Preparation And The Electronic Properties Of Aligned Carbon Nanotubes Array Film

In this thesis, aligned carbon nanotubes(ACNTs) array film are grown at low substrate temperature by hot filament radio frequency plasma enhanced chemical vapor deposition (HF-RF-PECVD) of a gas mixture of methane and hydrogen. The growth parameters such as sort of catalyst, substrate temperature, gas flow ratio, air pressure, growth time and radio power are considered on growth of ACNTs array film. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and laser Raman spectroscopy (Raman) are used to express the ACNTs array film. The study including the AC impedance property and cyclic voltammetry property of ACNTs array film electrode grown on nickel foam substrate. The main work is expressed as following:1. Preparation of catalystCatalysts are prepared by spin-coating solution on silicon substrate and quartz substrate. The experiment results show that, after drying and thermal decomposition, the Fe(NO₃)₃,Co(NO₃)₂,Ni(NO₃)₂ solutions spin-coated on silicon can be evenly nano scale distributed on substrate by heat treatment under N₂-H₂ environment for 60min. The density distribution of the catalyst particles are influenced by the concentration of solution. The catalyst particles prepared by 1 mol/L of Ni(NO₃)₂ solution is suitable for growth of ACNTs because of the size between 30～50nm and distribution denseness and uniformity. The catalyst particles prepared by dropping solution on substrate are gathered together and uneven distribution. Some catalyst particles prepared on this condition can offer the nuclear-condition of growth of ACNTs.Fe catalyst clusters are prepared on silicon substrate by magnetron sputtering. The experiment results show that the density and size of catalyst clusters increase by the increase of sputtering time. The catalyst clusters are distributed denseness and the size in nano scale when the sputtering time is set to 5 minutes. The ACNTs grown by this catalyst is distributed denseness and well aligned. When the sputtering time is set more than 20 minutes, the catalyst clusters are gathered to micron-level clumps no longer conform the condition of growth of ACNTs. 2. The effect of experiment parameters on growth of ACNTsIt is found that the diameter distribution is controlled by the size of catalyst particle. The diameters of CNTs change by the change of size of the catalyst particles. Transition metal such as Fe, Co, Ni can be used as catalysts on growth of ACNTs, and the catalytic activity Fe>Co>Ni. The substrate temperature is great influence on the growth of ACNTs. No ACNTs can be found when the substrate temperature is too low. The samples grown on extra high substrate temperature contain mass of impurity. And 500℃is a suitable substrate temperature on growth of ACNTs. Comparative analysis on different substrate shows that silicon and quartz substrates are both viable on growth of ACNTs. The best experiment parameters of growth ACNTs is as following: gas pressure 28Pa, gas mass flow ratio: CH₄:N₂:H₂=150:25:25, substrate temperature 500℃, radio power: 200w, growth time 60 minutes.3. Electronic properties of ACNTs electrodeThe AC impedance test of ACNTs electrode growth on nickel foam substrate shows that the electrode displays obvious characteristics of super capacitors at low frequency. And the electric capacity is related to the frequency.Cyclic voltammetry tests on ACNTs electrodes grown by different concentrations of solution as catalyst show that the electrodes have high capacity under the test condition of scanning potential of -0.2～+0.8V, scan rate of 1mV. The specific capacity of ACNTs electrode grown by 0.1mol/L Ni(NO₃)₂ solution as catalyst is up to 278.2F/g. The scan rate has great influence on the specific capacity of the electrode. The specific capacity decrease rapidly when the scan ratio increases.