Electrostatic capacitance and Faraday cage behavior of carbon nanotube forests

Abstract

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Strain relaxation and resonance of carbon nanotube forests under electrostatic loading

“…2. Measurement of the capacitance of CNT forests in our recent previous work [39] confirmed that the capacitance of a similar CNT forest micropillar is dominated by outer surfaces, and the electric field only penetrates several microns into the forest. Therefore, when force is applied by the electric field, the penetration depth is limited and the observed orientation change of the CNTs (see below) is restricted to the top surface where the field is greatest.…”

“…We further note that the CNT forest behaves as a Faraday cage [39], i.e., the electrostatic force acts only on its external surface, as indicated schematically by the red color in Fig. 2(d).…”

“…We first directly measured the capacitance of each CNT pillar, at varying gap distances, g, between the probe and the top surface of the pillar [39]. This relationship is shown in Fig.…”

“…The calculated electrostatic force decreases rapidly with increasing gap. The capacitance measurement (i.e., the distribution of the capacitance along the height [39]) was further used to calculate the distributed electrostatic force F ES (external force) applied to the CNT forest, based on the extracted capacitance area, as shown in Fig. 2(c).…”

“…The penetration depth depends on the density of the CNTs. We note that, since the magnitude of the electrostatic force is proportional to the capacitor area (extracted from the capacitance measurements [39]) and inversely proportional to the square of the length of field lines [40], the electrostatic pressure (namely, electrostatic force divided by the capacitance area) gets its maximal value at the top portion of the CNT forest.…”