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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方法不同之处在于,铬酸溶液可以更有效率地与非晶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,碳纳米管的表面形态、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20min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。
The chromic acid solution is used to post-treat the carbon nanotubes to modify the surface morphology of the carbon nanotubes and to change the surface structure of the carbon nanotubes to further enhance the field emission characteristics of the carbon nanotubes. The difference between the chromic acid solution post-treatment and the traditional nitric acid post-treatment method is that the chromic acid solution can more chemically react with the amorphous carbon and the carbon nanotubes. It can be expected that the surface morphology, chemical composition and field emission characteristics of the carbon nanotubes will greatly change after the carbon nanotubes are treated with a chromic acid solution. The field emission data show that the field emission current of carbon nanotubes treated with chromic acid solution for 20min has a significant increase compared with the field emission current without chromic acid solution treatment. However, long-term chromic acid solution treatment also reduces the carbon nanotube field emission characteristics. The reason for the enhancement of the field emission current of the carbon nanotubes treated with chromic acid solution for 20 min is mainly that the moderate chromic acid solution treatment can change the surface morphology of the carbon nanotubes and increase the surface density of the carbon nanotubes and reduce the field emission work function. However, prolonged treatment with chromic acid solution will cause the number of carbon nanotubes to decrease and the surface structure to be damaged, resulting in poor field emission characteristics of the carbon nanotubes.