Compositional and morphological analysis of AgCl films deposited by evaporation and R.F. sputtering

AgCl thin films in a range of thicknesses from 0.05 to 2 μm were deposited by evaporation and r.f. sputtering of AgCl as well as by co-evaporation of AgCl and silver. Their structure and composition were studied using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy, energy-dispersive X-ray analysis and optical absorption spectroscopy. Films grown by evaporation show a preferential grain orientation that depends on the deposition rate. They are stoichiometric except for chlorine enrichment at the surface, but exposure to an electron beam or UV light causes metallic silver formation. AgCl films grown by r.f. sputter deposition have greater surface roughness than those grown by evaporation, a random grain orientation and a grain size that depends on the sputtering conditions. Metallic silver is present in these films. Optical absorption measurements of co-evaporated films suggest that the metallic silver occurs in two forms, small dispersed particles in the AgCl matrix and larger particles at the grain boudaries.     

Intracellular Uptake and Toxicity of Ag and CuO Nanoparticles: A Comparison Between Nanoparticles and their Corresponding Metal Ions

An increased understanding of nanoparticle toxicity and its impact on human health is essential to enable a safe use of nanoparticles in our society. The aim of this study is to investigate the role of a Trojan horse type mechanism for the toxicity of Ag‐nano and CuO‐nano particles and their corresponding metal ionic species (using CuCl₂ and AgNO₃), i.e., the importance of the solid particle to mediate cellular uptake and subsequent release of toxic species inside the cell. The human lung cell lines A549 and BEAS‐2B are used and cell death/membrane integrity and DNA damage are investigated by means of trypan blue staining and the comet assay, respectively. Chemical analysis of the cellular dose of copper and silver is performed using atomic absorption spectroscopy. Furthermore, transmission electron microscopy, laser scanning confocal microscopy, and confocal Raman microscopy are employed to study cellular uptake and particle‐cell interactions. The results confirm a high uptake of CuO‐nano and Ag‐nano compared to no, or low, uptake of the soluble salts. CuO‐nano induces both cell death and DNA damage whereas CuCl₂ induces no toxicity. The opposite is observed for silver, where Ag‐nano does not cause any toxicity, whereas AgNO₃ induces a high level of cell death. In conclusion: CuO‐nano toxicity is predominantly mediated by intracellular uptake and subsequent release of copper ions, whereas no toxicity is observed for Ag‐nano due to low release of silver ions within short time periods.     

Synthesis of carbon nanofiber films and nanofiber composite coatings by laser-assisted catalytic chemical vapor deposition

Uniform carbon nanofiber films and nanofiber composite coatings were synthesized from ethylene on nickel coated alumina substrates by laser-assisted catalytic chemical vapor deposition. Laser annealing of a 50 nm thick nickel film produced the catalytic nanoparticles. Thermal decomposition of ethylene over nickel nanoparticles was initiated and maintained by an argon ion laser operated at 488 nm. The films were examined by scanning electron microscopy and by transmission electron microscopy. Overall film uniformity and structure were assessed using micro-Raman spectroscopy. Film quality was related to the experimental parameters such as incident laser power density and irradiation time. For long irradiation times, carbon can be deposited by a thermal process rather than by a catalytic reaction directly over the nanofiber films to form carbon nanocomposite coatings. The process parameters leading to high quality nanofiber films free of amorphous carbon by-products as well as those leading to nanofiber composite coatings are presented.     

