New models of fluid transport are expected to emerge from the confinement of liquids at the nanoscale, with potential applications in ultrafiltration, desalination and energy conversion. Nevertheless, advancing our fundamental understanding of fluid transport on the smallest scales requires mass and ion dynamics to be ultimately characterized across an individual channel to avoid averaging over many pores. A major challenge for nanofluidics thus lies in building distinct and well-controlled nanochannels, amenable to the systematic exploration of their properties. Here we describe the fabrication and use of a hierarchical nanofluidic device made of a boron nitride nanotube that pierces an ultrathin membrane and connects two fluid reservoirs. Such a transmembrane geometry allows the detailed study of fluidic transport through a single nanotube under diverse forces, including electric fields, pressure drops and chemical gradients. Using this device, we discover very large, osmotically induced electric currents generated by salinity gradients, exceeding by two orders of magnitude their pressure-driven counterpart. We show that this result originates in the anomalously high surface charge carried by the nanotube's internal surface in water at large pH, which we independently quantify in conductance measurements. The nano-assembly route using nanostructures as building blocks opens the way to studying fluid, ionic and molecule transport on the nanoscale, and may lead to biomimetic functionalities. Our results furthermore suggest that boron nitride nanotubes could be used as membranes for osmotic power harvesting under salinity gradients.

Simulations and measurements have established that water moves through carbon nanotubes with exceptionally high rates due to nearly frictionless interfaces1–4. These observations have stimulated interest in nanotube-based membranes for applications that range from desalination to nano-filtration and energy harvesting5–10, yet the exact water transport mechanisms inside the nanotubes and at the water-carbon interface continue to be controversially discussed11,12 because existing theories fail to provide a satisfying explanation for the limited number of experimental results available to date13. This is because even though controlled and systematic studies have explored transport through individual nanotubes8,9,14–7, none has met the considerable technical challenge of unambiguously measuring the permeability of a single nanotube11. Here we show that the pressure-driven flow rate across individual nanotubes can be determined with unprecedented sensitivity and without dyes from the hydrodynamics of water jets as they emerge from single nanotubes into a surrounding fluid. Our measurements reveal unexpectedly large and radius-dependent surface slippage in carbon nanotubes (CNT), and no slippage in boron-nitride nanotubes (BNNT) that are crystallographically similar to CNTs but differ electronically. This pronounced contrast between the two systems must originate from subtle differences in atomic-scale details of their solid-liquid interfaces, strikingly illustrating that nanofluidics is the frontier where the continuum picture of fluid mechanics confronts the atomic nature of matter.

International audienceHeat can be exchanged between two surfaces through emission and absorption of thermal radiation. It has been predicted theoretically that for distances smaller than the peak wavelength of the blackbody spectrum, radiative heat transfer can be increased by the contribution of evanescent waves(1-8). This contribution can be viewed as energy tunnelling through the gap between the surfaces. Although these effects have already been observed(9-14), a detailed quantitative comparison between theory and experiments in the nanometre regime is still lacking. Here, we report an experimental setup that allows measurement of conductance for gaps varying between 30 nm and 2.5 mu m. Our measurements pave the way for the design of submicrometre nanoscale heaters that could be used for heat-assisted magnetic recording or heat-assisted lithography

