P. Poncharal

Giant osmotic energy conversion measured in a single transmembrane boron nitride nanotube

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.

In situ imaging of field emission from individual carbon nanotubes and their structural damage

Field emission of individual carbon nanotubes was observed by in situ transmission electron microscopy. A fluctuation in emission current was due to a variation in distance between the nanotube tip and the counter electrode owing to a “head-shaking” effect of the nanotube during field emission. Strong field-induced structural damage of a nanotube occurs in two ways: a piece-by-piece and segment-by-segment pilling process of the graphitic layers, and a concentrical layer-by-layer stripping process. The former is believed owing to a strong electrostatic force, and the latter is likely due to heating produced by emission current that flowed through the most outer graphitic layers.

Raman spectra of misoriented bilayer graphene

We compare the main feature of the measured Raman scattering spectra from single layer graphene with a bilayer in which the two layers are arbitrarily misoriented. The profiles of the 2D bands are very similar having only one component, contrary to the four found for commensurate Bernal bilayers. These results agree with recent theoretical calculations and point to the similarity of the electronic structures of single layer graphene and misoriented bilayer graphene. Another new aspect is that the dependance of the 2D frequency on the laser excitation energy is different in these two latter systems.

Measuring physical and mechanical properties of individual carbon nanotubes by in situ TEM

Nanomaterials are a fundamental component of nanoscience and nanotechnology. The small size of nanostructures constrains the applications of well-established testing and measurement techniques, thus new methods and approaches must be developed for synthesis, property characterization and device fabrication. This has been the focus of our research, aiming at exploring state-of-the-art techniques for materials processing and characterization. This paper reviews our progress in using in situ transmission electron microscopy to measure the electric, mechanical and field emission properties of individual carbon nanotubes with well-defined structures. Quantum conductance was observed in defect-free nanotubes, which led to the transport of a superhigh current density at room temperature without heat dissipation. A nanobalance technique is demonstrated that can be applied to measure the mass of a tiny particle as light as 22 fg O 1f a 10 215 U: q 2000 Elsevier Science Ltd. All rights

Mechanical and electrostatic properties of carbon nanotubes and nanowires

Nano-scale manipulation and property measurements of individual nanowire-like structure is challenged by the small size of the structure. Scanning probe microscopy has been the dominant tool for property characterizations of nanomaterials. We have developed an alternative novel approach that allows a direct measurement of the mechanical and electrical properties of individual nanowire-like structures by in situ transmission electron microscopy (TEM). The technique is unique in a way that it can directly correlate the atomic-scale microstructure of the nanowire with its physical properties. This paper reviews our current progress in applying the technique in investigating the mechanical and electron field emission properties of carbon nanotubes and nanowires.

Nanomeasurements of individual carbon nanotubes by in situ TEM

Property characterization of nanomaterials is challenged by the small size of the structure because of the difficulties in manipulation. Here we demonstrate a novel approach that allows a direct measurement of the mechanical and electrical properties of individual nanotube-like structures by in situ transmission electron microscopy (TEM). The technique is powerful in a way that it can be directly correlated to the atomic-scale microstructure of the carbon nanotube with its physical properties, thus providing a complete characterization of the nanotube. Applications of the technique will be demonstrated in measurements of the mechanical properties, the electron field emission, and the ballistic quantum conductance of individual carbon nanotubes. A nanobalance technique is demonstrated that can be applied to measure the mass of a single tiny particle as light as 22 fg (1 f = 10-15 ).

Pressure-Mediated Doping in Graphene

Exfoliated graphene and few layer graphene samples supported on SiO(2) have been studied by Raman spectroscopy at high pressure. For samples immersed on a alcohol mixture, an electron transfer of ∂n/∂P ∼ 8 × 10(12) cm(-2) GPa(-1) is observed for monolayer and bilayer graphene, leading to giant doping values of n ∼ 6 × 10(13) cm(-2) at the maximum pressure of 7 GPa. Three independent and consistent proofs of the doping process are obtained from (i) the evolution of the Raman G-band to 2D-band intensity ratio, (ii) the pressure coefficient of the G-band frequency, and (iii) the 2D band components splitting in the case of the bilayer sample. The charge transfer phenomena is absent for trilayer samples and for samples immersed in argon or nitrogen. We also show that a phase transition from a 2D biaxial strain response, resulting from the substrate drag upon volume reduction, to a 3D hydrostatic compression takes place when going from the bilayer to the trilayer sample. By model calculations we relate this transition to the unbinding of the graphene-SiO(2) system when increasing the number of graphene layers and as function of the surface roughness parameters. We propose that the formation of silanol groups on the SiO(2) substrate allows for a capacitance-induced substrate-mediated charge transfer.

