Single- and few-walled carbon nanotubes grown at temperatures as low as 450 degrees c: electrical and field emission characterization.

Single-wall (SW-) and few-walled (FW-) carbon nanotubes (CNTs) were synthesized on aluminum/ cobalt coated silicon at temperatures as low as 450 degrees C by plasma enhanced chemical vapor deposition technique (PECVD). The SWCNTs and FWCNTs grow vertically oriented and well separated from each other. The cold field emission studies of as-grown SWCNTs and FWCNTs showed low turn-on field emission threshold voltages, strongly dependent of the nanotubes morphology. Current-voltage curves of individual CNTs, measured by conductive atomic force microscopy (CAFM), showed an electrical resistance of about 90 Komega, that is attributed mainly to the resistance of the contact between the CNTs and the conductive CAFM tip (Au and Pt).

Angular and local spectroscopic analysis to probe the vertical alignment of N-doped well-separated carbon nanotubes.

Vertically aligned well-separated N-doped multiwalled carbon nanotubes (CNTs) were grown on a silicon substrate by plasma enhanced chemical vapor deposition (PECVD). Angular near-edge X-ray absorption fine structure (NEXAFS) was used to investigate the vertical alignment of as-grown CNTs. In addition, both individual tubes and tube bundles were characterized by high-resolution electron energy loss spectroscopy (HREELS). Simultaneous analysis of both spectroscopic techniques provides information on chemical environment, orbital orientation between carbon and heteroatoms, and local curvature effects. We demonstrate the utility of NEXAFS as an in situ probe of CNTs.

Oriented carbon nanostructures containing nitrogen obtained by ion beam assisted deposition.

In this paper, we report the deposition of graphite multilayer containing nitrogen covering nanometric nickel particles. In-situ photoelectron emission spectroscopy (XPS) reveals the presence of nitrogen in the carbon layer covering the nickel particles. The field emission properties of the structures are reported. Atomic force microscopy displays regular domelike structures. Raman spectroscopy shows the characteristic frequencies associated with graphite and disordered structures. High-resolution transmission electron microscopy confirms the presence of multiwall well-organized graphite layers covering the nickel particles. Disorder increases on increasing nitrogen content. The samples were prepared in-situ by depositing first a few atomic layers of nickel and subsequent islands formation by thermal annealing. Then, an argon ion beam bombards an ultrapure carbon target and simultaneously the growing film is assisted with a second low-energy nitrogen ion beam (ion beam assisted deposition).