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

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2.3.3.1. Key Parameters <strong>of</strong> Chemical Vapor Deposition Method CNT growth mechanism has remained somewhat controversial despite being heavily investigated for years. In this part, <strong>the</strong> <strong>effects</strong> <strong>of</strong> important key parameters including catalyst thin films, thin film support layer, consideration <strong>of</strong> gases (hydrocarbons and flow rates), temperatures for both annealing and growth affecting <strong>the</strong> growth process <strong>of</strong> CNT are emphasized (Nessim 2010). In addition, <strong>the</strong> importance <strong>of</strong> <strong>oxidizers</strong> is mentioned in Chapter 3 in detail. 2.3.3.1.1. Catalyst Thin Film One <strong>of</strong> <strong>the</strong> indispensible parameters affecting <strong>the</strong> CNT growth is catalyst material, whose size, density and also types have important <strong>effects</strong> on <strong>the</strong> CNT diameter (Bonard, et al. 2002, Chhowalla, et al. 2001), and <strong>the</strong> growth rate (Lee, et al. 2002). Fur<strong>the</strong>rmore, it affects <strong>the</strong> morphology <strong>of</strong> both SWNT and MWNTs grown with <strong>the</strong> tip-growth or base-growth mechanisms. In addition, <strong>the</strong> areal density <strong>of</strong> particles determines <strong>the</strong> spacing between CNTs (Chhowalla, et al. 2001, Kind, et al. 1999). Ni, Co, Fe, Cr, Mn, Zn, Ti, Zr, Hf, Re, Sc, Y and Mo or a combination <strong>of</strong> <strong>the</strong>m have been used to determine <strong>the</strong> most suitable metal catalyst in <strong>the</strong> growth <strong>of</strong> CNT. However, it has been observed that Co (Ivanov, et al. 1994), Fe (Hernadi, et al. 1996) and Ni (Yudasaka, et al. 1994) (transition metals) or alloys <strong>of</strong> <strong>the</strong>m are <strong>the</strong> best catalyst choices among o<strong>the</strong>rs due to having finite carbon solubility (0.5wt%-1.5wt%) at high temperatures (800-900 o C) (Ando, et al. 2004, Dai 2002, Deck and Vecchio 2006, Dresselhaus, et al. 2001) and catalytically decomposing gaseous carbon-containing molecules (Moisala, et al. 2003). Lee et al. showed that respective CNT growth rate and <strong>the</strong> best product are based on <strong>the</strong> catalyst type in <strong>the</strong> order <strong>of</strong> Fe>Co>Ni (Lee, et al. 2002). It has also been stated that growing both MWNT and SWNTs is possible by means <strong>of</strong> <strong>the</strong>se three metals (Dupuis 2005). On <strong>the</strong> o<strong>the</strong>r hand, o<strong>the</strong>r elements such as Cu, Cr and Mn are used for only a limited amount <strong>of</strong> CNT growth (Vesselényi, et al. 2001). The CNT diameter matches <strong>the</strong> catalyst size as observed by Cheung et al. (Cheung 2002). The catalyst does not necessarily need to be a nano particle, even a bulk metal can catalyze <strong>the</strong> CNT growth. 15
2.3.3.1.2. Thin Film Support Layer Thin film support layer type may lead to different chemical or physical interactions between <strong>the</strong> catalyst metal and <strong>the</strong> supporting material. Additionally, <strong>the</strong> support layer have an important effect on mobility <strong>of</strong> catalyst nano particles (Dai 2002). Figure 2.12 shows that <strong>the</strong> catalyst orientation depending on <strong>the</strong> support layer differs during <strong>the</strong> growth process. It has been proven that <strong>the</strong> choice <strong>of</strong> underlayer is <strong>of</strong> critical importance for CNT growth. Figure 2.12. Schematic illustration <strong>of</strong> catalyst nano particles orientation (Source: Dupuis 2005) Quartz, silicon, silicon oxide (Zhang, et al. 2005), silica, alumina, alumina-silicate (zeolite), aluminium oxide (Hart and Slocum 2006, Hata, et al. 2004, Noda, et al. 2007), CaCO3, magnesium oxide (Xiong, et al. 2005, Xiong, et al. 2006) are used as substrates in CVD. The most common buffer layers are silica (SiO2) and alumina (Al2O3). Alumina materials are a better catalyst support layer than silica because <strong>of</strong> <strong>the</strong> fact that <strong>the</strong>re is a stronger metal-support interaction in alumina materials. The thickness <strong>of</strong> <strong>the</strong> underlayer has been found to influence <strong>the</strong> CNT growth critically (Nessim 2010). Thin (thick) catalytic metal films break into smaller (larger) catalytic nano particles, which produce smaller (larger) CNTs, for this reason, thin catalytic metal films (~ 1 nm) are necessary to grow SWNTs, thicker metal films (for example 10 nm) are used for MWNT growth (Yamada, et al. 2006). CNTs have successfully been grown on insulating substrates by many scientific teams all over <strong>the</strong> world. In contrast to 16
Page 1 and 2: THE EFFECTS OF OXIDIZERS ON THE DIA
Page 3 and 4: ACKNOWLEDGEMENTS During my master <
Page 5 and 6: ÖZET KİMYASAL BUHAR BİRİKTİRME
Page 7 and 8: TABLE OF CONTENTS LIST OF FIGURES .
