Investigation of size distribution of silver nanoparticles

In this work, we present a physical methodology of preparing silver nanoparticles suspended in the deionized water. For this purpose, we apply the DC spark method and present the size distribution (by Zetasizer) and optical properties (by UV/VIS) of the nanoparticles in two different voltages. The obtained results using the DC spark method show that the fabrication of silver nanoparticles in deionized water without any surfactants and stabilizers is relatively cheap and pollution free. Using the method, we could prepare the silver nanoparticles smaller than 5 nm.     

Power dependence of size of laser ablated colloidal silver nanoparticles

Silver nanoparticles have been produced by laser ablation of silver metal in nanopure water without any chemical additives. It has been observed that laser power has a control over the size of the nanoparticles. Increasing laser power shows a clear blue shift in the absorption peak of fabricated nanoparticles indicating that the average size of the particles decreases with increasing laser power. Ablation for longer period reduces the average size of nanoparticles which is attributed to the re-ablation of fabricated nanoparticles. A good correlation has been observed between the peak of the absorption spectrum measured by UV-VIS spectroscopy and the average particle size measured by scanning electron microscope imaging method. The value of the coefficient of correlation is determined to be 0.965.     

嵌入Ag纳米颗粒层的DNA忆阻器

构建了具有“Al/DNA-CTMAB/Ag NPs/DNA-CTMAB/ITO”结构的有机忆阻器件, 并对其电流-电压 (I-V)曲线进行测量. 结果表明, 嵌入Ag纳米颗粒层, 不仅可以增强器件的导电性, 而且忆阻特性也显著提高. 当颗粒粒径在15–20 nm范围时, 开-关电流比I_ON/I_OFF能够达到10³. 器件的I-V特性受扫描电压幅值V_A的影响, 随着V_A的增大, 高阻态的电流变化较小, 而低阻态的电流明显增大, 开(或关)电压V_SET (V_RESET)和I_ON/I_OFF增加. 实验还发现, 器件高低阻状态的相互转换取决于外加电场的方向, 说明该忆阻器具有极性.     

The effect of the deposition parameters on size, distribution and antimicrobial properties of photoinduced silver nanoparticles on titania coatings

Controlled photodeposition of silver nanoparticles (AgNP) on titania coatings using two different sources of UV light is described. Titania (anatase) thin films were prepared by the sol-gel dip-coating method on silicon wafers. AgNPs were grown on the titania surface as a result of UV illumination of titania films immersed in aqueous solutions of silver nitrate. UV xenon lamp or excimer laser, both operating at the wavelength 351 ± 5 nm, was used as illumination sources. The AFM topography of AgNP/TiO₂ nanocomposites revealed that silver nanoparticles could be synthesized by both sources of illumination, however the photocatalysis carried out by UV light from xenon lamp illumination leads to larger AgNP than those synthesized using the laser beam. It was found that the increasing concentration of silver ions in the initial solution increases the number of Ag nanoparticles on the titania surface, while longer time of irradiation results the growth of larger size nanoparticles. Antibacterial tests performed on TiO₂ covered by Ag nanoparticles revealed that increasing density of nanoparticles enhances the inhibition of bacterial growth. It was also found that antibacterial activity drops by only 10-15% after 6 cycles compared to the initial use.     

Effect of a thioalkane capping layer on the first hyperpolarizabilities of gold and silver nanoparticles

We have measured the first hyperpolarizabilities of thioalkane capped silver and gold metallic nanoparticles. The values found are β(AgC 12-10 nm) = (2.10 ± 0.23) × 10(-26) esu for 10 nm diameter silver nanoparticles and β(AuC 18-18 nm) = (3.37 ± 0.08) × 10(-26) esu for 18 nm diameter gold nanoparticles at the fundamental wavelength of 784 nm. By comparison to the corresponding values reported for citrate capped silver and gold metallic nanoparticles, after size corrections, decreases by factors of 4.3 and 6.5 respectively are observed. These decreases are tentatively attributed to the bonds formed between the gold and silver surface atoms and the sulfur atoms of the capping layer.     

Study of size dependent photoluminescence properties of copper doped sodium hexametaphosphate capped ZnS nanoparticles

Copper doped ZnS nanoparticles stabilized by sodium hexametaphosphate (SHMP) have been prepared via the wet chemical method using thiourea and sodium sulphide as chalcogenide sources. The XRD pattern showed that ZnS nanoparticles had zinc blende structure and line broadening suggests the formation of an amorphous compound. Absorption measurements were done for three different concentrations of dopant concentrations. The PL spectrum for the sample synthesized using Na₂S·9H₂O showed a sharp emission peak around 510 nm with full width at half maximum (FWHM)<10 nm. The role of the capping agent and sulphide source on optical properties of as synthesized nanoparticles by steady-state photoluminescence (PL) spectroscopy has been studied.     

