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

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insulating substrates, conductive layers have been used as an underlayer material by fewer teams in CNT growth (Nessim 2010). 2.3.3.1.3. Carbon Precursors Most commonly used CNT precursors in CVD process are methane (CH4) (Cassell, et al. 1999; Xiong, et al. 2005), ethylene (C2H4) (Futaba, et al. 2005, Futaba, et al. 2006, Hart and Slocum 2006, Hata, et al. 2004, Nessim, et al. 2008, Yamada, et al. 2006), acetylene (C2H2) (Patole, et al. 2008; Pint, et al. 2009a, Zhong, et al. 2009), benzene (C6H6) (Yang, et al. 2003) and carbon monoxide (CO) (Huang, et al. 2004). Each <strong>of</strong> <strong>the</strong>m has a particular decomposition temperature, <strong>the</strong>reby resulting in a different CNT growth temperature. There is a close relationship between <strong>the</strong> yield <strong>of</strong> CNTs and <strong>the</strong> injection time <strong>of</strong> <strong>the</strong> carbon source. The longer <strong>the</strong> injection time, <strong>the</strong> more molecules <strong>of</strong> hydrocarbon gases pass over <strong>the</strong> catalyst, with <strong>the</strong> result that <strong>the</strong> carbon yield <strong>of</strong> <strong>the</strong> deposits increases. Apart from <strong>the</strong> type <strong>of</strong> carbon precursor, its feed rate is also ano<strong>the</strong>r important parameter for CNT growth. It is known that high feed rates can increase <strong>the</strong> growth rate. Cheung et al. explained that different carbon species can be produced with <strong>the</strong> same diameter catalyst nano particles using different flow rates <strong>of</strong> carbon precursor gas (Cheung 2002). When <strong>the</strong> flow rate <strong>of</strong> <strong>the</strong> carrier gas is higher, nano particles with larger diameter grow. The reason why MWNT growth is easier than SWNT growth is that MWNT is possible to grow from most <strong>of</strong> <strong>the</strong> hydrocarbons, whereas SWNT grows from only selected hydrocarbons. 2.3.3.1.4. Temperature CNTs are typically grown in a temperature range from 550 °C to 1000 °C (Moisala, et al. 2003). However, <strong>the</strong> reaction temperature may vary in terms <strong>of</strong> <strong>the</strong> catalyst-support material pair. In order to accelerate <strong>the</strong> catalytic decomposition <strong>of</strong> hydrocarbon molecules and to increase <strong>the</strong> diffusion rate <strong>of</strong> carbon in <strong>the</strong> metal particle, experiments are carried out with increased temperatures (Moisala, et al. 2003). Moreover, <strong>the</strong> temperature is a crucial agent in <strong>the</strong> pre-growth treatment <strong>of</strong> <strong>the</strong> catalyst. 17
2.4. Growth Mechanism <strong>of</strong> Carbon Nanotube Two main growth models have been introduced for CNT growth whe<strong>the</strong>r <strong>the</strong> catalyst nano particles are at <strong>the</strong> tip <strong>of</strong> CNT or at <strong>the</strong> bottom side (Saito, et al. 1994). The former modelled by H<strong>of</strong>mann et al. (H<strong>of</strong>mann, et al. 2005) was called <strong>the</strong> tip-growth mechanism where <strong>the</strong> metal catalyst nano particle is lifted <strong>of</strong>f from <strong>the</strong> support surface during <strong>the</strong> growth process owing to weak support-catalyst interaction (Moisala, et al. 2003, Nessim 2010). The latter is called base-growth mechanism which was modelled by Puretzky et al. (Puretzky, et al. 2005). In this growth, <strong>the</strong> catalyst particle stays in a pinned way at <strong>the</strong> support surface while <strong>the</strong> tube grows up, so that CNT nucleates and grows above <strong>the</strong> catalyst (Moisala, et al. 2003, Nessim 2010). For <strong>the</strong> base-growth mechanism, <strong>the</strong>re is a strong interaction between <strong>the</strong> catalyst and substrate (Dresselhaus, et al. 2001). Figure 2.13 shows possible growth mechanisms <strong>of</strong> CNT explained by two groups. Figure 2.13. Schematic illustrations <strong>of</strong> CNT growth mechanisms a) Base-growth b) Tip-growth mechanism (Source: Ando, et al. 2004) 18
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 and 30: hydrocarbons (Cui, et al. 2003) wit
Page 31: 2.3.3.1.2. Thin Film Support Layer
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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