Nanocrystals for new materials
Strong, durable, light and flexible surfaces or materials are proving to be the next biggest advance after plastic. These materials are relying on nanotechnology to provide all the desirable properties that are at the cutting edge of science. In this spirit, the EU-funded project 'Self Assembly of Shape Controlled Colloidal Nanocrystals' (SA-Nano) investigated how special nanocrystals can automatically assemble themselves in developing some of these new surfaces. In recent years nanocrystals have led to the development of light emitting diodes (LEDs), photovoltaics, electronics and biological tagging, to name a few applications. This project aimed to develop new nanocrystal shapes to grow nanorods and tetrapods with metal featuring semiconductor and oxide tips. Many of these new hybrid nanocrystals have been combined with biomolecules for purposes of self assembly. Links between these nanocrystals in certain cases employed molecular and biomolecular bonding to generate chain-like assemblies of rods and three-dimensional (3D) networks of tetrapods, including propeller structures and patterned substrates. Rod alignment was achieved through microfluidics and various tools have been developed to model the self assembly processes of rods and tetrapods. Proximity effects on the electronic and optical properties of shape-controlled nanocrystals were also investigated. The properties of nanocrystals were studied by using optical, magnetic and scanning probe techniques, providing further insight on how they behave. The new aligned assemblies of rods and tetrapods have exhibited novel properties never seen before, allowing researchers to examine the structure and single electron charging energy against the distance between neighbouring nanorods. Unlike ordered multilayers of spherical nanocrystals, ordered arrays of nanorods have clearly shown coherent, unidirectional orientation along a given direction. These materials and systems with predictable composition and structure are paving the way to concrete applications. Assemblies of magnetic nanorods are also yielding new collective magnetic effects. Tetrapods are now being exploited in thin-film photovoltaic devices, incorporated in a host matrix made of a conductive polymer. This may lead to low-cost photovoltaics offering huge advantages in terms of environmental impact in energy conversion. Lastly, these new nanocrystals will also be useful in catalysis, i.e. in filtering out pollutants. SA-Nano successfully demonstrated the possibilities, and exploiting the results is only a matter of time. All these advances hold considerable potential for industrial applications and are set to take industry to the next level.
