Carbon nanotubes (CNTs), due to their unique electronic and extraordinary mechanical properties, have been receiving much attention for a wide variety of applications. Recently, plasma enhanced chemical vapour deposition (PECVD) has emerged as a key growth technique to produce vertically-aligned nanotubes. This paper reviews various plasma sources currently used in CNT growth, catalyst preparation and growth results. Since the technology is in its early stages, there is a general lack of understanding of growth mechanisms, the role of the plasma itself, and the identity of key species responsible for growth. This review is aimed at the low temperature plasma research community that has successfully addressed such issues, through plasma and surface diagnostics and modelling, in semiconductor processing and diamond thin film growth.

Cryogenic HC1-ice samples, chosen to maximize the possibility that the primary H20-HCl interactions will include molecular complexation of HC1 with H20, have been studied by infrared spectroscopy. A thorough review/extension of the spectroscopy of HCl (HBr) amorphous and crystalline hydrate films has revealed the need for a significant reassignment of the published crystalline hydrate infrared spectra. From this reassignment, and new data for the amorphous hydrates, the band position for the stretching mode of HCl (-2550 cm-l), DCl ( -1820 cm-I), and HBr (-2220 cm-l) complexed with HzO within the 1 : 1 amorphous hydrate mixture has been established. This band, together with the spectra of the ionic components of the amorphous hydrate mixtures, has then been used as a probe of the interaction of HC1 with the extensive ice surfaces present in samples of gas-phase ice nanocrystals (85 K) and microporous amorphous ice samples prepared at 15 K. This molecular complex band is observed as the dominant spectral feature that emerges as samples of microporous ice, coated with a thin film of HCl, are warmed through the 15-60 K range. However, the major infrared bands that develop upon warming the HCl/amorphous ice system above 60 K, or as ice nanocrystals are exposed to HC1 at 85 K, are those of the ionic amorphous hydrate mixtures. The results indicate that the limited molecular mobility and activation energy available at temperatures below -50 K result in the kinetic stabilization of the molecular complex of HCl H-bonded to the ice surface oxygen sites, while at temperatures above 60 K, HCl, in the presence of ice, ionizes as it forms amorphous hydrate surface layers, ultimately of a 1:l composition. This study reveals a qualitatively different ionization behavior of the hydrogen halides within the amorphous hydrate mixture than has been observed for the nitric and perchloric oxyacids (for which ionization is quite limited for the 1:l composition even into the stable liquid phase): a difference that presumably reflects the very strong hydrogen bonding of H3O+ to multiple neighbor chloride and bromide ions. The identification of the stretching-mode bands of the molecular H(D)X--HzO complex as a useful probe of the extent of ionization within noncrystalline hydrogen halidewater systems is an important byproduct of this study, a study that establishes the strong tendency of ice to form an amorphous ionic hydrate mixture when exposed to HX at temperatures above -60 K.

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Vertically aligned multiwalled carbon nanotube (MWCNT) arrays can mimic the hairs on a gecko’s foot and act as a dry adhesive. We demonstrate the van der Waals interactions originated dry adhesion between MWCNT array surfaces and various target surfaces over millimeter-sized contact areas. The adhesive strengths were measured over 10N∕cm2 in the normal direction and about 8N∕cm2 in the shear direction with glass surface. The adhesion strength over repeated cycles is limited by the relatively poor adhesion of MWCNTs to their growth substrate, which was improved significantly by adding molybdenum to the catalyst underlayer. We also measured the interfacial work of adhesion as a fundamental adhesion property at the interface. Our measured values of a few tens of mJ∕m2, which falls in the range of typical van der Waals interactions energies, provide a direct proof of the van der Waals dry adhesion mechanism. Furthermore, in contrast to other dry adhesives, we show that MWCNT adhesives are electrically and thermally conducting, which makes them a unique interfacial material.