Scientific researcher discovers exotic lead film

05 December 2013

Rachel Atkinson

Guild Fellow Dr Joe Smerdon has worked on the international collaboration

Pic: Several Pb atoms arranged in pentagons imaged using scanning tunneling microscopy. The red atoms are the top layer; the slightly less distinct green atoms are the next layer down.

An international collaboration including University of Central Lancashire (UCLan) researchers has discovered an exotic film of the element lead (Pb), in which the atoms are arranged in pentagonal and decagonal structures rather than in the usual cubic fashion.

This discovery is remarkable because it shows how, given the correct starting conditions, elements disobey conventional laws of matter to form exotic materials called quasicrystals.

Quasicrystals, the discovery of which led to the award of the 2011 Nobel Prize in Chemistry to Dan Shechtman of the Technion Institute in Israel, were first observed in alloyed systems comprising several elements.

Shechtman’s discovery was the starting point for a major field of research which is finding application in diverse areas such as in photonics, in coastal waveguides designed to prevent erosion by harmlessly dissipating the energy of the ocean, and in so-called superlenses, lenses made of metamaterials with negative refractive indices and no limit on their resolution.

"Although quasicrystalline thin films have been discovered before, all have been single layers. This new film extends these materials to the third dimension."

Experiments carried out by a team of researchers in the University of Liverpool’s Surface Science Research Centre, with input from UCLan academic Dr Joe Smerdon, have shown that single layers of atoms deposited on quasicrystalline surfaces exhibit the pentagonal and decagonal ordering of the underlying quasicrystal. The lead film was deposited atom by atom and the resulting structure was subsequently recorded by scanning tunnelling microscopy. The experimental observations were found to be consistent with theoretical results obtained by density functional theory - a state-of-the-art quantum mechanical modelling method.

Dr Smerdon, a Guild Fellow at UCLan, said: “Although quasicrystalline thin films have been discovered before, all have been single layers. This new film extends these materials to the third dimension. As most of the technologically relevant properties of materials depend crucially on their structure - think of graphite and diamond, which are both made entirely of carbon - the discovery of a new structure of material promises very different properties. For example, it will be very interesting to discover what effect quasicrystallinity has on the superconducting properties of Pb.”

This work was supported by the Engineering and Physical Sciences Research Council (EPSRC).

The research was published in the November issue of Nature Communications.