No abstract

Cu-Ag alloy nanoparticles (NPs) have been synthesized from micropowders of pure Cu and Ag using consecutively two non-equilibrium processes based on plasma and lasers in liquids. Plasma process reduces the size of initial micrometric powders down to nanometric size at which the laser fluence is sufficient to melt them, making alloying possible. Measurements at macroscopic (solution absorption), microscopic (scattering of individual NPs) and nanoscopic (electron microscopy) scales confirm alloying of NPs and homogenization in size and composition. This has noticeable effect on the final colloidal solution that absorbs yellow-orange light (550-600 nm) after laser treatment. The possibility to quench the as-formed liquid alloy leads to phase compositions that are not compliant with the phase diagram. With a synthesis rate of 360 mg/h, this process opens up interesting perspectives for non-equilibrium nanometallurgy of functional NPs.

Luminescent security labels are effective platforms for protection of consumer goods from counterfeiting. However, the lifetimes of such security approaches are limited due to narrow-band photoluminescent features of the label elements, which can be used for the protection technology disclosure. In this paper, a novel concept for the application of non-linear white-light luminescence from hybrid metal-semiconductor structures fabricated by direct femtosecond laser writing for the creation of physically unclonable security labels is proposed. A close connection is demonstrated between the internal composition of hybrid structures, which is controlled at the fabrication stage, and their non-linear optical signals. It is shown that the application of decorrelation procedure based on discrete cosine transform and polar codes for label coding can overcome the problem of the white-light photoluminescent spectra correlation. The proposed fabrication approach and coding strategy allows reaching a high degree of device uniqueness (up to 99%), bit uniformity (close to 0.5), and encoding capacity up to 1.25 × 10 437 in a single label element. The results demonstrate that the barriers for the application of white-light luminescent nano-objects for the creation of physically unclonable labels are removed.