  Vertically-aligned carbon nanotube (CNT) "forest" microstructures fabricated
by chemical vapor deposition (CVD) using patterned catalyst films typically
have a low CNT density per unit area. As a result, CNT forests have poor bulk
properties and are too fragile for integration with microfabrication
processing. We introduce a new self-directed capillary densification method
where a liquid is controllably condensed onto and evaporated from CNT forests.
Compared to prior approaches, where the substrate with CNTs is immersed in a
liquid, our condensation approach gives significantly more uniform structures
and enables precise control of the CNT packing density and pillar
cross-sectional shape. We present a set of design rules and parametric studies
of CNT micropillar densification by this method, and show that self-directed
capillary densification enhances the Young's modulus and electrical
conductivity of CNT micropillars by more than three orders of magnitude. Owing
to the outstanding properties of CNTs, this scalable process will be useful for
the integration of CNTs as functional material in microfabricated devices for
mechanical, electrical, thermal, and biomedical applications.
