铬酸溶液后处理增强碳纳米管的场发射特性

采用铬酸溶液对碳纳米管进行后处理,旨在修饰碳纳米管的表面形态及改变碳纳米管的表面结构,进一步增强碳纳米管的场发射特性.铬酸溶液后处理与传统以硝酸后处理的厅法不同之处在于,铬酸溶液可以更有效率地与非品质碳及碳纳米管发生化学反应.可以预期碳纳米管经过铬酸溶液处理后,碳纳米管的表而形态、化学组成及场发射特性会产生很大的变化.场发射的数据显示,经铬酸溶液处理20 min的碳纳米管场发射电流比未经过铬酸溶液处理的场发射电流有明显的增加.然而,长时间的铬酸溶液处理也会降低碳纳米管场发射特性.经铬酸溶液处理20min的碳纳米管场发射电流增强原因主要为适度的铬酸溶液处理可以改变碳纳米管的表面形态,使碳管的表面密度增大、场发射功函数降低.但过长时间的铬酸溶液后处理,又会造成碳纳米管数目减少及表面结构受到损害,导致碳纳米管场发射特性变差.

Enhancement of field emission from carbon nanotubes by post-treatment with a chromium trioxide solution

A simple method is described to functionalize the surface and to modify the structures of multi-walled carbon nanotubes (MWCNTs) grown on silicon substrates using chromium trioxide (CrO3) solution. Unlike nitric acid (HNO3) used in the conventional post-treatment for MWCNTs, the chemical reaction with CrO3 involves amorphous carbon and the carbon nanotubes themselves. It is expected that the surface morphology, chemical composition, and field emission of MWCNTs should be significantly changed after CrO3 solution treatment. The results showed that after 20 min of CrO3 solution treatment, the emission currents were enhanced compared with the as-grown MWCNTs. However, extended treatment over 20 min was found to degrade the field emission properties of the film. The enhancement in field emission after 20 min of CrO3 solution treatment can be ascribed to the modification of surface morphology, the increase in surface density of MWCNTs, and the lowering of the work function. Prolonged CrO3 treatment dissolves MWCNTs and thus results in a decrease in field emission.