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Bacterial behavior during filtration is complex and is influenced by numerous factors. The aim of this paper is to report on experiments designed to make progress in the understanding of bacterial transfer in filters and membranes. Polydimethylsiloxane (PDMS) microsystems were built to allow direct dynamic observation of bacterial transfer across different microchannel geometries mimicking filtration processes. When filtering Escherichia coli suspensions in such devices, the bacteria accumulated in the downstream zone of the filter forming long streamers undulating in the flow. Confocal microscopy and 3D reconstruction of streamers showed how the streamers are connected to the filter and how they form in the stream. Streamer development was found to be influenced by the flow configuration and the presence of connections or tortuosity between channels. Experiments showed that streamer formation was greatest in a filtration system composed of staggered arrays of squares 10 μm apart.

the latter and to achieve extremely high packing density. [9] The understanding of switching mechanisms at device level is a key factor for a technology to be viable at very large scale integration. Different types of resistive memory devices have been studied in the past years such as oxide-based memories (OxRAM) and conductive bridge random access memories (CBRAM). It should be noted that for both technologies it is very challenging to combine good cycling endurance, stable retention and high window margin (WM). Two distinct resistive states can be obtained based on a reversible filament formation (SET operation) and rupture (RESET operation) inside an insulating layer sandwiched between two electrodes; SET operation being the switching from a high resistive state (HRS) to a low resistive state (LRS) and RESET the reverse operation (HRS to LRS). In the case of CBRAM, metal ions coming from top electrode (TE) are introduced in the insulating layer. Working principle is based on a metallic filament formation and dissolution controlling performances. [10] These devices present high WM, relatively low endurance, and poor retention stability. [11,12] In the case of OxRAM, oxygen vacancies creation and annihilation inside the oxide dominates the switching mechanism. [13][14][15] This technology shows low WM combined to high endurance and stable retention. [3,16] While lots of effort have been done lately to improve switching speed and power consumption in RRAM, [17,18] several challenges need to be overcome, namely the high extrinsic (device to device) and intrinsic (cycle to cycle) variability in RRAM characteristics. [7] High WM could potentially help solving this variability by maximizing the ratio of HRS over LRS. Moreover, coupling high WM and high endurance (up to 10 8 cycles required for storage class applications [19] ) remains a critical issue. Combining CBRAM and OxRAM in one hybrid oxide-based CBRAM (hybrid-RRAM (HRRAM)) where filament can be composed of metal ions and oxygen vacancies could offer alternative performances such as high WM coupled with high endurance. Recent studies have identified materials issues in oxide and metal based RRAM. [20,21] However, material properties study is still lacking in HRRAM to guide stack choice (oxide vs electrodes) toward a given application. In a previous work, a trade-off between endurance, window margin, and retention was demonstrated. When comparing various HRRAM electrical performances and filament composition, Here, the impact of copper and oxygen vacancy balance in filament composition as a key factor for oxide-based conductive bridge random access memories (hybrid resistive random access memories (HRRAMs)) performances is investigated. To this aim, several RRAM technologies are studied using various resistive layers and top electrodes. Material analyses allow to highlight the hybrid aspect of HRRAM conductive filament. Density functional theory simulations are used to extract microscopic features and highlight differences from a material point of view. Integr...

The way in which bacterial communities colonize flow in porous media is of importance, but basic knowledge on the dynamic of these phenomena is still missing. The aim of this work is to develop microfluidic experiments in order to progress in the understanding of bacteria capture in filters and membranes. PDMS microfluidic devices mimicking filtration processes have been developed to allow a direct dynamic observation of bacteria across 10 or 20 lm width microchannels. When filtered in such devices, bacteria behave surprisingly: Escherichia coli, Pseudomonas aeruginosa or Staphylococcus aureus accumulate in the downstream zone of the filter and form large streamers which oscillate in the flow. In this study, streamer formation is put in evidence for bacteria suspension in non nutritive conditions in less than 1 h. This result is totally different from the one observed in same system with "inert" particles or dead bacteria which are captured in the bottleneck zone and are accumulated in the upstream zone. Observations within different flow geometries (straight channels, connected channels, and staggered row pillars) show that the bacteria streamer development is influenced by the flow configuration and, particularly by the presence of tortuosity within the microchannels zone. These results are discussed at the light of 3D flow simulations. In confined systems and in laminar flow, there is secondary flow (z-velocities) superimposed to the streamwise motion (in xy plane). The presence of the secondary flow in the microsystems has an effect on the bacterial adhesion. A scenario in three steps is established to describe the formation of the streamers and to explain the positive effect of tortuous flow on the development kinetics. V C 2014 AIP Publishing LLC. [http://dx

International audienceWe investigated origins of the resistivity change during the forming of ZrTe/Al$_2$O$_3$ based conductive-bridge resistive random access memories. Non-destructive hard X-ray photoelectron spectroscopy was used to investigate redox processes with sufficient depth sensitivity. Results highlighted the reduction of alumina correlated to the oxidation of zirconium at the interface between the solid electrolyte and the active electrode. In addition the resistance switching caused a decrease of Zr-Te bonds and an increase of elemental Te showing an enrichment of tellurium at the ZrTe/Al$_2$O$_3$ interface. XPS depth profiling using argon clusters ion beam confirmed the oxygen diffusion towards the top electrode. A four-layer capacitor model showed an increase of both the ZrO$_2$ and AlO$_x$ interfacial layers, confirming the redox process located at the ZrTe/Al$_2$O$_3$ interface. Oxygen vacancies created in the alumina help the filament formation by acting as preferential conductive paths. This study provides a first direct evidence of the physico-chemical phenomena involved in resistive switching of such devices

Nous présentons dans ce papier sans prétendre être exhaustifs tant le thème est vaste, quelques techniques d'obtention des couches minces les plus utilisées dans les laboratoires de recherche, les grands types et processus de croissance notamment pour les couches minces obtenues par évaporation sous vide, l'épitaxie et quelques mécanismes de relaxation des contraintes

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