Influence of catalyst thickness and temperature gradient on MWCNT growth and morphology in TCVD process M.H. Kara 1, 2, * , A. Awang Teh 1, 2 , R. Ahmad 1, 2 , M. Rusop 2 , and Z. Awang 1, * 1 Microwave Technology Centre; 2 NANO-ElecTronic Centre; Faculty of Electrical Engineering, Universiti Teknologi MARA 40450 Shah Alam, Selangor, Malaysia *Email: mohsenkara@yahoo.com , zaiki.awang@gmail.com Abstract— In this article the effect of catalyst thickness and reaction temperature on the formation of horizontal multi-wall carbon nanotube (MWCNT) was discussed to control product growth and morphology. MWCNTs were synthesized from methane by double-heater thermal catalytic vapor deposition method (TCVD) using a mixture of methanol and ammonia as active agents to promote the growth of nanotubes and nickel as a catalyst and are characterized by scanning electron microscopy (SEM) and Raman spectroscopy. Results from SEM indicated that, the diameter and density of tubes increased with increasing the catalyst thickness, whereas the effect of reaction temperature was on the growth efficiency and purity of nanotubes and lifetime of the catalyst. The most favorable temperature for the highest growth efficiency and purity was around 900 °C. However the optimal catalyst thickness was around 4 nm. Keywords:, TCVD, SEM, multiwalled carbon nanotubes, growth parameters, raman spectroscopy. I. INTRODUCTION Carbon nanotubes (CNTs) which consist of graphene sheets rolled up as hollow cylinders, first identified by Iijima in 1991[1]. Due to their extraordinary electronic, thermal, and mechanical properties, CNTs offer a promising route for enormous applications such as electronic devices, field emission displays, chemical, physical and bio-sensors, scanning probes, hydrogen storage, etc. [2-5]. Among other approaches for CNT synthesis, catalytic chemical vapor deposition (CVD), which has a broad category, including plasma enhanced CVD (PECVD), thermal CVD (TCVD), and hot filament CVD (HFCVD) [6 - 8], is the most common method, due to relatively lower reaction temperature, high purity, high yield and in-situ selective CNT growth on catalytically patterned substrates [9 - 11]. In our previous work [12], we found that the new precursor consist of CH3OH / NH3 with ratio of 8 to 5 respectively to enhance the growth of CNTs in methane ambient using TCVD method at fixed reaction temperature of 850°C. However the dimensions and structure of CNTs critically depend on the synthesis parameters, such as reaction temperature, synthesis time, carbon source gas, catalyst structure and thickness [13, 14]. Therefore, optimization of synthesis parameters is crucial for controlling product morphology in order to produce high quality aligned CNT. In this paper, we extended our systematic study through SEM observations by varying reaction temperature (800 – 1000 °C), and catalyst thickness (1 - 20 nm). The effect of synthesis time and carbon source gas flow rate on the CNT growth will be studied later in our next paper. II. EXPERIMENTAL DETAILS The fabrication of CNTs on P-type silicon substrates; size 1 cm by 1 cm, thickness 525 ± 25 μm and resistivity 1-10  cm were done using nickel (Ni) as catalyst. The first process is to remove any impurity and oxidization on the Si substrate surface. Then, a thin Ni film was deposited on cleaned substrates as catalyst using electron beam evaporator and the substrates were placed on an alumina boat before placed inside a double-heater TCVD. The first heater was set at 1000 °C to decompose methane, while the second was set at (800-1000 °C) for pre-treatment of the catalytic film. As A. Awang Teh et al. proposed [12] a precursor of ammonia and methanol solution at ratios of 5:8 was placed within the first heater to enhance the growth of CNT, while the substrates were located in the second heater. The second heater was first switched in flowing Argon at 200 bubbles /min. When the temperature of the second heater reached setting point and stayed stable, first heater was then switched on. As the temperature of the latter reached 1000 °C, the Ar supply was switched to methane gas at flow rate of 100 bubbles /min. The total growth time of the CNTs was 120 min. Finally, when both heaters were shut off, methane gas was then switched back to Argon to eliminate any air. After fabrication is completed, The CNT morphology was examined using JEOL JSM6360L SEM. 978-1-4577-0255-6/11/$26.00 ©2011 IEEE 783 TENCON 2011