Nanoantennas could revolutionise NEMS

Researchers from Monash University have invented tiny optical antennas which function like spotlights at the nanoscale, offering the potential to measure food safety, identify air pollutants and even quickly diagnose and treat deadly diseases. Their inventors envision applications in lab-on-a-chip devices and in the field of nano-electromechanical systems (NEMS).

Developed by PhD student Debabrata Sikdar and his supervisors, Professor Wenlong Cheng and Professor Malin Premaratne, the antennas are cubic in shape and composed of insulating materials - unlike previous versions, which were spherical and composed of conducting or semiconducting materials. They are said to be easier to fabricate and better at directing an ultranarrow beam of light where it is needed, with little or no loss due to heating and scattering.

“Analogous to nanoscale spotlights, the cubic antennas focus light with precise control over direction and beam width,” Sikdar said.

Schematic representation of unidirectional cubic nanoantennas inducing directionality to omnidirectional nanoemitters (light sources, eg, spasers, quantum dots) to precisely focus light with adjustable beam width and intensity, which can be tuned by adjusting the length of nanocube chain or intercube spacing. These ultranarrow directional beams can play multiple roles in lab-on-a-chip devices such as illumination sources in microfluidic analysis or minute deflection registers in nanocantilever-based sensors. All these signals are further detected in the photodetectors and get processed by on-chip signal processing circuitry for bio-molecular identification. Image credit: D Sikdar and M Premaratne/Monash University.

Writing in the Journal of Applied Physics, the researchers explained how the 200 nm nanocubes can be arranged in a chain in the path of visible and near-infrared light sources. The space between them and their number can be adjusted to fine-tune the light beam as needed for various applications; as the separation between cubes increases, the angular width of the beam narrows and directionality improves.

“Unidirectional nanoantennas induce directionality to any omnidirectional light emitters like microlasers, nanolasers or spasers, and even quantum dots,” said Sikdar. Spasers are similar to lasers, but employ minute oscillations of electrons rather than photons of light. Quantum dots are tiny crystals that produce specific colours based on their size.

Sikdar and his colleagues plan to begin constructing the unidirectional cubic NEMS antennas at the Melbourne Center for Nanofabrication. He stated that the devices could be suitable for “integrated optics-based biosensors to detect proteins, DNA, antibodies, enzymes, etc, in truly portable lab-on-a-chip platforms of the future”.

“They can also potentially replace the lossy on-chip IC (integrated circuit) interconnects, via transmitting optical signals within and among ICs, to ensure ultrafast data processing while minimising device heating,” he added.

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