We have synthesized boron-doped single wall carbon nanotubes
in
a high vacuum chemical vapor deposition (CVD) system using a new boron
precursor. Transmission electron microscopy was used in order to confirm
the presence of single wall carbon nanotubes and field emission scanning
electron microscopy to allow a qualitative characterization of the
produced tubes. To estimate the doping level, we compared the Raman
spectra with pure single wall carbon nanotubes and we found an upshifted
G band as an evidence of doping. X-ray photoelectron spectroscopy
analysis and ab initio electronic structure calculations reveals the
presence of substitutional boron atoms incorporated on the tubes.
We have also developed a simple method to determine quantitatively
in which temperature range the carbon nanotubes are produced more
efficiently by high vacuum CVD.
Phosphorus-doped multiwalled carbon nanotubes (P-MWNTs) have been successfully synthesized by spray pyrolysis methods using a solution of ferrocene and triphenylphosphine in toluene. Electron microscopy images reveal corrugated tubes with a special morphology, similar to a carbon necklace. P-MWNTs are shorter compared to undoped tubes grown in the same conditions using ferrocene and toluene as precursors. Raman spectroscopy characterization suggests the formation of more defective tubes as the phosphorus in the precursor solution was increased. X-ray photoelectron spectroscopy (XPS) revealing the chemical environment of the phosphorus atoms clearly indicates the presence of substitutional phosphorus in the nanotubes.
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