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International audience; Radio-Frequency (RF) contacts are key components on the International Thermonuclear Experimental Reactor (ITER) Ion Cyclotron Resonance Heating (ICRH) antenna, and these components are facing big challenges such as 2 kA operation current load and intensive sliding under up to 250 °C in high vacuum. Stainless steel (SS) 316L and CuCrZr are most likely to be applied as base materials for the conductor and the RF contacts louvers. To evaluate the performance of the selected materials, their electrical and tribological behaviors have to be studied. A multifunctional tribometer which can mimic the ITER ICRH RF contacts' relevant working conditions was designed and built in CEA. The contact resistance (Rc) and coefficient of friction (CoF) of CuCrZr-316L pair were researched on this tribometer.

While some applications of Micro-ElectroMechanical Systems (MEMS) have been successfully marketed in recent years (airbag accelerometers, micromirror arrays, pressure sensors), most of the micro-scale systemes, integrating surfaces in contact, suffer from reliability problems. Stiction, friction and wear phenomena can indeed lead to the early failure of the MEMS components. Recent studies highlight the interest of depositing dedicated coatings on MEMS components to increase their life duration. Indeed monolayer lubricant coatings (Flater, 2006), or thin coatings of SiC (Ashurst, 2004), Al2O3 (Mayer, 2003) or Diamond Like Carbon (Smallwood, 2006) have been evaluated in MEMS situ. This study investigates the effect of carbon-based coating deposited locally by Electron Beam Induced Deposition (EBID) on the contacting parts of nano-battering ram (van Spengen, 2006) and MEMS tribometer (van Spengen, to be published). These two recently developed MEMS systems allow measuring dynamically, on-chip and in-situ the adhesive and frictional properties of MEMS-scale contact geometries. Performances of coated and uncoated MEMS components have thus been compared and complemented by Scanning Electron Microscope analyses.

Conference held at Kanazawa, JAPAN, 16-19 October 2006. Presentation was "Best Poster" Awarded; International audience; Among Diamond-Like Carbon (DLC), some hydrogenated amorphous carbon (a-C:H) coatings may exhibit superlow friction behavior (i.e. friction coefficient in the millirange) under Ultra-High Vacuum environment. Hydrogen content, environment and some mechanical properties have been identified as key-requirements to achieve such low coefficient of friction. Nevertheless, this exceptional friction regime may last only few hundreds of cycles depending on the film nature. It is believed that adhesive phenomena may account for such drastic friction increase. In order to better understand the tribological mechanisms governing the achievement and loss of superlow friction, comparison of the wear tracks at different stages of friction with pristine surfaces have been performed by Atomic Force Microscopy (AFM) in contact mode. While surface of a-C:H films appears smooth by conventional means of observation, AFM revealed a nanostructured surface with pads of about 10 nm height and 100 nm wide. The wear of these pads during sliding seems to be correlated with the loss of superlow friction. The relations between topography and superlubricity of such materials will thus be discussed.

Diamond-Like Carbon (DLC) films have been shown to demonstrate various tribological behaviors: in ultra-high vacuum (UHV), with either friction coefficients as low as 0.01 or less and very mild wear, or very high friction coefficients (>0.4) and drastic wear. These behaviors depend notably on gaseous environment, hydrogen content of the film [1], and on its viscoplastic properties [2,3]. A relation between superlow friction in UHV and viscoplasticity has indeed been established for a-C:H films and confirmed for a fluorinated sample (a-C:F:H). In this study, nanoindentation and nanoscratch tests were conducted in ambient air, using a nanoindentation apparatus, in order to evaluate tribological behaviors, as well as mechanical and viscoplastic properties of different amorphous carbon films., Conference was held in Kobe, JAPAN 29th of May to 2nd of June 2005

Conference was held in Anaheim, CA, USA 28th of March to 1rst of April 2004; International audience; The aim of this study is to estimate the influence of water vapor environment on the nanotribological properties of carbon nanotubes coatings. They consist of perpendicularly aligned Multi Wall Carbon NanoTubes (MWCNT) with about 20 nm in diameter and 5 µm long, deposited on the Si (001) substrate by Chemical Vapor Deposition. Experiments were performed with an Atomic Force Microscope under varying relative humidity (0% to 100%). Through normal and lateral modes, adhesion and friction forces between the sample and the gold tip were measured respectively. The coatings present very low adhesion to the tip independently of humidity, probably due to the absence of water meniscus, linked to nanotubes' high hydrophobicity. High friction coefficients of 1~2 have been measured, irrespective of the humidity. A difference of surface chemistry between top and wall of nanotubes, bending behavior during friction, or transfer of nanotubes to the tip may relate to this anomalous tribological property.