Quasicrystalline structure formation in a classical crystalline thin-film system

The unusual ordering of quasicrystals can be induced in thin films of a regular crystalline material; here a two-dimensional quasicrystal has been achieved by growing thin films of the perovskite barium titanate on an appropriately oriented crystalline platinum substrate. Quasicrystals to order Quasicrystals are quite distinct from conventional crystals: their component parts are ordered, but they do not display the precise repeating patterns seen in crystals. These unusual structures can give quasicrystals novel — and potentially useful — properties. Quasicrystallinity is rare, restricted to a few specific materials, but Wolf Widdra and co-workers now show that quasicrystallinity can be induced in thin films of a regular crystalline material by exploiting the geometric mismatch between two different periodic systems. Specifically, they find that thin perovskite films made of barium titanate can be driven to adopt a quasicrystalline dodecahedral structure when grown on an appropriately oriented crystalline platinum substrate. Further development of this methodology might bring the concept of quasicrystallinity to a wider range of materials and technical applications. The discovery of quasicrystals 1 —crystalline structures that show order while lacking periodicity—forced a paradigm shift in crystallography. Initially limited to intermetallic systems 1 , 2 , 3 , 4 , the observation of quasicrystalline structures has recently expanded to include ‘soft’ quasicrystals in the fields of colloidal and supermolecular chemistry 5 , 6 , 7 , 8 , 9 . Here we report an aperiodic oxide that grows as a two-dimensional quasicrystal on a periodic single-element substrate. On a Pt(111) substrate with 3-fold symmetry, the perovskite barium titanate BaTiO 3 forms a high-temperature interface-driven structure with 12-fold symmetry. The building blocks of this dodecagonal structure assemble with the theoretically predicted Stampfli–Gähler tiling 10 , 11 having a fundamental length-scale of 0.69 nm. This example of interface-driven formation of ultrathin quasicrystals from a typical periodic perovskite oxide potentially extends the quasicrystal concept to a broader range of materials. In addition, it demonstrates that frustration at the interface between two periodic materials can drive a thin film into an aperiodic quasicrystalline phase, as proposed previously 12 . Such structures might also find use as ultrathin buffer layers for the accommodation of large lattice mismatches