Direct Probing of Water Adsorption on Liquid-Phase Exfoliated WS2 Films Formed by the Langmuir-Schaefer Technique.

Tungsten disulfide, a transition metal dichalcogenide, has numerous applications as active components in gas- and chemical-sensing devices, photovoltaic sources, photocatalyst substrates, etc. In such devices, the presence of water in the sensing environment is a factor whose role has not been well-understood. To address this problem, the in situ probing of H2O molecule adsorption on WS2 films supported on solid substrates has been performed in a near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) setup. Instead, on the individual nanoflakes or spray-coated samples, the measurements were performed on highly transparent, homogeneous, thin films of WS2 nanosheets self-assembled at the interface of two immiscible liquids, water and toluene, transferred onto a solid substrate by the Langmuir-Schaefer technique. This experiment shows that edge defects in nanoflakes, tungsten dangling bond ensuing the exfoliation in the liquid phase, represent active sites for the WO3, WO3-x, and WO3·nH2O formation under ambient conditions. These oxides interact with water molecules when the WS2 films are exposed to water vapor in the NAP-XPS reaction cell. However, water molecules do not influence the W-S chemical bond, thus indicating the physisorption of H2O molecules at the WS2 film surface.

The effect of Artemisia annua L. extract on microbiologically influenced corrosion of A36 steel caused by Pseudomonas aeruginosa.

The protective effect of A. annua against microbiologically influenced corrosion (MIC) of A36 steel caused by P. aeruginosa (PA) in a simulated marine environment was investigated using electrochemical, spectroscopic, and surface techniques. PA was found to accelerate the local dissolution of A36 which led to the formation of a porous α-FeOOH and γ-FeOOH surface layer. 2D and 3D profiles of treated coupons, obtained by optical profilometer, revealed the formation of crevices in the presence of PA. On the contrary, adding A. annua to the biotic medium led to the formation of a thinner, more uniform surface without significant damage. Electrochemical data showed that the addition of A. annua prevented the MIC of A36 steel with an inhibition efficiency of 60%. The protective effect was attributed to the formation of a more compact Fe3O4 surface layer, as well as the adsorption of phenolics, such as caffeic acid and its derivatives on the A36 steel surfaces, as detected by FTIR and SEM-EDS analysis. ICP-OES confirmed that Fe and Cr species more readily diffuse from A36 steel surfaces incubated in biotic media (Fe; 1516.35 ± 7.94 µg L-1 cm-2, Cr; 11.77 ± 0.40 µg L-1 cm-2) compared to the inhibited media (Fe; 35.01 ± 0.28 µg L-1 cm-2, Cr; 1.58 ± 0.01 µg L-1 cm-2).

Microstructure Formations Resulting from Nanosecond and Picosecond Laser Irradiation of a Ti-Based Alloy under Controlled Atmospheric Conditions and Optimization of the Irradiation Process.

This paper presents a study and comparison of surface effects induced by picosecond and nanosecond laser modification of a Ti6Al4V alloy surface under different ambient conditions: air and argon- and nitrogen-rich atmospheres. Detailed surface characterization was performed for all experimental conditions. Damage threshold fluences for picosecond and nanosecond laser irradiation in all three ambient conditions were determined. The observed surface features were a resolidified pool of molten material, craters, hydrodynamic effects and parallel periodic surface structures. Laser-induced periodic surface structures are formed by multi-mode-beam nanosecond laser action and picosecond laser action. Crown-like structures at crater rims are specific features for picosecond Nd:YAG laser action in argon-rich ambient conditions. Elemental analysis of the surfaces indicated nitride compound formation only in the nitrogen-rich ambient conditions. The constituents of the formed plasma were also investigated. Exploring the impact of process control parameters on output responses has been undertaken within the context of laser modification under different environmental conditions. Parametric optimization of the nanosecond laser modification was carried out by implementing an advanced method based on Taguchi's parametric design and multivariate statistical techniques, and optimal settings are proposed for each atmosphere.

Optical Emission Studies of Copper Plasma Induced Using Infrared Transversely Excited Atmospheric (IR TEA) Carbon Dioxide Laser Pulses.

Spatially resolved, time-integrated optical emission spectroscopy was applied for investigation of copper plasma produced by a nanosecond infrared (IR) transversely excited atmospheric (TEA) CO2 laser, operating at 10.6 µm. The effect of surrounding air pressure, in the pressure range 0.1 to 1013 mbar, on plasma formation and its characteristics was investigated. A linear dependence of intensity threshold for plasma formation on logarithm of air pressure was found. Lowering of the air pressure reduces the extent of gas breakdown, enabling better laser-target coupling and thus increases ablation. Optimum air pressure for target plasma formation was 0.1 mbar. Under that pressure, the induced plasma consisted of two clearly distinguished and spatially separated regions. The maximum intensity of emission, with sharp and well-resolved spectral lines and negligibly low background emission, was obtained from a plasma zone 8 mm from the target surface. The estimated excitation temperature in this zone was around 7000 K. The favorable signal to background ratio obtained in this plasma region indicates possible analytical application of TEA CO2 laser produced copper plasma. Detection limits of trace elements present in the Cu sample were on the order of 10 ppm (parts per million). Time-resolved measurements of spatially selected plasma zones were used to find a correlation between the observed spatial position and time delay.