Publication database
A bendable electrode is an essential component of flexible electronics. The resistance stability against deformation is highly desired for practice. In this work, a bendable Cu electrode is fabricated by femtosecond laser direct writing (FsLDW), involving photothermal reduction of Cu ions and deposition of Cu on polyethylene terephthalate (PET) substrate. A highly conductive Cu electrode with a sheet resistance of 0.56 Ω·sq−1 is obtained, which is improved by at least one order of magnitude over previous works. It is worth noting that the sheet resistance of the Cu electrode almost remains unchanged after 6000 downward bending cycles at a bending angle of 30° and shows a slight increase after 10 adhesion tests, demonstrating excellent bending stability and adhesive strength. The porous morphology of the deposited Cu may relieve bending stress, resulting in high deformation resistance. The temperature field simulation confirms sufficient heat accumulation during FsLDW for Cu ion reduction and PET surface melting, allowing for Cu embedding on the PET surface and improving adhesion between the Cu electrode and the substrate.
Femtosecond laser processing combines highly accurate structuring with low residual heating of materials, low thermal damage, and nonlinear absorption processes, making it suitable for the machining of transparent brittle materials. However, with high average powers and laser pulse repetition rates, residual heating becomes relevant. Here, we present a study of the femtosecond laser pulse-on-demand operation regime, combined with regular scanners, aiming to improve throughput and quality of processing regardless of the scanner’s capabilities. We developed two methods to define the needed pulse-on-demand trigger sequences that compensate for the initial accelerating scanner movements. The effects of pulse-on-demand operation were studied in detail using direct process monitoring with a fast thermal camera and indirect process monitoring with optical and topographical surface imaging of final structures, both showing clear advantages of pulse-on-demand operation in precision, thermal effects, and structure shape control. The ability to compensate for irregular scanner movement is the basis for simplified, cheaper, and faster femtosecond laser processing of brittle and heat-susceptible materials.
Laser polishing offers numerous advantages, one of which is the convenience of using the same system for the whole manufacturing process. In this work, an ultrashort pulse laser operating in a GHz burst regime was used to polish stainless steel. The aim was to minimise surface roughness, characterised by the average roughness parameter Ra. Different laser processing parameters (average laser power, number of pulses per burst, scanning speed, hatch size) were varied to polish samples that were covered in laser-induced periodic surface structures (LIPSS). Thermal effects, such as melt layer formation, were noticed and discussed. It was demonstrated that LIPSS can be erased and the initial surface roughness of 73 nm was reduced to 41 nm using 100 pulses per burst and burst fluence of FB = 0.15 J/cm2.
The cutting quality and strength of strips cut with femtosecond-duration pulses were investigated for different thicknesses of borosilicate glass plates. The laser pulse duration was 350 fs, and cutting was performed in two environments: ambient air and water. When cutting in water, a thin flowing layer of water was formed at the front surface of the glass plate by spraying water mist next to a laser ablation zone. The energy of pulses greatly exceeded the critical self-focusing threshold in water, creating conditions favorable for laser beam filament formation. Laser cutting parameters were individually optimized for different glass thicknesses (110–550 µm). The results revealed that laser cutting of borosilicate glass in water is favorable for thicker glass (300–550 µm) thanks to higher cutting quality, higher effective cutting speed, and characteristic strength. On the other hand, cutting ultrathin glass plates (110 µm thickness) demonstrated almost identical performance and cutting quality results in both environments. In this paper, we studied cut-edge defect widths, cut-sidewall roughness, cutting throughput, characteristic strength, and band-like damage formed at the back surface of laser-cut glass strips.
