Silver Target Research Articles

Preparation and characterization of heat-insulating Ag/TiO2 composite membranes based on magnetron sputtering technology

Abstract

In-flight plasma modification of nanoparticles produced by means of gas aggregation sources as an effective route for the synthesis of core-satellite Ag/plasma polymer nanoparticles

Core-satellite nanoparticles (NPs), i.e. nanoparticles with a core decorated by small nanoparticles, have become highly attractive in a wide range of applications that comprises for instance ultra-sensitive bio-sensing, bio-imaging, targeted drug delivery or catalysis. Although many methods had been developed to produce such nanomaterials, some challenges such as high complexity of used protocols or low purity of synthetized nanoparticles, are still faced. In this study we report on the detailed investigation of a novel, fully plasma-based strategy that allows for the fabrication of silver/plasma polymer core-satellite NPs. The studied deposition procedure utilizes in-flight sputter-deposition of silver onto plasma polymer (C:H:N:O) nanoparticles produced by means of a gas aggregation source (GAS). It is shown that the silver atoms generated by magnetron sputtering of a silver target in an auxiliary plasma chamber located in between the output orifice of the GAS and the main deposition chamber are effectively captured by C:H:N:O nanoparticles as they pass through the inoculation zone of the deposition system. This results in the formation of small Ag nano-islands on the surface of C:H:N:O nanoparticles as witnessed by transmission electron microscopy. Furthermore, it is demonstrated that the size and number of silver satellites may be varied by the magnetron current used for the silver sputtering.

Opacity Corrections for Resonance Silver Lines in Nano-Material Laser-Induced Plasma

Q-switched laser radiation at wavelengths of 355, 532, and 1064 nm from a Nd: YAG laser was used to generate plasma in laboratory air at the target surface made of nano-silver particles of size 95 ± 10 nm. The emitted resonance spectra from the neutral silver at wavelengths of 327.9 nm and 338.2 nm indicate existence of self-reversal in addition to plasma self-absorption. Both lines were identified in emission spectra at different laser irradiation wavelengths with characteristic dips at the un-shifted central wavelengths. These dips are usually associated with self-reversal. Under similar conditions, plasmas at the corresponding bulk silver target were generated. The recorded emission spectra were compared to those obtained from the nano-material target. The comparisons confirm existence of self-reversal of resonance lines that emerge from plasmas produced at nano-material targets. This work suggests a method for recovery of the spectral line shapes and discusses practical examples. In addition, subsidiary calibration efforts that utilize the Balmer series Hα-line reveal that other Ag I lines at 827.35 nm and 768.7 nm are optically thin under variety of experimental conditions and are well-suited as reference lines for measurement of the laser plasma electron density.

Effect of the Magnetic field and duration time on Thickness and Structure of Silver Thin films Deposition by Magnetron Sputtering

In this paper, the effect of magnetic field on thickness of silver (Ag) thin films were deposition on glass substrates by DC magnetron sputtering method of silver target were studied, with permanent and variable magnetic field. Ag thin films with (84,89,94,269,290) nm, thickness were prepared at different deposition times (10,30,60) sec. The crystalline structure of thin films was evaluated by X-ray diffraction (XRD) and the atomic force microscopy (AFM) were employed for surface morphological studies of the films. The results show that the thickness of the films increases with increases magnetic field to 250 Gauss, and when are greater than (250Gauss) the effect of magnetic field starts to decrease and be ineffective, and also the results indicate an increase of the grain size from (144.9 -276.7) nm and films surface roughness from (0.431-22.7) nm.

Tuning thermo-optic properties of BF and NR dyes using plasmonic silver nanoparticles

The linear and thermo-optical properties of two dyes-Basic Fuchsin and Neutral Red were tailored using plasmonic silver nanoparticles. The silver nanosol was synthesized using a mode-locked femtosecond laser ablation of a silver target. The synthesized nanoparticles were having an average size of 7 nm. The results were interpreted in terms of dye-nanoparticle interaction and the formation of dye-nanoparticle resonance hybrids.

Construction and Ion-Beam Characterization of Nuclear Targets

We report on the construction and ion-beam characterization of nuclear targets and thin films as part of the ongoing NuSTRAP group research program at the University of Athens. Two different techniques were used for the preparation of new targets, depending on the desired material and thickness. Self-supported, natural silver targets were manufactured by Physical Evaporation Deposition (PVD) through electrical resistance heating, using the evaporation apparatus at the INPP (NCSR “Demokritos”). Thick iron targets were constructed using the rolling technique at the INRASTES (NCSR “Demokritos”) facilities. The Rutherford Backscattering Spectrometry (RBS) was employed to characterize the newly manufactured and existing targets using proton and deuteron beams accelerated by the Tandem Van de Graff Accelerator (at INPP) at several energies. The results from the analysis of experimental spectra and corresponding simulations carried out with the simNRA software package are presented.

