Efficient CVD Growth of Single-Walled Carbon Nanotubes on Surfaces Using Carbon Monoxide Precursor

Abstract

Single Walled carbon nanotubes (SWNTs) were grown directly on flat substrates using chemical vapor deposition (CVD) method with carbon monoxide and hydrogen mixture as feeding gas. Comparing with other CVD methods, this new approach yields higher efficiency and more reproducible results in obtaining high quality SWNTs separated as individual nanotubes on substrates. Such samples can be used to fabricate nanodevices directly with no further purification or dispersion. Important factors that affect the nanotube growth and possible mechanisms are also discussed.Since their discovery, single-walled carbon nanotubes (SWNTs) have been heavily studied owing to their outstanding physical and chemical properties. 1 They are widely considered as ideal candidates for interconnections and active components in nanoscale electronic devices. Recent research has demonstrated SWNT-based nanodevices, such as quantum wires, 2 field-effect transistors, 3-5 field emitters, 6 etc. Until recently, most of the SWNT-based devices used materials synthesized by either the laser ablation method 7 or the arc method, 8 where the as-grown samples have to be purified and suspended in solvent before deposition on surfaces for device fabrication. The processes of purification and suspending nanotubes in solvent involve the use of highly oxidative chemicals and ultrasonication that are known to create defects on nanotubes and alter their electronic properties. For nanoscale electronics, defect-free SWNTs on surfaces are especially desirable. An alternative and successful way to fabricate nanotube devices is to use nanotubes grown directly on surfaces to avoid the undesired purification steps. However, up to now, surface growth of SWNTs has been limited to chemical vapor decomposition (CVD) of methane on metal nanoparticles supported on surfaces. [9][10][11][12] The growth conditions are critical for the preparation of nanotubes with high purity and efficiency. Here we report an improved CVD method for the growth of SWNTs on surfaces using monodispersed Fe/Mo nanoparticles as the catalyst and a mixture of carbon monoxide (CO) and hydrogen (H 2 ) as feed gas. In contrast to CVD of methane, 9-12 this method allows higher efficiency for nanotube growth and easier control of the growth conditions, thus offering more reproducible results.In our experiments, the catalysts are monodispersed Fe/ Mo nanoparticles (4.2 nm) prepared according to reference 13. The nanoparticles can be dissolved in nonpolar solvents such as hexane. They were deposited on the substrate by slow evaporation of the solution. The substrate was then annealed in air at 700°C for 10 min to remove the organic coating on the particles formed during their preparation steps. 13 Si/SiO 2 substrates were purchased from MEMC Electronic Materials with 500 nm SiO 2 layer. Alumina (sapphire A plane) and magnesium oxide substrates (Superconductive Components, Inc.) were also used. To grow nanotubes, we used a two-furnace setup (Figure 1). The substrates were loaded into the second furnac...

Reagent control over the composition of mixed metal oxide nanoparticles

“…Fe:Co ratio) prepared by the thermal decomposition in benzyl ether of Fe(acac) 3 and Co(acac) 2 , in the presence of a mixture of oleic acid and oleylamine surface capping ligands and HDD as an accelerating agent, is directly related to the composition of the metals in the precursor solution. However, the size and size distribution of the NPs were found to depend on the relative concentration of oleic acid, oleylamine, HDD and the metal precursor.…”

“…This is particularly true in the area of catalysis where small changes in composition can have large effects on the catalytic activity. [2][3][4][5][6][7] Recently, we have gained interest in the potential use of superparamagnetic NPs as traces in geological formations. The idea being that variation in the Curie temperature can be used as a method for differentiating one tracer from another and from naturally occurring background materials.…”

“…[16,17] We have previously reported that for the composition of cobalt-iron oxide (Co-Fe-O) NPs (i.e. Co:Fe ratio) as synthesised from the appropriate metal acac precursors, the Co concentration increases linearly with increasing Co(acac) 2 precursor concentration, and only a very small percentage of Co(acac) 2 was not directly incorporated into the NPs. [18] This suggested that the kinetics of the decomposition of each precursor [Fe(acac) 3 and Co(acac) 2 ] is near identical and that the composition of the NPs is statistically a function of the starting precursor mixture.…”

“…Co:Fe ratio) as synthesised from the appropriate metal acac precursors, the Co concentration increases linearly with increasing Co(acac) 2 precursor concentration, and only a very small percentage of Co(acac) 2 was not directly incorporated into the NPs. [18] This suggested that the kinetics of the decomposition of each precursor [Fe(acac) 3 and Co(acac) 2 ] is near identical and that the composition of the NPs is statistically a function of the starting precursor mixture. In the course of our studies, we have become interested in whether compositional control can be extended to other systems and what factors of the precursor stability, structure and reactivity control the composition of the final NP.…”

Su(4) mixed valence regime in carbon nanotube quantum dots

“…[7] and contacted by Cr/Au electrodes. The middle section of small-gap semiconducting nanotubes fills with electrons at positive V gate (Fig.…”