Measurement of bimodal size distribution of nanoparticles by using the spatial distribution of laser-induced plasma

Laser-induced breakdown detection was performed to monitor the nanoparticles in an aqueous solution by means of a two-dimensional optical imaging method. To verify the relationship between the particle size and the optical image of a laser-induced plasma, we investigated the characteristics of its spatial distribution corresponding to the number of breakdown events plotted on the laser beam propagating axis. It was found that, for particles smaller than 50 nm in diameter, the spatial distribution follows a single Gaussian curve. For particles in the diameter range from 100 to 1000 nm, however, the spatial distribution follows a sum of the multiple Gaussian curves with different peak positions and peak heights. We demonstrated that particles smaller than 20 nm in trace concentrations, which are mixed with larger particles in the diameter range of a few hundred nm, can be measured by a peak deconvolution of the spatial distribution of a laser-induced plasma. PACS 42.62.Eh; 52.25.Rv; 52.70.Nc     

用小角X射线散射研究纳米粒子的粒度分布

采用小角X射线散射中的对数高斯分布函数的方法，确定了纳米粒子的粒度分布。通过理论分析、计算，对氧化锌纳粒子进行实验测试。结果表明，氧化锌纳米粒子的平均半径尺寸为3．34nm，分布的标准偏差为1．35。     

Synthesis of Si nanoparticles with narrow size distribution by pulsed laser ablation

We synthesized Si nanoparticles by pulsed nanosecond-laser ablation. We applied a positive voltage bias during laser irradiation and effectively reduced size distribution. Scanning electron micrographs of samples showed the nanoparticles to be highly non-agglomerated. Si nanoparticles have the average diameter of 4–5 nm, the geometrical standard deviation of 1.35, and the density of 1.6 × 10¹²/cm². A MOS device showed excellent charge trap behavior with a flat-band voltage shift over 7 V, which can be applied for memory device applications.     

Synthesis and characterization of spherical and narrow size distribution indium oxide nanoparticles

This work reports the synthesis of indium oxide nanoparticles and their thermal, structural, microstructural and optical characterization. The preparation method is based on a surfactant-free room temperature soft chemistry route. Spherical indium oxide nanoparticles (about 8 nm in diameter) were obtained after thermal treatment of gels at 400 °C for 2 h, as shown by X-ray diffraction experiments and nitrogen adsorption measurements. Transmission electron microscopy observations confirm the single-crystalline nature of the produced nanoparticles. The photoluminescence emission spectrum at room temperature shows a broad peak with onset at approximately 315 nm as a result of quantum size effect as revealed by small-angle X-ray scattering.     

Synthesis of copper nanoparticles catalyzed by pre-formed silver nanoparticles

Synthesis of well dispersed copper nanoparticles was achieved by reduction of copper nitrate in aqueous solution using hydrazine monohydrate as a reducer in the presence of preformed silver nanoparticles as catalysts. It has been demonstrated that addition of silver nanoparticles to the reaction mixture leads to formation of aqueous dispersion of copper nanoparticles and also results in a drastic reduction in reaction time compared to procedures reported in the literature. The absorption spectrum of the dispersions, HR-TEM and STEM images and XRD pattern indicate the formation of copper nanoparticles with particle size in the range of 5–50 nm.     

Photoluminescence from colloidal silver nanoparticles

Highly luminescent singles of Ag sol with gradual changes were detected when adjusting the granularity and concentration of particles. It can be deduced that these Ag sols, composed of a large amount of silver nanoparticles and clusters, may have their surface energy bands alterable, which might be caused by the interactions between particles. A model that describes the shift of energy band is proposed, and it can be understood as the hybridization of elementary plasmons when interactions occur between particles. Besides, both hybridization and absorption-rescattering mechanisms were proposed to explain the changeable phenomena of photoluminescence with different concentrations.     

Effect of size on momentum distribution of electrons around vacancies in NiO nanoparticles

Very small nickel oxide nanoparticles were prepared by a sol–gel procedure using nickel nitrate hexahydrate and ammonium hydroxide as precursors. The particles are in the range of 5 nm–11 nm. The x-ray diffraction(XRD) crystallography and high resolution transmission electron microscopy(HRTEM) were employed to characterize the samples.They were found to be polycrystalline in nature and fcc(Na Cl-type) in structure, with the lattice parameter varying with annealing temperature. HRTEM pictures show that the as-prepared samples are hexagonal in shape. Positron annihilation spectroscopy was used to investigate the Doppler-broadened spectra of the samples. The S and W parameters revealed that the chemical surroundings and momentum distribution of the vacancy clusters vary with crystallite size.     