Simulations of hard X-ray generation by hot electrons in a silver target

A semi-analytical model is developed for the generation of X-ray bremsstrahlung in metallic targets with the inclusion of hot electron recirculation (refluxing). The hard bremsstrahlung and characteristic X-ray yields are calculated in relation to the thickness of a silver target for an s-polarised subpicosecond laser pulse intensity of 2 × 1019 W cm–2. The effect of hot electron recirculation in thin foils is shown to significantly improve the Kα radiation and bremsstrahlung yields in a photon energy of 10 – 100 keV. By contrast, the 0.1 – 1 MeV bremsstrahlung photon yield from thin foils with hot electron recirculation corresponds approximately to the highest photon yield from those targets in which recirculation is insignificant. We make a comparative analysis of the highest laser-to-X-ray energy conversion efficiencies obtained to date.

Formation of 107Cd radionuclide impurities during 18F production

Cd isotopes (107Cd and 109Cd) are generated from the silver target body during the bombardment of [18O]water in the routine production of 2-[18F]fluoro-2-deoxy-d-glucose ([18F]FDG) for PET (Positron Emission Tomography) diagnosis. Cadmium isotopes contribute significantly to the total activity of generated impurities and, due to being potentially radiotoxic to living organisms, they should be effectively reduced from FDG to prevent accidental injection of even small concentrations into patients. Purification of the final [18F]FDG can be based on a set of columns, fulfilling various functions in the cleaning process. To assess cadmium impurities and the efficiency of the purification process, a low background gamma spectrometry system with high resolution has been applied.Even activity of 3.5 kBq and 290 kBq has been measured on QMA (Sep-Pak Light Accell Plus QMA) columns for 109Cd and 107Cd isotopes, respectively. 107Cd activity in the five column set was higher than that of 109Cd. The rate of 18F production process was about 1 GBq/min, while that of 107Cd and 109Cd radionuclides was about 4.2 kBq/min and 50 Bq/min respectively.The same purification efficiency of both isotopes has been obtained at each step of the process. The production rate of 107Cd and 109Cd radionuclides was insignificant compared to the 18F production rate. Therefore [18F]FDG final product for use in injections before PET diagnostics was efficiently purified from cadmium radionuclide impurities.

Experiments and kinetic modeling of the ion energy distribution function at the substrate surface during magnetron sputtering of silver targets in radio frequency argon plasmas

The quality of the films obtained by magnetron sputtering depends on numerous parameters, including the energy of the ions impinging on the substrate. The energy distribution functions of Ar and Ag ions during magnetron sputtering of a silver target in rf argon plasmas are hereby reported. Measurements were carried out by plasma sampling mass spectrometry at (i) various bias voltages on the surface of the target at constant pressure and (ii) various operating pressures at constant bias voltage. A distinct high-energy tail is observed for the sputtered silver ions (ionized in the plasma) in comparison to the argon gas ions. The results indicate that the sputtered Ag atoms are not completely thermalized by collisions with background gas atoms over the range of experimental conditions investigated. To confirm such assertion, a model has been developed for the ejection of Ag atoms from the target, their transport in the gas phase, and their acceleration in the sheath at the surface of the mass spectrometer. Since sputtering occurs at low impinging ion energies, the energy distribution function of the extracted atoms cannot be represented by the usual Sigmund–Thomson distribution. It is rather assumed to be characterized by a bi-Maxwellian distribution, with one population related to the direct “classical” sputtering and the other one to indirect “2-step etching.” During the transport of Ag neutrals, both ionization and thermalization processes are considered. Finally, the rf sheath near the entry of the mass spectrometer oscillates at a period close to the transit time of the ions passing through it. This induces a complex energy gain also implemented in the model. An excellent agreement between the latter and experimental measurements is obtained. The results are used to probe the effect of the bias voltage and pressure on the fitting parameters, namely, the dc and rf components of the voltage drop in the sheath, the mean energy of the sputtered atoms, and the relative importance of the sputtered populations.

Antimicrobial silver targets glyceraldehyde-3-phosphate dehydrogenase in glycolysis of E. coli.

