In situ study of single-walled carbon nanotube growth in an environmental scanning electron microscope.

Monitoring individual single-walled carbon nanotubes (SWCNTs) during their growth is a highly sought-after goal in view of understanding the processes involved in the nucleation, elongation and termination which ultimately control the diameter and chiral selectivity. Here, we report on the first truly in situ observations of SWCNT growth in an environmental scanning electron microscope (ESEM). The CNT growth from lithographically patterned catalysts was investigated as a function of the catalyst type (Fe, Co or Ni), temperature, type of precursor (ethanol or acetylene), gas phase composition and pressure, and pretreatment conditions, and we report on the most appropriate conditions for SWCNT growth in ESEM conditions. We show that this approach allows the observation at the submicron scale of the different steps of the nanotube synthesis including the catalyst reduction, the growth and percolation of the nanotube network, and the deposition of individual nanotubes grown in the gas phase on the substrate. Despite these obvious advantages, we identified a few limitations which will need to be tackled for fully taking advantage of the approach, for instance for monitoring the growth of individual SWCNTs by ESEM, including the short lifetime of the catalyst nanoparticles, the preference for kite growth (by opposition to surface growth) and the influence of the electron beam on the nanotube growth.

Experimental evidence of a mechanical coupling between layers in an individual double-walled carbon nanotube.

We perform transmission electron microscopy, electron diffraction, and Raman scattering experiments on an individual suspended double-walled carbon nanotube (DWCNT). The first two techniques allow the unambiguous determination of the DWCNT structure: (12,8)@(16,14). However, the low-frequency features in the Raman spectra cannot be connected to the derived layer diameters d by means of the 1/d power law, widely used for the diameter dependence of the radial-breathing mode of single-walled nanotubes. We discuss this disagreement in terms of mechanical coupling between the layers of the DWCNT, which results in collective vibrational modes. Theoretical predictions for the breathing-like modes of the DWCNT, originating from the radial-breathing modes of the layers, are in a very good agreement with the observed Raman spectra. Moreover, the mechanical coupling qualitatively explains the observation of Raman lines of breathing-like modes, whenever only one of the layers is in resonance with the laser energy.

[ A registry of ischaemic cardiopathies among active workers at Electricité de France-Gaz de France. Program development and first results]. / Un registre des cardiopathies ischémiques chez les salariés en activité d'EDF et Gaz de France. Mise en place et premiers résultats.

BACKGROUND: The social security department of the French national electric and gas company has established an ischemic heart disease register among a population of about 140 000 employees based on sick leaves as well as deaths recorded with their medical cause. METHODS: History of the illness, medical tests and treatments were known retrospectively from the consulting physicians of the company. Acute coronary events recorded were: inaugural angina pectoris, myocardial infarction, sudden coronary death and fortuitous discovery of coronary disease. RESULTS: A first study conducted on employees during the 1993-1995 period showed infarction incidence age rates similar to those estimated from the French MONICA registers for France as a whole. Regional discrepancies were observed for myocardial infarction rates: Nord-Pas de Calais, Champagne-Ardennes, Lorraine, Franche-Comté and Limousin were at the most elevated risk (SIR=131, 155, 169, 125 and 178 resp). Large variations according to socio-economic status were observed. CONCLUSION: This register will permit studies on the links between socio-economic status at different professional career points and the occurrence of ischemic heart disease and the evaluation of the impact of psychosocial factors such as previous depressive disorders.