Feedstock-dependent nitrogen configurations of nitrogen-doped single-walled carbon nanotubes in a CVD process.

The modification of nitrogen configurations is a viable way to control the electronic properties of nitrogen-doped single-walled carbon nanotubes (N-doped SWCNTs). N-doped SWCNTs were synthesized by a conventional chemical vapor deposition process with a mixed carbon/nitrogen (C/N) feedstock. While higher feedstock flow rates promote the formation of encapsulated N2 molecules, lower flow rates show a predominance of pyridinic and graphitic nitrogen structures as revealed by X-ray photoemission spectroscopy.

Fingerprinting seamless single-walled carbon nanotube junctions via the migration of encapsulated N molecules from bottom to top: are arrays of VA-SWNTs continuous?

Structure control such as diameter changes along single-walled carbon nanotubes (SWNTs) can be achieved in arrays of vertically aligned (VA-) SWNTs by switching the feedstock during growth. The local nature of the macroscopic transition from one diameter to another is then questioned as one can either envisage seamless transitions or discontinuous individual SWNTs. Here, we demonstrate that encapsulated molecules can serve as markers to doubtlessly identify seamless interconnections in macroscopic samples.

From isotope labeled CH₃CN to N₂ inside single-walled carbon nanotubes.

The observation of one-dimensional N₂ inside single-walled carbon nanotubes raises the questions, how are the N₂ molecules formed and how do they manage to make their way to this peculiar place? We have used N(15) and C(13) isotope labeled acetonitrile during the synthesis of single-walled carbon nanotubes to investigate this process. The isotope shifts of phonons and vibrons are observed by Raman spectroscopy and X-ray absorption. We identify the catalytic decomposition of acetonitrile as the initial step in the reaction pathway to single-walled carbon nanotubes containing encapsulated N₂.

Reversible diameter modulation of single-walled carbon nanotubes by acetonitrile-containing feedstock.

Changing the carbon feedstock from pure ethanol to a 5 vol % mixture of acetonitrile in ethanol during the growth of vertically aligned single-walled carbon nanotubes (SWNTs) reduces the mean diameter of the emerging SWNTs from approximately 2 to 1 nm. We show this feedstock-dependent change is reversible and repeatable, as demonstrated by multilayered vertically aligned SWNT structures. The reversibility of this process and lack of necessity for catalyst modification provides insight into the role of nitrogen in reducing the SWNT diameter.

Diameter controlled chemical vapor deposition synthesis of single-walled carbon nanotubes.

In this study, we systematically investigated the influence of catalyst preparation procedures on the mean diameter of single-walled carbon nanotubes (SWNTs) synthesized by the alcohol catalytic chemical vapor deposition (ACCVD) process. It was found that the SWNT diameter is dependent upon both reduction temperature and time, with lower reduction temperature and/or shorter reduction time resulting in smaller diameter SWNTs. The morphology of the SWNTs also changed from vertically aligned to randomly oriented when the reduction temperature was below 500 degrees C.

Parametric study of alcohol catalytic chemical vapor deposition for controlled synthesis of vertically aligned single-walled carbon nanotubes.

In this study we examine catalyst preparation and chemical vapor deposition (CVD) parameters related to synthesis of single-walled carbon nanotubes (SWNTs) by alcohol catalytic CVD. We show that modifying the catalyst recipe considerably changes the average SWNT diameter, and vertically aligned arrays with an average diameter of 1.5 nm were obtained.

Unexpected oxidation of a diphosphine by bis(1,3-diphenylpropane-1,3-dionato)cobalt(II), [Co(dbm)2].

The reaction of bis(1,3-diphenylpropane-1,3-dionato)cobalt(II), [Co(dbm)(2)], with bis(diphenylphosphino)ethane (dppe) affords the coordination polymer catena-poly[[bis(1,3-diphenylpropane-1,3-dionato-kappa(2)O,O')cobalt(II)]-mu-ethylenebis(diphenylphosphine oxide)-kappa(2)O:O'], trans-[Co(C(15)H(11)O(2))(2)(C(26)H(24)O(2)P(2))](n), as a result of oxidation of the diphosphine. The Co atom is octahedral, with a CoO(6) coordination sphere, and the chelating dbm ligands adopt a trans configuration. The Co atom also lies on a centre of inversion, with a further symmetry centre bisecting the bridging ethylenebis(diphenylphosphine oxide) ligand.