Faculté des arts et des sciences – Département de physique - Travaux et publications
URI permanent de cette collectionhttps://hdl.handle.net/1866/2331
Cette collection accueille les publications savantes et d’autres types de travaux d’auteur.e.s associé.e.s à cette unité. Voir aussi la collection Thèses et mémoires de l'unité.
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Item Accès libre The molecular origin of the electrostatic gating of single-molecule field-effect biosensors investigated by molecular dynamics simulationsCôté, Sébastien; Bouilly, Delphine; Mousseau, Normand; Université de Montréal. Faculté des arts et des sciences. Département de physique (Royal Society of Chemistry, 2021-12-13)Field-effect biosensors (bioFETs) offer a novel way to measure the kinetics of biomolecular events such as protein function and DNA hybridization at the single-molecule level on a wide range of time scales. These devices generate an electrical current whose fluctuations are correlated to the kinetics of the biomolecule under study. BioFETs are indeed highly sensitive to changes in the electrostatic potential (ESP) generated by the biomolecule. Here, using all-atom solvent explicit molecular dynamics simulations, we further investigate the molecular origin of the variation of this ESP for two prototypical cases of proteins or nucleic acids attached to a carbon nanotube bioFET: the function of the lysozyme protein and the hybridization of a 10-nt DNA sequence, as previously done experimentally. Our results show that the ESP changes significantly on the surface of the carbon nanotube as the state of these two biomolecules changes. More precisely, the ESP distributions calculated for these molecular states explain well the magnitude of the conductance fluctuations measured experimentally. The dependence of the ESP with salt concentration is found to agree with the reduced conductance fluctuations observed experimentally for the lysozyme, but to differ for the case of DNA, suggesting that other mechanisms might be at play in this case. Furthermore, we show that the carbon nanotube does not impact significantly the structural stability of the lysozyme, corroborating that the kinetic rates measured using bioFETs are similar to those measured by other techniques. For DNA, we find that the structural ensemble of the single-stranded DNA is significantly impacted by the presence of the nanotube, which, combined with the ESP analysis, suggests a stronger DNA–device interplay. Overall, our simulations strengthen the comprehension of the inner working of field-effect biosensors used for single-molecule kinetics measurements on proteins and nucleic acids.Item Accès libre Optimising CNT-FET biosensor design through modelling of biomolecular electrostatic gating and its application to β-lactamase detectionGwyther, Rebecca E. A.; Côté, Sébastien; Lee, Chang-Seuk; Miao, Haosen; Ramakrishnan, Krithika; Palma, Matteo; Jones, D. Dafydd; Université de Montréal. Faculté des arts et des sciences. Département de physique (Nature research , 2024-08-29)Carbon nanotube field effect transistors (CNT-FET) hold great promise as next generation miniaturised biosensors. One bottleneck is modelling how proteins, with their distinctive electrostatic surfaces, interact with the CNT-FET to modulate conductance. Using advanced sampling molecular dynamics combined with non-canonical amino acid chemistry, we model protein electrostatic potential imparted on single walled CNTs (SWCNTs). We focus on using β-lactamase binding protein (BLIP2) as the receptor as it binds the antibiotic degrading enzymes, β-lactamases (BLs). BLIP2 is attached via the single selected residue to SWCNTs using genetically encoded phenyl azide photochemistry. Our devices detect two different BLs, TEM-1 and KPC-2, with each BL generating distinct conductance profiles due to their differing surface electrostatic profiles. Changes in conductance match the model electrostatic profile sampled by the SWCNTs on BL binding. Thus, our modelling approach combined with residue-specific receptor attachment could provide a general approach for systematic CNT-FET biosensor construction.Item Accès libre Data management plan - CERC in light-matter interactionsThouin, Félix; Silva, Carlos; Li, Hao; Dion-Bertrand, Laura-Isabelle; Université de Montréal. Faculté des arts et des sciences. Département de physique (2024-05-14)This data management plan shows how the data from the CERC on light-matter interactions directed by Prof. Carlos Silva Acuña will be collected, organized, named, stored, backed