## 3 Results and Discussion
### CNTs  
Figure 4 shows the Raman spectra of the samples grown at 500, 600, 700, and 800 \({}^{\circ}\)C on the surface of the substrate with the laser of 514 nm at room temperature. In all curves, two peaks centered at 1360 and 1593 cm\({}^{-1}\) were observed. Both of them correspond to the D and G bands of the graphitic phase, indicating the presence of crystalline graphitic MWCNTs [16]. With the increase of the synthesis temperature, the D peak narrowed and the G peak heights increased. The intensity ratio of D peak and G peak (\(I_{\rm D}\)/\(I_{\rm G}\)) is sensitive to structural defects in the MWCNTs. The smaller the ratio, the higher the degree of graphitization. The \(I_{\rm D}\)/\(I_{\rm G}\) ratio decreased with the increase of the synthesis temperature from 600 to 800 \({}^{\circ}\)C; the lowest \(I_{\rm D}\)/\(I_{\rm G}\) ratio (1.0) was found at 800 \({}^{\circ}\)C. The G peak of pure graphite is at 1582 cm\({}^{-1}\); the defects in the samples caused the blue shift of G peak, verifying that the products' defect concentration is relatively high. From the view of the HRTEM, the products are mainly nanotubes, as shown in Figure 6; we can prove that the products are CNTs. The \(I_{\rm D}\)/\(I_{\rm G}\) ratio of CNTs grown on stainless steel substrate by PECVD [17; 18; 19; 20; 21] is 1.0-1.5, similar to that by AMPCVD. The \(I_{\rm D}\)/\(I_{\rm G}\) ratio of CNTs grown on 316 stainless steel pretreated by oxidation processes is 0.48-0.56 at 800-900 \({}^{\circ}\)C [16], indicating that the stainless steel substrate mainly determines the quality of the CNTs and the quality of CNTs synthesized by AMPCVD is as good as other kinds of PECVD processes. According to the results of plasma spectrum detection and exhaust gas detection, the ethanol precursor almost completely decomposed into active groups by 200 W atmospheric pressure microwave plasma. The recombination of carbon groups into CNTs mainly depends on temperature. We introduced  
Figure 4: Raman spectra of the samples obtained at 500, 600, 700, and 800 \({}^{\circ}\)C on the substrate. Figure 3: The ethanol contents at different temperatures in the exhaust gas, with and without plasma treatment. the concept of conversion efficiency of carbon to describe the effect of temperature on the growth of CNTs. It represents the ratio of the carbon content of the grown CNTs to the total ethanol precursor. Figure 5 shows the SEM micrographs and the diameter distribution of the CNTs grown on the substrate with 200 sccm ethanol precursors at the temperature of 500, 600, 700, and 800 \({}^{\circ}\)C. The CNTs synthesized on the stainless steel substrate lie on the substrate face, with disordered orientation and uniform distribution, consistent with the results reported in the literature [19; 21], which use stainless steel substrate to grow CNTs by CVD and PECVD. It is proved that the morphology of CNTs is caused by the stainless-steel substrate. Figure 5a,d,g,j and 5b,e,h,k is the low magnification and high magnification images of the CNTs grown at the temperature of 500, 600, 700, and 800 \({}^{\circ}\)C, respectively. The total mass of CNTs increased with the increase of the temperature at the range of 500-800 \({}^{\circ}\)C. When the temperature is 800 \({}^{\circ}\)C, the total mass of CNTs is 300 mg. The carbon content of the total ethanol precursor is about 312 mg, indicating that approximately 96% of the precursor converted into CNTs. The precursor conversion efficiency at 500, 600, 700, and 800 \({}^{\circ}\)C was calculated, and they are 2%, 17%, 42%, and 96%, respectively. In the temperature range of 700-800 \({}^{\circ}\)C, the conversion efficiency of precursor increases significantly, indicating that the most suitable temperature for the growth of CNTs should be in the range of 700-800 \({}^{\circ}\)C; this needs further research. Figure 5c,f,i,l are the diameter distribution of the CNTs grown at the temperature of 500, 600, 700, and 800 \({}^{\circ}\)C, respectively. With the increase in temperature, the diameter of CNTs gradually increase.