Jump-to-contact instability: The nanoscale mechanism of droplet coalescence in air

We study experimentally by means of atomic force microscopy (AFM) the jump-to-contact instability between two droplets in air, with radii ranging between 0.7 and 74 μm. This instability which occurs at the nanoscale is responsible for droplet coalescence. The AFM experiments were conducted in contact and frequency-modulation modes where the interaction force and the frequency shift are monitored while the two droplet interfaces approach each other. The critical distance d_min at which the jump to contact takes place is determined by fitting the experimental curves by the theoretical expressions for theforce and the frequency shift. The results point out the existence of two regimes. For submicrometer droplets, d_min scales as (HReq/γ)^1/3 where Req is the equivalent droplet radius,H the Hamaker constant, and γ the surface tension of the liquid. For larger droplets,d_min no longer depends on the droplet size and scales as (H/γ)^1/2. This second scaling is the one that controls droplet coalescence in most situations

MUJER CON NIÑO EN BRAZOS [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201

Dynamics of anchored oscillating nanomenisci

We present a self-contained study of the dynamics of oscillating nanomenisci anchored on nanometric topographical defects around a cylindrical nanofiber with a radius below 100 nm. Using frequency-modulation atomic force microscopy (FM-AFM), we show that the friction coefficient surges as the contact angle is decreased. We propose a theoretical model within the lubrification approximation that reproduces the experimental data and provides a comprehensive description of the dynamics of the nanomeniscus. The dissipation pattern in the vicinity of the contact line and the anchoring properties are discussed as a function of liquid and surface properties in addition to the forcing conditions

Nanodevices for correlated electrical transport and structural investigation of individual carbon nanotubes

We report a new approach to the correlation of the structural properties and the transport properties of carbon nanotubes. Through an original combination of UV lithography, custom-made photosensitive sol–gel resist and deep reactive ion etching (RIE), we have successfully integrated membrane technology and nanodevice fabrication for the electrical connection of individual carbon nanotubes. After single wall nanotube (SWNT) deposition by molecular combing and contacting using high resolution electron beam lithography, we obtain a device that allows both the investigation of the nanotubes and the contact regions by transmission electron microscopy (TEM) and the measurement of the electronic transport properties of the same individual nano-object. The whole fabrication process is detailed and the demonstration that the micro membranes are suitable for both TEM inspection and nanoelectrode fabrication is given

Molecular desorption by a moving contact line

The interaction of the contact line with topographical or chemical defects at the nanometer scale sets the macroscopic wetting properties of a liquid on a solid substrate. Based on specific atomic force microscopy (AFM) experiments, we demonstrate that molecules physically sorbed on a surface are removed by a dynamic contact line. The mechanism of molecules desorption is directly determined by the capillary force exerted at the contact line on the molecules. We also emphasize the potential of AFM to clearly decorrelate the effects of topographical and chemical defects and monitor, with a subsecond time resolution, the dynamics of molecules adsorption on a surface

Near-field deformation of a liquid interface by atomic force microscopy

We experiment the interaction between a liquid puddle and a spherical probe by Atomic Force Microscopy (AFM) for a probe radius R ranging from 10 nm to 30 μm. We have developed a new experimental setup by coupling an AFM with a high-speed camera and an inverted optical microscope. Interaction force-distance curves (in contact mode) and frequency shift–distance curves (in frequency modulation mode) are measured for different bulk model liquids for which the probe-liquid Hamaker constant Hpl is known. The experimental results, analyzed in the frame of the theoretical model developed in Phys. Rev. Lett. 108, 106104 (2012) and Phys. Rev. E 85, 061602 (2012), allow to determine the “jump-to-contact” critical distance dmin below which the liquid jumps and wets the probe. Comparison between theory and experiments shows that the probe-liquid interaction at nanoscale is controlled by the liquid interface deformation. This work shows a very good agreement between the theoretical model and the experiments and paves the way to experimental studies of liquids at the nanoscale

Alignment and nano-connections of isolated carbon nanotubes

We report a new approach for the alignment and the electrical nano-connection of isolated carbon nanotubes (CNTs). Through a novel combination of proven technics, we have been able to align isolated carbon nanotubes and selectively contact those CNTs by high resolution electron beam lithography (HREBL). Resistance versus temperature (R(T)) experiments have been carried out to determine the reliability of the metal–CNTs interface and to probe the electronic conductance of the CNT

Probing the electronic properties of individual carbon nanotube in 35 T pulsed magnetic field

After optimization of the alignment and the nano-contact processes of isolated single wall and double-walls carbon nanotube, we investigate the high magnetic field effects on the electronic transport properties of an individual metallic CNT. We develop pioneer multi-probes magneto-transport experiments under a 35 T pulsed field which reveal an unexpected oscillatory behavior of RðHÞ inconsistent with existing theories

Unconventional magnetotransport phenomena in individual carbon nanotubes

We investigate the quantum transport in different individual carbon nanotubes in the light of magneto-transport experiments in intense (60T pulsed)magnetic field. Large magnetic fields are required to probe field dependent gap modulation and quantum interference effects along the circumference of the tube. Such experiments along with a control of the electrostatic doping of the tube by a back-gate voltage constitute an unique tool to explore the exceptional electronic properties of this material. We bring evidence that the field dependence of the conductivity is a fingerprint of the electronic conduction modes and their interplay with the band structure (helicity), the static disorder and the location of the Fermi level of the tube. We infer the characteristic lengths of the electronic transport (the electronic mean free path and the phase coherence length) which are differently modified by the Fermi level location, depending on the disorder

Long-range hydrodynamic forces in liquid FM-AFM

We study the effects of hydrodynamic forces in frequency-modulation AFM experiments (FM-AFM) in liquid. We first establish the theoretical equations needed to derive the interaction stiffness k_int and the damping β_int due to the hydrodynamic forces from the frequency shift and the excitation amplitude. We develop specific FM-AFM experiments to measure the variation of k_int and β_int over a large range of distance in water up to 200 μm. Comparison between theory and experiments point out that the evolution of k_int at short and long distance arises from unsteady hydrodynamic forces on the cantilever. On the other hand, βint is small at long distance and diverges at short probe-surface distance, as predicted by the classical Reynolds sphere model