Grazing-angle x-ray reflectivity ͑XRR͒ is described as an efficient, nondestructive, parameter-free means to measure the mass density of various types of amorphous carbon films down to the nanometer thickness range. It is shown how XRR can also detect layering if it is present in the films, in which case the reflectivity profile must be modeled to derive the density. The mass density can also be derived from the valence electron density via the plasmon energy, which is measured by electron energy-loss spectroscopy ͑EELS͒. We formally define an interband effective electron mass m*, which accounts for the finite band gap. Comparison of XRR and EELS densities allows us to fit an average m*ϭ0.87m for carbon systems, m being the free-electron mass. We show that, within the Drude-Lorentz model of the optical spectrum, m*ϭ͓1Ϫn(0) Ϫ2 ͔m, where n(0) is the refractive index at zero optical frequency. The fraction of sp 2 bonding is derived from the carbon K-edge EELS spectrum, and it is shown how a choice of ''magic'' incidence and collection angles in the scanning transmission electron microscope can give sp 2 fraction values that are independent of sample orientation or anisotropy. We thus give a general relationship between mass density and sp 3 content for carbon films.
Vertically aligned carbon nanotubes were grown at temperatures as low as 120 °C by plasma-enhanced chemical vapor deposition. A systematic study of the temperature dependence of the growth rate and the structure of the as-grown nanotubes is presented using a C2H2/NH3 system and nickel as the catalyst. The activation energy for the growth rate was found to be 0.23 eV, much less than for thermal chemical vapor deposition (1.2–1.5 eV). This suggests growth occurs by surface diffusion of carbon on nickel. The result could allow direct growth of nanotubes onto low-temperature substrates like plastics, and facilitate the integration in sensitive nanoelectronic devices.
A comprehensive study of the stress release and structural changes caused by postdeposition thermal annealing of tetrahedral amorphous carbon ͑ta-C͒ on Si has been carried out. Complete stress relief occurs at 600-700°C and is accompanied by minimal structural modifications, as indicated by electron energy loss spectroscopy, Raman spectroscopy, and optical gap measurements. Further annealing in vacuum converts sp 3 sites to sp 2 with a drastic change occurring after 1100°C. The field emitting behavior is substantially retained up to the complete stress relief, confirming that ta-C is a robust emitting material.
Electrical transport properties of boron-doped single-walled carbon nanotubes J. Appl. Phys. 113, 054313 (2013) Electric field induced needle-pulsed arc discharge carbon nanotube production apparatus: Circuitry and mechanical design Rev. Sci. Instrum. 83, 123907 (2012) Cylindric quantum wires in a threading magnetic field: A proposal of characterization based on zero bias electron transport J. Appl. Phys. 112, 123715 (2012) A doping-free approach to carbon nanotube electronics and optoelectronics AIP Advances 2, 041403 (2012) Magnetic and electrical properties of PbTiO3/Mn-Zn ferrite multiphase nanotube arrays by electro-deposition
A systematic study is presented of the influence of catalyst film thickness on carbon nanostructures grown by plasma-enhanced chemical-vapor deposition from acetylene and ammonia mixtures. We show that reducing the Fe∕Co catalyst film thickness below 3nm causes a transition from larger diameter (>40nm), bamboolike carbon nanofibers to small diameter (∼5nm) multiwalled nanotubes with two to five walls. This is accompanied by a more than 50 times faster growth rate and a faster catalyst poisoning. Thin Ni catalyst films only trigger such a growth transition when pretreated with an ammonia plasma. We observe a limited correlation between this growth transition and the coarsening of the catalyst film before deposition. For a growth temperature of ⩽550°C, all catalysts showed mainly a tip growth regime and a similar activity on untreated silicon, oxidized silicon, and silicon nitride support.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.