Critical Oxide Thickness for Efficient Single‐Walled Carbon Nanotube Growth on Silicon Using Thin SiO₂ Diffusion Barriers

Abstract

The ability to integrate carbon nanotubes, especially single-walled carbon nanotubes, seamlessly onto silicon would expand the range of applications considerably. Though direct integration using chemical vapor deposition is the simplest method, the growth of single-walled carbon nanotubes on bare silicon and on ultra-thin oxides is greatly inhibited due to the formation of a non-catalytic silicide. Using x-ray photoelectron spectroscopy, we show that silicide formation occurs on ultra-thin oxides due to thermally activated metal diffusion through the oxide. Silicides affect the growth of single-walled nanotubes more than multi-walled nanotubes due to the increased kinetics at the higher single-walled nanotube growth temperature. We demonstrate that nickel and iron catalysts, when deposited on clean silicon or ultra-thin silicon dioxide layers, begin to form silicides at relatively low temperatures, and that by 900 o C, all of the catalyst has been incorporated into the silicide, rendering it inactive for subsequent single-walled nanotube growth.We further show that a 4 nm silicon dioxide layer is the minimum diffusion barrier thickness which allows for efficient single-walled nanotube growth.

State of Transition Metal Catalysts During Carbon Nanotube Growth

“…11, 25 The thick SiO 2 prevents charge transfer from the heavily doped Si(100) substrates. Our relatively low process temperatures (mainly <600°C) exclude catalyst evaporation.…”

In-situ X-ray Photoelectron Spectroscopy Study of Catalyst−Support Interactions and Growth of Carbon Nanotube Forests

“…The Fe 2+ component disappears due to a transition to more stable Fe 3+ oxidation. 26,27 Furthermore, a marginal decline of the metallic peak can be observed which relates to a slight coarsening of the Fe film. The Al 2 O 3 support tends to stabilize interfacial Fe oxidation states, and we argue that this is what prevents excessive coalescence of Fe particles.…”

Selective growth of Co islands on ion beam induced nucleation centers in a native SiO2 film

“…22 Here cobalt acts as a catalyst and the surface oxide layer is necessary as a diffusion barrier. 23 In this paper we present a method for fabrication of patterns of metallic nanostructures. FIB lithography has been used to locally modify native SiO 2 layer on silicon substrate.…”