Leaky mode analysis of luminescent thin films: the case of ZnO on sapphire

Zinc oxide (ZnO) epitaxial thin films grown on c-sapphire substrates by pulsed laser deposition were investigated using angle and polarization-resolved photoluminescence spectroscopy. Side-emission spectra differed significantly from surface-emission spectra in exhibiting dominant, narrow, polarization-resolved peaks. These spectral features were attributed to leaky substrate modes in the layers. Observations were first verified using transmission calculations with non-adjustable parameters, which took into account the dispersion, the anisotropy of the ZnO refractive index and the dependence on film thickness. Results were consistent with Fabry-Perot-like interference being the origin of the distinctive ZnO luminescence observed at grazing incidence angles. A second analysis, based on the source terms method, was used in order to retrieve the bulk emission properties, including the wavelength-dependent quantum yield and the emission anisotropy. While ZnO thin films were considered here, this analysis method can be extended to any luminescent thin film of similar geometry, demonstrating the potential of leaky mode analysis for probing passive and active material properties

Assessment of atomic layer deposited TiO2 photocatalytic self-cleaning by quartz crystal microbalance

The self-cleaning properties emerging from photocatalytic effects consist in the elimination of an organic contamination layer by light-induced redox reactions. Quartz crystal microbalances (QCMs), monitoring the contaminant mass loss under UV illumination, were used to investigate this effect and its efficiency. A new setup dedicated to such purpose is introduced along with the results of a self-cleaning experiment performed with a 20-nm TiO2 thin film coated on a QCM by atomic layer deposition. In particular, a 10-nm paraffin oil thin film deposited under vacuum is shown to be degraded down to its complete removal according to a zeroth order photocatalytic reaction. Finally, the experimental opportunities offered by the new setup, such as a controlled environment composition, are presented.Peer reviewe

Reliability investigation of a carbon nanotube array thermal interface material

As feature density increases within microelectronics, so does the dissipated power density, which puts an increased demand on thermal management. Thermal interface materials (TIMs) are used at the interface between contacting surfaces to reduce the thermal resistance, and is a critical component within many electronics systems. Arrays of carbon nanotubes (CNTs) have gained significant interest for application as TIMs, due to the high thermal conductivity, no internal thermal contact resistances and an excellent conformability. While studies show excellent thermal performance, there has to date been no investigation into the reliability of CNT array TIMs. In this study, CNT array TIMs bonded with polymer to close a Si-Cu interface were subjected to thermal cycling. Thermal interface resistance measurements showed a large degradation of the thermal performance of the interface within the first 100 cycles. More detailed thermal investigation of the interface components showed that the connection between CNTs and catalyst substrate degrades during thermal cycling even in the absence of thermal expansion mismatch, and the nature of this degradation was further analyzed using X-ray photoelectron spectroscopy. This study indicates that the reliability will be an important consideration for further development and commercialization of CNT array TIMs

Synthesis and characterization of erbium complexes for near infrared optical amplification in organic media.

Afin d'offrir de nouvelles possibilités pou l'amplification optique dans le proche infrarouge, de nouvelles voies sont proposées pour la réalisation de composants organiques. La réalisation de composants à base de polymère pour l'amplification optique dans le proche infrarouge se heurte à la difficulté de conserver les propriétés optiques de l'erbium dans un environnement organique : sa durée de vie s'en trouve réduite de plusieurs ordres de grandeur. L'analyse des phénomènes limitants les propriétés de l'ion en matrice polymère ainsi qu'un examen des solutions proposées dans la littérature permettent de dégager plusieurs axes de recherche principaux. D'une part, la formulation du ligand peut être optimisée dans le but de retrouver les propriétés de l'erbium, d'autre part, l'utilisation de colorants organiques à forte section efficace d'absorption permet d'améliorer l'efficacité du pompage optique. Cette étude présente les résultats obtenus dans ces deux directions, en étudiant des complexes organiques perhalogénées pour minimiser les .interaction erbium hôte, ou en utilisant des complexes à très forte section efficace d'absorption dans le visible. L'étude de la deuxième voie, consistant en l'exploitation d'un transfert d'énergie colorant organique erbium a périrais de synthétiser et de caractériser des molécules dont les propriétés optiques sont méconnues : les phtalocyanines de lanthanides. L'étude d'un complexe de phtalocyanine d'erbium en particulier a permis de déterminer la dynamique du transfert d'énergie phtalocyanine erbium ainsi que son efficacité quantique.In order to offer new possibilities for near infrared optical amplification, new approaches are proposed for the design of organic devices. The fabrication of polymer devices for optical amplification in the near infrared region is difficult because of the change in properties, especially a drastic shortening in radiative lifetime, of the erbium ion in an organic medium. Several main axes of development. can be deduced from the literature. First, the organic chelate formulation can be adapted and optimised in order to weaken interactions between the lanthanide ion and the matrix, and second, the use of high absorption cross section ligands can optimise the pumping efficiency. This study presents the results obtained in these two directions, by studying perhalogenated organic complexes, or by using dye type ligands with a very high absorption cross section in the visible. The studies made in the second approach allowed to synthesize and çharacterize molecules with largely unknown optical properties : lanthanides phthalocyanines. The study of an erbium phthalocyanine in particular allowed the determination of the energy transfer dynamics, and the energy transfer quantum yield was determined to be close to one.CACHAN-ENS (940162301) / SudocSudocFranceF