Facile chemical synthesis of nano-silver powders for printable electronics applications

In this article, a simple and reproducible technique for the synthesis of silver nanoparticles in organic phase without using external reducing agents is reported. The organic phase contains silver acetate as precursor, oleic acid and oleyl amine as capping molecules and diphenyl ether as solvent. Monodispersed silver nanoparticles with an average size of 5?nm could be easily synthesised at large scale and it was possible to isolate the particles suitable for electronics applications. The formation of silver nanoparticles has been characterised in terms of optical absorption, transmission electron microscopy images and small-angle X-ray scattering. Recovered silver nanoparticles reveal X-ray diffraction of a well grown-up fcc-Ag lattice. Chemical and thermal characterisations of silver nanopowders were carried out using X-ray photoelectron spectroscopy and thermogravimetric analysis, respectively. For the latter purpose, concentrated dispersions of silver nanoparticles were prepared and used for depositing uniform thin layers. Thin films were sintered at low temperature to obtain conductive films and the films were characterised using scanning electron microscope. Electrical conductivity of the conductive films was in the range 2–3?×?10⁴?S?cm^?1.     

Electron beam initiated oxidation and coalescence of metal particles embedded in a plasma-polymer thin film matrix

Microstructural changes in plasma-polymer thin films with embedded indium or silver nanoparticles were initiated by electron beam irradiation. Oxidation of indium particles was realized by electron beam irradiation in situ with the electron microscope. By means of selected area electron diffraction it was demonstrated, that indium particles oxidize to smaller In₂O₃ crystallites. On the other hand, thermal annealing of the films results only in a formation of an indium oxide shell. At plasma-polymer films with embedded silver particles, the electron beam irradiation with a microfocus electron source results in an increase of the size of the embedded silver particles with a simultaneous decrease of the particle number (coalescence).     

Novel Nanomaterials Synthesis by Laser-Liquid-Solid Interaction

A novel laser-liquid-solid interaction (LLSI) technique has been developed that is highly flexible and allows engineering nanomaterials in form of particles, rods, and tubes from liquid precursors. Synthesis reaction takes place in a molecular level and reaction rate is controlled by laser energy input, precursor solution chemistry, and other processing parameters including interaction time, and thermal conductivity of solid that is spinning in the solution. By the proper selection of liquid precursor, mono-dispersed silver nanoparticles were produced with average particle size 7-10 nm. Alloy composed Ag and Ni were produced in the form of nanoparticles and nanotubes with an average diameter of 40 nm. HRTEM of nanorod exhibited that Ag acted as seed for the synthesis of immiscible of Ag-Ni alloy. Laser writing of silver exhibited 50% lower electrical resistivity and eliminated many intermediate steps involved as compared to conventional silver patterning process.     

Dielectric and optical properties of CaCu3Ti4O12 thin films containing Ag nanoparticles

Simple sol-gel techniques are used to prepare thin films of a high dielectric constant perovskite CaCu₃Ti₄O₁₂, containing different amounts of metallic silver nanoparticles. The formations of the silver nanoparticles are verified by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and optical absorption studies. The dielectric properties are found to be significantly affected by the presence of the silver nanoparticles. A maximum in the dielectric constant is observed at an intermediate metal particle concentration. This is explained in terms of the polarization at the particle-dielectric interface and the internal barrier layer capacitor effect. The optical absorption spectrum is compared with Mie theory in electrodynamics for the optical absorption of small particles to extract the particle size of the silver particle. Non-uniform distributions of Ag particles through the thickness of the thin films are reported.     

Electrical properties of silver paste prepared from nanoparticles and lead-free frit

Recently, PbO containing glass systems in commercial silver paste have been used due to their low glass transition temperature, good thermal and electrical properties. However, PbO is a hazardous material to both health and the environment. In this study, Pb-free silver paste was prepared by mixing commercial silver powder and silver nanoparticles. The commercial powder has an average particle size of 1.6 microm. The silver nanoparticles with particles size of 20-50 nm were synthesized by a chemical reduction method using surfactant. Pb-free frit was added into the mixed silver powder as the amounts of 3, 6 and 9 wt%. Using the obtained paste, thick films were fabricated by a screen printing on alumina substrate and the films were fired at temperature from 400 to 550 degrees C. The films had thickness of 6-11 microm and sheet resistivity of about 4-11 microomega cm.     

