Experimental study of the reduction of field emission by gas injection in vacuum for accelerator applications

LGEP 2014 ID = 1590International audienceField emission current from surfaces under vacuum and at high field strengths can be reduced by the injection of gas into the evacuated volume. In this paper, the effects of H 2 , He, N 2 , and Ar on this "dark" current emitted from a tungsten carbide point cathode for 2 cm gap distance is studied. Exposure to any of these gases at pressures on the order of 10 −3 –10 −2 Pa was found to reduce the emission current by up to 90% with a time constant on the order of ∼1 minute as compared to the current at 10 −6 Pa. The effect was strongly dependent on the gas nature, with Ar and N 2 having larger effects at lower pressures than He and H 2 . The reduction was reversible, with the current increasing to near its original value with a time constant on the order of ∼1–10 minutes after pumping down. The effect of the gas remained in the absence of electric field, whatever the gas pressure. Mechanisms for these and related phenomena are discussed

Tribological and electrical study of Fluorinated Diazonium Films as dry lubricants for electrical contacts

The need to operate in extreme environmental conditions (ultra high vacuum, high temperatures, aerospatial, etc.) and the miniaturisation toward microelectromechanical system is demanding new materials in the field of low-level electrical contacts lubrication. A dry and chemically immobilised layer avoiding the traditional wet lubricating fluids would have many advantages. We report here the first results on films obtained by the electrochemical reduction of different diazonium salts and their use as protective coatings able to lubricate the metallic surfaces of an electrical contact while preserving at the same time electrical conduction. The physicochemical properties of the films, elaborated from various diazonium salts, were studied by cyclic voltammetry and ATR FT-IR spectroscopy. Atomic force microscope was combined with a home-made wide-range current measurement system to investigate simultaneously the mechanical and electrical interactions between the doped diamond conductive tips and the evaporated gold surfaces coated with the diazonium films. The analysis of the simultaneous mechanical and electrical properties of the films in a nanocontact situation is shown to bring much insight into the electrical contact application

Memristive and neuromorphic behavior in a Li x CoO 2 nanobattery

International audienceThe phenomenon of resistive switching (RS), which was initially linked to non-volatile resistive memory applications, has recently also been associated with the concept of memristors, whose adjustable multilevel resistance characteristics open up unforeseen perspectives in cognitive computing. Herein, we demonstrate that the resistance states of Li(x)CoO2 thin film-based metal-insulator-metal (MIM) solid-state cells can be tuned by sequential programming voltage pulses, and that these resistance states are dramatically dependent on the pulses input rate, hence emulating biological synapse plasticity. In addition, we identify the underlying electrochemical processes of RS in our MIM cells, which also reveal a nanobattery-like behavior, leading to the generation of electrical signals that bring an unprecedented new dimension to the connection between memristors and neuromorphic systems. Therefore, these LixCoO2-based MIM devices allow for a combination of possibilities, offering new perspectives of usage in nanoelectronics and bio-inspired neuromorphic circuits

Fretting behaviour of tinned connectors under grease lubrication

International audienceFretting is a well known phenomena due to unwanted micro displacements leading to drastic electrical contact resistance increase. Much work has been done to understand and evaluate the critical parameters in view of finding solutions to alleviate the problem. Several paths have been proposed involving for example connector design and surface modification. The simplest surface modification process is depositing an organic thin film with specific properties. The effect of liquid lubricants on fretting of electrical contacts has been well studied and the lubrication efficiency has been shown to depend on the degradation modes of the contacts which involve the nature and type of metallic surface (Au, Ni, Sn, Ag, plating thickness). Another type of lubrication involves semi liquid films such as greases. While much work has been done on the effect of greases on the fretting-wear of mechanical devices, less has been devoted to electrical contacts. In such field the grease films must also maintain a low electrical resistance for durations corresponding to field service. The work presented here was performed with a standard fretting device imposing controlled constant amplitude sine vibrations under constant normal load to pin on flat tinned contacts. This laboratory test allows comparing the behaviour of different types of greases for a given set of experimental conditions. Different commercial greases are compared involving different thickeners and different base oils. Tests at room temperature show little variations in the electrical behaviour of the grease coated contacts. Nevertheless wear particles dispersion seems to vary. A very high increase of contact resistance is observed in some cases after heat treatment 10 days at 150°C. Polymerization was observed to occur with one of the formulations and it is suggested that the base oil/thickener choice might be unfavourable to contact application

Distribution of intercalated lithium in V2O5 thin films determined by SIMS depth profiling

The distribution of Li in the V2O5 films was determined before and after intercalation/deintercalation electrochemical cycles by time of flight secondary ion mass spectroscopy (ToF-SIMS) depth profiling. On deintercalation most of the inserted Li is removed except in the vicinity of the interface with the fluorine-substituted tin oxide, used as a conducting substrate. More surprisingly, Li was also found in the interface region of the part of the film that has not been immersed in the electrolyte and that had thus not been electrochemically controlled. This finding suggests that Li diffuses through the interface, in the plane of the electrode surface, during intercalation of the main body of the film. The SIMS results have been confirmed by proton beam analysis using the nuclear reaction between H and Li to produce characteristic alpha particles that reveal the distribution of Li, both inside and outside the electrochemically treated area of the electrode. The energy loss of the alpha particles on their way through the sample to the detector also reveals the Li concentration distribution inside the V2O5 films. Copyright (C) 2006 John Wiley & Sons, Ltd

Effect of fluorinated lubricants on the friction modes of tin electrical contacts submitted to fretting

Fretting remains a major cause of connector failure and can impair reliability in complex systems like automotive applications. Tin is particularly previous to fretting phenomena; we report here the first results of an analysis of tin and lubricated tin contacts, based on the analysis of the friction or slip regimes and the electrical behaviour. Lubricant properties are analysed in terms of friction behaviour and the effect of a special additive is examined