A new technique that enables metallic cube-shaped nanocrystals to spontaneously self-assemble into larger, complex materials could pave the way for the next generation of antennas and lenses. The metal nanocrystals developed at the University of California, San Diego, similar to tiny bricks or Tetris blocks, can spontaneously organize themselves into larger-scale structures with precise orientations relative to one another. Precise orientation is necessary so that the cubes, which are less than 0.1 µm, can confine or focus light at different wavelengths. UC San Diego nanoengineers have developed a technique that enables silver nanocubes to self-assemble into larger-scale structures for use in antennas and lenses. (Image: Tao Research Group, UC San Diego Jacobs School of Engineering) “Our findings could have important implications in developing new optical chemical and biological sensors, where light interacts with molecules, and in optical circuitry, where light can be used to deliver information,” said Andrea Tao, a nanoengineering professor. Tao’s team used chemically synthesized metal nanocrystals, which can be synthesized into different shapes, to construct objects such as lenses and antennas. In this experiment, the engineers created tiny crystalline silver cubes that confine light when organized into multiparticle groupings. Confining light into ultrasmall volumes could provide researchers with extremely sensitive optical sensors that monitor how single molecules move, react and change with time. To control how the cube organizes, Tao and her colleagues created a technique to graft polymer chains to the silver cube surfaces that modify how the cubes interact with one another. Objects typically pack side-by-side like Tetris blocks. Using simulations, Tao’s team predicted that placing short polymer chains on the cube surface would cause them to stack normally, while placing long polymer chains would cause the cubes to stack edge-to-edge. To demonstrate their technique, the researchers created macroscopic films of the nanocubes self-assembling into the two different orientations and showed that the films reflect and transmit different wavelengths of light. The findings appeared online June 10 in Nature Nanotechnology. For more information, visit: www.ucsd.edu