High-frequency nanotube mechanical resonators

We report on a simple method to fabricate high-frequency nanotube mechanical resonators reproducibly. We measure resonance frequencies as high as 4.2 GHz for the fundamental eigenmode and 11 GHz for higher order eigenmodes. The high-frequency resonances are achieved using short suspended nanotubes and by introducing tensile stress in the nanotube. These devices allow us to determine the coefficient of the thermal expansion of an individual nanotube, which is negative and is about -0.7E-5 1/K at room temperature. High-frequency resonators made of nanotubes hold promise for mass sensing and experiments in the quantum limit

Laser heating control with polarized light in isolated multi-walled carbon nanotubes

We are proposing a novel method of laser heating control only through change in polarization of the incident light, keeping its power density constant. The idea combines antenna effect found in isolated multi-walled carbon nanotubes and the possibility of their heating by light illumination. To observe this we used Raman spectroscopy technique, where the heating manifests itself in a pronounced downshift of the Raman G and 2D lines as a function of the polarization angle. Our method can be useful in field electron emission devices or in selective nanotubes heating and destruction. It can also be extended to other one dimensional nanoobjects, if only certain conditions are fulfilled.Comment: 11 page

Characterization of ion/electron beam induced deposition of electrical contacts at the sub-{\mu}m scale

We investigate the fabrication of electrical contacts using ion- and electron-beam induced deposition of platinum at the sub-\mu m scale. Halos associated with the metal surface decoration are characterized electrically in the 0.05-2 \mu m range using transport measurements, conducting atomic force microscopy and Kelvin probe microscopy. In contrast with IBID, EBID electrodes exhibit weakly conductive halos at the sub-\mu m scale, and can thus be used to achieve resist-free electrical contacts for transport measurements at the sub-\mu m scale. Four-point transport measurements using \mu m-spaced EBID contacts are provided in the case of a multiwalled carbon nanotube

Nonlinear damping in mechanical resonators based on graphene and carbon nanotubes

Carbon nanotubes and graphene allow fabricating outstanding nanomechanical resonators. They hold promise for various scientific and technological applications, including sensing of mass, force, and charge, as well as the study of quantum phenomena at the mesoscopic scale. Here, we have discovered that the dynamics of nanotube and graphene resonators is in fact highly exotic. We propose an unprecedented scenario where mechanical dissipation is entirely determined by nonlinear damping. As a striking consequence, the quality factor Q strongly depends on the amplitude of the motion. This scenario is radically different from that of other resonators, whose dissipation is dominated by a linear damping term. We believe that the difference stems from the reduced dimensionality of carbon nanotubes and graphene. Besides, we exploit the nonlinear nature of the damping to improve the figure of merit of nanotube/graphene resonators.Comment: main text with 4 figures, supplementary informatio

Novel Approach for Energy Spectrum Probing in Semiconducting Quantum Dots

A new technique has been used to probe the electronic properties of quantum dots. Here we discuss the case of semiconducting CdSe dots. This technique allows us to fill (or empty) semiconducting quantum dot with many electrons. The detection scheme is based on an original approach where the investigated particle is attached to only one electrode, a carbon nanotube. The conductance of the nanotube is measured as a function of a gate voltage $(V_{g}),$ which allows the detection of individual electrons transferred onto the quantum dot. For certain range of $V_{g}$ we noticed no electron transfer which is attributed to the energy gap of the CdSe quantum dot. Our study shows that single-electron detection with carbon nanotube transistor represents a new strategy to study the separation between the electronic discrete energy levels of the semiconducting quantum dot

Optical Interference Effects in Visible-Near Infrared Spectral Range for Arrays of Vertically Aligned Multiwalled Carbon Nanotubes

Based on the reflectance spectra for radiation wavelength from about 380 nm to 1.8 μm, the optical interference effects in vertically aligned multiwalled carbon nanotubes films are studied. We performed the measurements for two complementary polarization states of incoming radiation (s- and p-polarization) for nanotubes arrays sparse enough for interference effects to be possible to observe. By performing the measurements for different wavelengths and incidence angles, we mapped the evolution of interference maxima/minima of reflectance signal. The results from this novel approach indicate that for the radiation polarized perpendicularly to tubes axis (s-polarization), the real part of the effective refractive index can be estimated from the classic Fabry-Pérot model. In order to describe the differences between spectra obtained for s- and p-polarizations we discuss the most important factors that affect the reflectance signal in case of investigated nanotubes arrays

Charging and discharging of graphene in ambient conditions studied with scanning probe microscopy

4 páginas, 3 figuras.-- Trabajo presentado como comunicación oral a la "European Conference on Surface Science ECOSS27" celbrado en Holanda en septiembre de 2010: http://www.ecoss27.eu/By means of scanning probe microscopy we are able to inject charges in isolated graphene sheets deposited on SiO2/Si wafers and characterize the discharge induced by water in controlled ambient conditions. Contact potential differences between the graphene surface and the probe tip, measured by Kelvin probe microscopy, show a linear relationship with the tip bias during charge injection. The discharge depends on relative humidity and decays exponentially with time constants of the order of tens of minutes. We propose that graphene discharges through the water film adsorbed on the SiO2 surface.This work was supported by the Ministerio de Educación y Ciencia (MEC), Spain, through Grant No. FIS2006-12117- C04-01, and by the EXPLORA program NAN2007-29375-E.Peer reviewe

Kinetics of the thermal reduction process in graphene oxide thin films from in-situ transport measurements

We investigate the influence of the thermal annealing process on the transport properties of thin films made of graphene oxide. Specially developed methodology allows us to demonstrate that the thermal annealing process of graphene oxide thin films can be described as a kinetic process with one activation energy, which equals 0.94 eV ± 0.12 eV. Moreover, we show that the electrical transport mechanism evolves with the annealing temperature (reduction level) of GO thin films. We have noticed that the Variable Range Hopping transport model change from 3D, 2D to Efros-Shklvoskii with a reduction level. Our findings contribute to further understanding of the role of kinetics in thermal reduction processes of thin films made of graphene oxide and could be useful in applications in which electrical parameters need to be tuned