up, preserved, and shared.Item Accès libre Formation of crystalline Si1-xGex top layers by ion implantation in crystalline siliconNélis, Adrien; Chicoine, Martin; Schiettekatte, François; Terwagne, Guy; Université de Montréal. Faculté des arts et des sciences. Département de physique (Elsevier, 2023-02-27)Semiconductor nanocrystals incorporated in a dielectric film are widely studied as potential candidates to exceed the Shockley-Queisser theoretical conversion limit of photovoltaic cells. In this context, Ge nanocrystals embedded in SiO2 films seem to be among the best candidates. However, the charges generated in the dielectric film are hard to collect. For this reason, it would be better if the charges were generated in a semiconductor matrix such as silicon, which has better conductivity. However, implanted Ge atoms have poor mobility in a silicon matrix and thus Ge nanocrystals formation is not likely. But even if the formation of Ge nanocrystals seems difficult, it would still be interesting to form crystalline Si1-xGex alloys. This work investigates the formation of the Si1-xGex films by ion implantation and their crystallinity. 36 keV Ge ions were implanted in crystalline Si substrates, with fluences ranging from 5 × 1015 to 1.5 × 1017 Ge/cm2 at temperatures up to 600 °C. Rutherford Backscattering Spectrometry (RBS), Raman Spectroscopy, and Transmission Electron Microscopy (TEM) were used to investigate the microstructure of the Si1-xGex alloys. It is shown that germanium is mostly incorporated in the crystal network in substitutional sites. XRD, Raman spectroscopy, and TEM confirm that the Si1-xGex layer on top of the c-Si substrate is monocrystalline. TEM also indicates the possible presence of nanostructures, extended defects or both. Implantation was also carried out at temperatures up to 600 °C, with the objective of preserving the crystallinity and promoting Ge diffusion into nanoclusters. RBS shows that the Ge profile is more extended in depth for the sample implanted at 600 °C, compared to a room temperature implantation. As the energy of the ions is the same in both samples, this indicates that Ge is able to diffuse in depth during the implantation at 600 °C compared to implantation at ambient temperature. However, RBS/C shows that the minimal yield is higher for the implantation at 600 °C, indicating a high concentration of interstitials or that crystallinity is deteriorated, as confirmed by TEM.Item Accès libre In-plasma analysis of plasma–surface interactionsVinchon, Pierre; Asadollahi, Siavash; Coté, Claude; Marcet, Stephane; Atallah, S.; Dessureault, Émile; Chicoine, Martin; Sarkissian, Andranik; Leonelli, Richard; Roorda, Sjoerd; Schiettekatte, François; Stafford, Luc; Université de Montréal. Faculté des arts et des sciences. Département de physique (American Institute of Physics, 2023)During deposition, modification, and etching of thin films and nanomaterials in reactive plasmas, many active species can interact with the sample simultaneously. This includes reactive neutrals formed by fragmentation of the feed gas, positive ions, and electrons generated by electron-impact ionization of the feed gas and fragments, excited states (in particular, long-lived metastable species), and photons produced by spontaneous de-excitation of excited atoms and molecules. Notably, some of these species can be transiently present during the different phases of plasma processing, such as etching of thin layer deposition. To monitor plasma–surface interactions during materials processing, a new system combining beams of neutral atoms, positive ions, UV photons, and a magnetron plasma source has been developed. This system is equipped with a unique ensemble of in-plasma surface characterization tools, including (1) a Rutherford Backscattering Spectrometer (RBS), (2) an Elastic Recoil Detector (ERD), and (3) a Raman spectroscopy system. RBS and ERD analyses are carried out using a differentially pumped 1.7 MV ion beam line Tandetron accelerator generating a beam at grazing incidence. The ERD system is equipped with an absorber and is specifically used to detect H initially bonded to the surface; higher resolution of surface H is also available through nuclear reaction analysis. In parallel, an optical port facing the substrate is used to perform Raman spectroscopy analysis of the samples during plasma processing. This system enables fast monitoring of a few Raman peaks over nine points scattered on a 1.6 × 1.6 mm2 surface without interference from the inherent light emitted by the plasma. Coupled to the various plasma and