The technique involves placing a droplet of a nanorod suspension on the patterned substrate for a short while and then removing it. Thanks to the fact that water recedes much more slowly from the hydrophilic strip as compared with the hydrophobic stripe, the act of removing the droplet leaves a stripe of liquid film in the hydrophilic region. The liquid film evaporates very fast because of the large surface area of the liquid. This prevents the nanorods from agglomerating because they do not have enough time to collide and come together under the influence of capillary forces that are only at play for a brief period.

The researchers further showed that when longer-length nanorods were used, they aligned themselves along the stripe length and were orientated over long distances. They found that they could manage the assembly mode and degree of alignment of the nanorods by controlling the concentration of the rods in solution, and also by varying the ratio of a nanorod’s length and hydrophilic stripe width.

We believe that being able to control interparticle distance and orientation in this way will be very useful for future optical applications of gold nanorods and the method might even be extended to other nanoparticle materials, says the team.

More information about the research can be found in the journal Nanotechnology (in press).