Role of height and contact interface of CNT microstructures on Si for high current field emission cathodes

Regular arrays of vertically aligned microstructures consisting of entangled carbon nanotubes (CNTs) of different height and contact interface were grown on Si substrates with a bimetallic catalyst by water-assisted chemical vapor deposition. The arrays of high and wide CNT blocks (150–300 μm, 50–140 μm square) showed the ability to reach high stable field emission (FE) currents per block up to 300 μA due to the presence of multiple CNT emitters. However, significant outgrowth of the CNTs and limited mechanical stiffness of such blocks led to a limited FE homogeneity and alignment of the emitters. For the arrays of small rounded CNT bundles (∼5 μm, 20 μm diameter), well-aligned and highly efficient FE with maximum currents up to 40 μA per CNT bundle have been achieved. Unusual I-V curves with current saturation, strong activation effects and glowing spots just before destruction have been observed and are discussed by means of band structure considerations.