We have studied the lifetime, activity, and evolution of Fe catalysts supported on different types of alumina: (a) sputter deposited alumina films (sputtered/Fe), (b) electron-beam deposited alumina films (e-beam/Fe), (c) annealed e-beam deposited alumina films (annealed e-beam/Fe), (d) alumina films deposited by atomic layer deposition (ALD/Fe), and (e) c-cut sapphire (sapphire/Fe). We show that the catalytic behavior, Ostwald ripening, and subsurface diffusion rates of Fe catalyst supported on alumina during water-assisted growth or "supergrowth" of single-walled carbon nanotube (SWNT) carpets are strongly influenced by the porosity of the alumina support. The catalytic activity increases in the following order: sapphire/Fe < annealed e-beam/Fe < ALD/Fe < e-beam/Fe < sputtered/Fe. With a combination of microscopic and spectroscopic characterization, we further show that the Ostwald ripening rates of the catalysts and the porosity of the alumina support correlate with the lifetime and activity of the catalysts. Specifically, our results reveal that SWNT carpet growth is maximized by very low Ostwald ripening rates, mild subsurface diffusion rates, and high porosity, which is best achieved in the sputtered/Fe catalyst. These results not only emphasize the connection between catalytic activity and particle stability during growth, but guide current efforts aimed at rational design of catalysts for enhanced and controlled SWNT carpet growth.

A multilayer optical interference film has been developed using plasma-enhanced chemical vapor deposition (PECVD) of different organic precursor materials. A relatively large refractive index contrast for polymers (>0.2) is achieved by sequential plasma polymerization (PP) of octafluorocyclobutane (OFCB) and benzene. Gas-phase molecules of both precursors, excited by an argon plasma in a flowing afterglow reaction chamber, are deposited on a variety of substrates to form dense, pinhole-free, cross-linked polymer films. The PP-OFCB film yields a refractive index of 1.40, whereas PP-benzene exhibits a refractive index of 1.61 at 500 nm. We report here on the chemical (FTIR and XPS), optical (variable angle spectroscopic ellipsometry and UV-Vis spectrometry), and morphological (scanning electron microscopy) characterization of individually polymerized films of each component. These data are used to design a multilayer film with a notch at ∼1 µm. A ten-bilayer stack (alternating high and low refractive index) was fabricated by sequential deposition of high and low refractive index layers at approximately 1 / 4 λ optical thickness. Optical spectra of the experimental stack exhibit a notch wavelength within several nanometers of the design wavelength indicating good thickness control.

A novel growth method (carbon molecular beam epitaxy (CMBE)) has been developed to produce high-quality and large-area epitaxial graphene. This method demonstrates significantly improved controllability of the graphene growth. CMBE with C(60) produces AB stacked graphene, while growth with the graphite filament results in non-Bernal stacked graphene layers with a Dirac-like electronic structure, which is similar to graphene grown by thermal decomposition on SiC (000-1).

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