beam sources, the unique set of in-plasma surface characterization tools detailed in this study can provide unique time-resolved information on the modification induced by plasma. By using the ion beam analysis capability, the atomic concentrations of various elements in the near-surface (e.g., stoichiometry and impurity content) can be monitored in real-time during plasma deposition or etching. On the other hand, the evolution of Raman peaks as a function of plasma processing time can contribute to a better understanding of the role of low-energy ions in defect generation in irradiation-sensitive materials, such as monolayer graphene.Item Accès libre Raman-based mapping and depth-profiling of the relaxation state in amorphous siliconLussier, Alexandre W.; Bourbonnais Sureault, David; Chicoine, Martin; Martel, Richard; Martinu, Ludvik; Roorda, Sjoerd; Schiettekatte, François; Université de Montréal. Faculté des arts et des sciences. Département de physique (American Institute of Physics, 2024-02-09)We show that the micro-scale variations in the relaxation state of amorphous silicon (aSi) can be well-identified by Raman mapping over hundreds or thousands of µm2 in 1-2 hours. Pure and relaxed a-Si is obtained by self-implantation in crystalline silicon (c-Si) followed by an anneal at 500°C. It is then locally re-implanted over micro-sized patterns to produce unrelaxed aSi zones. Raman mappings are obtained by pointwise confocal µ-Raman and Hyperspectral Raman Imaging (RIMA). We also measure depth profiles of the relaxation state in re-implanted a-Si by scanning the edge of a re-implanted sample. We infer from the depth profiles that the minimal damage dose to fully de-relax a-Si is 0.04 displacements per atoms, which is an order of magnitude smaller than the fluence needed to fully amorphize c-Si.Item Accès libre Formation of crystalline Si1-xGex top layers by ion implantation in crystalline siliconNélis, Adrien; Chicoine, Martin; Schiettekatte, François; Terwagne, Guy; Université de Montréal. Faculté des arts et des sciences. Département de physique (Elsevier, 2023-02-27)Semiconductor nanocrystals incorporated in a dielectric film are widely studied as potential candidates to exceed the Shockley-Queisser theoretical conversion limit of photovoltaic cells. In this context, Ge nanocrystals embedded in SiO2 films seem to be among the best candidates. However, the charges generated in the dielectric film are hard to collect. For this reason, it would be better if the charges were generated in a semiconductor matrix such as silicon, which has better conductivity. However, implanted Ge atoms have poor mobility in a silicon matrix and thus Ge nanocrystals formation is not likely. But even if the formation of Ge nanocrystals seems difficult, it would still be interesting to form crystalline Si1-xGex alloys. This work investigates the formation of the Si1-xGex films by ion implantation and their crystallinity. 36 keV Ge ions were implanted in crystalline Si substrates, with fluences ranging from 5 × 1015 to 1.5 × 1017 Ge/cm2 at temperatures up to 600 °C. Rutherford Backscattering Spectrometry (RBS), Raman Spectroscopy, and Transmission Electron Microscopy (TEM) were used to investigate the microstructure of the Si1-xGex alloys. It is shown that germanium is mostly incorporated in the crystal network in substitutional sites. XRD, Raman spectroscopy, and TEM confirm that the Si1-xGex layer on top of the c-Si substrate is monocrystalline. TEM also indicates the possible presence of nanostructures, extended defects or both. Implantation was also carried out at temperatures up to 600 °C, with the objective of preserving the crystallinity and promoting Ge diffusion into nanoclusters. RBS shows that the Ge profile is more extended in depth for the sample implanted at 600 °C, compared to a room temperature implantation. As the energy of the ions is the same in both samples, this indicates that Ge is able to diffuse in depth during the implantation at 600 °C compared to implantation at ambient temperature. However, RBS/C shows that the minimal yield is higher for the implantation at 600 °C, indicating a high concentration of interstitials or that crystallinity is deteriorated, as confirmed by TEM.Item Accès libre Critical process temperatures for resistive InGaAsP/InP heterostructures heavily implanted by Fe or Ga ionsFekecs, André; Chicoine, Martin; Ilahi, Bouraoui; Spring Thorpe, Anthony J.; Schiettekatte, François; Morris, Denis; Charette, Paul G.; Arès, Richard; Université de Montréal. Faculté des arts et des sciences. Département