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

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Figure 4.2. The TCVD System at CNL Lab at Physics Department, IYTE Figure 4.3. Some thin films used for CNT growth in <strong>the</strong> quartz boat In <strong>the</strong> process, <strong>the</strong>re is a matter not to be forgotten that <strong>the</strong> quartz boat and <strong>the</strong> samples placed are located in <strong>the</strong> middle <strong>of</strong> <strong>the</strong> furnace where a <strong>the</strong>rmocouple is situated. Though <strong>the</strong> furnace temperature can reach to 1100 o C, <strong>the</strong> experiments were carried out at 750 o C, 760 o C and 770 o C in <strong>the</strong> work <strong>of</strong> <strong>the</strong> <strong>the</strong>sis. All CNT growth experiments were performed at atmospheric pressure. The CVD process consisted <strong>of</strong> <strong>the</strong> following sequential steps: As a first step, before <strong>the</strong> CNT growth, argon, whose purpose was to remove <strong>the</strong> contamination before and after <strong>the</strong> CNT growth process and to prevent <strong>the</strong> oxidation <strong>of</strong> samples, flew through 25
<strong>the</strong> tube as <strong>the</strong> carrier gas. Second, prepared catalyst films (supported on a Si wafer) were placed in <strong>the</strong> quartz boat, and placed is in <strong>the</strong> furnace. After heating <strong>the</strong> furnace to <strong>the</strong> desired growth temperature, both etching gas (H2) and oxidizer were started to be sent to do preannealing and form catalyst nano particles. Both H2 and <strong>the</strong> oxidizer provided <strong>the</strong> reduction from metal oxide catalyst to metal catalyst. CO2 was used as an oxidizer during all experiments. When <strong>the</strong> pretreatment time finished, CNT growth started with C2H4 flow through <strong>the</strong> tube for a predetermined time. When <strong>the</strong> growth time finished, firstly <strong>the</strong> hydrocarbon gas was turned <strong>of</strong>f and <strong>the</strong>n both <strong>the</strong> hydrogen gas and oxidizer were turned <strong>of</strong>f. The temperature was set to 0 o C and <strong>the</strong> system was left for cooling in Ar gas environment. Different gas flow rates and amount <strong>of</strong> oxidizer were investigated in this work. The flow rates <strong>of</strong> Ar, H2, C2H4 (150 sccm, 140 sccm, 80 sccm) were constant during all experiments. In addition growth time was also ano<strong>the</strong>r parameter for growing CNT, so <strong>the</strong> growth time was chosen as 15 minutes for all <strong>of</strong> <strong>the</strong> experiments in this study. 4.2.1. Growth with Oxidizers The main parameters studied in <strong>the</strong> experiments carried out in presence <strong>of</strong> CO2 were pretreatment time, oxidizer gas flows, sending moment and duration <strong>of</strong> oxidizer and rates <strong>of</strong> oxidizer in pretreatment and growth processes. As well as <strong>the</strong>se main parameters, different growth temperatures were also tried to determine <strong>the</strong> optimum temperature value in presence <strong>of</strong> CO2 as shown in Table 4.1. 26
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 and 32: 2.3.3.1.2. Thin Film Support Layer
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: Figure 4.1. The Magnetron Sputterin
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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