Converting electrons into photons with MoS2

Far-field photons excite silver nanowire plasmons. The wire plasmons propagate to the wire's distal end where they efficiently interact with the two-dimensional material semiconductor molybdenum disulfide (MoS2). The plasmons are absorbed in the MoS2 creating excitons that subsequently decay converting back into propagating photons. Credit: University of Rochester

In ICT we are using both photons and electrons. We are using photons on the information highways, optical fibres, we are using them in CDs and DVDs and we would like to use them also in chip to chip communications and even in intra-chip communications because photons have very very low heat dissipation, hence lower power consumption and cleaner signals. We use electrons ... everywhere, even for generating and detecting photons.

To convert electrons into photons we are using silicon with certain doping elements, like erbium, and we have become pretty good at that as you can see right now looking at your screen to read this post ;-)

Researchers, however, are never satisfied and this is what makes technology advance. At the University of Rochester a group of researchers teaming with another group at the Swiss Federal Institute of Technology in Zurich have found a way to convert electrons into photons using a one atom layer of MoS2 (molybdenum disulfide). MoS2 is a material that can be produced in form of a sheet one atom thick, like graphene, and I had posted a few news on the characteristics of this material, as a possibile alternative to graphene.

By using a laser they have been able to create a flow of plasmons (vibrating clouds of electrons) on a silver nano wire that move onto the surface of the MoS2 sheet and when they reach the edge they create a strong light (photons) emission. It works also the other way around with light hitting the MoS2 generating excitons that decay in plasmons on the silver nanowire, thus converting photons into electrons.

The interest in using plasmons derives from the fact that in plasmons electrons don't move, hence they do not (almost) waste energy into heat, but just vibrate in a coherent way (electrons do vibrate on their own... in plasmon this vibration is in synch and results in an electromagnetic field that is actually conveying the signal).

Having found a way to convert plasmons into photons is the crucial point. The researchers expect that the exploitation of this phenomenon will provide a boost to integrate in a single chip photonics and electronics sing photons for communications and drastically decrease power consumption. This in turns decreases dissipation and makes it possibile to create much more dense and performant chips. Long life to Moore's law!

Author - Roberto Saracco

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