Multilayered metal catalysts for controlling the density of single-walled carbon nanotube growth

Direct synthesis of high-quality single-walled carbon nanotubes on silicon and quartz substrates

“…In other approaches, catalytic metals were mounted on the substrate using dry processes such as sputtering or deposition [11][12][13][14][15]; however, these methods often suffered from a production of multi-walled carbon nanotubes (MWNTs). Dominant products of Nerushev et al [11] and Yoon et al [12] were MWNTs, although they reported to have synthesized some SWNTs based on their Raman spectra of low S/N ratio.…”

“…Dominant products of Nerushev et al [11] and Yoon et al [12] were MWNTs, although they reported to have synthesized some SWNTs based on their Raman spectra of low S/N ratio. Delzeit et al [13] synthesized SWNTs by depositing 20 nm of aluminum underlayer and 1 nm of Fe/Mo layer on a Si substrate. Hongo et al [14] synthesized relatively high-quality SWNTs by depositing 2 to 5 nm Fe on the A-face of sapphire crystal; Chemical Physics Letters, in press.…”

“…From the studies cited above, these deposition/sputter approaches are prone to accompany sintering of catalytic metals, as they often resulted in catalytic metal droplets of several tens of nanometers [12][13][14]. The sintering is partly caused by their higher temperature around 900 to 1000 °C to synthesize SWNTs on a Si substrate [4][5][6][11][12][13].…”

“…The sintering is partly caused by their higher temperature around 900 to 1000 °C to synthesize SWNTs on a Si substrate [4][5][6][11][12][13]. In addition, Arcos et al [15] demonstrated that the deposited 1 nm layer of Fe reacted with a Si substrate to form silicide at 850 °C, by which catalytic activity was deteriorated.…”

“…In addition, Arcos et al [15] demonstrated that the deposited 1 nm layer of Fe reacted with a Si substrate to form silicide at 850 °C, by which catalytic activity was deteriorated. Such a high-temperature based approach inherently involves a dilemma because, when one attempts to synthesize SWNTs without a support material, one needs to prepare a thick underlayer (20 nm of Al or Ir [13] or 80 nm of TiN [15]) between the catalytic metal and the Si substrate to avoid silicide formation. However, the metallic underlayer itself can be sintered into a droplet at elevated temperature, leading to a surface roughness.…”