Kayastha Vijaya Kumar, Ulmen Benjamin, Yap Yoke Khin
Department of Physics, Michigan Technological University, Houghton, MI 49931, USA.
Nanotechnology. 2007 Jan 24;18(3):035206. doi: 10.1088/0957-4484/18/3/035206. Epub 2007 Jan 3.
We observed current density (J) dependent degradation in field emission current from multiwalled carbon nanotubes (MWCNTs). These degradations are recoverable and can be explained by emission current-induced dislocations along the MWCNTs. MWCNTs grown by thermal chemical vapour deposition (CVD) can emit stable current continuously for at least 1200 min with upper current density limits of approximately 0.5 mA cm(-2). In contrast, this upper limit is<40 microA cm(-2) for nanotubes grown by plasma-enhanced CVD (PECVD), although higher J is possible with relatively shorter stability duration. High-resolution transmission electron microscopy and Raman spectroscopy indicate higher graphitic order of the thermal CVD grown MWCNTs as compared to PECVD grown MWCNTs. Our study suggests that graphitic order affects their upper performance limits of long-term emission stability, although the effects from adsorbates cannot be completely ignored. These results indicate that field emission cannot be considered as an ideal quantum tunnelling process. The effect of electron transport along CNTs before electron tunnelling must be considered.
我们观察到多壁碳纳米管（MWCNT）的场发射电流存在与电流密度（J）相关的退化现象。这些退化是可恢复的，并且可以用沿MWCNT的发射电流诱导的位错来解释。通过热化学气相沉积（CVD）生长的MWCNT可以连续稳定发射电流至少1200分钟，其电流密度上限约为0.5 mA cm⁻²。相比之下，通过等离子体增强化学气相沉积（PECVD）生长的纳米管，其电流密度上限<40 μA cm⁻²，尽管在相对较短的稳定持续时间内可以实现更高的J。高分辨率透射电子显微镜和拉曼光谱表明，与PECVD生长的MWCNT相比，热CVD生长的MWCNT具有更高的石墨化程度。我们的研究表明，石墨化程度会影响它们长期发射稳定性的性能上限，尽管吸附物的影响也不能完全忽略。这些结果表明，场发射不能被视为理想的量子隧穿过程。必须考虑电子隧穿之前沿碳纳米管的电子传输效应。
