刻线镍膜上沉积的碳纳米管场发射特性

Field Emission Properties of Carbon Nanotubes Films Grown on Patterned Ni Lines

利用微波等离子体化学气相沉积(MWPCVD)方法,在刻线的镍膜上沉积碳纳米管膜。通过SEM和拉曼光谱表征,讨论了催化剂厚度、制备温度、反应时间以及甲烷浓度对碳纳米管场发射的影响。结果表明:不同条件下制备的碳纳米管的场发射性能有很大差异,保持氢气的流量(100sccm)不变,当甲烷流量为5sccm、生长时间为5min、催化剂膜厚为150nm、温度为700～800℃时,场发射性能最好,开启场强为1.3V/μm,最大发射电流达到6.8mA/cm2。

Carbon nanotubes(CNTs) have attracted much attention because of their unique structure and properties since their discovery. One important potential application for the CNTs is as electron field emission sources in cold cathode flat panel displays as electron guns. Although a few of studies on the field emission properties of patterned aligned multi-wall nanotubes (MWNTs) were reported, the catalyst films were patterned by conventional photolithography and etching techniques. This method is too troublesome in application. In this paper, we prepared CNT patterns by a simple method, which is based on laser writing technology. Carbon nanotubes (CNTs) films were grown on patterned Ni lines coated substrate by microwave plasma chemical vapour deposition (MWPCVD). Ni films deposited on ceramics substrates by d.c. magnetron sputtering are used as catalysts for growing the CNTs. The ceramics substrates were mechanically polished using various grinding and polishing powders in order to uniform Ni film. Before growing CNTs, the Ni films were patterned to be lines by laser writing technology and then the CNTs were deposited on the catalyst patterns. The source gas for growing the CNTs was a mixture of H_2 and CH_4. The gas flow rate of H_2 is 100 sccm, and the growth pressure was 6.5×10~3 Pa, various deposition times were applied to control the length of the carbon nanotubes. Scanning electron microscopy (SEM) was used to determine the morphology of carbon nanotubes. Raman spectroscopy was 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 mica sheet with a suitable hole as the emission area. The gap between the anode and the cathode was 500 μm. The measurement was conducted under pressure of 3.6×10^(-5) Pa. By varying process conditions such as Ni layer thickness, gas flow rate, deposition time, reactive temperature, the optimum conditions for field electron emission were found. When gas flow rate of CH_4 was 5 sccm, Ni film thickness was 150 nm, deposition time was 5 min, and reactive temperature was 700～800 ℃, the field emission properties are best. At this condition, all nanotubes are well aligned as characterized by SEM. Turn-on field of 1.3 V/μm, emission current density of 6.8 mA/cm^2 and field enhancement factor of 8 477 were achieved.