The laser synthesis and processing of colloids represents a group of scalable and “green” synthesis methods of crystalline metal oxides, that have recently made encouraging progresses in preparing amorphous as well as defect-rich nanoparticles. The relevant conditions and mechanisms that allow the design of amorphous metal oxides (AMOs) remain unknown. Consequently, in this work the synthesis of Fe-based partially amorphous oxide nanoparticles (NPs) by pulsed laser ablation in water was studied. Furthermore, both laser pulse duration and the number of laser pulse in pulsed laser fragmentation in liquid (LFL) allow a precise control of amorphization of AMOs in water. Hereby, a high-fluence nanosecond-LFL provides a significantly higher amorphization rate, whereas picosecond-LFL always presents minor fractions of crystalline α-Fe even with a higher specific energy input and laser intensity. Consequently, the laser fluence required for the repeated melting and quenching of NP appears to be the decisive parameter to control amorphization. During laser synthesis and processing of colloids, the amorphization of AMOs appears to be linked to the apparent size reduction effect, while a complete full amorphization of AMOs may be attributed to the stronger oxidation effects. This work will stimulate future studies using laser-generated AMO NPs for further functional purposes.
Experimental investigation into ultrashort laser ablation by burst and Single Pulse (SP) modes on Polypropylene was performed. Isolated craters with different set of laser parameters were produced on flat polymer samples to assess the influence of the temporal separation between pulses on surface quality, removal rate (time needed to remove a certain volume) and ablation efficiency (pulse energy needed to remove a certain volume). The laser parameters that allow the development of structures with minimum redeposited material splashed around them and maximum removal rates were identified. Pulse energies of 2.5 μJ and 6 μJ were identified as the removal pulse energy threshold and the value from which a structure depth saturation starts, respectively.
The use of bursts provides improved quality and higher removal rates compared to the Single Pulse mode when the same number of pulses of identical pulse energies were emitted in both cases, even though the total eliminated volume is higher in the SP mode. The advantages of using bursts of 3 pulses are reported. Increasing the number of pulses per burst to 4 do not increase the removal rate when compared to bursts of 3 pulses.
Photopolymerization by four-beam interference lithography on a preheated SZ2080 sample was explored at different initial temperatures of the sample: 20 °C, 50 °C, 75 °C, 100 °C, 125 °C, and 150 °C, and at exposure times ranging from 0.5 s to 5 s. The average laser power selected was ∼100 mW for the 300 ps duration pulses at a 1 kHz repetition rate. The experimental results demonstrate that the higher initial temperature of the sample positively influences the crosslinking of the patterns. These findings will improve polymerization protocols for multi-beam interference lithography.
Direct generation of gold nanoparticles on ITO glass using a nanosecond laser is presented and the electrochemical properties of the gold modified ITO electrodes for detection of the ascorbic acid are analyzed. Gold nanoparticles were generated by nanosecond laser pulse irradiation of thin, 3–30 nm thick, gold films. It was found that diameters and the number of generated nanoparticles per unit area strongly depends on the thickness of the gold film when it is less than 10 nm. Furthermore, experiments have shown that the influence of laser processing parameters (the laser pulse energy and pulse number) to the size, the distribution and the area density of generated gold nanoparticles on ITO glass is negligible. Characterization of the electrochemical properties of the gold modified ITO electrodes by nanosecond laser showed that the fabricated electrodes could be employed in electrochemical sensing. Therefore, the demonstrated generation of gold nanoparticles on ITO by using the nanosecond laser approach opens new opportunities for the development of highly sensitive and low-cost electrochemical sensors.
In this paper the possibility to optimize the glass dicing process by controlling the axicon-generated Bessel beam ellipticity is presented. Single-shot intra-volume modifications in soda-lime glass followed by dicing experiments of 1 mm-thick samples are performed. The Bessel beam ellipticity is essential for glass dicing process. Such beam generates intra-volume modifications with transverse crack propagation in dominant direction. Orientation of these modifications parallel to the dicing direction gives significant advantages in terms of processing speed, glass breaking force and cutting quality.
The optical performance of high-resistivity silicon with a laser-ablated surface was studied in the transmission mode in the frequency range of 0.1-4.7 THz. A reciprocal relationship between the transmission brightness and the surface roughness was observed at discrete THz frequencies. The measured dispersion was reproduced by the THz wave scattering theory using an effective refractive index model. No significant differences between the samples processed either with psor ns-duration laser pulses in ambient air or in argon enriched atmosphere were found in the THz regime. It was demonstrated that the majority of optical losses of the silicon with the laser modified surface were due to the scattering of THz waves and not due to the absorption in silicon-compounds formed during the laser ablation.