Tuned optical properties of in-situ synthesized m-nitroaniline doped Ag/PVA nano-composites

Meta-nitroaniline (m-NA) doped silver/poly(vinylalcohol) (Ag/PVA) nanocomposites are prepared via in-situ reduction of silver salt by employing hydrazine hydrate (HH) in order to study the effect of the NLO active m-NA on the optical properties of nanoparticles of silver in the colloidal as well as self supported film form. Reduction of silver salt in aqueous alcoholic PVA with HH is done first followed by doping of the reaction mixture with m-NA. The UV-Visible absorption spectra show peak at about 400 nm for Ag nanoparticles due to surface plasmon resonance phenomenon, which gets blue shifted with the change in m-NA concentration. The Second Harmonic Generation (SHG) studies show improvement in intensity with increasing m-NA concentration up to a saturation point (approximately 2.52 wt% with respect to PVA). Further increase in m-NA concentration leads to decrease in SHG intensity. The solutions and the films are characterized by photoluminescence (PL), FTIR spectroscopy, XRD, SEM, TEM, and thermal analysis. m-NA doped composites showed better PL efficiency. SEM of the nanocomposite film shows uniform distribution of particles within the film. The particle size as shown by TEM is found to be less than 10 nm.     

Pulsed laser deposition of metal films and nanoparticles in vacuum using subnanosecond laser pulses

A study of silver, chromium, stainless-steel, and indium thin films prepared by subnanosecond laser deposition in vacuum is reported. We compare the laser ablation in vacuum at the weak- and tight-focusing conditions of a Ti:sapphire laser beam and analyze the nanoparticles synthesized in the latter case using absorption spectroscopy, x-ray fluorescence, atomic force microscopy, and scanning electron microscopy. Our results show that the nanoparticle formation can be accomplished using long laser pulses under tight-focusing conditions.     

Laser-ablated plasma for deposition of ZnO thin films on various substrates

We report optical and structural properties of ZnO films deposited by pulsed laser deposition technique on 1100) n-typesilicon and quartz substrates at various pressures of back ground gas. ZnO plasma was created using KrF laser 1248 nm) atvarious pressures of the ambient gas, oxygen. Laser induced plasma at varying fluence on the target was investigated using optical emission spectroscopy and 2-D images of the expanding plumes. X-ray diffraction, atomic force microscopy, and spectro-photometry were used to characterize as grown films.     

Helium ion bombardment of thin aluminium films

A study is presented of the effect of 5 keV helium ion bombardment on thin (about 2000 Å) aluminium films using proton backscattering, scanning and transmission electron microscopy and α particle energy loss spectroscopy. Measurements of helium content after irradiation using proton backscattering indicate low below-saturation retention for both room temperature and low temperature implantations (19% and 24% respectively). Electron microscopy examination of the films reveals a severe deformation in the form of coarse and fine-scale wrinkling whose amplitude increases with increasing helium dose. This deformation does not appear to be the result of bubble swelling. An attempt has been made to quantify the wrinkling by measuring the energy loss spectrum of α particles transmitted through irradiated films and the combination of these measurements with a simple sinusoidal deformation model indicates an increase in film area of up to 20%.     

Effect of laser irradiation on silica substrate contaminated by aluminum particles

A major issue in the use of high-power lasers, such as the Laser Megajoule (LMJ), is laser-induced damage of optical components. One potential damage initiator is particulate contamination, but its effect is hard to distinguish from that of other damage precursors. To do so, we introduced artificial contaminants typical of metallic pollution likely to be present on the optical components of the LMJ chains. More precisely, aluminum particles of two different sizes were placed on a silica sample. These dots were characterized by optical microscopy and profilometry. Then they were exposed to a laser beam with a pulse length of 6.5 ns at 1064 nm and fluences in the range from 1 to 40 J/cm(2). Each dot was characterized again with the same techniques and also by photothermal microscopy. To complete the experimental results, we performed numerical simulations with a one-dimensional Lagrangian hydrodynamics code. We show that the particle removal by laser irradiation produces a modification of the silica surface that does not evolve into catastrophic damage under subsequent irradiation. However, the effect does depend on the size of the dots. We demonstrate that a procedure exists that removes the dot and leaves the site capable of resisting high fluence.     

