Berger Claire, Poncharal Philippe, Yi Yan, de Heer Walt
School of Physics, Georgia Institute of Technology, Atlanta, Georgia, USA.
J Nanosci Nanotechnol. 2003 Feb-Apr;3(1-2):171-7. doi: 10.1166/jnn.2003.180.
The electrical transport in multiwalled carbon nanotubes is shown to be ballistic at room temperature with mean free paths on the order of tens of microns. The measurements are performed both in air and in the transmission electron microscope by contacting the free end of a nanotube pointing out of a fiber to a liquid metal and measuring the dependence of the nanotube resistance between the contacts. For a specific representative nanotube the resistance per unit length is found to be Rt = 31 +/- 61 omega/micron and the contact resistance with the liquid metal, Rc = 165 +/- 55 omega microns, corresponding to a mean free path l = 200 microns. Current-to-voltage characteristics are in accord with the electronic structure. The nanotubes survive high currents (up to 1 mA, i.e., current density on the order of 10(9) A/cm2). In situ electron microscopy shows that a relatively large fraction of the nanotubes do not conduct (even at high bias), consistent with the existence of semiconducting nanotubes. Discrepancies with other measurements are most likely due to damage caused to the outer layer(s) of the nanotubes during processing. The measured mean free path of clean, undamaged arc-produced multiwalled carbon nanotubes is several orders of magnitude greater than that for metals, making this perhaps the most significant property of carbon nanotubes.
研究表明，多壁碳纳米管在室温下的电输运呈弹道输运，平均自由程达几十微米量级。测量是在空气中以及在透射电子显微镜中进行的，通过将从纤维中伸出的纳米管的自由端与液态金属接触，并测量接触点之间纳米管电阻的依赖性。对于一根特定的代表性纳米管，发现其单位长度电阻为Rt = 31 +/- 61Ω/微米，与液态金属的接触电阻Rc = 165 +/- 55Ω微米，对应平均自由程l = 200微米。电流-电压特性与电子结构相符。纳米管能承受高电流（高达1 mA，即电流密度约为10(9) A/cm2）。原位电子显微镜显示，相当一部分纳米管不导电（即使在高偏压下），这与半导体纳米管的存在一致。与其他测量结果的差异很可能是由于在加工过程中纳米管外层受到损伤所致。所测量的清洁、未受损的电弧法制备的多壁碳纳米管的平均自由程比金属的平均自由程大几个数量级，这可能是碳纳米管最显著的特性。
