Elucidation of self-vibration phenomenon of carbon nanotubes in magnetic field and its application to nano-sensing

对碳纳米管（CNT）场电子发射体进行了原位透射电子显微镜（TEM）和扫描电子显微镜（SEM）研究，明确了碳纳米管（CNT）场电子发射体大振幅自发振动的来源。在瞬变电磁法中，场发射电流和外加电压都不是自发振动发生的决定性因素。相反，研究发现碳纳米管相对于对电极的方向很重要，即只有当碳纳米管被外加电场弯曲超过50°时才会观察到自发振动。对于自发振动的CNTs，振动起始电压与CNTs的直径有明显的相关性，而CNTs的长度对起始电压没有影响。另一方面，在扫描电镜中，即使弯曲超过50°的碳纳米管发射管也没有表现出任何自发振动。由于SEM样品阶段的磁场比TEM样品阶段的磁场小得多，TEM和SEM之间碳纳米管行为的差异表明磁场在诱导自发振动中的作用；即，通过碳纳米管的电流与磁场之间的洛伦兹力是感应大振幅振动的来源。

In-situ transmission electron microscopy (TEM) and scanning electron microscopy (SEM) of carbon nanotube (CNT) field electron emitters have been carried out in order to clarify the origin of spontaneous vibration with large amplitude. In TEM, neither field emission current nor applied voltage were decisive factors for the onset of the spontaneous vibration. Instead, it was found that the orientation of the CNT against the counter electrode was important, i.e., the spontaneous vibration was observed only when the CNT bent more than 50° by the applied electric field. For CNTs which showed spontaneous vibration, a correlation between the onset voltages for vibration and the diameter of CNTs are clearly found, but the length of CNTs showed no effect on the onset voltage. In SEM, on the other hand, even CNT emitters which bent more than 50° did not show any spontaneous vibration at all. Since the magnetic field at the SEM sample stage is much smaller than that at TEM sample stage, the difference in the CNT behavior between TEM and SEM indicates the role of the magnetic field in the induction of the spontaneous vibration; i.e., the Lorentz force between the electric current through the CNT and the magnetic field is the origin of the induction of large-amplitude vibration.