Nano-particle thin films of tin oxides

Nano-particle thin films of tin oxides were deposited on SiO₂ substrates by using radio frequency (RF) magnetron sputtering with various substrate temperatures, sputtering powers and oxygen partial pressures. The tin oxides thin films were then investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS data suggested that the deposited tin oxides thin films are almost made up of half of SnO₂ and half of SnO. The oxygen partial pressure nearly does not affect the chemical stoichiometry of the thin films in our deposition conditions. SEM results showed that the tin oxides thin films were formed by nano-particles with size of about 60 nm. Sputtering power has a strong influence on the particle size of the thin films. Increase of sputtering power will enlarge the size of the particles.     

Preparation of silver nanoparticles by photo-reduction for surface-enhanced Raman scattering

A substrate for surface-enhanced Raman scattering (SERS) has been developed. Based on the surface-catalyzed reduction of Ag⁺ by citrate on the silver nanoparticles surface under light irradiation, small silver seeds on a quartz slide can be enlarged. The optical properties and characteristics of the silver films have been investigated by ultraviolet-visible spectroscopy, scan electron microscope and atomic force microscopy (AFM). The results indicate that the particle size and shape are different at different reduction time. At the first 3 h, some triangular and hexagonal nanoparticles formed; with the reduction proceeding, the shape of the silver particles became irregular and the size became larger. The silver films obtained are very suitable as SERS active substrate. The relationship between SERS intensity and the reduction time has been investigated for 1,4-bis[2-(4-pyridyl)ethenyl]-benzene molecule adsorbed on the silver film. The SERS intensity reached a maximum at 8 h reduction. The AFM measurements indicate that roughness features with an average size of 100 nm are present on the surface, which yielded the strongest SERS signal. Pyridine was used as a probe molecule to investigate the enhancement factor (EF) of the silver films. According to the formalism of Tian and co-workers, the EF of the silver films is estimated to be 3.4 × 10⁵. The silver film that can remain active for more than 50 days would seem to be suitable for various analytical applications.     

Synthesis of high tap density spherical micro-size silver particles by liquid-phase reduction using response surface methodology

Mono-disperse and spherical micro-size silver particles with high tap density were prepared by using silver nitrate as metal source, ascorbic acid as reductant, sulfuric acid as dispersant and polyethylene glycol 4000 (PEG4000) as surfactant. The aim of this paper was to study the simultaneous effects of surfactant dosage (PEG4000/AgNO₃ mass ratio), silver nitrate concentration [AgNO₃], deionized water dosage in reductant solution, stirring rate and their interactions on properties of silver particles. For optimizing these parameters, irregular fractional factorial design of experiments was used. As-prepared silver particles were characterized by X-ray diffraction, scanning electron microscopy, laser particle size analyzer and tap density (tap density refers to the stacking density of particles after vibration compaction) meter. The results showed that silver particles were spherical, mono-disperse and with high tap density (>5.0 g/mL), average particle size of about 2–3 μm and narrow particle size distribution. By surveying the experiment results and analysis of variance, two mathematical models were obtained and optimized parameters were determined. Analysis of the variance demonstrated that the interaction of [AgNO₃] and stirring rate were the most significant factor affecting particle size and PEG4000/AgNO₃ mass ratio and [AgNO₃] were main significant factors affecting tap density. The predicted particle size and tap density were respectively 2.5 μm and 5.065 g/mL while the experimental results were 2.52 μm and 5.108 g/mL, which indicated that the models were in good agreement with the experimental data.     

