A first in integrated nanowire sensor...(ates and specialized assembly devices t...)

"Our main objective is a route toward integrated nanowire arrays that we can produce on any substrate even paper! and to reproduce them uniformly on a large scale," Javey says. "To do that, over the past two years our group has developed methods of printing nanowire arrays. After first growing the nanowires on a donor substrate, we transfer them to any desired substrate, including paper or plastic."

The Javey group has devised two printing methods, contact and roller. The roller method involves growing nanowires on the surface of a cylinder and rolling it across the application substrate, like painting with a paint roller.

Contact printing involves growing nanowires on a flat substrate, inverting it, and pressing it onto the desired substrate. Then the nanowires are detached by sliding the growth substrate away, leaving them attached to the application substrate. Due to the lack of strong surface chemical interactions between nanowires, the process is self-limited to the transfer of only one layer of nanowires. The printed nanowires are highly aligned in the direction of the sliding.

"This has an added advantage," Javey says. "Nanowires grow sticking out in random directions; they look like a bad hair day." But directionally sliding the array off the growth substrate, Javey says, "is like combing the hair to make it stand up straight."

This is a particular advantage because nanowire electronics need to be aligned for uniform performance. In the case of nanowire photosensors, alignment is essential for consistent response both to the intensity (brightness) of light and to its polarization, since the one-dimensional wires respond differently to polarization depending on their orientation. Because of their random orientations, the polarization response of "bad hair" nanowire arrays varies widely.

For their integrated nanowire pho
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