Fig 1: Plasmonic cloaking reduces light scattering in the gold-coated sections.

It could lead to a new class of devices that controls the flow of light at the nanoscale to produce both optical and electronic functions.

At the heart of the Stanford and University of Pennsylvania device are gold-covered silicon nanowires. By adjusting the ratio of metal to silicon — a technique called tuning the geometries — the engineers capitalized on favorable nanoscale physics to get the light reflected from the two materials to cancel each other out, making the device invisible. This phenomenon is known as destructive interference. An image showing light scattering from a silicon nanowire running diagonally from bottom left to top right. The brighter areas are bare silicon, while the dimmer sections are coated with gold, demonstrating how plasmonic cloaking reduces light scattering in the gold-coated sections.

Fig 1: An image showing light scattering from a silicon nanowire running diagonally from bottom left to top right. The brighter areas are bare silicon, while the dimmer sections are coated with gold, demonstrating how plasmonic cloaking reduces light scattering in the gold-coated sections. (Photos: Stanford Nanocharacterization Lab)

The rippling lightwaves in the metal and semiconductor created a separation of positive and negative charges in the materials, known as a dipole moment. The key was to create a dipole in the gold that is equal in strength but opposite in sign to the dipole in the silicon. When equally strong positive and negative dipoles meet, they cancel each other, and the system becomes invisible.

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