沉积工艺参数对碳纳米管薄膜场发射性能的影响

Effects of Deposition Conditions on Field Emission Properties of Carbon Nanotubes Films

利用微波等离子体化学气相沉积（MWPCVD）方法，在不锈钢衬底上直接沉积碳纳米管膜。通过SEM、拉曼光谱和XRD表征，讨论了制备温度和甲烷浓度对碳纳米管膜场发射的影响。结果表明：不同条件下制备的碳纳米管膜的场发射性能有很大差异，保持氢气的流量（100sccm）、生长时间（10min）、反应室压力不变，当甲烷流量为8sccm、温度为700—800℃时，场发射性能最好，开启场强仅为0．8V／μm，发射点分布密集、均匀。

Two basic types of methods are presently available to prepare CNTs field emission cathode. The first one is screen printing method by using CNTs paste. The large screen cathode can be made, but it is dif- ficult to control the uniform distribution of CNTs for such method. The CVD method is the second one that is ideally suited to grow film of nanotubes on pre-coating substrates with a metallic catalyst layer, which has been reported by many authors. Although a few of studies on the field emission properties of patterned aligned multiwall nanotubes （MWNTs） were reported, the catalyst films were patterned by conventional photolithography and etching techniques. This method is too troublesome in application. We reported the CNTs films were directly synthesized on stainless steel substrates by MWPCVD without pre-coating of catalyst layer, and especially investigated the influence of deposition conditions on field emission from such deposited carbon nanotubes films. The source gas for growing the CNTs was a mixture of H2 and CH4. The gas flow rate of H2 is 100 sccm, and the growth pressure was 6.7×10^3 Pa, deposition time was 10 min. Scanning electron microscopy （SEM） was used to determine the morphology of carbon nanotubes. Raman spectroscopy and XRD were used to analyze the structure of carbon nanotubes. The field emission characteristics of the samples were measured by using a diode structure. The transparent anode was made of coating phosphor onto an ITO coated glass plate. The CNT samples as the cathode were separated from the anode by a china sheet with a suitable hole as the emission area. The gap between the anode and the cathode was 500μm. The measurement was carried out in vacuum chamber under pressure of 6.5×10^-5 Pa. By varying deposition conditions such as gas flow rate, reactive temperature, the optimum conditions for field electron emission of CNTs were found. When gas flow rate of CH4 was 8 sccm, and reactive temperature was 700 -800℃, the field emission properties of CNTs are the best. At this condition, all CNTs are disorder growth, but are of uniform with the highest density as characterized by SEM. Turn-on field of CNTs is 0.8 V/μm, and emission sites are dense and uniform.