D. G. Larrude

Characterization of phosphorus-doped multiwalled carbon nanotubes

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.

Physicochemical structure of SiCx:H to improve DLC adhesion on steel

Diamond-like carbon (DLC) coatings show strident properties such as high wear resistance and ultra-low friction. However, a widespread use regarding energy efficiency issues is neglected due to the poor adhesion. Silicon adhesion interlayers (SiCx:H) were deposited at different temperatures from 50 to 500°C with hexamethyldisiloxane followed by DLC. The microstructure was analysed by atomic force microscopy, scanning electron microscopy and Raman spectroscopy. The chemical depth profiling and chemical mapping were performed by glow discharge optical emission spectroscopy and energy-dispersive spectroscopy, respectively. Hardness and critical loads were analysed by nanoindentation tests. At higher deposition temperatures the Si-containing interlayers show lower relative content of H, O and Si and higher relative content of C, allowing the formation of more C–C chemical bonds at the outermost DLC/SiCx:H interface, which is correlated to better adhesion. Finally, an atomistic model is proposed in order to explain the DLC debonding and bonding mechanisms.

Synthesis and characterization of silver nanoparticle-multiwalled carbon nanotube composites

Multiwalled carbon nanotubes (MWCNTs) grown by spray pyrolysis have been decorated with silver nanoparticles prepared via the silver mirror reaction. Good dispersion of silver nanostructures was obtained on the surface of MWCNTs, resulting in an efficient and simple wet chemistry method for increasing the reactivity of the carbon nanotubes surfaces. High-resolution transmission electron microscopy showed the orientations of the crystallography planes of the anchored silver nanoparticles and revealed their size distribution. Raman spectroscopy results confirm that the composite material preserves the integrity of the MWCNTs. Scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were also employed for sample characterization.

Multiwalled carbon nanotubes decorated with cobalt oxide nanoparticles

Multiwalled carbon nanotubes (MWCNTs) synthesized by spray pyrolysis were decorated with cobalt oxide nanoparticles using a simple synthesis route. This wet chemistry method yielded nanoparticles randomly anchored to the surface of the nanotubes by decomposition of cobalt nitrate hexahydrate diluted in acetone. Electron microscopy analysis indicated that dispersed particles were formed on the MWCNTs walls. The average size increased with the increasing concentration of cobalt nitrate in acetone in the precursor mixture. TEM images indicated that nanoparticles were strongly attached to the tube walls. The Raman spectroscopy results suggested that the MWCNT structure was slightly damaged after the nanoparticle growth.

Incorporation of Boron Atoms on Graphene Grown by Chemical Vapor Deposition Using Triisopropyl Borate as a Single Precursor

We synthesized single-layer graphene from a liquid precursor (triisopropyl borate) using a chemical vapor deposition. Optical microscopy, scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy measurements were used for the characterization of the samples. We investigated the effects of the processing temperature and time, as well as the vapor pressure of the precursor. The core-level XPS spectra revealed the presence of boron atoms incorporated into substitutional sites. This result, corroborated by the observed upshift of both G and 2D bands in the Raman spectra, suggests the p-doping of single-layer graphene for the samples prepared at 1000°C and pressures in the range of 75 to 25 mTorr of the precursor vapor. Our results show that, in optimum conditions for single-layer graphene growth, that is, 1000°C and 75 mTorr for 5 minutes, we obtained samples presenting the coexistence of pristine graphene with regions of boron-doped graphene.