ABSTRACT
The Double-Pulse (DP) version of the Laser-Induced Forward Transfer (LIFT) technique holds great potential to improve the resolution and flexibility of printing applications. In this study, we investigate the transfer of copper. A long laser pulse is first applied to melt thin copper films deposited on a transparent substrate, followed by an ultrashort laser pulse to initiate the transfer of the liquid material towards a receiver substrate. Time-resolved imaging experiments reveal that ejections from nanodrops to liquid jets with controllable diameters, from few micrometers down to the nanometers scale can be obtained with the control parameters of DP-LIFT. Comparing simulation and experiments we discuss how the ejection characteristics are governed by various factors including the shape, diameter and temperature of the melted pool created with the first long pulse. While the formation of microjets is due to the dynamical deformation of the melted film, as for the conventional LIFT process applied with liquid donors, the results indicate a different and distinct process for the formation of nanojets. We extrapolate from the observations a feature caused by the interaction of the shockwave, generated by the femtosecond laser irradiation, with the deformed surface of the pool. Ultimately, we establish the range of irradiation parameters leading to the observation of single separated microjets and nanojets. The latter are accompanied by nano printing demonstrations. Considering all accessible regimes together, a unique technological perspective is the possibility to achieve multi-scale printing from the same donor.
ABSTRACT
Redox enzymes can be envisioned as biocatalysts in various electrocatalytic-based devices. Among factors that play roles in bioelectrochemistry limitations, the effect of enzyme-enzyme neighboring interaction on electrocatalysis has rarely been investigated, although critical in vivo. We report in this work an in-depth study of gold nanoparticles prepared by laser ablation in the ultimate goal of determining the relationship between activity and enzyme density on electrodes. Nanosecond laser interaction with nanometric gold films deposited on indium tin oxide support was used to generate in situ gold nanoparticles (AuNPs) free from any stabilizers. A comprehensive analysis of AuNP size and coverage, as well as total geometric surface vs. electroactive surface is provided as a function of the thickness of the treated gold layer. Using microscopy and electrochemistry, the long-term stability of AuNP-based electrodes in the atmosphere and in the electrolyte is demonstrated. AuNPs formed by laser treatment are then modified by thiol chemistry and their electrochemical behavior is tested with a redox probe. Finally, enzyme adsorption and bioelectrocatalysis are evaluated in the case of two enzymes, i.e., the Myrothecium verrucaria bilirubin oxidase and the Thermus thermophilus laccase. Behaving differently on charged surfaces, they allow demonstrating the validity of laser treated AuNPs for bioelectrocatalysis.
