The way in which a gecko can stick to a wall has been scrutinized by scientists, who have spent time researching how to replicate van der Waals force in components and adhesives. A Rice University (Houston) graduate student recently applied this principle to a new method of pattern transfer, however, that could lead to advancements in novel carbon nanotube-based applications such as sensors and nanotube circuitry in electronic devices. While experimenting with using water vapor to clean up carbons on nanotubes, graduate student Cary Pint discovered that water could serve as the crux of a pattern-transfer technique. Employing chemical vapor deposition (CVD), Pint first grew single-walled carbon nanotubes on a substrate. Next, by etching the nanotubes with a blend of hydrogen gas and water vapor, he was able to weaken the bonds between the materials and the metal catalyst. This process readied the patterned single-walled carbon nanotubes for transfer to another substrate. After etching, Pint applied the nanotube-covered substrate to another surface. Likening the transfer method to a rubber stamp, Pint notes that upon 'stamping' the new surface with the nanotube-covered substrate, the nanotubes adhered to the new substrate thanks to van der Waals force. Thus, the technique was able to effectively transfer the nanotube pattern from one substrate to another within minutes. Furthermore, because the catalyst particles remain intact on the original substrate, it can be used as a template on which to grown another batch of carbon nanotubes, according to Pint. In addition to the pattern-transfer technique, Pint also determined a way to easily determine the range of diameters in a given batch of CVD-grown nanotubes. These processes and more are detailed in a paper authored by Pint and his colleagues that was published in the journal, ACS Nano.
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