Traditional nanosphere lithography (NSL) uses a monolayer of PS spheres as a mask, but regional boundaries formed in the monolayer due to stacking faults inevitably cause problems. After coating, the catalyst is arranged in a honeycomb pattern when the PS spheres are removed from the substrate. The regional boundaries and the vacancies in the self-assembled monolayer result in the deposition of different thicknesses of catalyst on these defective positions, which leads to non-uniform CNT growth.

Two NSL methods are commonly used to overcome the problem, one employing a double PS layer, the other using a monolayer metallic mask. However, both methods are complicated and difficult to control for large-scale fabrication. Nyan-Hwa Tai and his team from National Tsing Hua University have come up with an alternative approach, which involves the fabrication of close-packed CNT arrays using a catalyst-poisoning layer. The basic concept is to deposit a periodic poisoning layer over or underneath the catalyst layer to prevent CNT growth. As a result, a periodic CNT pattern can be obtained after growth through the CVD process (see process schematic).

The patterned CNT array has the potential to be used in the surface decoration of mobile phones, solar-cell electrodes, super capacitors and field emitters. INSL can also be extended to process other forms of nanomaterials, such as nanowires.

The researchers presented their work in Nanotechnology.