Impact of the annealing temperature on the optical performances of Er-doped Si-rich silica systems Impact of the annealing temperature on the optical performances of Er-doped Si-rich Silica systems

International audienceSeries of Er-doped Si-rich silicon oxide (SRSO:Er) layers were grown by magnetron sputtering at different temperatures from ambient to 500°C and then annealed between 600°C and 1100°C. They were characterized by spectroscopic and time-resolved photoluminescence (PL) measurements. Significant PL was detected at 1533 nm from the as-grown samples at T≥300°C excited by a non-resonant wavelength (476 nm), hence indicating the formation of Si-based sensitizers during the growth process. The PL intensity and the decay lifetime of Er 3+ ions were both greatly increased with the annealing temperature. An optimum temperature of annealing is obtained at 800°C, which is expected to favor the formation of very dense and small sensitizers. The fraction of Er coupled to sensitizers was found nearly 6-7 times higher than that reported so far in the literature. 1. Introduction The effective excitation cross section of Er 3+ ions in SiO 2 is increased by 10 3-10 4 with the insertion of Si-based sensitizers in the matrix. It was shown that an indirect excitation of Er 3+ ions occurs through Si nanoclusters (Si-nc) [1,2]. Such an energy transfer allows one to benefit from the broadband high absorbance of Si-nc for optical excitation and from the improved transport of carriers injected by electrical excitation. This paves the way to the achievement of Er 3+ population inversion by either optical or electrical pumping for integrated photonics, such as planar amplifier, laser, etc. Recent studies reported that, in conventional SRSO:Er materials, only a small fraction (<2%) of Er 3+ ions are effectively benefiting from the Si-nc-mediated excitation [3]. Such a low value is far from ensuring an inversion population of Er 3+ , but requires, on the contrary, more efforts and studies to enhance significantly the proportion of coupled Er in SRSO:Er samples. These latter are usually submitted to annealing processes to form Si nanoclusters (Si-nc) as sensitizers, to remove non-radiative defects and to activate (optically) the Er 3+ ions. Such a treatment may change, however, the structure of either the Si-based sensitizers or the Er 3+ ions. This work aims at investigating the influence of growth and annealing temperature on the optical properties of the SRSO:Er layers and to correlate it to the proportion of Er coupled to sensitizers

Thickness-dependent optimization of Er3+ light emission from silicon-rich silicon oxide thin films

This study investigates the influence of the film thickness on the silicon-excess-mediated sensitization of Erbium ions in Si-rich silica. The Er3+ photoluminescence at 1.5 μm, normalized to the film thickness, was found five times larger for films 1 μm-thick than that from 50-nm-thick films intended for electrically driven devices. The origin of this difference is shared by changes in the local density of optical states and depth-dependent interferences, and by limited formation of Si-based sensitizers in "thin" films, probably because of the prevailing high stress. More Si excess has significantly increased the emission from "thin" films, up to ten times. This paves the way to the realization of highly efficient electrically excited devices

Modification of erbium photoluminescence decay rate due to ITO layers on thin films of SiO2:Er doped with Si-nanoclusters

International audienceDuring the fabrication of MOS light emitting devices, the thin film of active material is usually characterized by photoluminescence measurements before electrical contacts are deposited. However, the presence of a conductive contact layer can alter the luminescent properties of the active material. The local optical density of states changes due to the proximity of luminescent species to the interface with the conductive medium (the top electrode), and this modifies the radiative rate of luminescent centers within the active layer. In this paper we report enhancement of the observed erbium photoluminescence rate after deposition of indium tin oxide contacts on thin films of SiO 2 :Er containing silicon nanoclusters, and relate this to Purcell enhancement of the erbium radiative rate

Towards population inversion of electrically pumped Er ions sensitized by Si nanoclusters

This study reports the estimation of the inverted Er fraction in a system of Er doped silicon oxide sensitized by Si nanoclusters, made by magnetron sputtering. Electroluminescence was obtained from the sensitized erbium, with a power efficiency of 10¿2 %. By estimating the density of Er ions that are in the first excited state, we find that up to 20% of the total Er concentration is inverted in the best device, which is one order of magnitude higher than that achieved by optical pumping of similar materials

