The ACTAlab at SUTD designs functional materials for Data Storage, Photonics, and Electronics applications. We also develop efficient materials design methods, which we then use to optimise the material for a specific application. The figure below summarises the research conducted in ACTAlab. At the heart we have chalcogenide materials, which often exhibit active properties, the inner blue circle shows the design methods that we employ (strain engineering, evolutionary atomistic materials design, nanostructural design, and combinatorial design), the purple outer circle shows the applications of our materials.
We use a combination of ab initio computational models and experimentation to optimise the nanostructure to achieve a particular property. By combining atomic structure measurements with density functional theory atomistic models we theoretically study the effects of changes to the material’s nanostructure on its properties. These structure–property correlations are then used as design blueprints for the growth of optimised materials.
The chalcogenides are materials composed of sulphur (S), selenium (Se) or tellurium (Te). The properties of chalcogenides are commonly tuned through a range of different mechanisms. For instance, amorphous chalcogenide films and bulk glasses exhibit optical properties that can be reversibly tuned by photons with energies similar to that of the material’s band gap. Other external stimuli such as pressure and heating can also be used to tune the properties.
Phase change data storage materials are commonly based on chalcogenide alloys. This special class of material exhibit extraordinarily large contrast between their optical and electrical properties when switched between the amorphous and crystalline states. For example the electrical sheet resistance of the prototypical phase change material, Ge2Sb2Te5, decreases by three orders of magnitude when the material is heated above its cubic crystallisation temperature. This particular transition can be induced by electrical Joule heating in just 500 ps. Perhaps the most technologically important aspect of chalcogenide phase change data storage materials is their inherent scalability, indeed films just 2 nm thick display phase change property contrast. The ACTA group has a special interest in developing improved phase change data storage materials and extending their use beyond data storage to novel applications in photonics.
A summary of current research projects within ACTA are given here and further information is also available on the ACTA group member’s web page.