A Siozios

Optical encoding by plasmon-based patterning: hard and inorganic materials become photosensitive

The photosensitivity of nanocomposite AlN films with embedded silver nanospheres is reported. It stems from localized surface plasmon resonances (LSPR) whose modulation is photoinduced by laser annealing that induces a combined effect of metallic nanoparticle enlargement and dielectric matrix recrystallization; the photoindunced changes of the refractive index of the matrix result in strong spectral shift of LSPR. We demonstrate the utilization of this process for spectrally selective optical encoding into hard, durable, and chemically inert films.

Sub-surface laser nanostructuring in stratified metal/dielectric media: a versatile platform towards flexible, durable and large-scale plasmonic writing

Laser nanostructuring of pure ultrathin metal layers or ceramic/metal composite thin films has emerged as a promising route for the fabrication of plasmonic patterns with applications in information storage, cryptography, and security tagging. However, the environmental sensitivity of pure Ag layers and the complexity of ceramic/metal composite film growth hinder the implementation of this technology to large-scale production, as well as its combination with flexible substrates. In the present work we investigate an alternative pathway, namely, starting from non-plasmonic multilayer metal/dielectric layers, whose growth is compatible with large scale production such as in-line sputtering and roll-to-roll deposition, which are then transformed into plasmonic templates by single-shot UV-laser annealing (LA). This entirely cold, large-scale process leads to a subsurface nanoconstruction involving plasmonic Ag nanoparticles (NPs) embedded in a hard and inert dielectric matrix on top of both rigid and flexible substrates. The subsurface encapsulation of Ag NPs provides durability and long-term stability, while the cold character of LA suits the use of sensitive flexible substrates. The morphology of the final composite film depends primarily on the nanocrystalline character of the dielectric host and its thermal conductivity. We demonstrate the emergence of a localized surface plasmon resonance, and its tunability depending on the applied fluence and environmental pressure. The results are well explained by theoretical photothermal modeling. Overall, our findings qualify the proposed process as an excellent candidate for versatile, large-scale optical encoding applications.

Laser-matter interactions, phase changes and diffusion phenomena during laser annealing of plasmonic AlN:Ag templates and their applications in optical encoding

Nanocomposite thin films incorporating silver nanoparticles are emerging as photosensitive templates for optical encoding applications. However, a deep understanding of the fundamental physicochemical mechanisms occurring during laser-matter interactions is still lacking. In this work, the photosensitivity of AlN:Ag plasmonic nanocomposites is thoroughly examined and a series of UV laser annealing parameters, such as wavelength, fluence and the number of pulses are investigated. We report and study effects such as the selective crystallization of the AlN matrix, the enlargement of the Ag nanoparticle inclusions by diffusion of laser-heated Ag and the outdiffusion of Ag to the films surface. Detailed optical calculations contribute to the identification and understanding of the aforementioned physical mechanisms and of their dependency on the laser processing parameters. We are then able to predetermine the plasmonic response of processed AlN:Ag nanocomposites and demonstrate its potential by means of optically encoding an overt or covert cryptographic pattern.

Influence of laser annealing on the structural properties of sputtered AlN:Ag plasmonic nanocomposites

We propose a process of deposition of plasmonic nanocomposites comprising magnetron sputtering of AlN:Ag multilayers combined with intermediate steps of flash annealing. When the AlN matrix structure was amorphous, thermal annealing induced the break-up of silver layers and the formation of homogeneously distributed spherical nanoparticles. On the other hand, in the case of a nanocrystalline AlN matrix, the larger nanoparticles were observed to form only at an interfacial and a surface zone. Further treatment by laser annealing was employed in order to photo-modulate the localized surface plasmon resonances (LSPRs) by promoting ripening of the nanoparticles. Using high resolution transmission electron microscopy, it was observed that laser annealing caused nanoparticle enlargement with a concurrent improvement of their separation, while retaining their average spherical shape. Optical reflectance measurements showed that better LSPR was obtained when the AlN matrix was amorphous due to the restrained nanoparticle ripening inside nanocrystalline AlN. Roughening at the film/substrate interface and film degradation after laser annealing at the employed radiation wavelength where reduced compared to similar samples grown by pulsed laser deposition. Based on finite difference time domain simulations and X-ray reflectivity measurements, this was attributed to the improved quality of the AlN matrix.

Influence of film thickness and annealing temperature in growth of Mg2Si thin films

In this work we examine the influence of film thickness and annealing temperature in the growth of Mg2Si thin films. Films were grown by dual cathode magnetron sputtering (DCMS) at room temperature. Two series of films were grown, one with thickness about 0.96μm (films-A) and another with (1.99μm) (films-B). Sputtered films were subsequently annealed in Ar gas atmosphere at temperatures 250°C, 300°C (films-B) and 380°C, 500°C (films-A). Results indicate that growth in films-A proceeds with the formation of two phases, a cubic (Fm-3m) and a strained (compressed) cubic with smaller lattice constant. When film thickness is doubled (films-B) material transforms into unstrained cubic phase. Annealing films-B at 300°C transforms them into the same compressed cubic phase that was observed in films-A. Further annealing of films-A causes a strain relief and at 500°C films are single phase.