A.M. Bonnot

Defects and stress analysis of the Raman spectrum of diamond films

Abstract Diamond films were deposited on silicon substrates at 750 °C, by the hot-filament technique, from a reactive CH 4 (0.1–2%) H 2 mixtures. Two wide Gaussian lines around 1330 and 1500 cm−1 with coupled variations in the whole preparation range appeared in the global Raman spectra. They were attributed to intermediate carbon defects in the diamond crystallites, which might control the confinement length of diamond phonons. Their contributions to the diamond line shift and width for all the samples is calculated and compared with the experimental results. The remaining shift is attributed to the stress (up to 1.2 GPa), while the origin of the remaining widening (large distribution of stress or Raman inactive additional defects) is discussed.

Batch processing of nanometer-scale electrical circuitry based on in-situ grown single-walled carbon nanotubes

We present a fabrication method for a nanometer-scale conducting network made of self-assembled single-walled carbon nanotubes. The electrical connection of the suspended nanotubes to the metallic contacts is obtained during the nanotube synthesis itself, which involves the hot-filament CVD technique. We directly characterize, without any further processing, the electronic transport properties of samples with different pad geometries. At room temperature, all tested samples show ohmic behavior in the kΩ range, for both two-probe and four-probe geometries. At low temperature, non-linear transport is observed and a large discrepancy of resistance arises between two-probe and four-probe geometries, suggesting the dominant influence of the contact resistance.

Analysis of mechanical properties of single wall carbon nanotubes fixed at a tip apex by atomic force microscopy

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.

Elastic scattering of light and reflectivity development during low pressure diamond film growth

Abstract Growth mechanisms of diamond films have been investigated by in-situ measurements of elastic scattering of light and reflectivity of 632.8 nm He-Ne laser radiation. Films were prepared by hot-filament chemical vapour deposition with methane and hydrogen. A systematic study of the influence of the synthesis conditions on the optical measurements has been undertaken. Scanning electron microscopy observations at the different stages of the growth have allowed us to relate the in-situ optical responses to the principal steps of the film formation. It will also be shown that the development of scattering of light with increasing deposition time allows us to determine the index of refraction of the film.

Carbon nanostructures and diamond growth by HFCVD: role of the substrate preparation and synthesis conditions

Abstract The feasibility of the hot filament assisted chemical vapour deposition (HFCVD) technique to synthesize carbon nanostructures on catalyst particles has been investigated using an atmosphere of methane diluted in hydrogen. Depending on the deposition temperature and the methane content, different carbon nanostructures were obtained. The peculiarity of the HFCVD technique appears to be its ability to favor a whisker like growth mode of carbon nanostructures for a particular range of the deposition parameters.

Self-assembled single wall carbon nanotube field effect transistors

We report detailed characterization of in-situ wired single wall carbon nanotube (SWNT) field effect transistors (FETs). They were batch processed using a single step technique based on hot filament chemical vapor deposition. Raw samples show an ambipolar field effect. The temperature dependence of the gain confirms the presence of Schottky barriers at the nanotube/metal interface. Moreover the gate dependence exhibits hysteresis at any temperature due to extraction and trapping of charges. Below 30 K, Coulomb blockade occurs at low drain-source bias and partially washes out the influence of the Schottky barriers.

Integration of self-assembled carbon nanotube transistors: statistics and gate engineering at the wafer scale

We present a full process based on chemical vapour deposition that allows fabrication and integration at the wafer scale of carbon-nanotube-based field effect transistors. We make a statistical analysis of the integration yield that allows assessment of the parameter fluctuations of the titanium–nanotube contact obtained by self-assembly. This procedure is applied to raw devices without post-process. Statistics at the wafer scale reveal the respective role of semiconducting and metallic connected nanotubes and show that connection yields up to 86% can be reached. For large scale device integration, our process has to implement both wafer-scale self-assembly of the nanotubes and high transistor performances. In order to address this last issue, a gate engineering process has been investigated. We present the improvements obtained using low and high κ dielectrics for the gate oxide.

Stabilization of diamond relative to different substrate—carbon interfaces: a nucleation model for CVD diamond growth based on a charge transfer consideration

Abstract The interaction between the carbon phase and the substrate is the determining factor in chemically vapor deposited diamond thin film growth processes. Considering the similarity between (1,1,1) diamond planes and (0,0,0,1) graphite planes, we present calculation results concerning the stabilization geometry in respect with interfacial charge transfer between a substrate and or a graphite sheet. We then propose a nucleation model for CVD diamond films based on corrugated graphite precursors.

In-situ investigation of low-pressure diamond growth by elastic scattering of light and reflectance spectroscopy

Abstract The growth of diamond on silicon by the use of a hot filament and methane-hydrogen (0.5–2 vol.%) was investigated by measuring the elastic scattering and reflectivity of 1.96 eV radiation. A systematic study of the influence of the experimental parameters governing the diamond growth has been undertaken and correlated to in-situ optical measurements. This shows, as diamond gros, a strong increase of the elastic scattering and a simultaneous decrease of the reflectivity. These measurements have allowed to follow, in-situ , the diamond growth and estimate, in real time, of the crystal sizes.

Alteration of superconductivity and radial breathing modes in suspended ropes of carbon nanotubes by organic polymer coatings

We have altered the superconductivity of a suspended rope of single walled carbon nanotubes, by coating it with organic polymers. Upon coating, the normal state resistance of the rope changes by less than 20 percent. But superconductivity, which on the bare rope shows up as a substantial resistance decrease below 300 mK, is gradualy suppressed. We correlate this to the suppression of radial breathing modes, measured with Raman Spectroscopy on suspended Single and Double-walled carbon nanotubes. This points to the breathing phonon modes as being responsible for superconductivity in carbon nanotubes.