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Cutting-edge chemistry The chemistry of alien atmospheres Have you ever wondered what a distant planet is made of? Contented yourself with Wallace & Gromit’s cheese hypothesis? Daniel Johnson wants you to think again velocity of a body (the same effect that makes the siren of a passing ambulance rise and fall in pitch). The spectrometer has been in service since 2006; astronomers have been using the Doppler shift to find exoplanets for years. So what’s new? © nasa Well, previously astronomers measured the Doppler shift in a star’s spectrum caused by the planet’s gravitational field. The much heavier star barely moves, spinning in a small circle at only a few kilometres per hour. But Birkby and her team flipped this around, using the Doppler shift caused by the planet’s motion around the star (around 400,000 km h-1). Black holes and revelations Britain’s first astronaut, Helen Sharman, wrote about the science of alien planets and black holes when the first planet from another galaxy was discovered in the Milky Way: http://bit.ly/16xbYVj 6 | The Mole | September 2013 Astronomers using the European Southern Observatory’s Very Large Telescope (VLT) have developed a new method that could allow us to analyse the make-up of exoplanets (planets outside of our solar system) in greater detail than ever before. According to results presented this summer, the new technique will allow astronomers to ‘search for water on hundreds of worlds without space-based telescopes’. Hunting for water meant looking at longer wavelengths where the Earth’s atmosphere starts to obstruct what they are looking for. High in Chile’s Atacama Desert, the VLT is ideally placed to minimise atmospheric effects, but still the spectrum received a combination of signals: from the exoplanet, the star itself and some distortion owing to our atmosphere. However, the Doppler effect shifted the exoplanet’s contribution while the rest of the spectrum stayed the same. This is where the spectrometer comes in. Its extremely high resolution can distinguish individual water lines in the spectrum, allowing the overall pattern to be identified. A needle in a spectral haystack An analogy for the process is this: imagine you’re looking for a needle in a haystack. Unfortunately, the needle is moving. You must discount the hay (the spectrum of the star and atmospheric distortion) and find the moving needle (the water signal). Your one advantage? You know what the needle looks like. The implications? It will be easier to look for planets that may harbour those green aliens, for a start. Furthermore, having improved the technique for water, the team, led ‘Of course we were delighted when we saw the signal jump by Jayne Birkby of Leiden University, Netherlands, may out at us,’ said Birkby, conveying her excitement that this now move on to other atmospheric molecules such as technique could be used ‘to look for Earth-twin planets’. O2, CO2 and CH4. The researchers can now move on to looking for more Old principles, new method atmospheric molecules, building up a picture of the The method itself is a lesson in how old principles can atmospheres and histories of thousands of exoplanets. be combined to make huge advances. The technique It raises the tantalising prospect of one day finding a uses a high-resolution infrared spectrometer mounted planet with a similar atmosphere to our own, where life on the VLT. Just as important is the relationship between may have existed or even exists today. Then things really the Doppler shift of electromagnetic radiation and the get exciting. www.rsc.org/TheMole Electronic tattoos Flexible electronics Emma Stoye investigates a super-stretchy conductor © Joseph Xu/ University of Michigan US researchers have made the stretchiest electrical conductor yet using gold nanoparticles embedded in an elastic polymer. The new material can stretch to over five times its size while still conducting well enough to power small devices. Find out how temporary tattoos containing flexible electronics can be used to monitor racing car drivers with this article from Chemistry World: http://rsc.li/1ctlxsy Finding materials that can conduct when stretched is a huge challenge within flexible electronics. Existing approaches, which involve coiling wires, liquid inks or embedding conductive particles in stretchy materials, have achieved limited success. The biggest hurdle, says lead scientist Nicholas Kotov from the University of Michigan, is combining two properties that counteract each other. ‘If we increase the stretchability of a material we automatically decrease the conductivity because we are increasing the gap between the conducting elements,’ he says. ‘On the other hand, adding more conductive elements increases stiffness and reduces stretchability.’ Nanoparticles Kotov and his group have overcome this trade-off using spherical gold nanoparticles dispersed through sheets of polyurethane. When this approach has been tried with other conductors, such as carbon nanotubes, conductivity drops as the material is stretched. But instead of spreading further apart when the material is stretched, the gold nanoparticles form a branching network of conductive chains so conductivity stays high. ‘We knew from our experience with nanoparticles in solutions that a lot of particles have the ability to selforganise – it’s intrinsic to nanoscale matter,’ says Kotov. ‘Our approach worked really well – because of this self- organisation we were able to get high conductivity and amazing stretchability.’ He also says nanoparticles other than gold could be used in the same way. The new super-stretchy material can still conduct electricity when stretched to five times its original size Without stretching, the material has a high conductance of 11,000 S cm-1. When stretched to over twice their original length, conductance is 2400 S cm-1. It even conducts when stretched to 5.8 times its length at 35 S cm-1, which is still enough to power some small devices. This is a significant improvement on existing stretchy carbon nanotube containing conductors, few of which can even stretch more than twice their length, let alone maintain conductivity. Applications There are several potential applications for such an elastic conductor. Kotov says it could feature in flexible gadgets or soft robots, and his group are currently trying to use it to create soft, stretchable medical implants and sensors, in particular for use in the brain. © Joseph Xu/ University of Michigan John Rogers, a nanofabrication expert at the University of Illinois, Urbana-Champaign, US, agrees this is a promising development. ‘These types of conducting materials could provide new options in engineering design,’ he says. ‘The next steps will be to determine routes for integrating these materials into functional systems and assessing their performance compared to alternatives.’ www.rsc.org/TheMole Scanning electron microscopy image of the flexible conductor when it's stretched 110% September 2013 | The Mole | 7