Abstract
A plasma-enhanced chemical vapour deposition reactor has been developed to synthesis horizontally aligned carbon nanotubes. The width of the aligning sheath was modelled based on a collisionless, quasi-neutral, Child’s law ion sheath where these estimates were empirically validated by direct Langmuir probe measurements, thereby confirming the proposed reactors ability to extend the existing sheath fields by up to 7 mm. A 7 mbar growth atmosphere combined with a 25 W plasma permitted the concurrent growth and alignment of carbon nanotubes with electric fields of the order of 0.04 V μm−1 with linear packing densities of up to ~5 × 104 cm−1. These results open up the potential for multi-directional in situ alignment of carbon nanotubes providing one viable route to the fabrication of many novel optoelectronic devices.
Highlights
Carbon nanotubes (CNTs), high aspect ratio graphitic nano-rods of concentrically nested graphene planes, have a wide range of novel properties that have been exploited to develop field emission electron sources [1,2], X-ray sources [3,4] and optical polarising media [5,6]
CNTs can be aligned by post-synthesis alignment, where external forces such electric fields, such as by dielectrophoresis [7,8,9] orientate the nanotubes once dispersed onto a substrate, often by means of a liquid medium
In our previous work we demonstrated vertically aligned CNT synthesis using plasma enhanced chemical vapour deposition (PE-CVD) [38,39] where the alignment occurs concurrently with growth
Summary
Carbon nanotubes (CNTs), high aspect ratio graphitic nano-rods of concentrically nested graphene planes, have a wide range of novel properties that have been exploited to develop field emission electron sources [1,2], X-ray sources [3,4] and optical polarising media [5,6]. This limits the broadness of the technique to a very limited, and rather costly, set of substrates, such as sapphire or quartz, though high degrees of alignment and uniformity have been evidenced [25,32]. Techniques based on magnetic fields, electric fields and gas flow have shown perhaps the most promise They are rapid, parallel processes that offer simplicity and the ability to fabricate high density arrays. It has been argued that the nanotubes highly anisotropic polarisability induced large dipole moments when they interact with the local electric field This interaction produces large aligning torques which governs the growth orientation.
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