CNT synthesis methods overview:
•Arc discharge synthesis
•Laser ablation synthesis
•Thermal synthesis
•Chemical vapor deposition
•High-pressure carbon monoxide synthesis
•Flame synthesis
•PECVD synthesis
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5.3. Synthesis of one-dimensional nanostructures 5.3.1. Synthesis of carbon nanotubes.
Arc discharge synthesis
• Arc discharge was the first recognized method for producing both SWCNTs and MWCNTs, and has been optimized to be able to produce gram quantities of either.
• Currently, most growth is carried out in an Ar: He gas mixture.
• The current standard widely used for SWCNT production is a Y:Ni mixture that has been shown to yield up to 90%
SWCNT, with an average diameter of 1.2 to 1.4 nm
5.3. Synthesis of one-dimensional nanostructures 5.3.1. Synthesis of carbon nanotubes.
Laser ablation synthesis
The laser ablation technique uses a 1.2 at. % of cobalt/nickel with 98.8 at.% of graphite composite target that is placed in a 1200°C quartz tube furnace with an inert atmosphere of ~500 Torr of Ar or He and vaporized with a laser pulse
5.3. Synthesis of one-dimensional nanostructures 5.3.1. Synthesis of carbon nanotubes.
Thermal synthesis: CVD,
The CVD process encompasses a wide range of synthesis techniques, from the gram-quantity bulk formation of nanotube material to the formation of individual aligned SWCNTs on SiO2substrates for use in electronics.
Simply put, gaseous carbon feedstock is flowed over transition metal nanoparticles at medium to high temperature (550 to 1200°C) and reacts with the nanoparticles to produce SWCNTs
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5.3. Synthesis of one-dimensional nanostructures 5.3.1. Synthesis of carbon nanotubes.
High-pressure carbon monoxide synthesis 1. One of the recent methods for
producing SWCNTs in gram to kilogram quantities is the HiPco process.
2. One of the recent methods for producing SWCNTs in gram to kilogram quantities is the HiPco process.
3. The metal catalyst is formed in situ when Fe(CO)5or Ni(CO)4is injected into the reactor along with a stream of carbon monoxide (CO) gas at 900 to 1100°C and at a pressure of 30 to 50 atm.
5.3. Synthesis of one-dimensional nanostructures 5.3.1. Synthesis of carbon nanotubes.
PECVD synthesis
(PECVD) systems have been used to produce both SWCNTs and MWCNTs.
For SWCNT synthesis in the direct PECVD system, the researchers heated the substrate up to 550 to 850°C, utilized a CH4/H2 gas mixture at 500 mT, and applied 900 W of plasma power as well as an externally applied magnetic field.
The remote PECVD
system utilized by Li et al. used CH4/Ar held at 500 mT, with only 50 to 75 W of plasma power.
5.3. Synthesis of one-dimensional nanostructures 5.3.1. Synthesis of carbon nanotubes.
Specifics of CVD growth method (self reading) 2.3.1 Growth mechanics
2.3.2 Carbon feedstock 2.3.3 Catalyst
2.3.3.1 Unsupported catalyst 2.3.3.2 Supported catalyst 2.3.3.3 Vapor phase catalyst
2.4 Recent advances in SWCNT growth control 2.4.1 Location and orientation control
2.4.1.1 Catalyst patterning 2.4.1.2 Suspended aligned SWCNTs 2.4.1.3 Aligned SWCNTs on substrates 2.4.2 Growth of ultralong SWCNTs
2.4.3 Water-assisted high-yield growth of SWCNTs 2.4.4 Diameter and chirality control
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5.3. Synthesis of one-dimensional nanostructures 5.3.1. Synthesis of carbon nanotubes.
Growth mechanics:
CNT growth in CVD can be split into two basic types depending on the location of the catalyst, so-called gas phase growth, and substrate growth. The mechanism can be classed into “surface carbon diffusion” and “bulk carbon diffusion”.
•Surface carbon diffusion: The “cracked” carbon diffuses around the surface of solid metal particle.
•Bulk carbon diffusion: The “cracked” carbon dissolves in the metal liquid droplet. The droplet dissolves the carbon until it reaches saturation (V-L-S).
•In substrate growth, once the nanotube begins to grow by either surface or bulk carbon diffusion, the CNT will undergo either base growthor tip growth.
•Tip and base growth is dominated mechanism for MWCNTs and SWCNTs growth, respectively.
5.3. Synthesis of one-dimensional nanostructures 5.3.2. Synthesis of nanowires
Vapor phase growth of nanowires
•Vapor–liquid–solid growth
•Oxide-assisted growth
•Vapor–solid growth
•Carbothermal reactions
Solution based growth of nanowires
•Highly anisotropic crystal structures
•Template-based synthesis
•Solution–liquid–solid process
•Solvothermal synthesis
5.3. Synthesis of one-dimensional nanostructures 5.3.2. Synthesis of nanowires
Vapor–liquid–solid growth (1)
The liquid alloy becomes supersaturated with Ge, precipitation of the Ge nanowire occurs at the solid-liquid interface.
Real-time observations of Ge nanowire growth in an in situ high-temperature TEM, which demonstrate the validity of the VLS growth mechanism.
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5.3. Synthesis of one-dimensional nanostructures 5.3.2. Synthesis of nanowires
Vapor–liquid–solid growth (2)
GaAs, GaP, GaAsP, InAs, InP, InAsP II-VI seminconductior ZnS, ZnSe, CdSe, Oxide semiconductor SnO2, ZnO, TiO2, WO2.. Have been synthesized.
ZnO nanowires
Diameter nanowires controll
5.3. Synthesis of one-dimensional nanostructures 5.3.2. Synthesis of nanowires
•Vapor–solid growth
Vapor-solid growth is a catalyst-free process whereby deposition occurs when vapor condenses to form a solid.
The vapor then can solidify, forming a small crystal on the substrate (see Figure b). This crystal can now act as a
“seed” to promote further deposition of the local vapor (see Figure c).
5.3. Synthesis of one-dimensional nanostructures 5.3.2. Synthesis of nanowires
•Template-based synthesis
The various inorganic materials include Au, Ag, Pt, TiO2, MnO2, ZnO, SnO2,In2O3, CdS, CdSe, CdTe,
Nanowires themselves can be used as templates to generate the nanowires of other materials. The template may be coated to the nanowire (physical) forming coaxial nanocables
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