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Electrochemical impedance measurement of a carbon nanotube probe electrode

机译：碳纳米管探针电极的电化学阻抗测量

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摘要

We measured and analyzed the electrochemical impedance of carbon nanotube (CNT) probe electrodes fabricated through the physical separation of insulated CNT bridges. The fabricated CNT electrodes were free-standing CNTs that were completely covered with an insulator, except for their tips. Typical dimensions of the nanoelectrodes were 1-10nm in CNT diameter, 80-300nm in insulator diameter, 0.5-4μm in exposed CNT length and 1-10μm in probe length. The electrochemical impedance at frequencies ranging from 40Hz to 1MHz was measured in physiological saline. The measured impedance of the CNT electrode was constant at 32MΩ at frequencies below 1kHz and was inversely proportional to frequency at frequencies above 10kHz. By means of comparison with the parasitic capacitive impedance of the insulator membrane, we confirmed that the electrode was sufficiently insulated such that the measured constant impedance was given by the exposed CNT tip. Consequently, we can use the CNT electrode for highly localized electrochemical impedance measurements below 1kHz. Considering an equivalent circuit and the nanoscopic dimensions of the CNT electrode, we demonstrated that the constant impedance was governed by diffusion impedance, whereas the solution resistance, charge-transfer resistance and double-layer capacitance were negligible.
机译：我们测量并分析了通过绝缘CNT桥的物理分离而制造的碳纳米管（CNT）探针的电化学阻抗。所制造的CNT电极是自立式CNT，除了尖端外，它们完全被绝缘体覆盖。纳米电极的典型尺寸是：CNT直径为1-10nm，绝缘体直径为80-300nm，暴露的CNT长度为0.5-4μm，探针长度为1-10μm。在生理盐水中测量了40Hz至1MHz频率下的电化学阻抗。在低于1kHz的频率下，CNT电极的测量阻抗恒定为32MΩ，与高于10kHz的频率成反比。通过与绝缘膜的寄生电容阻抗进行比较，我们确认了电极已充分绝缘，因此所测得的恒定阻抗由裸露的CNT尖端给出。因此，我们可以将CNT电极用于1kHz以下的高度局部化的电化学阻抗测量。考虑到等效电路和碳纳米管电极的纳米尺寸，我们证明了恒定阻抗受扩散阻抗控制，而溶液电阻，电荷转移电阻和双层电容可忽略不计。

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