Using a novel fabrication method, researchers have put together two arrays of nanoparticles separated by just the space of a single atom — 0.34 nanometres — using a single layer of graphene as a spacer between them1. No other technique has achieved such closeness between nanoparticles in a consistent manner. This could open the doors to a new class of exquisitely sensitive photo detectors and other opto-electronic devices.
The researchers from Indian Institute of Science, Bangalore, brought the nanoparticles together as close as 0.34 nanometres and achieved a much larger field enhancement than before. “One of the things we wanted to do was to make the process scalable,” said Ambarish Ghosh, one of the authors.
When two nanoparticles made of noble metals are placed just nanometres apart and light is shone on them, the electromagnetic field is tremendously enhanced at the junction of the particles.
To achieve the precise separation, the scientists used an oblique angle technique to deposit silver on a silicon wafer patterned with polystyrene particles. This made the silver sit atop the beads. Subsequently, they transferred graphene using standard protocols.
The second layer of silver was deposited, again at an angle, resulting in two arrays of silver nanoparticles separated by the graphene layer — the space of a single atom. To ensure a large field enhancement, the researchers built a photo-detector prototype to demonstrate that the photo-response of graphene increases a hundred-fold compared to similar photo detectors.
