Quasikristall from Fullerenes

Researchers have been fascinated by a new material class called quasikristals for around 35 years. Their discovery was awarded the Nobel Prize in 2011. For a long time, quartz crystals were only found in ternary alloys, ie metals consisting of three different atomic species. Later, other systems such as liquid crystals or perovskite films were added. Researchers at the Forschungszentrum Jülich have now discovered another class of quasikristals and have clarified how the particular arrangement of the molecules is achieved by means of computer simulations.

Two-dimensional quasi-crystal structure of fullerenes with twelve-fold symmetry Copyright: Nature Communications (2017), DOI: 10.1038 / ncomms15367 (CC BY 4.0)

Due to their special structure, quasic crystals exhibit a number of special physical properties. They are already used today for pans or catalysts. The newly discovered class is particularly interesting for optical applications, for example for the production of photonic crystals. It also provides new opportunities for studying magnetic systems and the development of memory devices for quantum computers.

Classical crystals have a periodic structure, the elementary cells of which repeat themselves at regular intervals, similar to a checkerboard pattern. The possibilities for such structures are limited: in two dimensions, for example, only two, three, four and six-fold symmetries can be joined seamlessly.Quasi-crystals, on the other hand, also allow other symmetries – five-folds, for example, or the now discovered two-dimensional structure with twelve-fold symmetry, whose triangular and quadrangular basic elements of fullerenes spread irregularly over the substrate.

Researchers from the Jülich Peter Grünberg Institute (PGI-1, PGI-5, PGI-7) deposited the fullerenes known as “football molecules” on a platinum-titanium alloy. By means of computer-intensive ab initio simulations on the Jülich supercomputer JUQUEEN, they succeeded in directing the arrangement of the fullerenes to the specific interaction with the underlying alloy. In the future, the detailed findings could make it possible to produce tailor-made quartz crystals with certain qualities.

The diagram shows from top to bottom, how the platinum-titanium alloy builds up where the energetically preferred places are (blue points), as schematically the fullerene molecules arrange themselves to an aperiodic order of triangles and quadrangles and then goes into one High-resolution scanning tunnel micrograph of the quasi-crystalline structure. Copyright: Research Center Jülich / S. Karthäuser

Source : Forschungszentrum Jülich