Electroluminescence efficiencies of erbium in silicon-based hosts

International audienceWe report on room-temperature 1.5 lm electroluminescence from trivalent erbium (Er3þ) ionsembedded in three different CMOS-compatible silicon-based hosts: SiO2, Si3N4, and SiNx. We showthat although the insertion of either nitrogen or excess silicon helps enhance electrical conductionand reduce the onset voltage for electroluminescence, it drastically decreases the external quantumefficiency of Er3þ ions from 2% in SiO2 to 0.001% and 0.0004% in SiNx and Si3N4, respectively.Furthermore, we present strong evidence that hot carrier injection is significantly more efficient thandefect-assisted conduction for the electrical excitation of Er3þ ions. These results suggest strategiesto optimize the engineering of on-chip electrically excited silicon-based nanophotonic light sources

Differentiating between models of Epothilone binding to microtubules using tubulin mutagenesis, cytotoxicity, and molecular modeling

This is the peer reviewed version of the following article: Entwistle, R. A., Rizk, R. S., Cheng, D. M., Lushington, G. H., Himes, R. H., & Gupta, M. L. (2012). Differentiating between models of Epothilone binding to microtubules using tubulin mutagenesis, cytotoxicity, and molecular modeling. ChemMedChem, 7(9), 1580–1586. http://doi.org/10.1002/cmdc.201200286, which has been published in final form at doi.org/10.1002/cmdc.201200286. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Microtubule stabilizers are powerful anti-mitotic compounds and represent a proven cancer treatment strategy. Several classes of compounds in clinical use or trials, such as the taxanes and epothilones, bind to the same region of β-tubulin. Determining how these molecules interact with tubulin and stabilize microtubules is important both for understanding the mechanism of action and enhancing chemotherapeutic potential, e.g. reducing side effects, increasing solubility, and overcoming resistance. Structural studies using nonpolymerized tubulin or stabilized polymers have produced different models of epothilone binding. Here, we used directed mutagenesis of the binding site on Saccharomyces cerevisiae β-tubulin to analyze interactions between Epothilone B and its biologically relevant substrate, dynamic microtubules. Five engineered amino acid changes contributed to a 125-fold increase in Epothilone B cytotoxicity independent of inherent microtubule stability. The mutagenesis of endogenous β-tubulin was done in otherwise isogenic strains. This facilitated the correlation of amino acid substitutions with altered cytotoxicity using molecular mechanics simulations. The results, which are based on the interaction between Epothilone B and dynamic microtubules, most strongly support the binding mode determined by NMR spectroscopy-based studies. This work establishes a system for discriminating between potential binding modes and among various compounds and/or analogues using a sensitive biological activity-based readout

Subjective Decision-Making in Healthcare: The Case of Vaccinations

Although an understanding of socio-scientific issues is purported to influence and inform individuals’ behavior and decision-making, this may ultimately depend on the level of control any person feels they have to enact change. Current major issues such as global warming and consequent climate change or the production of genetically modified foods, may well appear to be out of the control of individuals. Consequently, people may look to the government to enact legislation to deal with these. However, one area where individuals have almost total control, in most western societies at least, is that of vaccination. In this study, 33 university graduates (largely university lecturers) from science and non-science backgrounds were interviewed in an attempt to ascertain their attitudes to vaccination programs and to determine where they obtained their own information from in relation to vaccinations. The small sample of this inquiry precludes generalisation. However, the preliminary findings indicated that in general, background (science or non-science) did not appear to be a determinant of support for vaccination programs, and although both groups drew on a wide range of information sources about vaccination, the most common sources of information cited by the participants included general practitioners or health care workers. Furthermore, despite being aware of some side effects, they generally had high confidence in vaccine safety

Size dependence of refractive index of Si nanoclusters embedded in SiO2

he complex refractive index of SiO2 layers containing Si nanoclusters (Si-nc) has been measured by spectroscopic ellipsometry in the range from 1.5 to 5.0 eV. It has been correlated with the amount of Si excess accurately measured by x-ray photoelectron spectroscopy and the nanocluster size determined by energy-filtered transmission electron microscopy. The Si-nc embedded in SiO2 have been produced by a fourfold Si+ ion implantation, providing uniform Si excess aimed at a reliable ellipsometric modeling. The complex refractive index of the Si-nc phase has been calculated by the application of the Bruggeman effective-medium approximation to the composite media. The characteristic resonances of the refractive index and extinction coefficient of bulk Si vanish out in Si-nc. In agreement with theoretical simulations, a significant reduction of the refractive index of Si-nc is observed, in comparison with bulk and amorphous silicon. The knowledge of the optical properties of these composite layers is crucial for the realization of Si-based waveguides and light-emitting devices