Synthesis of a diamond-like carbon nanofiber film

An international team of researchers, led by the distinguished Professor Rodney S. Ruoff (Department of Chemistry) of the Center for Multidimensional Carbon Materials (CMCM), within the UNIST Institute for Basic Sciences (IBS), summarized a film composed of densely packed diamond-like carbon nanofibers. As described in a recent article published in the journal ACS Nano, the researchers noted that the new carbon material has a high concentration of tetravalently bonded carbon atoms (diamond-like nanofibers have many C atoms with four other atoms bonded to them; this is also referred to as “carbon bonded to sp3 “).

“The diamond-like carbon nanofiber films were synthesized by heating copper nanoparticles a few nanometers in diameter on a substrate, in acetylene gas and hydrogen,” says Kee Han Lee. “The synthesized fibers were very dense and formed a film. These densely packed nanofibers could also be separated into a powder form that could potentially expand their applications.”

In this study, the team was able to identify the parameters that influence the packing density of the nanofibers, namely the hydrogen gas concentration and the size of the copper nanoparticle catalyst. The packing density could be significantly increased by adjusting these parameters, which led to the formation of a warped film.

Various techniques such as X-ray photoelectron spectroscopy, solid state nuclear magnetic resonance, elemental analysis and elemental composition of Raman spectroscopy, and the chemical bonding structure in these diamond-like nanofibers, and it has been found that atoms of carbon bonded to sp3 (sp3: sp2 carbon atoms of about 2 predominate) (C atoms bonded to sp2 are attached to three other atoms instead of four – as in graphene and graphite – while in diamond, all atoms of C are “linked with sp3”). The hydrogen content within the nanofibers of approximately 25-50 atom% was determined using Raman spectroscopy and elemental analysis.

“With its high sp3 carbon content, this material is different from other steam grown carbon nanofibers, including nanotubes, which are mostly composed of stacked graphene layers and carbon nanocoils that have an sp3 carbon ratio: sp2 of about 0.25, “says Sun Hwa Lee.

The electrical resistivity (1.2 ± 0.1 × 10⁶ Ω cm – is electrically insulating), density (2.5 ± 0.2 g cm^-3; the density of the diamond is 3.5 g cm^-3), surface (28 ± 0.7 m2 g^-1), chemical inertia and wettability towards various liquids were determined. These properties were similar or “better” than most of the reported diamond-like carbon films, but the mechanical properties of this diamond-like carbon nanofiber film turned out to be completely different from conventional, continuous, similar carbon films. diamond, because it is composed of nanofibers.

‘We have discovered a new form of carbon, and our work could be expected to inspire others to study further along this research path,’ said the distinguished Professor Ruoff. “We do basic science of new carbon materials, among other things, and are interested in eventually making pure diamond fibers, along with further studies on this type of diamond-like carbon nanofiber.”