Carbon Nanotubes Array Grown on Substrates Patterned by Combined Lithographic Techniques

Field emission is one of the most promising potential applications of carbon nanotubes (CNTs). These nanostructures combine positively a geometrical effect (local exhaltation of the electric field due to a strong curvature radius) and an electronic effect (weak work function) as well as they display strong chemical inertness and thermal conductivity, which open the way to the realization of convenient electrons sources for vacuum electronics such as flat panels and cold cathodes. Field emission measurements obtained on CNTs grown on SiO2/Si(100) substrates by the DC HF CCVD process where a dispersion of metallic catalytic transition metal (Co, Ni) particles was previously performed, showed that the thresholds of emission were strongly dependent on the nature of the material. Therefore they were within the range 1-4 V/ m for CNTs. By contrast they ranged above 10V/mm either for carbon nanofibers or nanocones. However, the current densities were quire variable and often reached a rapid saturation both due to screening of the field by the high density of CNTs and to conductivity limitations of the substrate. Therefore, we used patterned surfaces to grow array of CNTs emitters. Patterned surfaces were obtained by controlled deposition of metallic spots by a combination of lithographics techniques, using either photons, electrons or ion beams. Array of particle islands of Co or Ni were obtained in the range 5-100 nm. Under proper CVD conditions we could grow subsequently one CNT by metallic island if the size of the metallic island did not exceed 60 nm.