Skip to main content

Hybrid organic-inorganic nanostructures for photonics and optoelectronics

Final Report Summary - ICARUS (Hybrid organic-inorganic nanostructures for photonics and optoelectronics.)

The Icarus ITN project had a range of different technical aims and objectives. A key theme was the development of new types of ‘hybrid’ material systems for use in advanced optical devices. The project involved a close and effective collaboration between 8 of the EU’s leading materials science / physics research groups, and explored a range of hybridization schemes to coupled different functional semiconductor or metallic materials together in an attempt to develop new optical technologies. The hybridization schemes we explored were highly challenging, and in many cases involved developing new materials combinations or the use of optical techniques to couple remotely separated electronic materials in specially designed optical cavities. In many cases, the work performed has significantly extended the state of the art, leading to a range of high profile publications (5 Nature group publications and a further Nature group paper expected). At least two inventions from the project have been patented.

WP1 Energy transfer in hybrid semiconductor devices: In this work-package (WP), we were interested in exploring the optical and electronic properties of combinations of organic (carbon-based) and inorganic semiconductors, with our aim being to control the transfer of energy flow between the materials. Here, we used a short-range coupling technique to transfer energy between an organic thin film and an inorganic semiconductor material. This allowed us to both explore the physics of the process and also demonstrate a surprisingly high efficiency of energy transfer, with our work suggesting advanced applications of hybrid semiconductor materials in optoelectronic technologies. By combining different types of inorganic semiconductor (quantum wells and colloidal quantum dots), we were able to develop novel types of solar cells that have the potential to increase the efficiency of current technologies.

WP2 Active manipulation of hybrid excitations: In this WP, we studied basic effects in new types of semiconductor materials, again based around their applications in optoelectronics. We used advanced laser measurement techniques to explore a range of new carbon-based materials for ‘plastic’ solar cells and hybrid semiconductor systems composed of organic materials and metal-oxides. Our work on ultrafast energy transfer in ultra-thin organic donor/acceptor blends involved the development of new laser-spectroscopy techniques and was published in the journal Scientific Reports (a Nature group journal). The work performed in this WP thus allowed us to uncover a range of fundamental processes that contribute to the body of knowledge on these materials and helped explain some of their basic properties. Other spectroscopy work (published in Nature Communications) on nano crystals allowed us to evidence lasing effects from a single nanocrystal. We also performed detailed theoretical studies where we calculated the optical properties of coupled molecules, or energy transfer processes between organic and inorganic semiconductor thin films. In particular, we identified new combinations of semiconductor and metallic films that will help to control the flow of energy within an optical device.
We also developed novel materials that could self-assemble, forming structures in which the electronic interactions between functional nanoparticles could be controlled. Here, we exploited the versatility of a DNA ‘origami’ technique to prepare inorganic-organic nanoscale hybrids with potential for energy transfer, amongst other applications One route to achieve this was to use DNA as a scaffold to assemble nanoparticles having defined separation distances. This work was published in Nature Nanotechnology, and describes techniques that could be used to construct structures used in a range of technologies including solar-energy harvesting and materials for controlling new chemical processes (chemical catalysis).

WP3 Optical non-linearity and stimulated scattering: This part of the project achieved a number of very high-impact results, with two papers published in Nature Materials. Our aim was to explore effects that occur when organic semiconducting materials are placed in optical cavities that ‘trap’ light, and thereby create new types of optical excitations termed ‘cavity polaritons’. Such excitations are a mixture between light and matter and thus have very different properties from their constituent parts. Here, we first published a series of papers detailing the basic physics of cavity polaritons in both organic and inorganic-semiconductor cavities and using both laser spectroscopy and advanced theoretical methods. In addition to our identification of a new type of excitation called a ‘Braggoriton’, we developed fast laser techniques to follow very high frequency energy oscillations in organic-exciton polariton states for the first time. The highlight of this work package was the demonstration by two groups that new ‘quantum’ effects could be seen in organic (plastic) films. We showed that polariton states could interact together to form a polariton-condensate having macroscopic coherence. Such quantum effects were shown to occur in relatively simple optical structures at room-temperature, and are thus of interest for applications in new types of laser or light-source. Other work also showed that light could be used to facilitate energy transfer between organic molecules placed in a cavity, with such structures acting as model system to understand natural photosynthetic processes.

WP4 Lasing in hybrid micro- and nano structures: In this WP, we explored new types of optical resonator device. We used advanced lithographic techniques to write periodic structures (photonic crystals) into materials at length-scales around that of the wavelength of light. Thus in the same way that nature generates iridescence from a butterfly’s wing, such periodic structures can be used in new types of optical technology. Here we explored the development of types of structure that could be used in lasers and in chemical sensors. We also developed an optical printing technique to place single metallic nanoparticles into a photonic crystal, allowing us to transfer energy between light trapped in the photonic crystal with electronic oscillations at the nanoparticle surface (so-called surface-plasmons). The same printing technique was also developed to print rod-shaped nanoparticles on a surface with a given orientation, offering the opportunity to utilize plasmon states with very high precision. Here, optical printing of spherical gold nanoparticles on photonic crystal nanocavities presents significant advantages over previously developed approaches, namely through its higher simplicity, higher operational speed and potential for scale-up. Laser-printing of metallic nanoparticles is envisaged as a highly valuable technique to construct new types of photonic and plasmonic devices and sensors. Plasmon technologies are currently of great interest for their applications as ultra-sensitive biomedical sensors. We also performed optical simulations to design a new type of optical cavity containing a localized defect state. The structures developed are expected to trap light with very high efficiency in a very small physical volume, permitting the emission of quantum light emitters placed in the cavity to be modified (either accelerated or suppressed). Such structures are of great interest as light sources for ultra-secure information transfer. Two patents have been filed by IBM to protect this concept.

WP5 Injection-driven polariton devices: In this WP, we developed new types of electronic devices based on ‘organic’ cavity-polaritons. We made a detailed experimental and theoretical exploration of the basic mechanisms that controlled device efficiency, and provided predictions for the neccessary future development of this technology. Importantly, we also created devices that contained both organic and inorganic semiconductors that supported ‘hybrid’ polariton states. We showed that energy could be funneled into such hybrid states with our work opening a route to realize a new type of laser device. This advance represents a significant step towards an electrically-pumped hybrid-semiconductor laser diode.

Impact. This project has had a number of important results. We have shown that quantum effects are important in ‘plastic’ based polariton systems. This result is likely to stimulate much more experimental and theoretical research in this area, with futuristic applications for such type of technology being in quantum-based computers. The project also addressed the development of materials for solar-energy harvesting, and demonstrated means to improve the efficiency of current silicon based solar cells and thus facilitate the development of new types of renewable energy technologies. Other work performed prototyped new technologies that could be applied in a range of sensor technologies that will have potential application in healthcare technologies and as environmental pollution monitors. The project produced two patents that were granted to IBM that describe a new type of optical-cavity structure together with new technologies to fabricate such cavity structures. These patents form part of a portfolio of technologies that will be important in coming decades in which computing speeds and memory sizes become every larger.
As well as advancing the state of leading technologies that will contribute to the quality of life of the EU’s citizens (through faster computing, medical-sensor technology and renewable energy technologies as described above), the project trained a group of young scientists to very high level in some of the EU’s leading research group. Many of these young scientists have already found employment in various research groups and are starting their careers as future research leaders. Further details on the results of the project can be obtained from Prof. David Lidzey at the University of Sheffield (d.g.lidzey@sheffield.ac.uk) or through the Icarus project website www.icarus.group.shef.ac.uk/