since single - walled carbon nanotubes ( swcnts ) were discovered in 1993 , they have generated significant research activities due to their particular microstructures , unique properties and great potential applications in many fields . a single - walled nanotube can be described as a single layer of a graphite crystal that is rolled up into a seamless cylinder , with both ends capped with hemispheres made of hexagonal and pentagonal carbon rings . with remarkable properties , swcnts can be explored to be used in novel applications like pressure sensors , flow sensors and hydrogen storage [ 2 - 6 ] . because swcnts possess so many unique properties , the synthesis of swcnts becomes a subject of a significant global research effort . up to now , a number of methods for preparing swcnts have been reported , such as electric arc discharge , laser ablation methods   and catalytic chemical vapor deposition ( ccvd ) [ 9 - 13 ] . among them , the ccvd method is becoming a dominant way for scaling up the production of swcnts at relatively low cost . in the ccvd method , methane , acetylene , hexane , alcohol and other hydrocarbons are used as carbon feedstock . the catalysts are generally supported on ai2o3 or mgo and consist of fe , co , mi , mo or mixtures of those metals . in the synthesis of swcnts by ccvd method , the temperature plays a key role . in this paper , we report the synthesis of swcnts by catalytic decomposition of methane over mo2-fe10/mgo catalyst and give a temperature window using raman spectroscopy . with the relatively intensity of d band to the g band ( id / ig ) and the transmission electron microscopy images of samples a mixture of mg(no3)26h2o , ammonium molybdate , citric acid , h2o and fe(no3)29h2o at a weight ratio of 10:0.07m:4:1:0.16n ( m = 2,n = 10 , marked with mo2-fe10/mgo ) was stirred for 6 h at 90 c and dried at 150 c overnight , then ground into a fine powder . finally , the powder was calcined in air ( air flow : 30 ml / min ) for 30 min at 550 c before used for swcnts growth . the growth of swcnts was carried out in a fluidized - bed which is shown in fig . the temperature was raised to the setting value in ar atmosphere at a flow rate of 200 ml / min before ch4was introduced into the reactor at 60 ml / min for 30 min , then ch4was turned off and the furnace was cooled to room temperature in an ar flow . sketch map of the fluidized bed reactor the raman spectra were recorded by a renishaw invia spectrophotometer at room temperature and in a back - scattering geometry , with ar laser at 514.5 nm . figure 2shows the raman spectra for materials grown at different growth temperature ( a : 750 c ; b : 800 c ; c : 850 c ; d : 900 c ; e : 950 c ) . in fig . 2a , only the g band ( tangential mode ) , d band ( related to disordered graphite or amorphous ) and a shoulder at 1604 cm(the fundamental e2gmode of graphite ) are presented . in the lower wavenumber region ( 100300 cm ) , the radial breath modes ( rbm ) which represent the existence of swcnts are hardly shown . the data show no swcnts are formed and there are only poorly multi - walled carbon nanotubes ( mwcnts ) and organized carbon in the sample . the relatively high intensity of the d band relative to g band ( id / ig = 0.72 ) indicates mass amorphous carbon content or more defect concentration in the mwcnts . ( a ) 750 c , ( b ) 800 c , ( c ) 850 c , ( d ) 900 c and ( e ) 950 c when temperature increases to 800 c , raman spectrum of the sample ( fig . 2b ) shows several weak rbm bands in the lower wavenumber region ( 100300 cm ) . this revealed that swcnts formed at 800 c . from the tem image ( fig . 3a ) , we can observe that there are a few single swcnt and swcnts bundle with different diameters . according to the equation rbm = 6.5 + 223.75/dt ( cm ) , the diameter of swcnts synthesized at 800 c varies from 0.86 to 1.73 nm , which accords with the result of the tem image ( fig . id / ig , is observed to decrease with increasing temperature ( at 800 c , the id / ig is 0.47 ) . transmission electron microscope images of samples formed undera800 c , b850 c , c900 c andd950 c raman spectrum of the sample grown at 850 c ( fig . ( 100300 cm ) , two outstanding rbm bands are presented . according to the formula , the peaks at 147 and 169 cm correspond to the swcnts with diameter of 1.59 and 1.38 nm , respectively . the tem image ( fig . 3b ) reveals that the product consists of single and bundle swcnts with even diameters . the intensity ratio becomes lower with id / ig = 0.32 and the tem shows that there are only a few amorphous carbons in the swcnts bundle . the rbm mode is observed as a strong band at 160 cmin the raman spectrum at 900 c ( fig . the relatively lower intensity , id / ig = 0.14 , indicates a lower amount of amorphous carbon content or a lower defect concentration in the swcnts . 3c , the swcnts in the bundle have even diameters and appear clean and uncoated . it is well known that when the diameter distribution of swcnts is more narrow , the application values of swcnts are higher . at this growth temperature , only one strong band at 160 cmin the raman spectrum , this shows the diameter distribution of swcnts is very narrow . all the results show high - quality swcnts have been synthesized at 900 c . by increasing growth temperature to 950 c , more amorphous carbons are formed in the swcnts bundles due to the self - decomposition of ch4 . the tem images show that swcnts are coated by more and more amorphous carbons , and when the temperature increases to 950 c , swcnts are hardly observed . in order to study the influence of growth temperature on the purity of prepared tube samples , we give the curve ( fig . 4 , two kinds ofid / igdistributions can clearly be distinguished . from 750 to 900 c , theid / igdecreases with increasing growth temperature . when the temperature is higher than 900 c , theid / igincreases with growth temperature . in the former stage , swcnts are formed gradually with increasing growth temperature and the content of swcnts in the products increases . in the latter stage , more and more amorphous carbons are formed , and when the growth temperature increases to 950 c , only a few swcnts are shown in the results and are coated by plenty of amorphous carbons . a temperature window of swcnts growth by catalytic chemical vapor deposition of ch4over mo - fe / mgo catalyst has been studied . the results suggest that when the temperature is lower than 750 c , only a few swcnts are formed , and when the temperature is higher than 950 c , more and more amorphous carbons are formed in the swcnts bundles due to the self - decomposition of ch4 . the temperature window of swcnts efficiently growth is between 800 and 950 c , and the optimum growth temperature is about 900 c .
a temperature window for the synthesis of single - walled carbon nanotubes by catalytic chemical vapor deposition of ch4over mo2-fe10/mgo catalyst has been studied by raman spectroscopy . 
 the results showed that when the temperature is lower than 750 c , there were few swcnts formed , and when the temperature is higher than 950 c , mass amorphous carbons were formed in the swcnts bundles due to the self - decomposition of ch4 . 
 the temperature window of swcnts efficient growth is between 800 and 950 c , and the optimum growth temperature is about 900 c . 
 these results were supported by transmission electron microscope images of samples formed under different temperatures . 
 the temperature window is important for large - scale production of swcnts by catalytic chemical vapor deposition method .