Holographic Optical Traps Manipulate and Assemble Multiple Nanowires

Anne L. Fischer

In the nanoworld, loads of devices can be packed into a small area. But to get them there, these tiny objects must be organized into a structure, which is not easy to do with lithographic methods or even with optical tweezers. To address this challenge, researchers at Harvard University in Cambridge, Mass., and at New York University have developed a holographic approach to nanoassembly that enables the simultaneous manipulation of multiple nanowires.

Nanowires can be cut (a), bent and fused (b) with intense, focused beams of light. Courtesy of David G. Grier.

The scientists used a holographic trapping technique that they originally demonstrated by shining a beam of light through an inexpensive toy that they had ordered from a scientific surplus catalog. What was originally a 4 × 4 array generator turned out to be effective for creating arrays of optical traps, explained David G. Grier, a member of the team from New York University.

After that, they turned to computer holography and started projecting sequences of holograms with spatial light modulators, producing several hundred traps from a single beam of light. They have patented this technique, which forms the basis of the product offerings of Arryx Inc. in Chicago.

In their current work, the researchers had the goal of trapping 20- to 100-nm-diameter semiconductor nanowires using 400-nm light. “[It] is like trying to grab spaghetti with an oven mitt,” Grier said.

To prevent the nanowires from sticking to any surface, they used a chemical stabilization process. Getting the structures to stay in place after stabilization became a challenge, however, so they also employed optical and chemical destabilization to make the nanowires stick where they wanted them.
Using the holographic trapping method, they trapped 10 to 20 nanowires at a time and manipulated the structures in 3-D relative to each other into interesting configurations. It worked so well that their next step is to understand why, so they can optimize it.

Optics Express, Oct. 31, 2005, pp. 8906-8912.