Controlling the structure of single-wall carbon nanotubes during their synthesis by chemical vapor deposition remains a challenging issue. Here, using a specific synthesis protocol and ex situ transmission electron microscopy, we perform a statistical analysis of the structure of the tubes and of the catalyst particles from which they grow. We discriminate two nucleation modes, corresponding to different nanotube-particle junctions, that occur independently of the particle size. With the support of tight binding calculations, we show that a direct control of the nanotube diameter by the particle can only be achieved under growth conditions close to thermodynamic equilibrium.

We report on the first tunable resonant Raman scattering study performed on suspended isolated and coupled single-wall carbon nanotubes, unambiguously identified by electron diffraction. Besides the confirmation of the relation between the structural properties, the radial breathing frequency and the optical resonances for isolated metallic nanotubes, we evidence that interacting nanotubes experience drastic modifications of their resonance fingerprints. We first demonstrate a degeneracy lifting of an electronic level in a bundle of identical zigzag nanotubes. We then show the existence of a strong energy transfer mediated by a mechanical coupling between two nonidentical bundled nanotubes.

We demonstrate the wafer-scale integration of single electron memories based on carbon nanotube field effect transistors (CNFETs) using a process based entirely on self assembly. First, a "dry" self assembly step based on chemical vapor deposition (CVD) allows the growth and connection of CNFETs. Next, a "wet" self-assembly step is used to attach a single 30 nmdiameter gold bead in the nanotube vicinity via chemical functionalization. The bead is used as the memory storage node while the CNFET operated in the subthreshold regime acts as an electrometer exhibiting exponential gain. Below 60 K, the transfer characteristics of goldCNFETs show highly reproducible hysteretic steps. Evaluation of the capacitance confirms that these current steps originate from the controlled storage of single electrons with a retention time that exceeds 550 s at 4 K.

We studied composition, structure, and growth parameters of amorphous diamond-like carbon ͑DLC͒ and carbon nitride (CN x ) films deposited by pulsed laser deposition in vacuum and in nitrogen atmosphere. The composition (0рN/Cр0.4), the structural and the electronic properties of the deposited carbon and carbon nitride films were investigated for different laser fluences ͑1-12 J/cm 2 ͒. Electron energy loss spectroscopy, x-ray photoelectron spectroscopy, and micro-Raman spectroscopy indicated an increase in sp 3 -bonded carbon sites in the DLC films and an increase in N-sp 3 C bonded sites in the CN x films with increasing deposition laser fluence. Raman spectroscopy also showed the presence of a small amount of CwN bonds in the CN x films. Furthermore, we observed that keeping the nitrogen pressure constant ( Pϭ100 mTorr͒ the increase in the deposition laser fluence is reflected by an increase in the nitrogen content in the films. All the results have been discussed in the framework of different theoretical models.

We report low-temperature electronic transport in batch-processed single-walled carbon nanotube (SWNT) field-effect transistors (FETs). SWNTs are in situ synthesized and wired between submicrometer metallic electrodes in a single-step process involving hot-filament-assisted chemical vapor deposition. FETs show a pronounced ambipolar field effect between 1 and 300 K. Moreover, the gate dependence exhibits hysteresis at any temperature because of the extraction and trapping of charges. We find Schottky barriers at the SWNT/metal contact to be responsible for the field effect. Below 30 K, potential barriers along the SWNT induce a Coulomb blockade at low drain-source bias, leading to the suppression of the field-effect gain and inducing fluctuations in the transconductance.

No abstract

No abstract

An investigation of the mechanical properties of single wall carbon nanotubes (SWNT) fixed at a tip apex was performed using a frequency modulation-atomic force microscope (FM-AFM). The FM-AFM method allows the measurement of conservative and non-conservative forces separately and unambiguously. The FM-AFM analysis provides information that aids the understanding of the effects of the interaction between the free SWNT end and the surface: the resonant frequency shifts provide information on the effective SWNT spring constant, while the damping signal gives information on the type of contact between the tube and the surface. The variation of the damping signal as a function of the tip surface distance shows that the additional energy loss produced by the interaction between the tube and the surface is mostly due to an adhesion hysteresis. As a result, the increase of the damping signal is correlated to the existence of intermittent contact situations. The whole variations show how the contact between the free SWNT end and the surface modifies the elastic response of the tube.