High-aspect-ratio, free-form patterning of carbon nanotube forests using micro-electro-discharge machining

Abstract

This paper reports post-growth processing of vertically aligned carbon nanotube forests for the formation of high-aspect-ratio, three-dimensional microstructures in the material. High-frequency pulses of electrical discharge are generated to locally machine the nanotubes in order to create target shapes in a forest. Machining is performed in both dielectric oil and air. The optimal processing is demonstrated in air with a pulse voltage and peak current of 30 V and 60 mA, respectively, providing a discharge gap of ~ 10 µm. The minimized discharge energy and gap are shown to achieve an aspect ratio of 20 with the smallest feature of 5 µm in forests. Multilayer, three-dimensional geometries with vertical and angled surfaces are successfully obtained without disordering the vertical orientation of the nanotubes. Scanning electron microscopy and energy-dispersive X-ray spectroscopy are used for the surface analysis of the micromachined forests, revealing the dependence of their surface characteristics on the discharge conditions.