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

Abstract

ABSTRACT.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 film's 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.

Laser Annealing as a Platform for Plasmonic Nanostructuring

“…Finally, the optical reflectivity spectrum for five pulses (Figure 4c, blue solid line) exhibits a broad LSPR band, resembling the broadening of the LSPR band for two applied pulses at 193 nm (Figure 4b, green solid line), but blue-shifted compared to the band for two pulses of 193 nm indicating a surrounding medium that is less optically dense than AlN (e.g. outdiffused Ag nanoparticles in air) [20].…”

“…AlN:Ag nanocomposite films (70-100 nm thick) were grown on n-type c-Si(100) wafers via pulsed laser deposition (PLD) in an in-house-built high-vacuum system (P b < 5 × 10 −8 mbar) using the third harmonic of a Nd:YAG laser (6 ns pulse duration, fluence 30 J/cm 2 at 10 Hz repetition rate). More details on sample preparation can be found elsewhere [19,20]. The resulting nanocomposite films consisted of an amorphous AlN matrix with embedded pure Ag nanospheres, as displayed in the transmission electron microscopy (TEM) image in the inset of Figure 3.…”

“…The resulting nanocomposite films consisted of an amorphous AlN matrix with embedded pure Ag nanospheres, as displayed in the transmission electron microscopy (TEM) image in the inset of Figure 3. The embedded nanospheres exhibited LSPR, spectrally located at around 420 nm [20].…”

“…To get an insight into the light absorption dynamics inside the film during LA, finite-difference time-domain (FDTD) simulations of a 60 nm thick nanostructured AlN:Ag film were performed, where Ag consists of 3 nm diameter inclusions at 15% volume filling ratio randomly distributed inside the AlN matrix [20]. Laser light, for both wavelengths (193 nm and/ or 248 nm), is normally incident on the AlN:Ag film.…”

“…Plasmonic nanoparticles have become an increasingly common research area as well as becoming a key component in many important applications, such as solar energy harvesting [1][2][3][4][5][6], chemical sensing via surface-enhanced spectroscopies [7,[8][9][10][11][12][13][14], cancer treatment [15,16] and optical encoding of information [17][18][19][20] to name a few. The main reason behind their adaptability, to these and other prominent applications, is their unique optical properties that allow for the manipulation of light below the diffraction limit.…”