Silver has long been used as an antibacterial agent, yet its molecular targets remain largely unknown. Using a custom-designed coupling of gel electrophoresis with inductively coupled plasma mass spectrometry (GE-ICP-MS), we identified six silver-binding proteins in E. coli. The majority of the identified proteins are associated with the central carbon metabolism of E. coli. Among them, we unveil that GAPDH, an essential enzyme in glycolysis, serves as a vital target of Ag+ in E. coli for the first time. We demonstrate that silver inhibits the enzymatic function of GAPDH through targeting Cys149 in its catalytic site. The X-ray structure reveals that Ag+ coordinates to Cys149 and His176 with a quasi-linear geometry (S-Ag-N angle of 157°). And unexpectedly, two Ag+ ions coordinate to Cys288 in the non-catalytic site with weak argentophilic interaction (Ag···Ag distance of 2.9 Å). This is the first report on antimicrobial Ag+ targeting a key enzyme in the glycolytic pathway of E. coli. The findings expand our knowledge on the mode of action and bio-coordination chemistry of silver, particularly silver-targeting residues in proteins at the atomic level.

Imaging spectroscopy of Ag plasmas produced by infrared nanosecond laser ablation

Spatially and temporally resolved optical emission spectroscopy has been used to study plasmas formed by 1064 nm pulsed laser ablation of silver targets in a vacuum.

RE-irradiation of silver nanoparticles obtained by laser ablation in water and assessment of their antibacterial effect

The rapid evolution of resistant bacteria is a huge problem in medicine because makes the treatment of infections more and more difficult. The bactericidal properties of noble metal nanoparticles could be a solution.In this work silver nanoparticles were produced by using two nanosecond Nd:YVO4 lasers operating at 1064 and 532 nm respectively to ablate a silver target submerged in pure de-ionized water. Part of the resulting colloidal solution was injected as a fine stream by a compressed air system and re-irradiated one and three times with the same laser to resize and get uniform nanoparticles.The obtained nanoparticles by ablation and re-irradiation consisted of crystalline Ag nanoparticles with a bimodal size distribution. The particle size has been reduced by subsequent laser re-irradiation with both laser sources, reaching a 40% of mean size reduction. Inhibitory effects on the proliferation of Staphylococcus aureus was demonstrated on silver nanoparticles obtained after re-irradiation with the infrared laser.

How the re-irradiation of a single ablation spot affects cavitation bubble dynamics and nanoparticles properties in laser ablation in liquids

Fundamental theoretical and experimental studies on the formation of nanoparticles and cavitation during laser synthesis of colloids usually employ single-pulse conditions, whereas studies of the properties of nanoparticles naturally require prolonged ablation. We explored how a defined number of pulses changes a silver target’s surface geometry and thereby the dynamics of the laser-induced cavitation bubble and the resulting properties of the nanoparticles. The shape of the cavitation bubble transforms from hemispherical to almost spherical. The indirectly calculated mass concentration in the cavitation bubble follows a decay with the number of laser pulses. Surprisingly, the ablated mass does not set the volume of the extended cavitation bubble, as one would expect, because of the linear dependency of both the volume of the bubble and the ablation mass per pulse on the laser fluence. No influence of the altered cavitation bubble on the nanoparticles was identified. Instead, clear evidence of a high share of silver nanoclusters (d < 3 nm) with improved instrumentation (ultracentrifuge) was found in all samples at our low concentration conditions. The influence of these reactive species on the final particle size was found to be much larger than the cavitation bubble variations caused by prolonged surface ablation. In addition, no correlation was observed between the size of the primary particles (∼8 nm) and the mass concentration in the cavitation bubble.

Influence of substrate temperature on the properties of Ag-C films produced by DC Magnetron Sputtering

Silver-carbon films (Ag-C), rich in silver, deposited by DC magnetron sputtering from a silver target (Ag) into silicon substrate (100) in atmosphere of argon/acetylene plasma, have been studied in function of the substrate temperature (as-deposited, 200°C and 300°C). The Ag-C films were obtained using an acetylene gas flow of 0.3 sccm and dc cathode current of 180mA. Ag-C films were characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. It has been observed the decrease of graphite-like bonds in the Ag-C films with the substrate temperature. The SEM revealed that the substrate temperature promotes changes on the surface morphology. These changes on the chemistry and surface morphology are discussed in terms of atoms diffusion on the surface and the chemical composition of the Ag-C films.

