He created a “photonic graphene” to generate highly efficient lasers and LEDs and store sun energy.
Very few breakthroughs in the physics and science of materials domains have spurred so much interest as graphene, whose discovery in 2004 earned its “parents,” researchers Andre Geim and Konstantin Novoselov of the University of Manchester, the 2010 Nobel Prize in Physics. This reputation is well deserved: composed of pure carbon atoms (just like diamonds and graphite), graphene is considered the lightest, strongest, thinnest, most transparent and most conductive material ever found. Some envisage that it might replace plastics, steel, and even silicon as the star of all possible and dreamt of applications in 21st century.
However, it is not the direct use of graphene that motivated Jorge Bravo, a young researcher with a PhD in Physics in 2006 from the Autonomous University of Madrid (Spain), followed by four years of postdoctoral research at MIT (Massachusetts Institute of Technology), to closely look at graphene's properties. Bravo's field is photonics, which is the study of light and the development of light-based devices, such as LEDs, lasers, optical fibres. Through his research, he developed a “photonic equivalent” of graphene, having the same properties in terms of propagation: if electrons move freely on a two-dimensional graphene plane (graphene is a plane layer of carbon atoms, just one atom thick), leading to his superconductive characteristics, photons would equally move freely in Bravo's high-efficiency LEDs. Illuminating large areas with a fraction of the energy used today is precisely what Bravo's patented new LED technology allows.
The other “graphene-like” characteristic Bravo was particularly interested in is the capacity to store and transport solar energy, something which is very costly today and could be revolutionised by the innovative material devised by him and his team.
To accomplish that, Bravo relied on a physical phenomenon known as Dirac dispersion. “Many of graphene's unique electronic properties emerge from its Dirac-like electronic energy spectrum. Similarly, it was expected that a nanophotonic system featuring Dirac dispersion would open a path to a number of important research avenues” he explains. Bravo and his research team achieved this feature by designing and producing a layered material where a layer of germanium, a semiconductive material similar to silicon, is trapped between two layers of amorphous silicon, which blocks any optical propagation other than along the two-dimensional plane. All layers show a hexagonal hole structure that is responsible for Dirac dispersion, which has a fundamental impact, as “it allows the presence of a single coupling state that the light may assume, even over a large area.” If photons have a single state, they do not interfere (couple) with one another, and energy can travel very large distances without any loss. In turn, this opens the path to an incredibly effective way to store energy, as sunlight (which contains a broad spectrum of wavelengths) can be used to generate and extremely coherent light, which in turn can be stored through photochemical reactions, and re-transformed into light when needed, something impossible to do efficiently with incoherent light. Another application of Bravo's “photonic graphene.”