Scientists at the University of Rochester and Swiss Federal Institute of Technology in Zurich have devised an experimental circuit consisting of a silver nanowire and a single-layer atomically thin flake of molybendum disulfide (MoS2) — a step toward building computer chips capable of transporting digital information at light speed.

The researchers used a laser to excite electromagnetic waves called plasmons (vibrating electron clouds) at the surface of the wire, causing an MoS2 flake at the far end of the wire to generate strong light emission. MoS2 excitons can also decay into nanowire plasmons, they found.

This interaction an be exploited for creating nanophotonic integrated circuits, said Nick Vamivakas, assistant professor of quantum optics and quantum physics at the University of Rochester and senior author of the paper in the journal Optica published Thursday.

Photonic devices can be much faster than electronic ones, but they are bulkier and cannot be miniaturized nearly as well as electronic circuits. The new results hold promise for guiding the transmission of light and maintaining the intensity of the signal in very small dimensions.

In bulk MoS2, electrons and photons interact as they would in traditional semiconductors like silicon and gallium arsenide. But when MoS2 is trimmed down to an atomically thin layer, the transfer of energy between electrons and photons becomes highly efficient.*

Combining electronics and photonics on the same integrated circuits could drastically improve the performance and efficiency of mobile technology. The researchers say the next step is to create a near-field detector based on MoS2 and an MoS2 light-emitting diode coupled to on-chip nanoplasmonic circuitry.

* The key to MoS2’s desirable photonic properties is in the structure of its energy band gap. As the material’s layer count decreases, it transitions from an indirect to direct band gap, which allows electrons to easily move between energy bands by releasing photons. (Graphene is inefficient at light emission because it has no band gap.)

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Abstract of Optica paper

The continually increasing demands for higher-speed and lower-operating-power devices have resulted in the continued impetus to shrink photonic components. We demonstrate a primitive nanophotonic integrated circuit element composed of a single silver nanowire and single-layer molybdenum disulfide (MoS2) flake. Using scanning confocal fluorescence microscopy and spectroscopy, we find that nanowire plasmons can excite MoS2 photoluminescence and that MoS2 excitons can decay into nanowire plasmons. Finally, we show that the nanowire may serve the dual purpose of both exciting MoS2 photoluminescence via plasmons and recollecting the decaying exciton as nanowire plasmons. The potential for subwavelength light guiding and strong nanoscale light–matter interaction afforded by our device may facilitate compact and efficient on-chip optical processing.