Resistive switching in silicon suboxide films

We report a study of resistive switching in a silicon-based memristor/resistive RAM (RRAM) device in which the active layer is silicon-rich silica. The resistive switching phenomenon is an intrinsic property of the silicon-rich oxide layer and does not depend on the diffusion of metallic ions to form conductive paths. In contrast to other work in the literature, switching occurs in ambient conditions, and is not limited to the surface of the active material. We propose a switching mechanism driven by competing field-driven formation and current-driven destruction of filamentary conductive pathways. We demonstrate that conduction is dominated by trap assisted tunneling through noncontinuous conduction paths consisting of silicon nanoinclusions in a highly nonstoichiometric suboxide phase. We hypothesize that such nanoinclusions nucleate preferentially at internal grain boundaries in nanostructured films. Switching exhibits the pinched hysteresis I/V loop characteristic of memristive systems, and on/off resistance ratios of 104:1 or higher can be easily achieved. Scanning tunneling microscopy suggests that switchable conductive pathways are 10 nm in diameter or smaller. Programming currents can be as low as 2 μA, and transition times are on the nanosecond scale

The Role of Imaging in Measuring Disease Progression and Assessing Novel Therapies in Aortic Stenosis

Aortic stenosis represents a growing health care burden in high-income countries. Currently, the only definitive treatment is surgical or transcatheter valve intervention at the end stages of disease. As the understanding of the underlying pathophysiology evolves, many promising therapies are being investigated. These seek to both slow disease progression in the valve and delay the transition from hypertrophy to heart failure in the myocardium, with the ultimate aim of avoiding the need for valve replacement in the elderly patients afflicted by this condition. Noninvasive imaging has played a pivotal role in enhancing our understanding of the complex pathophysiology underlying aortic stenosis, as well as disease progression in both the valve and myocardium. In this review, the authors discuss the means by which contemporary imaging may be used to assess disease progression and how these approaches may be utilized, both in clinical practice and research trials exploring the clinical efficacy of novel therapies

Various X-ray diffraction investigations to study the oxidation mechanism of yttrium implanted chromium at elevate temperatures

Attention is paid on the role played by yttrium implantation on the isothermal oxidation behaviour of pure chromium at high temperature. Chromium specimens were oxidized in synthetic air at 800, 900 and 1000 $^{\circ}$C. Many techniques such as Thermogravimetry, Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and in situ XRD were used to characterise the oxide scale formed on chromium-implanted specimens. We have shown that the presence of yttrium limits the nitrogen diffusion through the scale into the metallic matrix. Thus the formation of chromium nitrides is reduced and a better scale adherence is observed. Implanted yttrium has a beneficial effect on the chromium oxidation up to 900$^{\circ}$C. We have shown, by in situ XRD, that it is related to the presence of the yttrium mixed oxide YCrO$_3$ in the scale at high temperature.Cette étude porte sur l'oxydation du chrome pur dans l'air synthétique à 800, 900 et 1000 $^{\circ}$C. Plusieurs techniques, telles que l'analyse thermogravimétrique (ATG), la microscopie électronique à balayage (MEB) et la diffraction des rayons X (DRX) in situ, ont été employées pour caractériser les couches d'oxyde formées sur le chrome implanté à l'yttrium. Nous avons pu montrer que la présence de l'yttrium limite la diffusion de l'azote au travers de la couche d'oxyde et dans la matrice métallique sous-jacente. Ainsi, la formation des nitrures de chrome est plus faible et une meilleure adhérence de la couche d'oxyde est observée. L'yttrium implanté montre un effet bénéfique sur l'oxydation du chrome jusqu'à une temperature de 900$^{\circ}$C. Nous avons pu montrer par diffraction des rayons X in situ que ce phénomène est lié à la présence de l'oxyde mixte YCrO$_3$ dans la couche formée à haute température

Migrability of PVC plasticizers from medical devices into a simulant of infused solutions

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Yttrium implantation and addition element effects on high temperature oxidation behaviour of reference steels

Yttrium implanted and unimplanted various reference steels were oxidized at 700 °C, under controlled atmosphere (oxygen partial pressure: 0.04 Pa), for 24 h to observe the yttrium implantation and the addition element effects on steel high temperature oxidation behaviours. Yttrium implantation effects on reference steels were characterized using analytical and structural techniques such as Rutherford Backscattering Spectrometry (RBS), Reflection High Energy Electron Diffraction (RHEED), X-ray Diffraction (XRD) and Glancing Angle X-ray Diffraction (GAXRD). Yttrium implanted and unimplanted reference steel oxidation behaviours were observed by thermogravimetry and in situ high temperature X-ray diffraction. Our results clearly show that yttrium implantation and high temperature oxidation induced the formation of several yttrium mixed oxides which closely depend on the reference steel addition elements. Moreover, these yttrium mixed oxides seem to be responsible for the improved reference steel oxidation resistance at high temperature

Étude par diffraction des rayons X de la nitruration plasma d'un acier 304L – Influence sur l'oxydation à 1000 ∘^{\circ}C

