Diameter Dependence of Aligned Growth of Carbon Nanotubes on A-Plane Sapphire Substrates
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- Category: Tungsten & Sapphire Growth Furnace News
- Published on Thursday, 12 December 2013 09:25
Aligned carbon nanotubes have great potential for advanced nanotube transistors and integrated circuits. In this article, we studied the carbon nanotube alignment mechanism using a chemical vapor deposition growth on a-plane sapphire substrates. We synthesized carbon nanotubes of different diameters by controlling the catalyst size and observed that nanotubes of smaller diameters had a higher degree of alignment. In addition, a surprising observation was that misaligned nanotubes had a preferred orientation. Furthermore, we developed a numerical simulation method to calculate interaction energy between a-plane sapphire surface and carbon nanotubes of different diameters. The calculated results were in good agreement with our experimental observations, which confirmed the observed diameter-dependent alignment and the preferred orientation for misaligned nanotubes.
The thermal stability of sapphire was investigated at atmospheric pressure using the in situ gravimetric monitoring (GM) method. The weight change of a sapphire substrate was monitored at various hydrogen partial pressures in carrier gas (Pmath image) at temperatures over 1200 °C. Although the sapphire substrate was stable up to 1450 °C in an inert carrier gas (Pmath image = 0.0 atm), sapphire decomposition started to occur at 1200 °C in H2 carrier gas (Pmath image = 1.0 atm). Moreover the activation energy and order of reaction for sapphire surface decomposition changed at approximately 1300 °C. These results indicate that the rate-limiting reaction for sapphire decomposition shifts near 1300 °C.
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