de physique (Elsevier, 2015-07-30)We report on critical ion implantation and rapid thermal annealing (RTA) process temperatures that produce resistive Fe- or Ga-implanted InGaAsP/InP heterostructures. Two InGaAsP/InP heterostructure compositions, with band gap wavelengths of 1.3 μm and 1.57 μm, were processed by ion implantation sequences done at multiple MeV energies and high fluence (1015 cm−2). The optimization of the fabrication process was closely related to the implantation temperature which influences the type of implant-induced defect structures. With hot implantation temperatures, at 373 K and 473 K, X-ray diffraction (XRD) revealed that dynamic defect annealing was strong and prevented the amorphization of the InGaAsP layers. These hot-implanted layers were less resistive and RTA could not optimize them systematically in favor of high resistivity. With cold implantation temperatures, at 83 K and even at 300 K, dynamic annealing was minimized. Damage clusters could form and accumulate to produce resistive amorphous-like structures. After recrystallization by RTA, polycrystalline signatures were found on every low-temperature Fe- and Ga-implanted structures. For both ion species, electrical parameters evolved similarly against annealing temperatures, and resistive structures were produced near 500 °C. However, better isolation was obtained with Fe implantation. Differences in sheet resistivities between the two alloy compositions were less than band gap-related effects. These observations, related to damage accumulation and recovery mechanisms, have important implications for the realization ion-implanted resistive layers that can be triggered with near infrared laser pulses and suitable for ultrafast optoelectronics.Item Accès libre Hydrogen analysis depth calibration by CORTEO Monte-Carlo simulationMoser, M.; Reichart, P.; Bergmaier, A.; Greubel, C.; Schiettekatte, François; Dollinger, G.; Université de Montréal. Faculté des arts et des sciences. Département de physique (Elsevier, 2015-10-21)Hydrogen imaging with sub-μm lateral resolution and sub-ppm sensitivity has become possible with coincident proton–proton (pp) scattering analysis (Reichart et al., 2004). Depth information is evaluated from the energy sum signal with respect to energy loss of both protons on their path through the sample. In first order, there is no angular dependence due to elastic scattering. In second order, a path length effect due to different energy loss on the paths of the protons causes an angular dependence of the energy sum. Therefore, the energy sum signal has to be de-convoluted depending on the matrix composition, i.e. mainly the atomic number Z, in order to get a depth calibrated hydrogen profile. Although the path effect can be calculated analytically in first order, multiple scattering effects lead to significant deviations in the depth profile. Hence, in our new approach, we use the CORTEO Monte-Carlo code (Schiettekatte, 2008) in order to calculate the depth of a coincidence event depending on the scattering angle. The code takes individual detector geometry into account. In this paper we show, that the code correctly reproduces measured pp-scattering energy spectra with roughness effects considered. With more than 100 μm thick Mylar-sandwich targets (Si, Fe, Ge) we demonstrate the deconvolution of the energy spectra on our current multistrip detector at the microprobe SNAKE at the Munich tandem accelerator lab. As a result, hydrogen profiles can be evaluated with an accuracy in depth of about 1% of the sample thickness.Item Accès libre Engineering visible light emitting point defects in Zr-implanted polycrystalline AlN filmsAghdaei, Azin; Pandiyan, R.; Bouraoui, Ilahi; Chicoine, Martin; El Gowini, M.; Schiettekatte, François; Frechette, Luc G.; Morris, Denis; Université de Montréal. Faculté des arts et des sciences. Département de physique (American Institute of Physics, 2020-12-22)We have investigated the impact of thermal annealing gaseous atmosphere of argon, nitrogen, and forming gas on the structural and optical properties of thin polycrystalline AlN films subjected to high-energy zirconium ions implantation. X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and atomic force microscopy measurements show that the structural and morphological properties of the Zr-implanted AlN films depend on the annealing gaseous environment. Post-implantation annealing under argon atmosphere yields the lowest structured surface roughness with increased grain size. Photoluminescence spectroscopy revealed multiple point defects