Growth of highly oriented carbon nanotubes by plasma-enhanced hot filament chemical vapor deposition

Abstract

Highly-oriented, multi-walled carbon nanotubes were grown on polished polycrystalline and single crystal nickel substrates by plasma enhanced hot filament chemical vapor deposition at temperatures below 666°C. The carbon nanotubes range fiom 10 to 500 nm in diameter and 0.1 to 50 pm in length depending on growth conditions. Acetylene is used as the carbon source for the growth of the carbon nanotubes and ammonia is used for dilution gas and catalysis. The plasma intensity, acetylene to ammonia gas ratio and their flow rates, etc. affect the diameters and uniformity of the carbon nanotubes. [2]. Nanotube alignment is particularly important to enable both fundamental studies and applications, such as flat panel displays, vacuum microelectronics, chargeable batteries, etc. However, only one report exists on the growth of aligned carbon nanotubes by thermal decomposition of acetylene in nitrogen gas at temperature above 700°C on mesoporous silica containing iron nanoparticles [6] before our report on growth of large arrays of well-aligned carbon nanotubes on glass [16]. Here we report the growth of highly-oriented, multi-walled carbon nanotubes on nickel substrates at low temperatures by the same method (plasma enhanced hot tungsten-filament chemical vapor deposition) described in our previous paper [16]. The motivation to grow carbon nanotubes on Ni substrates is for the applications of using carbon nanotubes as battery electrodes and energy storage. We use acetylene (C2H2) to provide carbon for the growth of the carbon nanotubes and ammonia (NH3) gas for both dilution gas and catalysis. The catalytic role of ammonia is discussed in our previous paper [ 161.The base pressure of the deposition chamber is < 6 x Torr. We grew carbon nanotube films in a pressure of 1 -20 Torr maintained by flowing acetylene and ammonia gases with a total flow rate of 120 -200 sccm. We varied the acetylene-to-ammonia volume ratio fiom 1 : 2 to 1 : 10 for different experimental runs. Both polished polycrystalline and single-crystal Ni substrates were used. After stabilizing the working pressure, the tungsten filament coil powered by a DC source and the plasma-generator were turned on to generate heat and plasma. Under the present experimental set-up, the temperature of samples is estimated to be below 666 "c (which is the strain point of the display glass provided by Corning Inc.) since the display glass sit side by side with the Ni did not show any noticeable deformation after the experiments [ 161 and also Ni is not red-hot by visual observation. Growth durations were fiom 10 min to 5 h depending on the desired carbon nanotube lengths. Samples were examined by scanning electron microscopy (SEM, Hitachi S-4000) to measure tube lengths, diameters, site distributions, alignment, density and uniformity. High-resolution transmission electron microscopy (TEN was used to determine 2 the microstructure of individual tubes. Samples were also examined by x-ray diffraction, Raman spectroscopy, and x-ray photoemission spectroscopy to stud...

Recent Advances in Vapor Chamber Transport Characterization for High-Heat-Flux Applications

“…For this analysis, wetting contact angles were assumed based on the observations of Rossi et al [219] and Kim et al [220], and continuum approximations for capillary dynamics [220], surface tension [221], and viscous drag [222] were shown to be justified. Properties were obtained as a function of nanowire diameters and number densities consistent with typical fabrication processes [223][224][225]. …”

Growth of a single freestanding multiwall carbon nanotube on each nanonickel dot

“…2͑e͒ have not been previously observed using this growth method. [10][11][12] Significant variation in the height ͑0.1-5 m͒ of the grown bundles is observed ͑recent experiments showed that the variation in height is smaller than 20%͒, with no apparent relationship between height and spatial position. We note that even though the heights are different by more than a factor of 10, the base diameters are approximately uniform ͑ϳ150 nm͒.…”

“…Aligned growths of carbon nanotubes have been produced by chemical vapor deposition ͑CVD͒ on mesoporous silica with imbedded iron particles. 9 The growth of large arrays of well aligned carbon nanotubes has been demonstrated on glass, 10 on nickel, 11 and on silicon. 12,13 Here we report the growth of an array of individual multiwall carbon nanotubes onto a grid of patterned metal.…”

“…The final Ni pattern remained after resist/metal liftoff in acetone. The patterned substrate was loaded into a plasma-enhanced-hot-filament-͑CVD͒ system described previously [10][11][12] with a base pressure below 10 Ϫ6 Torr. Growth was performed at a pressure of 1-10 Torr with an acetylene ammonia mixture of 40:160 ͑standard cubic centimeter per minute, both acetylene and ammonia were highly purified with a minimum purity of 99.99%͒.…”

Density and production of NH and NH2 in an Ar–NH3 expanding plasma jet

“…NH 3 plasmas are, for example, used for modifying the wettability and biocompatibility of polymers, 1-3 for improving the gas permeability of membranes, 4 for inducing surface passivation of electronic devices, 5,6 and for nitridation of dielectric and metallic materials. 7,8 Ammonia is also admixed in plasmas used for the synthesis of carbon nanotubes 9,10 and for ligand abstraction and nitridation during atomic layer deposition of metal nitrides. [11][12][13] One of the most important applications of NH 3 -based plasmas in industry to date is, however, the deposition of silicon nitride films.…”