films by sol-gel process

Gold-dispersed Pb 1−1.5xLa xTiO 3 (PLT[x × 100]) thin films were prepared by a sol-gel process. Volume fraction of Au and La content x of the films were varied from 0 to 10 vol.% and from 0 to 0.3, respectively. Refractive index of the matrix increased with increasing crystal size of PLT. Not only the refractive index of matrix but also the static dipole electric field of the matrix was considered to affect the optical properties of the films. χ (3) of 5 vol.% gold-dispersed PLT20 film was 1.0 × 10 −7 esu at 532 nm that was far from the plasma resonance wavelength of the film.

Electrical transport and superconductivity in a Au-YBa2Cu3O7 percolation system.

Percolation behaviors of normal-state conductivity and superconductivity have been studied in a Au-Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ granular system. The normal-state conductivity shows a percolation threshold at a Au volume fraction ${p}_{\mathrm{Au}}$ of 23%, whereas the superconducting network shows a threshold at ${p}_{\mathrm{Au}}\ensuremath{\sim}60%$. The presence of Au has negligible effect on the superconducting Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ phase. In the dilute limit, the ratio of the Meissner signal to the diamagnetic-shielding signal approaches unity.

Superconducting Au-YBa2Cu3O7 composites

Superconducting Au-YBa2Cu3O7 composites have been fabricated over a Au volume fraction range of 0–100%. Microstructure measurement indicates that Au and YBa2Cu3O7 form well-separated phases. The superconducting transition temperature Tc was found unaffected by the presence of Au. The composites exhibit low normal state resistivity and much improved ductility. The results suggest that Au is an excellent metal host for making ultrafine YBa2Cu3O7 granular solids.