and defect complexes related emission bands in the visible range. A series of absorption bands have been observed using photoluminescence excitation spectroscopy. The origin of the emission or absorption bands is identified and attributed to various types of point defects and defect complexes, theoretically reported for AlN. New emission and absorption peaks at 1.7eV (730nm) and 2.6eV (466nm), respectively, have been identified and attributed to the (ZrAl–VN)0 defect complexes.Item Accès libre Polyphenol-peptide interactions in mitigation of Alzheimer’s disease : role of biosurface-induced aggregationGaudreault, Roger; Hervé, Vincent; Van De Ven, Theo; Mousseau, Normand; Ramassamy, Charles; Université de Montréal. Faculté des arts et des sciences. Département de physique (IOS Press, 2021-05-08)Alzheimer’s disease (AD) is the most common age-related neurodegenerative disorder, responsible for nearly two-thirds of all dementia cases. In this review, we report the potential AD treatment strategies focusing on natural polyphenol molecules (green chemistry) and more specifically on the inhibition of polyphenol-induced amyloid aggregation/disaggregation pathways: in bulk and on biosurfaces. We discuss how these pathways can potentially alter the structure at the early stages of AD, hence delaying the aggregation of Aβ and tau. We also discuss multidisciplinary approaches, combining experimental and modelling methods, that can better characterize the biochemical and biophysical interactions between proteins and phenolic ligands. In addition to the surface-induced aggregation, which can occur on surfaces where protein can interact with other proteins and polyphenols, we suggest a new concept referred as “confinement stability”. Here. on the contrary, the adsorption of Aβ and tau on biosurfaces other than Aβ- and tau-fibrils, e.g. red blood cells (RBCs), can lead to confinement stability that minimizes the aggregation of Aβ and tau. Overall, these mechanisms may participate directly or indirectly in mitigating neurodegenerative diseases, by preventing protein self-association, slowing down the aggregation processes, and delaying the progression of AD.Item Accès libre Corilagin and 1,3,6-Tri-O-galloyl-β -D-glucose : potential inhibitors of SARS-CoV-2 variantsBinette, Vincent; Côté, Sébastien; Haddad, Mohamed; Nguyen, Phuong Trang; Bélanger, Sébastien; Bourgault, Steve; Ramassamy, Charles; Gaudreault, Roger; Mousseau, Normand; Université de Montréal. Faculté des arts et des sciences. Département de physique (2021-06-28)The COVID-19 disease caused by the virus SARS-CoV-2, first detected in December 2019, is still emerging through virus mutations. Although almost under control in some countries due to effective vaccines that are mitigating the worldwide pandemic, the urgency to develop additional vaccines and therapeutic treatments is imperative. In this work, the natural polyphenols corilagin and 1,3,6-tri-Ogalloy-β-D-glucose (TGG) are investigated to determine the structural basis of inhibitor interactions as potential candidates to inhibit SARS-CoV-2 viral entry into target cells. First, the therapeutic potential of the ligands are assessed on the ACE2/wild-type RBD. We first use molecular docking followed by molecular dynamics, to take into account the conformational flexibility that plays a significant role in ligand binding and that cannot be captured using only docking, and then analyze more precisely the affinity of these ligands using MMPBSA binding free energy. We show that both ligands bind to the ACE2/wild-type RBD interface with good affinities which might prevent the ACE2/RBD association. Second, we confirm the potency of these ligands to block the ACE2/RBD association using a combination of surface plasmon resonance and biochemical inhibition assays. These experiments confirm that TGG and, to a lesser extent, corilagin, inhibit the binding of RBD to ACE2. Both experiments and simulations show that the ligands interact preferentially with RBD, while weak binding is observed with ACE2, hence, avoiding potential physiological side-effects induced by the inhibition of ACE2. In addition to the wild-type RBD, we also study numerically three RBD mutations (E484K, N501Y and E484K/N501Y) found in the main SARS-CoV-2 variants of concerns. We find that corilagin could be as effective for RBD/E484K but less effective for the RBD/N501Y and RBD/E484K-N501Y mutants, while TGG strongly binds at relevant locations to all three mutants, demonstrating the significant interest of these molecules as potential inhibitors for variants