Influence of the environment during a photodegradation of multilayer films

The influence of different stratosphere parameters on the degradation of a multilayer film was investigated. The selected multilayer was a three polymeric layers film, a polyamide 6 film inserted between two poly(ethylene terephthalate) (PET) films. Samples were exposed for several ageing under ultraviolet radiations (filtered at 270 nm), varying the atmosphere at 55 mbar pressure (atm, atm + ozone, N2, and T = −55 °C or +23 °C). Evolution of it mechanical properties defined by uniaxial tractions, thermo-optical properties defined by spectrophotometry UV–vis-NIR, chemical properties defined by FTIR-ATR, and thermal and dielectric properties defined, respectively, by differential scanning calorimetry (DSC) and dynamical dielectric spectroscopy (DDS), were investigated. Our results showed that UV irradiation causes multilayer films degradations, that is, principally decrease of UV transmittance and stress and strain at break (−50%). An increase of the ageing temperature causes an acceleration of these degradations. Degradations principally occur on the PET side of the multilayer exposed to UV radiation. Moreover, the DDS analysis shows a plasticization effect of the primary mode in the polyamide 6 due to photo-oxidation. Oxygen diffusion is the principal element for this plasticization, indeed it not occurs in a nonoxidative environment (nitrogen), or at low ageing temperature (−55 °C)

Conductive-probe atomic force microscopy characterization of silicon nanowire

The electrical conduction properties of lateral and vertical silicon nanowires (SiNWs) were investigated using a conductive-probe atomic force microscopy (AFM). Horizontal SiNWs, which were synthesized by the in-plane solid-liquid-solid technique, are randomly deployed into an undoped hydrogenated amorphous silicon layer. Local current mapping shows that the wires have internal microstructures. The local current-voltage measurements on these horizontal wires reveal a power law behavior indicating several transport regimes based on space-charge limited conduction which can be assisted by traps in the high-bias regime (> 1 V). Vertical phosphorus-doped SiNWs were grown by chemical vapor deposition using a gold catalyst-driving vapor-liquid-solid process on higly n-type silicon substrates. The effect of phosphorus doping on the local contact resistance between the AFM tip and the SiNW was put in evidence, and the SiNWs resistivity was estimated

TRPM7 Kinase Controls Calcium Responses in Arterial Thrombosis and Stroke in Mice

Objective: TRPM7 (transient receptor potential cation channel, subfamily M, member 7) is a ubiquitously expressed bifunctional protein comprising a transient receptor potential channel segment linked to a cytosolic alpha-type serine/threonine protein kinase domain. TRPM7 forms a constitutively active Mg2+ and Ca2+ permeable channel, which regulates diverse cellular processes in both healthy and diseased conditions, but the physiological role of TRPM7 kinase remains largely unknown. Approach and Results: Here we show that point mutation in TRPM7 kinase domain deleting the kinase activity in mice (Trpm7(R/R)) causes a marked signaling defect in platelets. Trpm7(R/R) platelets showed an impaired PIP2 (phosphatidylinositol-4,5-bisphosphate) metabolism and consequently reduced Ca2+ mobilization in response to stimulation of the major platelet receptors GPVI (glycoprotein VI), CLEC-2 (C-type lectin-like receptor), and PAR (protease-activated receptor). Altered phosphorylation of Syk (spleen tyrosine kinase) and phospholipase C gamma 2 and beta 3 accounted for these global platelet activation defects. In addition, direct activation of STIM1 (stromal interaction molecule 1) with thapsigargin revealed a defective store-operated Ca2+ entry mechanism in the mutant platelets. These defects translated into an impaired platelet aggregate formation under flow and protection of the mice from arterial thrombosis and ischemic stroke in vivo. Conclusions: Our results identify TRPM7 kinase as a key modulator of phospholipase C signaling and store-operated Ca2+ entry in platelets. The protection of Trpm7(R/R) mice from acute ischemic disease without developing intracranial hemorrhage indicates that TRPM7 kinase might be a promising antithrombotic target

Etude de puits quantiques semiconducteurs par microscopie et spectroscopie à effet tunnel

