**2. Experimental Method**

Fig. 1 shows the schematic of the chemical vapor deposition (CVD) system used for centi‐ meter long CNT array growth. The reactor consists of a 2 inch quartz tube placed inside a high temperature furnace (Barnstead International, type F79400 tube furnace) and four massflow controllers (MFC) which control the flow rate of the gas reactants such as hydrogen, ethylene, water vapor and argon. A water bubbler is also installed to provide water vapor using argon carrier gas. A window on the side of the reactor is used to acquire real-time images of CNT arrays and to record data with a digital camera (Olympus E510) controlled by a computer.

**Figure 1.** Schematic of the CVD system for direct observation of the centimeter long carbon nanotube arrays during their growth. The top view of the reactor is shown.

The substrates were parts of 4 inch silicon wafers (100) with SiO2 (500 nm) on the top. The buffer and catalyst layers based on Al2O3 (15 nm thick)/Fe (1 nm thick) were deposited on the wafers using e-beam evaporation. After the deposition, the substrates were annealed for several hours at 400 ºC in Air. All the experiments were performed using the following optimized recipe for centimeter long CNT arrays: 560 mmHg of argon, 60 mmHg of hydro‐ gen, and 140 mmHg of ethylene as a carbon precursor. The water concentration in the reac‐ tor was near 900 ppm measured by a quadrupole mass spectrometer (QMS). The total pressure was kept at one atmosphere during the growth and the temperature varied from 690 ºC to 840 ºC. Real-time images of the CNT array growth were recorded from the moment that ethylene was introduced into the reactor. The images were used to study the growth mecha‐ nism and kinetics of the CNT growth. Scanning electron microscopy (SEM, Phillips XL30 ESEM), high resolution transmission electron microscopy (HRTEM, JOEL 2000 FX) and Micro-Raman spectroscopy (Renishaw inVia Reflex Micro-Raman) were employed to characterize the CNT morphology.