of SARSCoV-2.Item Accès libre Pressure effect on diffusion of carbon at the 85.91◦ 100 symmetric tilt grain boundary of α-ironRahman, Md Mijanur; El-Mellouhi, Fedwa; Bouhali, Othmane; Becquart, Charlotte; Mousseau, Normand; Université de Montréal. Faculté des arts et des sciences. Département de physique (American Physical Society, 2021-04-19)The diffusion mechanism of carbon in iron plays a vital role in carburization processes, steel fabrication, and metal dusting corrosion. In this paper, using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo algorithm with on-the-fly catalog building that allows to obtain diffusion properties over large time scales taking full account of chemical and elastic effects coupled with an EAM potential, we investigate the effect of pressure on the diffusion properties of carbon in 85 . 91 ∘ ⟨ 100 ⟩ symmetric tilt grain boundaries (GB) of α -iron up to a pressure of 12 kbar at a single temperature of 600 K. We find that, while the effect of pressure can strongly modify the C stability and diffusivity in the GB in ways that depend closely on the local environment and the nature of the deformation, isotropic and uniaxial pressure can lead to opposite and nonmonotonous effects regarding segregation energy and activation barriers. These observations are relevant to understanding of the evolution of heterogeneous materials, where variations of local pressure can alter the carbon diffusion across the material.Item Accès libre Diffusion mechanism of bound Schottky defect in magnesium oxideMahmoud, Sami; Carrez, Philippe; Landeiro Dos Reis, Marie; Mousseau, Normand; Cordier, Patrick; Université de Montréal. Faculté des arts et des sciences. Département de physique (American Physical Society, 2021-03-25)In simple ionic crystals, intrinsic point defects must satisfy electrical neutrality and exist as Schottky defects. In magnesium oxide (MgO), a Schottky defect is then a combination of anionic and cationic vacancies. Since vacancies are charged, the stable configuration of the Schottky defect corresponds to a bound pair of vacancies of opposite signs. In this study, we investigate the kinetics of formation and migration of such a bound pair on long timescales reaching in some cases thousands of seconds using the kinetic activation-relaxation technique, an off-lattice kinetic Monte Carlo method with an event catalog built on-the-fly during static molecular simulations. We show that the diffusion of this bound Schottky defect involves the migration of vacancies bounded to the first and third neighbor sites of the crystal structure with an apparent migration energy which cannot be inferred from the migration energies expected from isolated defects. Overall, this study gives insights and constraints on the oxygen diffusion mechanism reported experimentally in high-purity MgO samples.Item Accès libre Molecular interactions of tannic acid with proteins associated with SARS-CoV-2 infectivityHaddad, Mohamed; Gaudreault, Roger; Sasseville, Gabriel; Nguyen, Phuong Trang; Wiebe, Hannah; Van De Ven, Theo; Bourgault, Steve; Mousseau, Normand; Ramassamy, Charles; Université de Montréal. Faculté des arts et des sciences. Département de physique (MDPI, 2022-02-27)The overall impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on our society is unprecedented. The identification of small natural ligands that could prevent the entry and/or replication of the coronavirus remains a pertinent approach to fight the coronavirus disease (COVID-19) pandemic. Previously, we showed that the phenolic compounds corilagin and 1,3,6-tri-O-galloyl-β-D-glucose (TGG) inhibit the interaction between the SARS-CoV-2 spike protein receptor binding domain (RBD) and angiotensin-converting enzyme 2 (ACE2), the SARS-CoV-2 target receptor on the cell membrane of the host organism. Building on these promising results, we now assess the effects of these phenolic ligands on two other crucial targets involved in SARS-CoV-2 cell entry and replication, respectively: transmembrane protease serine 2 (TMPRSS2) and 3-chymotrypsin like protease (3CLpro) inhibitors. Since corilagin, TGG, and tannic acid (TA) share many physicochemical and structural properties, we investigate the binding of TA to these targets. In this work, a combination of experimental methods (biochemical inhibition assays, surface plasmon resonance, and quartz crystal microbalance with dissipation monitoring) confirms the potential role of TA in the prevention of SARS-CoV-2 infectivity through the inhibition of extracellular RBD/ACE2 interactions and TMPRSS2 and 3CLpro