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本文主要研究了一种新型基于碳纳米管(CNT)场发射原理和气体吸附的低压氢传感技术。CNT通过化学气相沉积(CVD)直接生长在镍合金基底。部分样品有氢传感性能,即小电流恒压场发射在氢分压下逐步增加,而电流增长速率随着氢压强的增大而加快;另一部分样品则没有传感效应。拉曼测试表明有传感特性的样品晶体性好,D峰/G峰比值R值小于1,而无传感效应的R值大于1。第一性原理模拟研究表明:氢在碳纳米管表面发生解离化学吸附时,使碳纳米管的有效功函数降低,从而使CNT具有氢传感效应;而在晶体性差的CNT表面,氢原子优先吸附在缺陷位,功函数不发生变化。加热测试显示:传感样品温度在500-600℃时脉冲发射电流的变化与氢传感测试时持续场发射下电流变化大致相同,证明场发射焦耳加热是促进氢的解离吸附、进而使电流增长的一个重要因素。
In this paper, a new low-pressure hydrogen sensing technique based on the carbon nanotube (CNT) field emission principle and gas adsorption is mainly studied. CNTs grow directly on the nickel alloy substrate by chemical vapor deposition (CVD). Some of the samples have hydrogen sensing performance, that is, the emission of small current constant voltage increases gradually under the hydrogen partial pressure, while the current growth rate increases with the increase of hydrogen pressure; the other part of the sample has no sensing effect. Raman tests showed that the sensitized samples had good crystallinity, R value of D peak / G peak ratio less than 1, and sensorless R value greater than 1. The first-principles simulations show that when hydrogen dissociates on the surface of carbon nanotubes, the effective work function of the carbon nanotubes decreases, so that the hydrogen-sensing effect of CNTs is obtained. On the surface of poor-crystallinity CNTs, hydrogen atoms Preferential adsorption in the defect position, the work function does not change. The heating test shows that the change of pulse emission current at the temperature of 500-600 ℃ is almost the same as that of the continuous field emission at the time of hydrogen sensing test. It is proved that the field emission Joule heating promotes the dissociative adsorption of hydrogen, An important factor for growth.