Slippage and boundary layer probed in an almost ideal gas by a nanomechanical oscillator

We have measured the interaction between $^4$He gas at 4.2$~$K and a high-quality nano-electro-mechanical string device for its first 3 symmetric modes (resonating at 2.2$~$MHz, 6.7$~$MHz and 11$~$MHz with quality factor $Q > 0.1$ million) over almost 6 orders of magnitude in pressure. This fluid can be viewed as the best experimental implementation of an almost-ideal monoatomic and inert gas which properties are tabulated. The experiment ranges from high pressure where the flow is of laminar Stokes-type presenting slippage, down to very low pressures where the flow is molecular. In the molecular regime, when the mean-free-path is of the order of the distance between the suspended nano-mechanical probe and the bottom of the trench we resolve for the first time the signature of the boundary (Knudsen) layer onto the measured dissipation. Our results are discussed in the framework of the most recent theories investigating boundary effects in fluids (both analytic approaches and Monte-Carlo DSMC simulations)

Spin-Valve Effect of the Spin Accumulation Resistance in a Double Ferromagnet - Superconductor Junction

We have measured the transport properties of Ferromagnet - Superconductor nanostructures, where two superconducting aluminum (Al) electrodes are connected through two ferromagnetic iron (Fe) ellipsoids in parallel. We find that, below the superconducting critical temperature of Al, the resistance depends on the relative alignment of the ferromagnets' magnetization. This spin-valve effect is analyzed in terms of spin accumulation in the superconducting electrode submitted to inverse proximity effect

Fabrication of stable and reproducible sub-micron tunnel junctions

We have performed a detailed study of the time stability and reproducibility of sub-micron $Al/AlO_{x}/Al$ tunnel junctions, fabricated using standard double angle shadow evaporations. We have found that by aggressively cleaning the substrate before the evaporations, thus preventing any contamination of the junction, we obtained perfectly stable oxide barriers. We also present measurements on large ensembles of junctions which prove the reproducibility of the fabrication process. The measured tunnel resistance variance in large ensembles of identically fabricated junctions is in the range of only a few percents. Finally, we have studied the effect of different thermal treatments on the junction barrier. This is especially important for multiple step fabrication processes which imply annealing the junction.Comment: 4 pages, 3 figure

Transverse conductivity in the sliding CDW state of NbSe_3

The dynamical properties of longitudinal and transverse conduction of NbSe$_3$ single-crystals have been simultaneously studied when the current is applied along the b axis (chain direction). In the vicinity of the threshold electric field for CDW sliding, the transverse conduction sharply decreases. When a rf field is applied, voltage Shapiro steps for longitudinal transport are observed as usual, but also current Shapiro steps in the transverse direction. The possible mechanisms of this effect are discussed.Comment: 4 pages, 5 figures, accepted in PR

On-chip thermometry for microwave optomechanics implemented in a demagnetization cryostat

We report on microwave optomechanics measurements performed on a nuclear adiabatic demagnetization cryostat, whose temperature is determined by accurate thermometry from below 500$~\mu$K to about 1$~$Kelvin. We describe a method for accessing the on-chip temperature, building on the blue-detuned parametric instability and a standard microwave setup. The capabilities and sensitivity of both the experimental arrangement and the developed technique are demonstrated with a very weakly coupled silicon-nitride doubly-clamped beam mode of about 4$~$MHz and a niobium on-chip cavity resonating around 6$~$GHz. We report on an unstable intrinsic driving force in the coupled microwave-mechanical system acting on the mechanics that appears below typically 100$~$mK. The origin of this phenomenon remains unknown, and deserves theoretical input. It prevents us from performing reliable experiments below typically 10-30$~$mK; however no evidence of thermal decoupling is observed, and we propose that the same features should be present in all devices sharing the microwave technology, at different levels of strengths. We further demonstrate empirically how most of the unstable feature can be annihilated, and speculate how the mechanism could be linked to atomic-scale two level systems. The described microwave/microkelvin facility is part of the EMP platform, and shall be used for further experiments within and below the millikelvin range.Comment: 14 pages with appendi

Spin-valve effect of spin-accumulation resistance in a double ferromagnet/superconductor junction

International audienc

Spin-valve effect of spin-accumulation resistance in a double ferromagnet/superconductor junction

International audienc

Thermoelectric nanogenerator networks: a viable source of power for autonomous wireless sensors

International audienc

Neuron-gated silicon nanowire field effect transistors to follow single spike propagation within neuronal network

International audienceSilicon nanowire field effect transistors SiNW-FETs provide a local probe for sensing neuronal activity at the subcellular scale, thanks to their nanometer size and ultrahigh sensitivity. The combination with micro-patterning or microfluidic techniques to build model neurons networks above SiNW arrays could allow monitoring spike propagation and tailor specific stimulations, being useful to investigate network communications at multiple scales, such as plasticity or computing processes. This versatile device could be useful in many research areas, including diagnosis, prosthesis, and health security. Using top-down silicon nanowires-based array, we show here the ability to record electrical signals from matured neurons with top-down silicon nanowires, such as local field potential and unitary spike within ex-vivo preparations and hippocampal neurons grown on chip respectively. Furthermore, we demonstrate the ability to guide neurites above the sensors array during 3 weeks of cultures and follow propagation of spikes along cells. Silicon nanowire field effect transistors are obtained by top-down approach with CMOS compatible technology, showing the possibility to implement them at manufacturing level. These results confirm further the potentiality of the approach to follow spike propagation over large distances and at precise location along neuronal cells, by providing a multiscale addressing at the nano and mesoscales