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

Antenna-assisted picosecond control of nanoscale phase transition in vanadium dioxide

Nanoscale devices in which the interaction with light can be configured using external control signals hold great interest for next-generation optoelectronic circuits. Materials exhibiting a structural or electronic phase transition offer a large modulation contrast with multi-level optical switching and memory functionalities. In addition, plasmonic nanoantennas can provide an efficient enhancement mechanism for both the optically induced excitation and the readout of materials strategically positioned in their local environment. Here, we demonstrate picosecond all-optical switching of the local phase transition in plasmonic antenna-vanadium dioxide (VO2) hybrids, exploiting strong resonant field enhancement and selective optical pumping in plasmonic hotspots. Polarization- and wavelength-dependent pump-probe spectroscopy of multifrequency crossed antenna arrays shows that nanoscale optical switching in plasmonic hotspots does not affect neighboring antennas placed within 100 nm of the excited antennas. The antenna-assisted pumping mechanism is confirmed by numerical model calculations of the resonant, antenna-mediated local heating on a picosecond time scale. The hybrid, nanoscale excitation mechanism results in 20 times reduced switching energies and 5 times faster recovery times than a VO2 film without antennas, enabling fully reversible switching at over two million cycles per second and at local switching energies in the picojoule range. The hybrid solution of antennas and VO2 provides a conceptual framework to merge the field localization and phase-transition response, enabling precise, nanoscale optical memory functionalities

TSPO ligands stimulate ZnPPIX transport and ROS accumulation leading to the inhibition of P. falciparum growth in human blood

After invading red blood cells (RBCs), Plasmodium falciparum (Pf) can export its own proteins to the host membrane and activate endogenous channels that are present in the membrane of RBCs. This transport pathway involves the Voltage Dependent Anion Channel (VDAC). Moreover, ligands of the VDAC partner TranSlocator PrOtein (TSPO) were demonstrated to inhibit the growth of the parasite. We studied the expression of TSPO and VDAC isoforms in late erythroid precursors, examined the presence of these proteins in membranes of non-infected and infected human RBCs, and evaluated the efficiency of TSPO ligands in inhibiting plasmodium growth, transporting the haem analogue Zn-protoporphyrin-IX (ZnPPIX) and enhancing the accumulation of reactive oxygen species (ROS). TSPO and VDAC isoforms are differentially expressed on erythroid cells in late differentiation states. TSPO2 and VDAC are present in the membranes of mature RBCs in a unique protein complex that changes the affinity of TSPO ligands after Pf infection. TSPO ligands dose-dependently inhibited parasite growth, and this inhibition was correlated to ZnPPIX uptake and ROS accumulation in the infected RBCs. Our results demonstrate that TSPO ligands can induce Pf death by increasing the uptake of porphyrins through a TSPO2-VDAC complex, which leads to an accumulation of ROS

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

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

Effect of yttrium ion implantation on the oxidation of alumina formers at 1173 K

The effect of yttrium implantation on the oxidation behaviour of a commercial alumina forming FeCrAl alloy (Kanthal A1) has been investigated during isothermal exposures in air at 1173 K. The kinetic curve of the undoped specimen exhibits an initial transient stage during the first 6 hours, followed by a parabolic regime. The scale growth kinetics of the yttrium-implanted alloy obeys a parabolic rate law with two subsequent stages with a much lower rate constant during the second stage. Kinetic results indicate that yttrium implantation significantly reduces the growth rate of the oxide scale. In situ X-ray diffraction reveals a marked influence of the reactive element on the composition of the oxide scale. Yttrium suppresses the formation of transition alumina and promotes the growth of α-Al2O3, thereby leading to the earlier formation of a protective oxide scale