Control of carbon nanostructure: From nanofiber toward nanotube and back

Abstract

The unique properties of carbon nanofibers (CNFs) make them attractive for numerous applications ranging from field emitters to biological probes. In particular, it is the deterministic synthesis of CNFs, which requires precise control over geometrical characteristics such as location, length, diameter, and alignment, that enables the diverse applications. Catalytic plasma enhanced chemical vapor deposition of vertically aligned CNFs is a growth method that offers substantial control over the nanofiber geometry. However, deterministic synthesis also implies control over the nanofiber’s physical and chemical properties that are defined by internal structure. Until now, true deterministic synthesis has remained elusive due to the lack of control over internal graphitic structure. Here we demonstrate that the internal structure of CNFs can be influenced by catalyst preparation and ultimately defined by growth conditions. We have found that when the growth rate is increased by 100-fold, obtained through maximized pressure, plasma power, and temperature, the resulting nanofibers have an internal structure approaching that of multiwalled nanotubes. We further show that the deliberate modulation of growth parameters results in modulation of CNF internal structure, and this property has been used to control the CNF surface along its length for site specific chemistry and electrochemistry.