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A single Nitrogen Vacancy (NV) center hosted in a diamond nanocrystal is positioned at the extremity of a SiC nanowire. This novel hybrid system couples the degrees of freedom of two radically different systems, i.e. a nanomechanical oscillator and a single quantum object. The dynamics of the nano-resonator is probed through time resolved nanocrystal fluorescence and photon correlation measurements, conveying the influence of a mechanical degree of freedom given to a non-classical photon emitter. Moreover, by immersing the system in a strong magnetic field gradient, we induce a magnetic coupling between the nanomechanical oscillator and the NV electronic spin, providing nanomotion readout through a single electronic spin. Spin-dependent forces inherent to this coupling scheme are essential in a variety of active cooling and entanglement protocols used in atomic physics, and should now be within the reach of nanomechanical hybrid systems.Owing to recent developments in cavity opto-and electro-mechanics [1-3], it is now realistic to envision the observation of macroscopic mechanical oscillators cooled by active or traditional cryogenic techniques close to their ground state of motion. This conceptually elegant accomplishment would give access to a vast playground for physicists if the resonator wavefunction could be coherently manipulated such as to create, maintain and probe Fock or other non-classical states. It would provide a remarkable opportunity to extend the pioneering experiments with trapped ions [4] to encompass macroscopic objects. However, standard continuous measurements techniques used to actively cool and probe the resonator [5], when utilized to manipulate its quantum state, tend to blur its non-classical nature. An attractive alternative consists in interfacing the mechanical degrees of freedom with a single quantum object such as a 2-level system whose quantum state can be externally controlled [6][7][8][9][10][11]. Successful realization of this type of coupling between a nanomechanical oscillator in the quantum regime and a phase qubit was recently reported [12] and motivates the development of similar hybrid quantum systems presenting extended coherence times at room temperature and compatible with continuous measurement approaches.Here we report a first step in this direction by coupling a nanomechanical oscillator to a single negatively-charged Nitrogen Vacancy (NV) defect hosted in a diamond nanocrystal attached to its extremity (fig 1a). In that context, the NV defect appears as an attractive quantum system, both for its optical and electronic spin properties. Indeed, perfect photostability at room temperature makes the NV defect a robust and practical single-photon source [13,14]. Moreover, the NV defect ground state is a spin triplet (fig 1b) which can be initialized and read-out by optical means, and manipulated by resonant microwave excitation with an unprecedented coherence time for a solid-state system under ambient conditions [15,16]. Such properties are at the heart of diamond-base...

In this Letter, we perform an experimental study of ionic transport and current fluctuations inside individual carbon nanotubes (CNTs). The conductance exhibits a power law behavior at low salinity, with an exponent close to 1/3 versus the salt concentration in this regime. This behavior is rationalized in terms of a salinity dependent surface charge, which is accounted for on the basis of a model for hydroxide adsorption at the (hydrophobic) carbon surface. This is in contrast to boron nitride nanotubes which exhibit a constant surface conductance. Further, we measure the low frequency noise of the ionic current in CNTs and show that the amplitude of the noise scales with the surface charge, with data collapsing on a master curve for the various studied CNTs at a given pH.

The field of nanofluidics has shown considerable progress over the past decade thanks to key instrumental advances, leading to the discovery of a number of exotic transport phenomena for fluids and ions under extreme confinement. Recently, van der Waals assembly of 2D materials 1 allowed fabrication of artificial channels with ångström-scale precision 2 . This ultimate confinement to the true molecular scale revealed unforeseen behaviour for both mass 2 and ionic 3 transport. In this work, we explore pressure-driven streaming in such molecular-size slits and report a new electro-hydrodynamic effect under coupled pressure and electric force. It takes the form of a transistor-like response of the pressure induced ionic streaming: an applied bias of a fraction of a volt results in an enhancement of the streaming mobility by up to 20 times. The gating effect is observed with both graphite and boron nitride channels but exhibits marked materialdependent features. Our observations are rationalized by a theoretical framework for the flow dynamics, including the frictional interaction of water, ions and the confining surfaces as a key ingredient. The material dependence of the voltage modulation can be traced back to a contrasting molecular friction on graphene and boron nitride. The highly nonlinear transport under molecular-scale confinement offers new routes to actively control molecular and ion transport and design elementary building blocks for artificial ionic machinery, such as ion pumps. Furthermore, it provides a versatile platform to explore electro-mechanical couplings potentially at play in recently discovered mechanosensitive ionic channels 4 .

Ion transport through nanopores drilled in thin membranes is central to numerous applications, including biosensing and ion selective membranes. This paper reports experiments, numerical calculations, and theoretical predictions demonstrating an unexpectedly large ionic conduction in solid-state nanopores, taking its origin in anomalous entrance effects. In contrast to naive expectations based on analogies with electric circuits, the surface conductance inside the nanopore is shown to perturb the three-dimensional electric current streamlines far outside the nanopore in order to meet charge conservation at the pore entrance. This unexpected contribution to the ionic conductance can be interpreted in terms of an apparent electric size of the solid-state nanopore, which is much larger than its geometric counterpart whenever the number of charges carried by the nanopore surface exceeds its bulk counterpart. This apparent electric size, which can reach hundreds of nanometers, can have a major impact on the electrical detection of translocation events through nanopores, as well as for ionic transport in biological nanopores.