Dubravka Milovanovic

Agglomeration in core-shell structure of CuAg nanoparticles synthesized by the laser ablation of Cu target in aqueous solutions

Metallic copper Cu and bimetallic copper?silver CuAg nanoparticles (NPs) are generated by the ablation of copper bulk target in water and aqueous Ag colloidal solution, respectively. The experiments were performed using nanosecond Nd:YAG laser operating at 1064 nm. The generated NPs are characterized by UV?vis absorption spectroscopy, laser-induced breakdown spectroscopy, dynamic light scattering and scanning electron microscopy. The conducted investigations can be summarized as follows: (i) CuAg NPs colloidal solution possess the absorption in UV?vis spectral region, which can be attributed to the Cu-component; (ii) the primary bimetallic CuAg NPs have near uniform dimensions with diameter of about 15 nm, and as a rule, they are grouped into larger agglomerates without defined morphology; (iii) the obtained Cu NPs have mainly spherical form with average diameters up to 20 nm. Both types of NPs show a tendency towards the formation of large agglomerates with different morphology. Bimetallic NPs show the plasmon resonance in the vicinity of 640 nm with a good coincidence with formation of the colloidal solution of pure Cu NPs. The results also demonstrate that the core?shell structure (Ag-rich core/Cu-rich shell) is important for the formation of the bimetallic NPs, also agreeing very well with theory.

Influence of picosecond laser irradiation on nickel-based superalloy surface microstructure

The investigation presented in this paper was carried out on the nickel-based superalloy, Nimonic 263, a material widely used at elevated temperatures and pressures. The samples were exposed to a Nd3+:YAG pulsed laser, at a wavelength of 1064 nm and a pulse duration of 170 ps, and the estimated threshold damage was 2 mJ. Different pulse energies and numbers of pulses were applied in air and helium-enriched atmospheres. Spots obtained by the laser interaction with the material were observed by optical and scanning electron microscopes and analyzed by energy-dispersive spectroscopy. Vickers microhardness tests were performed. In this paper, the changes that had occurred at the sample surface microstructure as a result of laser–material interaction are discussed with the aim of contributing to the determination of optimal laser parameters in the laser surface treatment process.

Properties of plasma induced by pulsed CO2 laser on a copper target under different ambient conditions

Optical emission spectroscopy was applied for investigation of copper plasma induced by a nanosecond transversely excited atmospheric CO2 laser, operating at 10.6 μm. The effect of the background gas (air, Ar, He and N2) and pressure (1–25 mbar) on plasma formation was examined. The plasma shielding effect was more pronounced for background gases with lower ionization potential than for He. The increase of He pressure from 1 to 25 mbar resulted in fivefold increase of Cu atomic line intensity.

Validation and uncertainty estimation of UPLC-PDA method for the analysis of polycyclic aromatic hydrocarbons in concrete

Human exposure to persistent organic contaminants, from building materials, negatively affects peoples health and overall quality of life. This paper presents the validation and uncertainty assessment of the analytical method, developed for the simultaneous determination of 16 EPA polycyclic aromatic hydrocarbons (PAHs) in solid-solid concrete by ultra-performance liquid chromatography with photo diode-array detector. Linearity of calibration curves was good over the whole range of calibration. Limits of detection varied between 0.2 and 2.9μgkg-1. The accuracy in terms of recovery of the validated method is within the range from 54 to 106%. The developed method proved to be appropriate for analysis of PAHs and can be used for the quality control testing of concrete during the construction of new buildings, the old residences and related buildings associated with sick-building syndrome. In addition, this is the first reported method described for the evaluation of PAHs in solid-solid concrete.

Effects of the pulse duration in laser modification of nano-sized WTi film on Si substrate

A study of morphological and composition changes of the WTi/Si system induced by nanosecond and picosecond laser pulses is presented. A 190?nm thick WTi film was deposited on a silicon substrate of n-type (100). The pulsed laser systems used were: nanosecond TEA CO2 laser (emission, 10.6??m; pulse FWHM; pulse duration 120?ns) and picosecond Nd:YAG laser (emission, 532?nm; pulse FWHM; pulse duration 40?ps). During experiments the used fluences (?) had similar values, ?1 = 20?J??cm ? 2 in case of the TEA CO2 laser and ?2 = 16?J?cm ? 2 for the Nd:YAG laser. The laser-induced morphological and composition modifications showed a dependence on pulse duration. Generally, the following morphological changes were observed: (i)?ablation/exfoliation of the WTi thin film, (ii)?appearance of hydrodynamic features such as resolidified material, and (iii)?formation of nano-sized grains and globules. Overall morphological modifications were more pronounced after the picosecond laser action. The surface composition analysis showed a quite different distribution of sample components depending on the pulse duration. Formation of the silicon dioxide (SiO2) was recorded only in the case of irradiation of the WTi/Si system by picosecond laser pulses.