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.
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.
Static and dynamic mechanical deflections were eLectrically induced in cantilevered, multiwalled carbon nanotubes in a transmission electron microscope. The nanotubes were resonantly excited at the ...fundamental frequency and higher harmonics as revealed by their deflected contours, which correspond closely to those determined for cantilevered elastic beams. The elastic bending modulus as a function of diameter was found to decrease sharply (from about I to 0.1 terapascals) with increasing diameter (from 8 to 40 nanometers), which indicates a crossover from a uniform elastic mode to an elastic mode that involves wavelike distortions in the nanotube. The quality factors of the resonances are on the order of 500. The methods developed here have been applied to a nanobalance for nanoscopic particles and also to a Kelvin probe based on nanotubes.
Carbon Nanotube Quantum Resistors Frank, Stefan; Poncharal, Philippe; Wang, Z. L. ...
Science,
06/1998, Letnik:
280, Številka:
5370
Journal Article
Recenzirano
Odprti dostop
The conductance of multiwalled carbon nanotubes (MWNTs) was found to be quantized. The experimental method involved measuring the conductance of nanotubes by replacing the tip of a scanning probe ...microscope with a nanotube fiber, which could be lowered into a liquid metal to establish a gentle electrical contact with a nanotube at the tip of the fiber. The conductance of arc-produced MWNTs is one unit of the conductance quantum G$_0$ = 2e$^2$/h = (12.9 kilohms)$^{-1}$. The nanotubes conduct current ballistically and do not dissipate heat. The nanotubes, which are typically 15 nanometers wide and 4 micrometers long, are several orders of magnitude greater in size and stability than other typical room-temperature quantum conductors. Extremely high stable current densities, J > 10$^7$ amperes per square centimeter, have been attained.
Multiwalled carbon nanotubes are shown to be ballistic conductors at room temperature, with mean free paths of the order of tens of microns. The measurements are performed both in air and in high ...vacuum in the transmission electron microscope on nanotubes that protrude from unprocessed arc-produced nanotube-containing fibers that contact with a liquid metal surface. These experiments follow and extend the original experiments by Frank et al. (Science 1998 , 280 1744), which demonstrated for the first time the large current carrying capability, very low intrinsic resistivities, and evidence for quantized conductance. This indicated 1D transport, that only the surface layer contributes to the transport, and ballistic conduction at room temperature. Here, we follow up on the original experiment including in-situ electron microscopy experiments and a detailed analysis of the length dependence of the resistance. The per unit length resistance ρ < 100 Ω/μm, indicating free paths l > 65 μm, unambiguously demonstrates ballistic conduction at room temperature up to macroscopic distances. The nanotube−metal contact resistances are in the range from 0.1 to 1 kΩμm. Contact scattering can explain why the measured conductances are about half of the expected theoretical value of 2 G0. For V > 0.1 V, the conductance rises linearly (dG/dV∼0.3 G0/V) reflecting the linear increase in the density-of-states in a metallic nanotube above the energy gap. Increased resistances (ρ = 2−10 kΩ/μm) and anomalous I−V dependences result from impurities and surfactants on the tubes. Evidence is presented that ballistic transport occurs in undoped and undamaged tubes for which the top layer is metallic and the next layer is semiconducting. The diffusive properties of lithographically contacted multiwalled nanotubes most likely result from purification and other processing steps that damage and dope the nanotubes, thereby making them structurally and electronically different than the pristine nanotubes investigated here.
The formation of carbon nanotubes in a pure carbon arc in a helium atmosphere is found to involve liquid carbon. Electron microscopy shows a viscous liquid-like amorphous carbon layer covering the ...surfaces of nanotube-containing millimeter-sized columnar structures from which the cathode deposit is composed. Regularly spaced, submicrometer-sized spherical beads of amorphous carbon are often found on the nanotubes at the surfaces of these columns. Apparently, at the anode, liquid-carbon drops form, which acquire a carbon-glass surface due to rapid evaporative cooling. Nanotubes crystallize inside the supercooled, glass-coated liquid-carbon drops. The carbon-glass layer ultimately coats and beads on the nanotubes near the surface.
Friction at the nanoscale has revealed a wealth of behaviours that depart strongly from the long-standing macroscopic laws of Amontons-Coulomb. Here, by using a 'Christmas cracker'-type of system in ...which a multiwalled nanotube is torn apart between a quartz-tuning-fork-based atomic force microscope (TF-AFM) and a nanomanipulator, we compare the mechanical response of multiwalled carbon nanotubes (CNTs) and multiwalled boron nitride nanotubes (BNNTs) during the fracture and telescopic sliding of the layers. We found that the interlayer friction for insulating BNNTs results in ultrahigh viscous-like dissipation that is proportional to the contact area, whereas for the semimetallic CNTs the sliding friction vanishes within experimental uncertainty. We ascribe this difference to the ionic character of the BN, which allows charge localization. The interlayer viscous friction of BNNTs suggests that BNNT membranes could serve as extremely efficient shock-absorbing surfaces.
Optomechanics, which explores the fundamental coupling between light and mechanical motion, has made important advances in manipulating macroscopic mechanical oscillators down to the quantum level. ...However, dynamical effects related to the vectorial nature of the optomechanical interaction remain to be investigated. Here we study a nanowire with subwavelength dimensions coupled strongly to a tightly focused beam of light, enabling an ultrasensitive readout of the nanoresonator dynamics. We determine experimentally the vectorial structure of the optomechanical interaction and demonstrate that a bidimensional dynamical backaction governs the nanowire dynamics. Moreover, the spatial topology of the optomechanical interaction is responsible for novel canonical signatures of strong coupling between mechanical modes, which leads to a topological instability that underlies the non-conservative nature of the optomechanical interaction. These results have a universal character and illustrate the increased sensitivity of nanomechanical devices towards spatially varying interactions, opening fundamental perspectives in nanomechanics, optomechanics, ultrasensitive scanning force microscopy and nano-optics.
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