Carbon Nanotubes: Structure, Synthesis & Applications

1. Structure & Chirality

Carbon nanotubes (CNTs) are cylindrical fullerene structures with sp² hybridized carbon atoms. Single-walled CNTs (SWCNTs) have diameters 0.4–2 nm; multi-walled CNTs (MWCNTs) have 2–100 walls with 0.34 nm interlayer spacing. The chiral vector C_h = na₁ + ma₂ defines the tube structure. Armchair (n,n) tubes are always metallic; zigzag (n,0) are metallic when n mod 3 = 0; chiral (n,m) are metallic when (n-m) mod 3 = 0. About 1/3 of random SWCNTs are metallic, 2/3 semiconducting.

2. Synthesis Methods

Arc discharge (Iijima, 1991): graphite electrodes under He atmosphere, ~3000°C, produces MWCNTs. Laser ablation: pulsed laser vaporizes graphite target with metal catalyst, yields high-quality SWCNTs. Chemical Vapor Deposition (CVD): carbon precursor (CH₄, C₂H₂) over catalyst nanoparticles (Fe, Co, Ni) at 600–1200°C. Plasma-enhanced CVD enables lower temperatures. Water-assisted CVD ("super-growth") achieves millimeter-long aligned forests. HiPco process uses CO at high pressure with Fe(CO)₅ catalyst.

3. Electronic & Mechanical Properties

Metallic SWCNTs have ballistic conductance: resistance independent of length up to ~1 μm. Current density: >10⁹ A/cm² (1000× copper). Semiconducting tubes have band gaps inversely proportional to diameter: E_g = 2γ₀a_{CC}/d ≈ 0.7 eV for 1 nm tube. Young's modulus: ~1 TPa (strongest material known). Tensile strength: 30–100 GPa. Thermal conductivity: ~3500 W/mK (exceeds diamond). Aspect ratios up to 10⁸. Elastic strain limit: ~5% vs. ~0.1% for steel.

4. Functionalization & Processing

Covalent functionalization: oxidation creates -COOH groups for further chemistry; reduces conductivity. Non-covalent: π-π stacking with pyrene derivatives, surfactant wrapping (SDS, SDBS), DNA wrapping for chirality sorting. Dispersion challenges: van der Waals bundling (0.5 eV/nm). Sorting techniques: density gradient ultracentrifugation, gel chromatography, aqueous two-phase extraction. Aligned CNT arrays via CVD on patterned catalysts. CNT fibers spun from forests or solutions.

5. Applications

Nanoelectronics: CNT field-effect transistors (CNTFETs) approaching 5 nm nodes. IBM demonstrated wafer-scale CNT circuits. Composites: 0.5–5 wt% CNTs in polymers increase strength 30–50% and add conductivity. Energy: CNT anodes improve Li-ion battery capacity 2×; CNT-based supercapacitors. Displays: CNT transparent conductive films replace ITO. Sensors: functionalized CNTs detect ppb-level gases. Biomedical: CNT drug delivery, biosensors. Structural: CNT-reinforced concrete reduces cracking 25%.

Try it live

Everything above runs in your browser — open Brownian Motion — Nanoparticle Diffusion Simulator and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.