activity. Moreover, molecular docking prediction followed by dynamic simulation and molecular mechanics Poisson–Boltzmann surface area (MMPBSA) free energy calculation also shows that TA binds to RBD, TMPRSS2, and 3CLpro with higher affinities than TGG and corilagin. Overall, these results suggest that naturally occurring TA is a promising candidate to prevent and inhibit the infectivity of SARS-CoV-2.Item Accès libre Insights on the effect of water content in carburizing gas mixtures on the metal dusting corrosion of ironBentria, El Tayeb; Salawu, Omotayo Akande; Ramesh, Abitha; Laycock, Nicholas; Hamer, Wouter; Mousseau, Normand; Becquart, Charlotte; Bouhali, Othmane; El-Mellouhi, Fedwa; Université de Montréal. Faculté des arts et des sciences. Département de physique (Elsevier, 2021-12-07)Constituents of syngas, such as water, carbon monoxide and sulfides, can cause the degradation of the steel pipes they move through, leading to carbon dusting and corrosion. In spite of considerable attention to this process, many questions remain about its origin. We conduct reactive molecular dynamics simulations of multi-grain iron systems exposed to carburizing gas mixtures to investigate the effect of water content on metal dusting corrosion. To simulate carbon monoxide (CO) dissociation followed by carbon diffusion, we employ an extended-ReaxFF potential that allows accounting for both the high C atoms coordination in bulk iron as well as the lower C coordination at the iron surface and interfaces. The reactions happening in the sample at different water con- centrations and at different time frames are explored. We demonstrate that the presence of water on a clean Fe surface promotes different catalytic reactions at the beginning of the simulations that boost the C, H, O diffusion into the sample. At later stage, the formation of oxide scale leads to an elevated concentration of H2O/OH molecules on the surface due to the decrease in Fe affinity to dissociate water. This results into blocking the Fe catalytic sites leading to lower C and O diffusion to the bulk of the sample.Item Accès libre Zirconia-titania-doped tantala optical coatings for low mechanical loss Bragg mirrorsLalande, Émile; Lussier, Alexandre W.; Lévesque, Carl; Ward, Marianne; Baloukas, Bill; Martinu, Ludvik; Gabriele, Vajente; Billingsley, Garilynn; Ananyeva, Alena; Bassiri, Riccardo; Fejer, Martin M.; Schiettekatte, François; Université de Montréal. Faculté des arts et des sciences. Département de physique (American Vacuum Society, 2021-06-10)The noise caused by internal mechanical dissipation in the high refractive index amorphous thin films in dielectric mirrors is an important limitation for gravitational wave detection. The objective of this study is to decrease this noise spectral density, which is linearly dependent on such dissipation and characterized by the loss angle of the Young’s modulus, by adding zirconia to titania-doped tantala, from which the current mirrors for gravitational wave detection are made. The purpose of adding zirconia is to raise the crystallization temperature, which allows the material to be more relaxed by raising the practical annealing temperature. The Ta, Ti and Zr oxides are deposited by reactive magnetron sputtering in an Ar:O2 atmosphere using radio-frequency and high power impulse plasma excitation. We show that thanks to zirconia, the crystallization temperature rises by more than 150◦C, which allows one to obtain a loss angle of 2.5 × 10−4 , that is, a decrease by a factor of 1.5 compared to the current mirror high-index layers. However, due to a difference in the coefficient of thermal expansion between the thin film and the silica substrate, cracks appear at high annealing temperature. In response, a silica capping layer is applied to increase the temperature of crack formation by 100◦C.Item Accès libre Comparison of three radio-frequency discharge modes on the treatment of breast cancer cells in vitroBoisvert, Jean-Sébastien; Lafontaine, Julie; Glory, Audrey; Wong, Philip; Coulombe, Sylvain; Université de Montréal. Faculté de médecine. Département de radiologie, radio-oncologie et médecine nucléaire; CHUM. Centre de recherche (Institute of Electrical and Electronics Engineers, 2019)Non-thermal plasmas (NTPs) are known for their ability to induce thermal-free cytotoxic effects on cancer cells. However, as the variety of NTP devices increases, comparison of their cytotoxic effect becomes increasingly essential. In this work, we compare the cytotoxicity of three different radio-frequency NTPs. MDA-MB-231 triple negative