Plasma ignition threshold disparity between silver nanoparticle-based target and bulk silver target at different laser wavelengths

Plasma ignition threshold of nanoparticle-based and bulk silver targets was measured in air. The plasma was initiated by a Nd:YAG laser at wavelengths of 355, 532, and 1064 nm. The plasma ignition was monitored utilizing the prominent Ag I line at 546.5 nm. Lower ignition thresholds of the nanoparticle-based silver target were estimated at 0.4 ± 0.02, 0.34 ± 0.04, and 0.27 ± 0.035 J cm−2 coupled with the different laser wavelengths, respectively. In contrast, the bulk silver target plasma exhibited an order of magnitude higher ignition threshold. A three orders of magnitude enhanced emission intensity from the nano-based target over the bulk target was achieved at lower levels of laser irradiation. A reduction of the thermal diffusion length of the nanosilver was assumed in order to theoretically predict this reduction in the plasma threshold. In addition, the effect of self-reversal on the resonance lines was taken into consideration.

Theoretical considerations over the production of silver nanoparticles by laser ablation confined in distilled water

Laser ablation of a silver target confined in distilled water allowed us to obtain silver nanoparticles. However, to have knowledge of their production by this method, common instruments for measurement of the silver concentration in a colloidal solution are employed, this is due to laser ablation and is usually considered a top-down physical approach in the synthesis of nanoparticles. In consequence, this research has suggested an alternative to know the silver nanoparticles production through theoretical considerations, which depends on laser parameters and intrinsic properties of a silver target. Theoretically, this result has given us a silver concentration around 0.029 mg ml − 1 and from of transmission electron micrographs were obtained a size distribution, where it was fitted with one Gaussian peak, being the smaller sizes the most frequent. The mean peak was centered at 12 nm, having a nanoparticle mass of 7 × 10 − 18 g, and regarding a relation with the silver concentration, the nanoparticles production was around 4 × 1012 nanoparticles ml − 1.

Laser–plasma driven green synthesis of size controlled silver nanoparticles in ambient liquid

This article explores the expansion behavior of laser produced silver plasma in stationary and stirring liquid media using space resolved optical emission spectroscopy and plasma instigated size controlled synthesis of silver nanoparticles via laser ablation. Second harmonics (532 nm) of an Nd:YAG laser was employed for the ablation of a silver target in ambient liquid for plasma formation. Calculation of plasma parameters — electron temperature and electron number density were done for different laser fluences and in various liquid media at room temperature. The Electron temperature (Te) was measured by exploiting the Boltzmann plot method and the electron number density (ne) was estimated from Stark broadened profiles of isolated lines from optical emission spectra. UV–Vis spectroscopy, fluorescence spectroscopy and high-resolution transmission electron microscopy further substantiated the optical and morphological characteristics of silver nanoparticles. Obtained novel versatile results pave way for a far-reaching understanding in creation and characterization of silver plasma, in ambient liquid; and provides a methodical green approach towards the synthesis of metallic nanoparticles that can be fine tuned for size and morphology, by varying laser parameters.

Investigation of alpha particle induced reactions on natural silver in the 40–50 MeV energy range

Natural silver targets have been irradiated by using a 50 MeV alpha-particle beam in order to measure the activation cross sections of radioisotopes in the 40–50 MeV energy range. Among the radio-products there are medically important isotopes such as 110mIn and 111In. For optimizing the production of these radioisotopes and regarding their purity and specific activity the cross section data for every produced radioisotope are important. New data are measured in this energy range and the results of some previous measurements have been confirmed. Physical yield curves have been calculated by using the new cross section data completed with the results from the literature.

SERS active Ag-SiO2 nanoparticles obtained by laser ablation of silver in colloidal silica.

Highly stable Ag–SiO2 nanoparticle composites were first obtained by laser ablation of a silver target in an aqueous colloidal dispersion of silica and examined by UV–vis absorption spectroscopy, transmission electron microscopy and Raman spectroscopy. The surface enhanced Raman scattering (SERS) activity of these nanocomposites was tested using 2,2’-bipyridine as a molecular reporter and excitation in the visible and near-IR spectral regions. The computational DFT approach provided evidence of ligand adsorption on positively charged adatoms of the silver nanostructured surface, in a very similar way to the metal/molecule interaction occurring in the corresponding Ag(I) coordination compound.

Silver and Antibiotic, New Facts to an Old Story.

The therapeutic arsenal against bacterial infections is rapidly shrinking, as drug resistance spreads and pharmaceutical industry are struggling to produce new antibiotics. In this review we cover the efficacy of silver as an antibacterial agent. In particular we recall experimental evidences pointing to the multiple targets of silver, including DNA, proteins and small molecules, and we review the arguments for and against the hypothesis that silver acts by enhancing oxidative stress. We also review the recent use of silver as an adjuvant for antibiotics. Specifically, we discuss the state of our current understanding on the potentiating action of silver ions on aminoglycoside antibiotics.