Ultrasensitive magnetometers based on carbon-nanotube mechanical resonators.

We describe herein how a nanoelectromechanical system based on a carbon nanotube used as a force sensor can enable one to assess the magnetic properties of a single and very small nano-object grafted onto the nanotube. Numerical simulations performed within the framework of the Euler-Bernoulli theory of beams predict that the magnetic field dependence of the nanotube mechanical resonance frequency is a direct probe for the nano-object magnetic properties and that a sensitivity around a few (few hundreds) Bohr magnetic moments at low temperature (room temperature) can be expected.

Ultrasensitive mass sensing with a nanotube electromechanical resonator.

Shrinking mechanical resonators to submicrometer dimensions (approximately 100 nm) has tremendously improved capabilities in sensing applications. In this Letter, we go further in size reduction using a 1 nm diameter carbon nanotube as a mechanical resonator for mass sensing. The performances, which are tested by measuring the mass of evaporated chromium atoms, are exceptional. The mass responsivity is measured to be 11 Hz x yg(-1) and the mass resolution is 25 zg at room temperature (1 yg = 10(-24) g and 1 zg = 10(-21) g). By cooling the nanotube down to 5 K in a cryostat, the signal for the detection of mechanical vibrations is improved and corresponds to a resolution of 1.4 zg.

Imaging mechanical vibrations in suspended graphene sheets.

We carried out measurements on nanoelectromechanical systems based on multilayer graphene sheets suspended over trenches in silicon oxide. The motion of the suspended sheets was electrostatically driven at resonance using applied radio frequency voltages. The mechanical vibrations were detected using a novel form of scanning probe microscopy, which allowed identification and spatial imaging of the shape of the mechanical eigenmodes. In as many as half the resonators measured, we observed a new class of exotic nanoscale vibration eigenmodes not predicted by the elastic beam theory, where the amplitude of vibration is maximum at the free edges. By modeling the suspended sheets with the finite element method, these edge eigenmodes are shown to be the result of nonuniform stress with remarkably large magnitudes (up to 1.5 GPa). This nonuniform stress, which arises from the way graphene is prepared by pressing or rubbing bulk graphite against another surface, should be taken into account in future studies on electronic and mechanical properties of graphene.

Aharonov-Bohm conductance modulation in ballistic carbon nanotubes.

We report on magnetoconductance experiments in ballistic multiwalled carbon nanotubes threaded by magnetic fields as large as 55 T. In the high temperature regime (100 K), giant modulations of the conductance, mediated by the Fermi level location, are unveiled. The experimental data are consistently analyzed in terms of the field-dependent density of states of the external shell that modulates the injection properties at the electrode-nanotube interface, and the resulting linear conductance. This is the first unambiguous experimental evidence of Aharonov-Bohm effect in clean multiwalled carbon nanotubes.

Gate-dependent magnetoresistance phenomena in carbon nanotubes.

We report on the first experimental study of the magnetoresistance of double-walled carbon nanotubes under a magnetic field as large as 50 T. By varying the field orientation with respect to the tube axis, or by gate-mediated shifting the Fermi level position, evidence for unconventional magnetoresistance is presented and interpreted by means of theoretical calculations.