Synthesis of single-walled carbon nanotubes from atomic-layer-deposited Co3O4 and Co3O4/Fe2O3 catalyst films

Abstract

We have investigated the synthesis of single-walled carbon nanotubes (SWCNTs) employing Co3O4 films prepared by atomic layer deposition (ALD). These films dewet into Co catalyst nanoparticles in the furnace before starting CNT growth by chemical vapor deposition (CVD). The facile Co3O4 ALD process allows for excellent film thickness control and very reproducible growth of high quality SWCNTs even from ultrathin, single-digit cycle ALD films. We demonstrate CNT growth on planar and 3-dimensional geometries. A detailed study using a combination of Raman spectroscopy as well as scanning and transmission electron microscopy reveals that the density and diameter distribution of the catalyst particles and resulting CNTs can be controlled by the number of ALD cycles. Moreover, we demonstrate straightforward preparation of Fe/Co bimetallic catalysts by mixing ALD processes of Co3O4 and Fe2O3. Finally, the wide temperature window of Co3O4 ALD allows for patterning of the catalyst via standard electron-beam lithography, as the deposition temperature is low enough to prevent resist reflowing. We conclude that ALD is an ideal technique to deposit Co3O4 catalyst films for SWCNT synthesis in a well-controlled manner, with several advantages over other materials and deposition techniques.