Development of polycrystalline silicon waveguides by laser crystallization

Silicon (Si) is an excellent material for integrated photonics devices as its high refractive index allows for small device footprints. To date, most of the work in this area has leveraged the single crystal silicon-on-insulator platforms, which are relatively expensive to produce and thus drive up component costs. Here we propose an alternative method to fabricate crystalline silicon waveguides by laser processing of an amorphous starting material. As well as reducing production costs, this approach has the added advantage of removing the substrate dependence so that more flexible alternatives can be considered. This method has previously been applied to a-Si wires grown inside silica capillaries and shown to produce very large crystallites [1]. Here we demonstrate preliminary results of laser-induced crystallization of a-Si films and micro-patterned wires produced by chemical vapor deposition (CVD) on SiO2 substrates. The samples have been crystallized using a c.w. argon-ion laser at 488nm. Crystallized tracks have been written by scanning the focused beam across the samples using different laser intensities and scanning speeds. The resulting material quality is then studied using Raman spectrometry, optical and electronic microscopy and X-ray diffraction. For the planar films, we have produced crystallite sizes on the order of hundreds of nanometers to a few microns; similar to those obtained via conventional pulsed Excimer laser crystallization [2]. However, for the micro-patterned samples, we have found that it is possible to grow crystals that almost cover the entire width of the wire, over lengths of up to 18µm, considerably larger than what is typically reported for polysilicon waveguide devices [3]. Furthermore, this laser crystallization method has been observed to reform the surface of the Si wires resulting in very smooth sidewall profiles (as shown in Fig. 1) which is very important for low loss optical transmission in photonic devices

A silicon/lithium niobate hybrid photonic material platform produced by laser processing

Silicon (Si) and lithium niobate (LiNbO3) are two materials that are synonymous with the electronics and photonics industries respectively and are supported by a significant amount of technological know-how. It has been suggested and demonstrated recently that Si could also be used for the production of integrated photonic devices, however its performance can be limited by the transmission cutoff at short wavelengths, a relatively high two-photon absorption, and a zero second order nonlinear optical susceptibility. LiNbO3 on the other hand is a very good dielectric material with very little electronic functionality and high second order nonlinearity. Thus, as these two materials have complementary properties, there is significant merit in combining them into a single hybrid system that will benefit from the properties of its constituents, as demonstrated via direct bonding in [1]. Here we propose a route for producing such a hybrid material system via local laser processing of a low cost, easy to produce amorphous silicon (a-Si) film deposited onto a single crystal LiNbO3 substrate. This research is based on recent encouraging results of a laser based crystallization process obtained in a-Si core optical fibres that not only produced crystallites with very large aspect ratios, but also allowed for tuning of the Si bandgap [2].The emphasis of this laser-processing route has been on achieving structures with large crystals and low surface roughness in order to obtain good photonic and electronic device performance. Interestingly it was revealed that, apart from the expected local crystallization of the a-Si film, this particular system exhibited a plethora of interesting and potentially useful effects including the direct formation of optical waveguides in LiNbO3, enabled ferroelectric domain reversal and the spontaneous formation of periodic structural features on the Si film, shown in the figure below

Laser processing of amorphous silicon on lithium niobate for photonic applications

Silicon (Si) and lithium niobate (LiNbO3) are two materials that are synonymous with the electronics and photonics industries respectively and are supported by a significant amount of technological know-how. It has been suggested and demonstrated recently that Si could also be used for the production of integrated photonic devices, however its performance can be limited by the transmission cutoff at short wavelengths, a relatively high two-photon absorption, and lack of second order nonlinear optical susceptibility. LiNbO3 on the other hand is a very good dielectric material with high second order nonlinearity but with very little electronic functionality. It can be envisaged however that these two materials have complementary properties therefore there is significant merit in combining them into a single hybrid system that will benefit from the properties of its constituents as demonstrated in [1] on a directly bonded single crystal hybrid. In this contribution we will present results on laser processing of amorphous silicon films deposited on LiNbO3 and other substrates suggesting a new route for the fabrication of Si based photonic circuits. This research is based on recent encouraging results of a laser based crystallization process obtained in a-Si core optical fibres that not only obtained crystallites with very large aspect ratio but also allowed for tuning of the Si bandgap [2]. &more..

New Insights into the Evolution of Metazoan Tyrosinase Gene Family

Tyrosinases, widely distributed among animals, plants and fungi, are involved in the biosynthesis of melanin, a pigment that has been exploited, in the course of evolution, to serve different functions. We conducted a deep evolutionary analysis of tyrosinase family amongst metazoa, thanks to the availability of new sequenced genomes, assessing that tyrosinases (tyr) represent a distinctive feature of all the organisms included in our study and, interestingly, they show an independent expansion in most of the analyzed phyla. Tyrosinase-related proteins (tyrp), which derive from tyr but show distinct key residues in the catalytic domain, constitute an invention of chordate lineage. In addition we here reported a detailed study of the expression territories of the ascidian Ciona intestinalis tyr and tyrps. Furthermore, we put efforts in the identification of the regulatory sequences responsible for their expression in pigment cell lineage. Collectively, the results reported here enlarge our knowledge about the tyrosinase gene family as valuable resource for understanding the genetic components involved in pigment cells evolution and development

Measurement of the cross-section and charge asymmetry of WW bosons produced in proton-proton collisions at s=8\sqrt{s}=8 TeV with the ATLAS detector

This paper presents measurements of the $W^+ \rightarrow \mu^+\nu$ and $W^- \rightarrow \mu^-\nu$ cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables, submitted to EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13

Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in √s=13 TeV pp collisions with the ATLAS detector

A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell W and Z bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of √s=13  TeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139  fb−1. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015–2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV

Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at √ s = 8 TeV with the ATLAS detector

Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb−1 of √ s = 8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT > 120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between Emiss T > 150 GeV and Emiss T > 700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presente

Search for direct stau production in events with two hadronic tau-leptons in root s=13 TeV pp collisions with the ATLAS detector

A search for the direct production of the supersymmetric partners ofτ-leptons (staus) in final stateswith two hadronically decayingτ-leptons is presented. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of139fb−1, recorded with the ATLAS detector at the LargeHadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected StandardModel background is observed. Limits are derived in scenarios of direct production of stau pairs with eachstau decaying into the stable lightest neutralino and oneτ-lepton in simplified models where the two staumass eigenstates are degenerate. Stau masses from 120 GeV to 390 GeV are excluded at 95% confidencelevel for a massless lightest neutralino

A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

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