Low-temperature scanning tunneling spectroscopy (STS) under ultrahigh vacuum was used to investigate In0.53 Ga0.47 As/In0.52 Al0.48 As quantum-well (QW) structures, grown by molecular beam epitaxy on lattice-matched InP(111)A substrates. In a first part, as a preliminary step, the (111)A epitaxial surface of n-type In0.53 Ga0.47 As was studied by STS. It was found that the surface Fermi level is located in the conduction band, close to the bulk Fermi level, and can be partially controlled by varying the n-type impurity density in the bulk. This result was confirmed by determining the conduction-band dispersion relation at the surface. Such partial unpinning of the surface Fermi level indicates a low density of acceptorlike surface states. It was proposed that these states originate from native point defects located at the surface. In a second part, based on the results of the first part, (111)A-oriented In0.53 Ga0.47 As surface QWs grown on top of In0.52 Al0.48 As barriers were studied by STS. The STS measurements were performed at the (111)A epitaxial surface of the In0.53 Ga0.47 As QW, in order to probe with nanometer-scale resolution the in-plane spatial distribution of electronic local density of states. It was confirmed that electron subbands are formed in the QW, and that the electron density in the QW can be varied owing to the partial unpinning of the surface Fermi level. It was found that a phenomenon of percolation of localized states occurs in each subband tail, due to the presence of a disorder potential in the QW. The percolation thresholds were determined by using a semiclassical model. The origin of the disorder potential was ascribed to the random distribution of the native point defects at the QW surface. It was also found that a bound state splits off from each subband minimum in the vicinity of a positively charged native point defect. Both the binding energy and the Bohr radius of the bound states could be directly determined. Moreover, it was shown that the binding energy and the Bohr radius are functions of the QW thickness, in quantitative agreement with variational calculations of hydrogenic impurity states.Des puits quantiques à base d'hétérostructures In0.53 Ga0.47 As/In0.52 Al0.48 As, fabriqués par épitaxie par jets moléculaires sur substrats InP(111)A, sont étudiés par microscopie et spectroscopie à effet tunnel à basse température et sous ultra-vide. La première partie est consacrée à une étude de la surface épitaxiée (111)A de In0.53 Ga0.47 As de type n. Il est découvert que le niveau de Fermi de surface est positionné dans la bande de conduction, à proximité du niveau de Fermi de volume, et peut être partiellement contrôlé en variant la concentration d'impuretés de type n dans le volume. Ce résultat est confirmé en déterminant la relation de dispersion de la bande de conduction en surface. Un tel dépiégeage partiel du niveau de Fermi de surface indique que la densité d'états de surface accepteurs est faible. Il est proposé que ces états proviennent de défauts ponctuels natifs localisés à la surface. La deuxième partie, basée sur les résultats obtenus dans la première partie, est consacrée à une étude de puits quantiques In0.53 Ga0.47 As de surface, déposés sur des barrières In0.52 Al0.48 As selon la direction (111)A. Les mesures sont conduites sur la surface épitaxiée (111)A du puits quantique In0.53 Ga0.47 As, de manière à pouvoir sonder à l'échelle du nanomètre la distribution de densité locale d'états électroniques dans le plan du puits quantique. Il est confirmé que des sous-bandes électroniques sont formées dans le puits quantique, et que la concentration d'électrons dans le puits peut être contrôlée du fait du dépiégeage partiel du niveau de Fermi de surface. Il est découvert qu'un phénomène de percolation d'états localisés survient dans la queue de chaque sous-bande, ce qui indique la présence d'un potentiel désordonné dans le puits quantique. Les seuils de percolation sont déterminés en utilisant un modèle semi-classique. L'origine du potentiel désordonné est attribuée à une distribution aléatoire des défauts ponctuels natifs à la surface du puits quantique. Il est également découvert qu'un état lié apparaît au bas de chaque sous-bande à proximité d'un défaut ponctuel natif de type donneur. L'énergie de liaison et le rayon de Bohr des états liés peuvent être directement déterminés. De plus, il est démontré que l'énergie de liaison et le rayon de Bohr sont fonctions de l'épaisseur du puits quantique, en accord quantitatif avec des calculs variationnels d'impuretés dans le modèle de l'atome d'hydrogène

Scanning tunneling spectroscopy o semiconductor quantum-well structures

InGaAs/InAlAs quantum wells, fabricated by molecular beam epitaxy on InP(111)A substrates, were investigated by scanning tunneling spectroscopy. In a first part, the (111)A epitaxial surface of n-type InGaAs was studied. It was found that the surface Fermi level is partially unpinned, indicating a low density of acceptor surface states. In a second part, InGaAs surface quantum wells were studied. It was found that a phenomenon of percolation of localized states occurs in each subband tail, due to the presence of a disorder potential in the quantum well. It was also found that a bound state splits off from each subband minimum in the vicinity of a positively charged native point defect. It was shown that the binding energy and the Bohr radius are functions of the quantum well thickness, in quantitative agreement with the hydrogenic model.Des puits quantiques InGaAs/InAlAs, fabriqués par épitaxie par jets moléculaires sur substrats InP(111)A, sont étudiés par microscopie et spectroscopie à effet tunnel. La première partie est consacrée à une étude de la surface épitaxiée (111)A de InGaAs de type n. Il est découvert que le niveau de Fermi de surface n est que partiellement piégé, ce qui indique que la densité d'états de surface accepteurs est faible. La deuxième partie est consacrée à une étude de puits quantiques InGaAs de surface. Il est découvert qu'un phénomène de percolation d'états localisés survient dans la queue de chaque sous-bande, du fait de la présence d'un potentiel désordonné dans le puits quantique. Il est également découvert qu'un état lié apparaît au bas de chaque sous-bande à proximité d'un défaut ponctuel natif de type donneur. L'énergie de liaison et le rayon de Bohr sont fonctions de l'épaisseur du puits quantique, en accord quantitatif avec le modèle de l'atome d'hydrogène.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Multilayer films ageing under ultraviolet radiations: Complementary study by dielectric spectroscopy

International audienceThe effect of ultraviolet (UV) irradiation on a multilayer film made of poly(ethylene terephthalate)/Polyamide 6/poly(ethylene terephthalate) was investigated by uniaxial tractions, UV-visible-NIR and Fourier transformed infra-red-attenuated total reflection spectroscopy, differential scanning calorimetry (DSC), and dynamic dielectric spectroscopy (DDS). The multilayer was exposed to ultraviolet radiations (filtered at 270 nm) for 7 days, in air. The complexity of the multilayer thermograms recorded by DSC and DDS has required the study of each film constituting the multilayer to assess each the contribution of each one of them. A deterioration in mechanical properties and a decrease in UV transmission for low wavelengths are observed. These evolutions seem to result to the photo-oxidation of the poly(ethylene terephthalate) film mainly localized at the exposed layer. This layer acts as a UV protection filter for the other layers. However, the DDS analyses show a plasticization effect of the primary mode in the Polyamide 6, which is evidence of photo-oxidation