Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “nanotubes”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Growth of Carbon Nanotubes Using Mixed-Metal Catalysts That Include Heavy Refractory Metals as Catalyst Stabilizers

Here, we report new findings from studies of a novel technique to augment the growth of CNTs. In this method, the catalytic metals used for CNT growth are combined with high-melting-point heavy refractory metals, which serve to stabilize the metal catalyst nanoparticles, from which the CNTs nucleate and grow. Our study investigates the combination of an iron catalyst with tungsten and osmium refractory stabilizers. We find that both tungsten and osmium enhance the lifetime of the iron catalyst particles by a factor of approximately two. Tungsten stabilizer resulted in production of CNTs longer by a factor of 1.25 compared to those produced using a pure iron catalyst, while the osmium stabilizer did not significantly affect the ultimate length of the CNTs due to the decreased CNT growth rate with a combined Fe/Os catalyst. These results suggest a possible new route toward producing CNTs with lengths sufficient for materials applications.

Park, Wonjung [Univ. of Tampa, FL (United States)]↗
DOE OSTI2024

Remote-Contact Catalysis for Target-Diameter Semiconducting Carbon Nanotube Arrays

Electrostatic catalysis has been an exciting development in chemical synthesis (beyond enzymes catalysis1 ) in recent years, boosting reaction rates and selectively producing certain reaction products2 . Most of the studies to date have been focused on using external electric field (EEF) to rearrange the charge distribution in small molecule reactions such as Diels-Alder addition3 , carbene reaction4 , etc. However, in order for these EEFs to be effective, a field on the order of 1 V/nm (10 MV/cm) is required, and the direction of the EEF has to be aligned with the reaction axis5 . Such a large and oriented EEF will be challenging for large-scale implementation, or materials growth with multiple reaction axis or steps. Here, we demonstrate that the energy band at the tip of an individual single-walled carbon nanotube6 (SWCNT) can be spontaneously shifted in a high-permittivity growth environment, with its other end in contact with a low-work function electrode (e.g., hafnium carbide or titanium carbide7 ). By adjusting the Fermi level at a point where there is a substantial disparity in the density of states (DOS) between semiconducting (s-) and metallic (m-) SWCNTs8 , we achieve effective electrostatic catalysis for s-SWCNT growth assisted by a weak EEF perturbation (200V/cm). This approach enables the production of high-purity (99.92%) s-SWCNT horizontal arrays with narrow diameter distribution (0.95±0.04 nm), targeting the requirement of advanced SWCNT-based electronics for future computing9-11. These findings highlight the potential of electrostatic catalysis in precise materials growth, especially for s-SWCNTs, and pave the way for the development of advanced SWCNT-based electronics12.

Wang, Jiangtao↗