Laser-ablated plasma for deposition of ZnO thin films on various substrates

We report optical and structural properties of ZnO films deposited by pulsed laser deposition technique on (100) n-type silicon and quartz substrates at various pressures of back ground gas. ZnO plasma was created using KrF laser (248 nm) at various pressures of the ambient gas, oxygen. Laser induced plasma at varying fluence on the target was investigated using optical emission spectroscopy and 2-D images of the expanding plumes. X-ray diffraction, atomic force microscopy, and spectro-photometry were used to characterize as grown films.     

不同中和度聚苯乙烯-丙烯酸粒子的聚乙二醇悬液剪切增稠特性研究

实验采用无皂乳液聚合法,以NaHCO_3为中和剂,合成了一系列不同中和度的聚苯乙烯-丙烯酸(PS-AA)粒子。分别通过一步法、两步法合成了两种PS-AA粒子,并通过扫描电镜(SEM)观察了两种粒子的微观形貌。采用高能球磨法将粒子分散到聚乙二醇中,制备得到PS-AA/PEG剪切增稠液(STF),并通过动态流变仪稳态扫描测试了其聚乙二醇悬液的剪切增稠特性,结果表明用两步法合成的粒子作分散相可制备出优良的剪切增稠液。通过红外光谱、热重-DSC、扫描电镜、激光粒度分布仪对不同中和度的粒子进行了表征,并通过动态流变仪对其聚乙二醇悬液流变性能进行表征。结果表明,实验成功合成了不同中和度且表面光滑、粒径均一的核壳状的PS-AA粒子,并以此制备出性能优异的剪切增稠液,得出最优中和度为45%和50%。其中50%中和度PS-AA粒子,其质量浓度为64%的聚乙二醇悬液最大粘度高达2 200Pa·s,该性能在抗外力防护领域研究成果内出类拔萃。     

Synthesis of carbon films containing diamond particles by electrolysis of methanol

Carbon films containing diamond particles were deposited onto a Si (100) substrate by electrolysis of methanol under a direct current potential of 1200 V, with a current density of about 52 mA/cm², at atmospheric pressure and in the temperature range of 50-55 °C. The surface morphology, microstructure and crystalline structure of the deposited films were characterized by scanning electron microscopy (SEM), Fourier transformation infrared (FTIR) spectroscopy, Raman spectroscopy and transmission electron microscopy (TEM) respectively. The SEM images show that the films are formed by particle clusters and a surrounding glassy phase. The Raman spectra of the films indicate that the particle clusters are composed of diamond and that the glassy phase is composed of amorphous carbon. The FTIR measurements suggest the existence of hydrogen which is mainly bonded to the sp³ carbon in the films. The transmission electron diffraction patterns further indicate that the particles in the films consist of single-crystalline diamond. Both TEM and Raman measurements have confirmed unambiguously the formation of diamond crystals in the deposit, although the particles are not uniformly distributed on the entire surface.     

Metal nanoparticles incorporation during the photopolymerization of polypyrrole

In this work we present a route to prepare intrinsically conducting polymer (ICPs)/Silver nanoparticles composite through the photon polymerization process. The method consists to use the transition metals ions assisted by UV light to polymerize the pyrrole monomer. At the same time that the monomer is polymerized the silver ions are reduced and the silver metal particle are produced and incorporated to the polymer matrix. The composite films were characterized by conductivity measurements, UV/vis and FTIR spectroscopy, X-ray diffraction, and scanning electronic microscopy. The morphological properties of incorporated silver nanoparticles were examined with respect to the nature of substrates, exposure time and monomer ratios. Soon after a silver nitrate solution containing Pyrrol is excited by an UV light, a black deposition appears on glass walls or other substrates, such PET (poly(ethylene terephthalate) immersed in the solution, however if the solution is set aside and protected from light, the same black films takes more than 48 h to form. The UV–visible absorption, X-ray diffraction, infrared analysis and conductivity measurements confirm the formation of silver particles and pyrrole polymerization with composite conductivity in the order of 10⁻³ S cm⁻¹.