This work presents the influence of various nitridation parameters on the 304L steel oxidation at 1000 $^{\circ}$C, in air under atmospheric pressure. Nitridation temperatures were ranging between 300 $^{\circ}$C and 430 $^{\circ}$C with exposure times lasting from 2 to 8 hours. At 300 and 430 $^{\circ}$C, the nitridation treatment leads to the solid solution surface formation $\gamma$-N without any nitride formation. After oxidation at 1000 $^{\circ}$C of blank specimens, X ray diffraction reveals the FeCr$_2$O$_4$ spinel formation. This oxide does not act as a good diffusion barrier. With nitrogen treated specimens, the higher the nitridation temperature is and the longer the exposure time is, better is the oxidation behaviour at 1000 $^{\circ}$C. We then observe that the Cr$_{1,3}$Fe$_{0,7}$O$_3$ oxide is more present in the oxide sale from the very beginning of the oxidation test which is correlated to a final lower mass gain.Cette étude porte sur l'influence des paramètres de nitruration plasma sur l'oxydation de l'acier 304L à 1000 $^{\circ}$C, sous air, à la pression atmosphérique. Les températures employées lors de la nitruration ont été de 300 $^{\circ}$C et 430 $^{\circ}$C pour des durées de nitruration variant entre 2 et 8 heures. A 300 et 430 $^{\circ}$C, la nitruration conduit à la formation d'une solution solide $\gamma$-N en surface sans provoquer la formation de nitrures. Après oxydation à 1000 $^{\circ}$C du 304L non nitruré, la diffraction des rayons X révèle la formation d'une couche de type spinelle FeCr$_2$O$_4$ qui ne semble pas jouer le rôle de barrière de diffusion. Pour les échantillons préalablement nitrurés, plus la température de nitruration est élevée et plus la durée du traitement est longue, meilleur est le comportement en oxydation. Nous observons alors l'oxyde Cr$_{1,3}$Fe$_{0,7}$O$_3$ en proportion importante dès le début de l'oxydation et une prise de masse finale plus faible

In situ and glancing angle X-ray diffraction of the structure change during and after the high temperature oxidation at 1000 ∘^{\circ}C in air of an yttrium-implanted 304 steel

A study has been made of the initial stages of oxidation of yttrium ion implanted 304 steel in an attempt to shed some light on the so-called `reactive element effect' observed on chromia forming alloys. In situ XRD was used in order to observe the initial local structural changes during the high temperature oxidation process, while glancing angle XRD was used to monitor the longer range structural transformations taking place near the surface after cooling of oxidised samples. The treatment by ion implantation promotes the intensive establishment of the chromic layer, which leads to the inhibition of the formation of iron rich oxides, by preventing the diffusion of iron through the more compact and more uniform layer initially formed than it would be in the absence of yttrium. However, the identification of yttried phases could not be established.L'effet bénéfique d'un traitement par implantation ionique d'yttrium sur un acier 304 a été mis en évidence par le suivi d'analyses in situ développées par diffraction des rayons X au cours de son oxydation isotherme à 1000$^{\circ}$C sous air. Malgré l'altération superficielle du substrat, le traitement par implantation ionique favorise l'établissement accéléré de la couche de chromine et inhibe la formation au cours du processus d'oxydation des oxydes contenant du fer, réputés peu protecteurs, car faiblement adhérents. Des analyses conduites après refroidissement des échantillons oxydés par diffraction des rayons X sous incidence rasante révèlent la localisation de la structure spinelle au manganèse à l'interface le plus externe. L'identification de phases yttriées n'a cependant pu être établie

Influence of the mode of introduction of a reactive element on the high temperature oxidation behavior of an alumina-forming alloy. Part III: The use of two stage oxidation experiments and in situ X-ray diffraction to understand the oxidation mechanisms

International audienceThe aim of this work was to investigate several different yttrium introduction routes to improve the high temperature oxidation resistance of a Fe-20Cr-5Al model alloy. Y2O3 sol-gel coatings, Y2O3 metal-organic chemical vapor deposition (MOCVD) coatings, yttrium. ion implantation and yttrium as alloying element (0.1 wt.%) were the different methods of introduction of the reactive element. Both isothermal and cyclic oxidation tests showed that the surface introduction of yttrium or yttrium oxide did not drastically improve the oxidation behavior of the steel. Complementary experiments were performed to understand the lack of major beneficial effects of the so-treated samples. Two stage oxidation experiments under 200 mbar O-16(2) and O-18(2) followed by secondary neutral mass spectrometry (SNMS) were performed to understand the alumina scale growth mechanisms, according to the introduction route of the reactive element. The results exhibited that the yttrium induced an increase of the inward transport of oxygen through the alumina scale compared to the untreated specimen. Nevertheless, the outward transport of aluminum was generally observed, except for the specimen containing Y as alloying element, which exhibited only a single O-18 peak close to the metal/oxide interface. Phase transformations during the oxidation at 1100 degrees C were registered by in-situ X-ray diffraction (XRD). The untreated alloy was only covered by a thin layer of alpha-Al2O3. For implanted specimens, yttrium was incorporated in Y3Al5O12 and YAlO3 phases. All the YAlO3 is transformed into Y3Al5O12 after less than 10 h. For the MOCVD or the sol-gel coated samples, the primary formed YAlO3 phase was progressively transformed into Y3Al5O12. For the Fe-20Cr-5Al-0.1Y alloy, no yttrium containing phases could be detected, even after 40 h of oxidation test at 1100 degrees C