A universal and ultrasensitive vectorial nanomechanical sensor for imaging 2D force fields

The miniaturization of force probes into nanomechanical oscillators enables ultrasensitive investigations of forces on dimensions smaller than their characteristic length scales. It also unravels the vectorial character of the force field and how its topology impacts the measurement. Here we present an ultrasensitive method for imaging two-dimensional vectorial force fields by optomechanically following the bidimensional Brownian motion of a singly clamped nanowire. This approach relies on angular and spectral tomography of its quasi-frequency-degenerated transverse mechanical polarizations: immersing the nanoresonator in a vectorial force field not only shifts its eigenfrequencies but also rotates the orientation of the eigenmodes, as a nanocompass. This universal method is employed to map a tunable electrostatic force field whose spatial gradients can even dominate the intrinsic nanowire properties. Enabling vectorial force field imaging with demonstrated sensitivities of attonewton variations over the nanoprobe Brownian trajectory will have a strong impact on scientific exploration at the nanoscale.Miniaturization of force probes into nanomechanical oscillators enables ultrasensitive investigations of forces on dimensions smaller than their characteristic length scale. Meanwhile it also unravels the force field vectorial character and how its topology impacts the measurement. Here we expose an ultrasensitive method to image 2D vectorial force fields by optomechanically following the bidimensional Brownian motion of a singly clamped nanowire. This novel approach relies on angular and spectral tomography of its quasi frequency-degenerated transverse mechanical polarizations: immersing the nanoresonator in a vectorial force field does not only shift its eigenfrequencies but also rotate eigenmodes orientation as a nano-compass. This universal method is employed to map a tunable electrostatic force field whose spatial gradients can even take precedence over the intrinsic nanowire properties. Enabling vectorial force fields imaging with demonstrated sensitivities of attonewton variations over the nanoprobe Brownian trajectory will have strong impact on scientific exploration at the nanoscale.

EFFECT OF GAS ADSORPTION ON THE ELECTRICAL PROPERTIES OF SINGLE WALLED CARBON NANOTUBES MATS

Single wall nanotubes have been made by arc-discharge method. Residual impurities (fullerenes, amorphous carbon, catalyst metals…) have been removed by tangential filtration process followed by high temperature annealing under vacuum (1200 °C). In this work we present results on the influence of the surrounding gas nature (N 2 , H 2 , CO 2 , H 2 O…) on the electrical resistivity of carefully outgassed mat of such samples. In particular, we have observed that the sample resistance exhibits a strong dependence on water contamination during the transfer to the measurement reactor.

Contacts, non-linear transport effects and failure in multi-walled carbon nanotubes

Pristine arc-produced multi-walled carbon nanotubes are contacted to liquid mercury in situ in a transmission electron microscope. The conductance G(V) for all tubes increases with increasing bias voltage V. This is related to the electronic density of the nanotubes. Similar G(V) behaviour is observed for HOPG-graphite contacted in air with Hg, with dG(V)/dV~0.3G0. Variations observed in the conductance are related to nanotube–Hg contact effects. For tubes barely touching the Hg surface, the conductance is low (typically G(V=0)~0.1–0.5G0); G(V) may maximize around V=1.5–2 V or continue to increase linearly depending on the MWNT–Hg contact. For good contacts the maximum low-bias conductance is 1G0. Non-conducting tubes are observed having a low-bias conductance smaller than 10−3G0. High-voltage tube failure usually occurs at the contact with Hg for clean tubes, or at tube defects. An important phenomenon is the formation of a Hg bubble near the contact nanotube–Hg surface when the nanotube is negatively biased, under high bias current conditions, indicating the heating effect of hot electrons injected into the mercury.