Mysterious expanding ice crystals in the moons of Saturn and Neptune may be of interest to future developers of microelectronics. Neutron scattering has discovered that methanol crystals that may be found in outer solar system 'ice lavas' have unusual expansion properties. The unexpected finding by a British planetary geologist using neutrons at the Institut Laue-Langevin and the ISIS neutron source will interest developers of 'nano-switches' – single atom thick valves used in ‘micro-electronics’ at the nano scale.
Neutron scattering has discovered that methanol crystals that may be found in outer solar system ‘ice lavas’ have unusual expansion properties. The unexpected finding by a British planetary geologist using neutrons at the Institut Laue-Langevin and the ISIS neutron source will interest developers of ‘nano-switches’ – single atom thick valves used in ‘micro-electronics’ at the nano scale.
Dr Dominic Fortes, UCL (University College London) made the discovery whilst investigating the internal structure of icy moons, such as Neptune’s Triton, to explain the icy eruptions seen by passing space-craft. By studying the behaviour of methanol monohydrate, a known constituent of outer solar system ice, under conditions like those within the moons’ interiors Fortes hoped to understand its role in volcanism.
Fortes measured structural changes in methanol crystals over a range of temperatures and pressures. He found that when heated at room pressure they would expand enormously in one direction whilst shrinking in the other two dimensions. However when heated under an even pressure they expanded in two directions, whilst compressing in the third. This unexpected expansion (elongating and thinning) under uniform pressure is known as negative linear compressibility (NLC).
Whilst these results form the next step towards understanding outer solar system volcanic activity, Fortes’ discovery is of significant interest for material scientists developing nanotechnology. The predictable expansion of NLC materials in a particular direction under pressure makes them a good candidate for nano-switches where their shape-shifting properties can be used like a microscopic, pressure-controlled valve directing the flow of electricity.
NLC materials are extremely rare with only around 15 known examples. What causes this property is still relatively unknown. Scientists hope better understanding of the phenomenon can bring forward potential technological application.
“Currently the use of NLC materials in technologies such as nano-switches is purely theoretical and limited by our lack of understanding of the underlying physics”, says Prof. Reinhard Neder chairman of the ILL crystallographic committee who approved Dr Fortes beam-time at the world’s flagship centre for neutron science. “However, the simple structure of methanol monohydrate gives us a good chance to understand the source of this property and how to look for it in other more commercially viable materials.”
“It was certainly unexpected,” explains Dr Fortes. “As a planetary geologist my focus is understanding the mechanisms behind volcanic eruptions in the outer solar system. If my results open doors for more applied science back on Earth, that’s a bonus.”
Professor Richard Wagner, Director at the Institut Laue Langevin added “This research is a good example of how even basic academic studies can have completely unpredictable benefits in other areas of science and technology. It’s because of discoveries like this that the ILL strives to maintain our delivery of world leading neutron science in both ‘fundamental’ and ‘applied’ fields.”
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More information: Science vol 331. February 2011 p742 – 746 Fortes, Suard and Knight, DOI:10.1126/science.1198640
