*2.1.5 Laser ablation method*

*21st Century Surface Science - a Handbook*

*2.1.3 Electric arc discharge method*

called Plasma Arcing method.

**Diameter of electrodes:** 5–20 μm. **Gap between electrodes:** 1 mm. **Current:** 50–120 amperes.

**Temperature:** 3000–3500°C.

pure graphite anode and produces C+

*2.1.3.1 Description*

**Voltage:** 20–25 V.

electrodes.

helium gas.

pump [24].

such as argon gas. The hydrocarbon gas (carbon source) is pumped into the quartz tube which undergoes pyrolysis reaction and forms vapor carbon atoms. These carbon atoms bind to the substrate and join to eachother by Vanderwaal force of attraction and grow as multi-walled carbon nanotubes (MWCNTs) on the substrate [23]. To synthesize single-walled carbon nanotubes catalyst nanoparticles of Fe, Co, Ni are used. The obtained CNTs are further purified to get the pure form of CNTs.

Carbon nanotubes are synthesized by electric arc discharge method which is also

**Electrodes:** Pure graphite rods (both positive and negative electrode). The positive electrode is adjustable from outside to maintain the gap between the two

**Inert gas pressure:** 100–500 torr (No CNT formed below 100 torr). Inert gas is used for cooling and condensation of atoms to form the CNTs. Inert gas determines the structure of carbons to be present in CNTS. Commonly used inert gas is

**Reactor:** It contains a quartz chamber which is connected to vacuum pump and a diffusion pump to inert gas supply. Initially the chamber is made vacuum by the vacuum pump and then the chamber is filled with helium gas by the diffusion

In this method, a potential of 20–25 V is applied across the pure graphite electrodes separated by 1 mm distance and maintained at 500 torr pressure of flowing helium gas filled inside the quartz chamber **Figure 2**. When the electrodes are made to strike each other under these conditions it produces an electric arc. The energy produced in the arc is transferred to the anode which ionizes the carbon atoms of

ions and forms plasma (Plasma is atoms or

*2.1.4 Procedure for synthesis of CNTs by Electric arc discharge method*

**30**

**Figure 2.** *Electric arc method.*

**Physical vapor deposition (PVD):** PVD is a technique by which a material can be vaporized into gaseous form and then deposited on the surface of a substrate.

**Target source:** The most common carbon source target used is solid graphite which is irradiated by laser source and vaporized into vapor carbon atoms.

**Laser source:** Laser source used for vaporization of target material into target vapor atoms can be continuous laser source such as CO2 laser or pulsed laser source such as Nd:YAG laser (Neodymium doped Yttrium Aluminum Garnet, Nd:Y3Al5O12) .

**Substrate used:** The substrate used in this method is the water cooled copper collector on which the vaporized carbon atoms deposit and grow as CNTs.

**Inert gas atmosphere:** Argon gas is commonly used as inert gas which flows at a constant flow rate towards the water cooled copper collector.
