The authors present a simple and efficient technique for laser writing of arbitrary nanopatterns across a large surface area without using projection masks. It is based on the unique near-field focusing effect of a self-assembled particle array on the surface interacting with an angular incident laser beam. The spot resolution can be down to 80 nm. More than 6 ϫ 10 6 nanolines and c-shaped uniform patterns were fabricated simultaneously over an area of 5 ϫ 5 mm 2 by a few laser shots.
Based on medium-tuned optical field enhancement effect around a self-assembled particle-lens array (PLA) irradiated with a femtosecond (fs) laser source, we demonstrated that high-precision periodical array of micro/nano-structures can be readily fabricated on glass surface or inside glass in large areas in parallel without any cracks or debris. The technique has potential for rapid fabrication of three-dimensional structures in multiple layers inside glass.
Laser cleaning has been considered as a promising technique for the preparation of aluminium alloy surfaces prior to joining and welding and has been practically used in the automotive industry. The process is based on laser ablation to remove surface contaminations and aluminium oxides. However the change of surface chemistry and oxide status may affect corrosion behaviour of aluminium alloys. Until now, no work has been reported on the corrosion characteristics of laser cleaned metallic surfaces. In this study, we investigated the corrosion behaviour of laser-cleaned AA7024-T4 aluminium alloy using potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). The results showed that the laser-cleaned surface exhibited higher corrosion resistance in 3.5 wt.% NaCl solution than as-received hot-rolled alloy, with significant increase in impedance and decrease in capacitance, while SVET revealed that the active anodic points appeared on the as-received surface were not presented on the laser-cleaned surfaces. Such corrosion behaviours were correlated to the change of surface oxide status measured by glow discharge optical emission spectrometry (GDOES) and X-ray photoelectron spectroscopy (XPS). It was suggested that the removal of the original less protective oxide layer consisting of MgO and MgAl 2 O 4 on the as-received surfaces and the newly formed more protective oxide layer containing mainly Al 2 O 3 and MgO by laser cleaning were responsible for the improvement of the corrosion performance.
We have prepared carbon‐supported nanoparticles with the heterogeneous structure of a PdPt shell on a PdCo core which are effective for the oxygen reduction reaction (ORR) in the presence of methanol. The preparation was based on the galvanic replacement reaction between PdCo/C nanoparticles and PtCl42–, a method of general utility which can be extended to the preparation of other core‐shell electrocatalysts. The heterogeneous PdCo‐core and PtPd‐shell architecture was confirmed by multiple techniques including high resolution transmission electron microscopy, energy dispersive X‐ray spectroscopy, powder X‐ray diffraction and X‐ray photoelectron spectroscopy. The activity of the PdCo@PdPt/C catalyst in ORR was evaluated in acidic solutions both with and without methanol (0.1 M). The results showed four to sixfold increases in activity over a standard Pt/C catalyst with no apparent loss of catalyst stability. It is inferred that the strain effect from the lattice mismatch between the shell and core components is the major contributor for the enhancement of ORR activity and selectivity.
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