Effect of particle size distribution on magnetic behavior of nanoparticles with uniaxial anisotropy

The effect of particle size distribution on the field and temperature dependence of the hysteresis loop features like coercivity(H_C), remanence(M_R), and blocking temperature(T_B) is simulated for an ensemble of single domain ferromagnetic nanoparticles with uniaxial anisotropy. Our simulations are based on the two-state model for T T_B and the metropolis Monte-Carlo method for T T_B. It is found that the increase in the grain size significantly enhances H_C and T_B. The presence of interparticle exchange interaction in the system suppresses H_C but causes MRto significantly increase.Our results show that the parameters associated with the particle size distribution(D_(d,δ)) such as the mean particle size d and standard-deviation δ play key roles in the magnetic behavior of the system.     

Enhanced light trapping for the silver nanoparticles embedded in the silica layer atop the silicon substrate

The optical properties of the structures with silver nanoparticles embedded in the silica layer atop the silicon substrate are simulated by the finite-difference time-domain method. The effects of nanoparticle size, period, silica layer thickness, and the angle of incidence of the illuminated light on optical transmissions are studied. It is found that there is the red-shift for the maximum of the total light transmitting into the silicon substrate as the silica layer thickness increases. The electric field intensity distributions and the average power densities for the structure with largest optical transmission is studied, and the strong electric field intensities are found in the silica regions surrounding to the silver nanoparticles, which can help the light energy going into the silicon substrate. By controlling the structure parameters, the optical transmissions of the structures with the silica layer can have higher optical transmissions than the cases without the silica layer. The silica layer plays the role as the graded refractive index layer between the air and the silicon substrate, and the light power from the incident wave can transmit into the silicon substrate with less optical reflections for choosing a suitable silica layer thickness. A guideline to design the structures with high optical transmissions for the solar spectra is given. This study cannot only be useful for the solar cells applications, but also other antireflection applications.     

Thermal conductivity of nanofluids and size distribution of nanoparticles by Monte Carlo simulations

Nanofluids, a class of solid–liquid suspensions, have received an increasing attention and studied intensively because of their anomalously high thermal conductivites at low nanoparticle concentration. Based on the fractal character of nanoparticles in nanofluids, the probability model for nanoparticle’s sizes and the effective thermal conductivity model are derived, in which the effect of the microconvection due to the Brownian motion of nanoparticles in the fluids is taken into account. The proposed model is expressed as a function of the thermal conductivities of the base fluid and the nanoparticles, the volume fraction, fractal dimension for particles, the size of nanoparticles, and the temperature, as well as random number. This model has the characters of both analytical and numerical solutions. The Monte Carlo simulations combined with the fractal geometry theory are performed. The predictions by the present Monte Carlo simulations are shown in good accord with the existing experimental data.     

Corrosion processes of triangular silver nanoparticles compared to bulk silver

Excessive corrosion of silver nanoparticles is a significant impediment to their use in a variety of potential applications in the biosensing, plasmonic and antimicrobial fields. Here we examine the environmental degradation of triangular silver nanoparticles (AgNP) in laboratory air. In the early stages of corrosion, transmission electron microscopy shows that dissolution of the single-crystal, triangular, AgNP (side lengths 50–120 nm) is observed with the accompanying formation of smaller, polycrystalline Ag particles nearby. The new particles are then observed to corrode to Ag₂S and after 21 days nearly full corrosion has occurred, but some with minor Ag inclusions remaining. In contrast, a bulk Ag sheet, studied in cross section, showed an adherent corrosion layer of only around 20–50 nm in thickness after over a decade of being exposed to ambient air. The results have implications for antibacterial properties and ecotoxicology of AgNP during corrosion as the dissolution and reformation of Ag particles during corrosion will likely be accompanied by the release of Ag⁺ ions.     

Atomic number dependent non-local pseudopotentials

A new ab initio method is introduced for constructing accurate pseudopotentials. A new model is obtained with a simple and realistic analytical expression. This contains explicitly both important characteristics of the atomic observables, namely the regular dependence on the atomic number and the non-locality. The application to the Li-like ions of the first row is presented. The whole spectrum of energy eigenvalues is reproduced within 0.3% and HF wavefunctions within 0.5%.