Dc Koutsogeorgis

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.

Intrinsic photoluminescence from low temperature deposited zinc oxide thin films as a function of laser and thermal annealing

An investigation into the modification of low temperature deposited ZnO thin films by different annealing processes has been undertaken using laser, thermal and rapid thermal annealing of 60 nm ZnO films deposited by high-target-utilization sputtering. Single-pulse laser annealing using a KrF excimer laser (λ = 248 nm) over a range of fluences up to 318 mJ cm−2 demonstrates controlled in-depth modification of internal film microstructure and luminescence properties without the film degradation produced by high temperature thermal and RTA processes. Photoluminescence (PL) properties show that the ratio of defect related deep level emission (DLE, 450–750 nm, 2.76–1.65 eV) to excitonic near band-edge emission (NBE at 381 nm, 3.26 eV) is directly correlated to processing parameters. Thermal and rapid thermal processing results in the evolution of a strong visible orange/red DLE PL (with peaks at 590 nm, 2.10 eV and 670 nm, 1.85 eV) dominated by defects related to excess oxygen. At higher temperatures, the appearance of a green/yellow emission (530 nm, 2.34 eV) indicates a transition of the dominant radiative transfer mechanism. In contrast, laser processing removes defect related DLE and produces films with intense NBE luminescence, correlated to the observed formation of large grains (25–40 nm).

Pulsed KrF laser annealing of ZnS : Mn laterally emitting thin film electroluminescent displays

Abstract Pulsed KrF (248-nm) laser annealing was investigated as a post-deposition process for RF sputtered ZnS:Mn phosphor layers used in laterally emitting thin film electroluminescent (LETFEL) displays. LETFEL devices consist of a phosphor layer sandwiched between two insulating thin films (Y 2 O 3 ), grown onto silicon substrates patterned with micro-mirrors (SiO 2 ). The micro mirror structure permits surface viewing by reflecting laterally emitted light due to internal waveguiding effects. Laser irradiation of the uncoated phosphor layer was performed using KrF excimer 248-nm laser pulses of 20 ns under an argon overpressure of 10.34 bars to limit laser ablation. The influence of the laser irradiation fluence on the LETFEL performance was investigated from 0.3 to 1.5 J/cm 2 . In this paper, we have reported the brightness-voltage characteristics of laser annealed, non-annealed and thermally annealed devices at 500°C for ∼1 h. It is shown that the onset for light emission (threshold voltage) decreases with laser annealing. Using this novel method of annealing, the brightness of LETFEL devices is observed to increase with increasing laser fluence.

Decay time characteristics of La2O2S:Eu and La2O2S:Tb for use within an optical sensor for human skin temperature measurement

We focus on the development of a remote temperature sensing technology, i.e., an optical laser-based sensor, using thermographic phosphors for medical applications, particularly within an electromagnetically hostile magnetic resonance imaging (MRI) environment. A MRI scanner uses a strong magnetic field and radio waves to generate images of the inside of the body. The quality of the image improves with increasing magnetic resonance; however, the drawback of applying a greater magnetic strength is the inducement of heat into the body tissue. Therefore, monitoring the patients temperature inside MRI is vital, but until now, a practical solution for temperature measurement did not exist. We show europium doped lanthanum oxysulphide (La(2)O(2)S:Eu) and terbium doped lanthanum oxysulphide (La(2)O(2)S:Tb) are both temperature sensitive to a low temperature range of 10-50 degrees C when under ultraviolet (UV) excitation. The emission spectra and decay time characteristics of these phosphors were demonstrated. The results indicate that La(2)O(2)S:Eu has a quenching rate of 13.7 m degrees C(-1) and 4 m degrees C(-1) at 512 nm and 538 nm, respectively. In addition, La(2)O(2)S:Tb has a lower quenching rate of 4.19 m degrees C(-1) at 548 nm due to its faster decay time.

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.

P-169: Optimization of the Electrical and Optical Properties of Ink-Jet-Printed SnO(2):Sb using Thermal Annealing and Excimer-Laser Processing

Sb doped SnO2 has been formulated and inkjet printed onto borosilicate glass substrates. The resultant films have been post processed using traditional thermal annealing up to 440°C and laser processing with a KrF excimer laser (λ = 248nm). Sheet resistance values of 700Ω/□ have been achieved with thermal annealing, whilst transparency remains >85% in the visible region. As a result of laser processing significant decreases in sheet resistance of the inkjet printed layers have been demonstrated indicating the viability of inkjet printing onto flexible substrates. The optical transmittance of the laser processed films has been shown to remain >85%. Initial measurements indicate that thermal and laser post processes reduce surface roughness.

Laser annealing of thin film electroluminescent devices deposited at a high rate using high target utilization sputtering

This paper presents the photoluminescent (PL) and electroluminescent (EL) characteristics of ZnS:Mn deposited at room temperature using high target utilization sputtering (HiTUS). Significant improvements in PL intensity are seen when ZnS:Mn is deposited using HiTUS instead of conventional RF magnetron sputtering. When incorporated as part of a complete EL device with yttrium oxide forming the dielectric layers and indium tin oxide used as the top contact electrode, localized laser annealing of the ZnS:Mn phosphor layer is shown to provide enhancement of the EL characteristics.

Photoluminescence enhancement of ZnO via coupling with surface plasmons on Al thin films

We present that the ultra-violet emission of ZnO can be enhanced, as much as six-times its integral intensity, using an Al thin interlayer film between the Si substrate and ZnO thin film and a post-fabrication laser annealing process. The laser annealing is a cold process that preserves the chemical state and integrity of the underlying aluminum layer, while it is essential for the improvement of the ZnO performance as a light emitter and leads to enhanced emission in the visible and in the ultraviolet spectral ranges. In all cases, the metal interlayer enhances the intensity of the emitted light, either through coupling of the surface plasmon that is excited at the Al/ZnO interface, in the case of light-emitting ZnO in the ultraviolet region, or by the increased back reflection from the Al layer, in the case of the visible emission. In order to evaluate the process and develop a solid understanding of the relevant physical phenomena, we investigated the effects of various metals as interlayers (Al, Ag, a...