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Control of carbon nanotube growth directions and morphology by direct current plasma enhanced chemical vapor deposition


Vertical alignment of individual carbon nanotubes (CNTs) and CNT arrays during their growth has been demonstrated by many groups; however, there has been much less progress towards more complicated morphologies. In this work, I show the ability to use direct current plasma enhanced chemical vapor deposition to control the growth direction of CNTs. By careful engineering of the cathode geometry, the electric field directions within the cathode plasma sheath are controlled and the CNTs grow along these customized field lines. The ability to dramatically change the growth direction of CNTs and create sharp bends and zigzag structures is also demonstrated. A model for the electric fields within the plasma sheath and in the region of CNT growth is proposed. Using this model to assist in the experimental design of the electrode geometries, both the CNT growth directions and sharp bend angles can be predicted to within 2⁰. Additional morphology control over CNTs is also demonstrated including the ability to control the carbon capping to allow easy re-growth of CNTs, a method of opening the ends of aligned CNTs without using any wet chemical processing or oxidation step, the creating of multiple aligned branchings formed from a single CNT creating Y- or T- junctions of desired angles, and the creation of three dimensional structures such as coiled CNTs. The novel CNT morphologies created in this work could serve useful in a variety of applications and initial results are presented for their use as a catalyst particle support structure for potential fuel cell applications, field emission sources for flat panel display or projection e-beam lithography, improved probe tips for scanning probe microscopy, and templates for guided growth of nerve cells

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