Ultrathin crystals of the layered transition-metal dichalcogenide MoS 2 ͑semiconducting͒ and TaS 2 ͑metallic͒ were obtained by mechanical peeling or chemical exfoliation techniques and electrically contacted using electron-beam lithography. The MoS 2 devices showed high field-effect mobility in the tens of cm 2 / V s and an on/off ratio higher than 10 5. The TaS 2 devices remained metallic despite the fabrication process and showed an enhancement of the superconducting transition temperature and disappearance of the charge density wave phase anomaly at low temperature.
Electromechanical resonators are a key element in radio-frequency telecommunication devices and thus new resonator concepts from nanotechnology can readily find important industrial opportunities. Here, the successful experimental realization of AM, FM, and digital demodulation with suspended single-walled carbon-nanotube resonators in a field-effect transistor configuration is reported. The crucial role played by the electromechanical resonance in demodulation is clearly demonstrated. The FM technique is shown to lead to the suppression of unwanted background signals and the reduction of noise for a better detection of the mechanical motion of nanotubes. The digital data-transfer rate of standard cell-phone technology is within the reach of these devices.
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.
The optical properties of single-wall carbon nanotubes are very promising for developing novel opto-electronic components and sensors with applications in many fields. Despite numerous studies performed using photoluminescence or Raman and Rayleigh scattering, knowledge of their optical response is still partial. Here we determine using spatial modulation spectroscopy, over a broad optical spectral range, the spectrum and amplitude of the absorption cross-section of individual semiconducting single-wall carbon nanotubes. These quantitative measurements permit determination of the oscillator strength of the different excitonic resonances and their dependencies on the excitonic transition and type of semiconducting nanotube. A non-resonant background is also identified and its cross-section comparable to the ideal graphene optical absorbance. Furthermore, investigation of the same single-wall nanotube either free standing or lying on a substrate shows large broadening of the excitonic resonances with increase of oscillator strength, as well as stark weakening of polarization-dependent antenna effects, due to nanotube-substrate interaction.
RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to the journal that you are submitting your paper to)We report the observation of self-oscillations in a bottom-up nanoelectromechanical system (NEMS) during field emission driven by a constant applied voltage. An electromechanical model is explored that explains the phenomenon and that can be directly used to develop integrated devices. In this first study we have already achieved ~50% DC/AC (direct to alternative current) conversion. Electrical selfoscillations in NEMS open up a new path for the development of high speed, autonomous nanoresonators, and signal generators and show that field emission (FE) is a powerful tool for building new nano-components.Within the nanodevice world, nanoelectromechanical systems (NEMS) based on resonant components are having a revolutionary impact on basic research in nanomechanics 1,2 and in technological
Optical detection of an individual single nano-object on an opaque substrate and direct determination of its absorption cross section is demonstrated using reflective spatial modulation spectroscopy. This method is applied to optical imaging and investigation of individual single-wall carbon nanotubes in the 1.6 nm diameter range on silicon substrates, which are also individually characterized by atomic force microscopy, scanning electron microscopy, and in situ micro-Raman spectroscopy. Absorption cross sections on the order of 10 −17 cm 2 per carbon atom are measured for the investigated semiconducting carbon nanotubes, with a light polarization absorption anisotropy of about 2.
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