breast cancer cells are treated in suspension in DMEM culture medium by the effluents of a single radiofrequency (RF) discharge device operating in three modes, namely the and modes of the capacitively coupled radio-frequency (CCRF) discharge and a RF plasma jet mode. All three discharge modes reduce the proliferative capacity of MDA-MB-231 cells, but the treatment time required to reach the same efficacy is more than ten times longer using the and the modes than using the jet mode. In all cases, using the appropriate treatment time, cells exhibit an impaired proliferation and eventually start to show signs of cell death (about 48 h after treatment). The three discharge modes also induce nuclear DNA damages. Plasma-produced H2O2 was not found to contribute to the cytotoxicity of the treatment. Furthermore, short-lived reactive species (gas phase or liquid phase species with a lifetime below 1 s) are expected to play a dominant role over the long-lived reactive species in the anti-cancer effect of all three discharge modes.Item Accès libre Mitigating Alzheimer’s disease with natural polyphenols: a reviewGaudreault, Roger; Mousseau, Normand; Université de Montréal. Faculté des arts et des sciences. Département de physique (Bentham Science, 2019-03-14)According to Alzheimer’s Disease International (ADI), nearly 50 million people worldwide were living with dementia in 2017, and this number is expected to triple by 2050. Despite years of research in this field, the root cause and mechanisms responsible for Alzheimer’s disease (AD) have not been fully elucidated yet. Moreover, promising preclinical results have repeatedly failed to translate into patient treatments. Until now, none of the molecules targeting AD has successfully passed the Phase III trial. Although natural molecules have been extensively studied, they normally require high concentrations to be effective; alternately, they are too large to cross the blood-brain barrier (BBB). In this review, we report on AD treatment strategies, with a virtually exclusive focus on green chemistry (natural phenolic molecules). These include therapeutic strategies for decreasing amyloid- β (Aβ) production, preventing and/or altering A β aggregation, and reducing oligomers cytotoxicity such as curcumin, (-)- epigallocatechin-3-gallate (EGCG), morin, resveratrol, tannic acid, and other natural green molecules. We also examinewhether consideration should be given to potential candidates used outside of medicine and nutrition, through a discussion of two intermediate-sized green molecules, with very similar molecular structures and key properties, which exhibit potential in mitigating Alzheimer’s disease.Item Accès libre A coupled 2 x 2D Babcock-Leighton solar dynamo model. II Reference dynamo solutionsSt-Laurent-Lemerle, Alexandre; Charbonneau, Paul; Université de Montréal. Faculté des arts et des sciences. Département de physique (American Astronomical Society, 2017-01)In this paper we complete the presentation of a new hybrid 2 × 2D flux transport dynamo (FTD) model of the solar cycle based on the Babcock–Leighton mechanism of poloidal magnetic field regeneration via the surface decay of bipolar magnetic regions (BMRs). This hybrid model is constructed by allowing the surface flux transport (SFT) simulation described in Lemerle et al. to provide the poloidal source term to an axisymmetric FTD simulation defined in a meridional plane, which in turn generates the BMRs required by the SFT. A key aspect of this coupling is the definition of an emergence function describing the probability of BMR emergence as a function of the spatial distribution of the internal axisymmetric magnetic field. We use a genetic algorithm to calibrate this function, together with other model parameters, against observed cycle 21 emergence data. We present a reference dynamo solution reproducing many solar cycle characteristics, including good hemispheric coupling, phase relationship between the surface dipole and the BMR-generating internal field, and correlation between dipole strength at cycle maximum and peak amplitude of the next cycle. The saturation of the cycle amplitude takes place through the quenching of the BMR tilt as a function of the internal field. The observed statistical scatter about the mean BMR tilt, built into the model, acts as a source of stochasticity which dominates amplitude fluctuations. The model thus can produce Dalton-like epochs of strongly suppressed cycle amplitude lasting a few cycles and can even shut off entirely following an unfavorable sequence of emergence events.