Aug 12, 2009
Inverse nanosphere lithography orders CNT array
Materials experts in Taiwan have developed a simple method for fabricating uniform periodic CNT arrays dubbed inverse nanosphere lithography (INSL). The technique provides partial alleviation of stacking defects of polystyrene (PS) spheres in the self-assembled monolayer, which improves the uniformity of the array. Also, the size and period of the CNT array can be adjusted by careful choice of the PS sphere diameter.
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.
About the author
The work was performed in the Department of Materials Science and Engineering at National Tsing Hua University in Taiwan and was supported by the National Science Council, Taiwan under contract no. NSC 95-2221-E-007-062-MY3. Tsung-Yen Tsai recently received his PhD degree in the department and will work in the Advance Carbon Nano-materials Lab of the department as a postdoctoral researcher. Dr Tsung-Han Chen was a PhD student instructed by Prof. Shih-Chin Chang who is a faculty member of the department. Hui-Chen Hsu was a masters student of the lab. Dr Thomas Joseph Palathinkal was a PhD student of the lab and is now is a postdoctoral researcher at Tamkang University. Prof. Nyan-Hwa Tai is the head of the Advance Carbon Nano-materials Lab.