Page 9 and 10: LIST OF FIGURES Figure Page Figure
Page 11 and 12: Figure 5.12. The growths with CO2 (
Page 13 and 14: Figure 5.36. Raman spectra
Page 15 and 16: Table 5.12. The amounts of<
Page 17 and 18: first two methods, arc discharge an
Page 19 and 20: Graphite is the mo
Page 21 and 22: preferred nanotube type because <st
Page 23 and 24: Figure 2.7. An illustration <strong
Page 25 and 26: Table 2.1. Advantages and disadvant
Page 27 and 28: 2.3.2. The Laser-Ablation Method Th
Page 29: hydrocarbons (Cui, et al. 2003) wit
Page 33 and 34: 2.4. Growth Mechanism of</s
Page 35 and 36: (Amama, et al. 2009, Hata, et al. 2
Page 37 and 38: that the small amo
Page 39 and 40: Figure 4.1. The Magnetron Sputterin
Page 41 and 42: the tube as <stron
Page 43 and 44: Table 4.1 (cont.) FeAlO15CNT840 750
Page 45 and 46: their diameter rou
Page 47 and 48: The principle of R
Page 49 and 50: Figure 4.6. Schematic picture showi
Page 51 and 52: 5.1.1. AFM Results There exists a p
Page 53 and 54: a ) Figure 5.2. AFM micrographs <st
Page 55 and 56: c Figure 5.3. (cont.) Element Wt %
Page 57 and 58: Table 5.2. (cont.) FeAlO12CNT771 76
Page 59 and 60: a b c e Figure 5.4. The growths wit
Page 61 and 62: Figure 5.5. (cont.) Count 35 30 25
Page 63 and 64: Due to the lack <s
Page 65 and 66: a c e Figure 5.8. The growths with
Page 69 and 70: Table 5.6 shows that the</s
Page 71 and 72: a c e Figure 5.12. The growths with
Page 75 and 76: In this part, for the</stro
Page 77 and 78: For FeAlO15 substrate, two differen
Page 79 and 80: For FeAlO16 substrate, two differen
Page 81 and 82:
e f Figure 5.20. (cont.) Due to <st
Page 83 and 84:
5.2.1.3. CNT Formation at Different
Page 85 and 86:
Count 30 25 20 15 10 5 0 a 5 10 15
Page 87 and 88:
Count 35 30 25 20 15 10 5 0 a CNT 8
Page 89 and 90:
Count 40 35 30 25 20 15 10 5 0 a CN
Page 91 and 92:
Count 45 40 35 30 25 20 15 10 5 0 a
Page 93 and 94:
Count 30 25 20 15 10 5 0 a 5 10 15
Page 95 and 96:
for SWNTs, there i
Page 97 and 98:
Table 5.17. (cont.) FeAlO15 CNT773
Page 99 and 100:
Intensity (a.u.) 2700 1800 900 CNT8
Page 101 and 102:
Intensity (a.u.) 2100 1400 700 CNT9
Page 103 and 104:
whole face. The formed catalyst par
Page 105 and 106:
Diameter Diameter 10 8 6 4 2 0 5 5
Page 107 and 108:
5.4. Statistical Analysis Results A
Page 109 and 110:
Kurtosis value is a descriptor <str
Page 111 and 112:
Very thin Fe films were grown on Si
Page 113 and 114:
REFERENCES Amama, P.B., C.L. Pint,
Page 115 and 116:
Hasegawa, K. and S. Noda. 2011a. Mi
Page 117 and 118:
Makita, Y., S. Suzuki, H. Kataura,
Page 119 and 120:
Vesselényi, I., K. Niesz, A. Siska
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