| Discharge characteristics of DC glow plasma was investigated in this paper and preparation technology of carbon nanotube was established. We study the prepared carbon nanotube with Scanning Electronic Microscope(SEM) as well as Transmission Electron Microscope(TEM) and Raman spectrum. we have study effect of technology condition for growth feature of carbon nanotube. 1 Characteristics of discharge Characteristics of DC glow discharge at high press were researched. the glow appears at low pressure, the discharge region were composed of four zones with the gas pressure increasing: cathode-glow layer, Faraday dull area, sphere of plasma, and anode-glow layer. Discharge status of each zone was investigated. the cathode-glow layer was the main zone of potential fall. the vest electron with low energy exist in this zone, the gas could not be excited and ionized by electron. In Faraday dull area, the electron energy was low, the elastic collision was dominated among electron and particles. the plasma sphere was the main zone of exciting and ionizing particles. the electrode distant was a great factor to affect the glow state. the plasma sphere disappear when the electrode distant was decreased to certain distance. the longitudinal direction size of plasma sphere increasing with the electrode distant promoting, the across direction size of plasma was invariant. This discharge feature is very important to deposited carbon nanotube. We investigated the relationship between the electrode distant and discharge voltage, discharge voltage take on liner increasing with the electrode distant increasing. When DC discharge current was low at high pressure, the voltage increasing fast with current increasing. but discharge voltage could reach saturation state when discharge current reach to certain value. The gas pressure was more high, the current corresponding to saturation discharge was more low. 2 The establishment of preparation technology of carbon nanotube Electrode distance was a great factor to affect discharge feature. we utilized this feature to established preparation technology of carbon nanotube at high pressure. the aurum-nickel membrane serve as catalyst, the compound gas of methane and hydrogen were carbon sources gas. The glow was appears at low pressure. the electrode distant was keep to 5mm, no plasma exist in this state. When gas pressure and methane concentration reach to prearrange experimental value. the electrode distant was increasing to 25mm, the plasma sphere appears, the carbon nanotube could be prepared in this state. The preparation technology of parameter range was investigated. We have compared the preparation condition of diamond film with that of carbon nanotube. The growth study of carbon nanotube on multi-species substrate indicated that carbon nanotube can not be deposited on pure nickel membrane. When the thickness of nickel membrane exceed 80nm and aurum membrane exceed 60nm, there was no carbon nanotube deposited on substrate. in the condition of aurum membraneˊs thickness was 40nm and nickel membraneˊs thickness was 20nm, 40nm,60nm respectively. The carbon nanotube could be prepared. 3 SEM was employed to analyze the influences of substrate temperature, reaction pressure, components of reaction gases and thickness ratio of Au film to Ni film on the CNTs'growth feature. (1)The effect of substrate temperature for the growth feature of carbon nanotube CNTs were not obtained at 500℃and 900℃;a few CNTs of low density were prepared at 600℃; long and dense CNTs with homogenous diameter grew at 700 ℃; while, at 800 ℃, it can be seen obviously that the CNTs of bigger diameter and lower density congregated together owning to the high substrate temperature. The temperature range of preparing CNTs was from 600℃to 800℃, 700℃is the best deposited temperature. (2)The effect of reaction pressure for the growth feature of carbon nanotube The diameter of CNTs are different at the different gas pressure which was range from 60torr to 90torr, while it is homogenous at 75torr. Further more, at 90torr, thick CNTs are more than thin ones and they twist and transversely connect together. (3)The effect of methane concentration for the growth featureof carbon nanotubeThe CNTs, only a few of which have branches, have homogenous diameter when the methane concentration is 8% and 12%. Yet, the diameter increased obviously when methane concentration was 16%. When methane concentration rose to 20%, it can be seen that thin CNT grew on thick CNT, which is called branch, and the diameter is non-homogenous. (4)The effect of thickness of the catalyst membrane for the growth feature of carbon nanotube. The diameter of CNTs are different corresponding to different thickness of catalyst layer. The diameter increased along with the increasing of the thickness 4 Study on the Raman spectroscopy of CNTs The Raman features of SWCNTs and MWCNTs have been introduced. For our CNTs, the bands centre at ～1580cm-1 and ～1350cm-1, and it can be confirmed that our CNTs are MWCNTs. The influences of methane concentration on the peak height ratio were discussed. The peak height ratio decreased along with the increase of mechane concentration, which indicates that the atoms of sp2 hybrid relatively increased and the graphitization of CNTs enhanced. At the mean time, along with the increase of methane concentration, the blue shift, ranging from 12cm-1 to 23cm-1, of G peak increased. The temperature doesn't have clearly effect on the blue shift value and FWHM of G peak, but it affects the FWHM of D peak greatly, which is bigger at a lower temperature. the height of D peak is higher than that of G peak. at a higher temperature, the increase of D peak height is bigger than that of G peak. 5 Study of CNTs by TEM In the condition of methane concentration variety only. the TEM observation indicated that the carbon nanotube with homogeneous diameter is obtained and it is 20nm when methane concentration was 5%. in the condition of methane concentration was 20%, the diameter of carbon nanotube is 80nm. and the nanotube diameter is non-homogeneous. the diameter of thin nanotube is 20nm. The diameter of carbon nanotube is 30nm and 50nm when the substrate temperature was 700℃and 800℃respectively.
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