the effects of oxidizers on the diameters of the carbon nanotubes ...

CHAPTER 4
EXPERIMENTAL PROCESS
This chapter involves experimental details about <strong>the</strong> <strong>the</strong>sis work and consists <strong>of</strong>
three main parts. In <strong>the</strong> first part, <strong>the</strong> catalyst film deposition process by DC magnetron
sputtering is discussed. The second part deals with <strong>the</strong> <strong>the</strong>rmal CVD process in detail.
The third part gives details <strong>of</strong> <strong>the</strong> characterization techniques <strong>of</strong> grown CNTs which are
SEM, AFM and Raman Spectroscopy.
4.1. Catalyst Film Deposition by DC Magnetron Sputtering Process
In this work, deposition <strong>of</strong> very thin Fe catalyst film onto <strong>the</strong> Al2O3/SiO2/Si
substrates was carried out by utilizing <strong>the</strong> DC magnetron sputtering method, which was
<strong>the</strong> most popular technique used to fabricate <strong>the</strong> thin film materials from <strong>the</strong> point <strong>of</strong>
good surface uniformity, growth on substrates, and its cost effectiveness. For this
current work, AJA ATC Orion 5 UHV sputtering system was used (Figure 4.1).
(100) Si wafers with 2-inch diameter and a typical resistivity <strong>of</strong> 1-20 ohm-cm
purchased to be used as support layer were cleaned chemically in methanol for 15 min
in an ultrasonic bath and rinsed with ultra-pure water for 15 min prior to growth. The
commercial silicon films were first oxidized by dry <strong>the</strong>rmal oxidation system. 10-15 nm
thick alumina (Al2O3-barrier) and than 0.5-3 nm thick iron (Fe catalyst) layers were
deposited on a silicon dioxide (SiO2) wafer by DC magnetron sputtering. At <strong>the</strong> end <strong>of</strong>
this process, Fe/Al2O3/SiO2/Si substrates were ready for growing CNTs on <strong>the</strong>m.
The magnetron sputtering process depended on <strong>the</strong> movement <strong>of</strong> electrons and
ions in a magnetic field and <strong>the</strong> generation <strong>of</strong> ion-induced secondary electrons at <strong>the</strong>
target takes place in an evacuated chamber. The chamber pressure was evacuated to a
pressure <strong>of</strong> 10 -6 Torr by means <strong>of</strong> turbomolecular pump and depositions were performed
at a rate <strong>of</strong> 0.1 A o /s and 20 W at a growth pressure <strong>of</strong> 0.5 mTorr under Ar ambient. This
system was controlled by a computer.
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