(529e) Growth of Small Diameter Carbon Nanotubes Using High-Melting Point Transition Metal Catalyst Promoters

Brian Everhart¹, Rahul Rao², Benji Maruyama², Placidus Amama¹

¹Tim Taylor Department of Chemical Engineering, Kansas State University,

Manhattan, KS, 66506

²Air Force Research Laboratory, Wright-Patterson Air Force Base, OH, 45433

Synthesis of small diameter single wall carbon nanotubes (SWNTs) has long been a goal within the fields of catalysis and nanotechnology. Current as-grown SWNTs vary in diameter and chirality, resulting in variations in structural and electronic properties. Typically, these tubes are comprised of approximately two-thirds semiconducting tubes and one-third metallic tubes. Furthermore, larger diameter semiconducting SWNTs (s-SWNTs) have very small bandgaps, as the bandgap is inversely proportional to diameter. Numerous applications, including photovoltaics and photocatalysis, require s-SWNTs with relatively large bandgaps, necessitating the growth of small diameter tubes. Commercially available s-SWNTs are incredibly expensive, as they require extensive post-growth processing. Other methods of achieving high selectivities of s-SWNTs and m-SWNTs involve controlling tube diameter via supported catalyst on substrates. By using high melting-point transition metals, such as ruthenium, as catalyst promoters, small diameter tubes, including high band-gap s-SWNTs can be obtained. Experiments have been performed in the Autonomous Research System (ARES), allowing for high throughput experimentation to probe the multi-parameter reaction space that’s intrinsic to CNT growth. Ruthenium has been used as a growth promoter on cobalt catalyst to show substantial reduction in tube diameters, confirmed by multi-excitation Raman spectroscopy. Increasing the amount of ruthenium beyond a certain threshold, however, negatively impacts CNT growth.