The bow-tie-shaped plasmonic nanostructure described in a paper titled “Efficient light generation from enhanced inelastic electron tunnelling” published in Nature Photonics consists of two single crystals silver cuboids joined at one corner, yet separated by a 1.5nm thin insulating polymer (PolyVinylPyrrolidone or PVP).
Applying a voltage across the tiny junction allows electrons to tunnel from one corner to the next through the PVP barrier, transferring some of their energy to surface plasmon polaritons along the metal-insulator interface which then radiate that energy into photons.
The extremely small feature sizes and specific geometry of the junction make it particularly efficient at tunnelling electrons inelastically, meaning more energy can be transferred from the tunnelling electrons to the plasmon polaritons. Hence the authors report a more efficient light generation, up to 2%, an improvement of two orders of magnitude over previous work, they claim.
The new light emitting device architecture was selected using computational methods and numerical simulations.
Simulations show that the color of the emitted light is determined by the geometry of the junction structures, in this case behaving as an optical antenna.
Based on the chemical reagents they use for solution-based device fabrication, the researchers can dictate the size and shape of the crystals that they synthesize in solution, obtaining atomically accurate structures with flat faces and extremely sharp corners.
Although the light conversion efficiency remains too low for practical use today, this new research opens up new ways to fabricate ultra-compact optical sources. Now the researchers are exploring different geometries and materials to further boost light emission efficiency.
University of California San Diego – www.ucsd.edu