Effects of electrode shape in micro-electro-discharge patterning of carbon nanotube forests

Abstract

This paper reports the performance of different tool electrode structures in micropatterning of vertically aligned carbon nanotube (CNT) forests through dry micro-electro-discharge machining (μEDM). Micro cylindrical electrodes of tungsten with flat and hemispherically rounded tips were employed in this study. The rounded-tip electrode was shaped using a custom wet μEDM process. Both types of electrodes were used to pattern arrays of micro test slots at different depths and discharge voltages on a multi-walled CNT forest from which the resultant discharge gaps were experimentally characterized. The rounded-tip electrode showed a 2.1–2.4× reduction in the discharge gap with applied voltages of 15–20 V, suggesting its potential to improve the lateral resolution of the patterning process when compared with the flat-tip case. Finite element analysis of the process configuration with these two electrodes was conducted and showed good agreement with the improvement factors of the discharge gap experimentally observed. However, the process using the rounded-tip electrode resulted in larger variations on the bottom surfaces of the created patterns, while the use of the flat-tip electrode provided higher uniformity on these surfaces, revealing an apparent trade-off relationship between the discharge gap and the patterning uniformity for the two electrode types under the tested conditions. Elemental analysis of the processed CNT forest surfaces showed no detectable contamination from the electrodes onto the forest structures patterned using either electrode.