"It seems counterintuitive," said Brongersma, "but you can cover a semiconductor with metal even one as reflective as gold and still have the light get through to the silicon. As we show, the metal not only allows the light to reach the silicon where we can detect the current generated, but it makes the wire invisible, too."
The engineers have shown that plasmonic cloaking is effective across much of the visible spectrum of light and that the effect works regardless of the angle of incoming light or the shape and placement of the metal-covered nanowires in the device. They likewise demonstrate that other metals commonly used in computer chips, like aluminum and copper, work just as well as gold.
To produce invisibility, what matters above all is the tuning of metal and semiconductor.
"If the dipoles do not align properly, the cloaking effect is lessened, or even lost," said Fan. "Having the right amount of materials at the nanoscale, therefore, is key to producing the greatest degree of cloaking."
In the future, the engineers foresee application for such tunable, metal-semiconductor devices in many relevant areas, including solar cells, sensors, solid-state lighting, chip-scale lasers, and more.
In digital cameras and advanced imaging systems, for instance, plasmonically cloaked pixels might reduce the disruptive cross-talk between neighboring pixels that produces blurry images. It could therefore lead to sharper, more accurate photos and medical images.
"We can even imagine reengineering existing opto-electronic devices to incorporate valuable new functions and to achieve sensor densities not possible today," concluded Brongersma. "There
|Contact: Andrew Myers|
Stanford School of Engineering